Construct Pitched Roofs Trade Notes - TAFE NSW · TYPES OF ROOFS There are many styles of roof, most of which are made up from variations on specific types. Some of these roof types

Carpentry & Construction Hornsby CPCCCA3007A 2016

CERT III, Carpentry & Construction Hornsby TAFE Page 1

Construct Pitched

Roofs Trade Notes



WEEK 1:

INTRODUCTION TO PITCHED ROOF FRAMING

Definitions:

Roof: “A roof is the weatherproofed upper covering of a building or structure, which is

designed to protect the interior from atmospheric elements such as sun, rain, hail, snow,

frost and wind.”

Flat roof: Is a roof with a minimum of slope to allow water run-off, usually with a fall of

1 in 40 but a minimum of 1 in 60. These are usually confined to sheet roofs with the

sheets being full length, no joins, for a slope less than 1 in 40.

Pitched roof: This is a roof with a slope, or pitch, greater than 1 in 12 or 5 degrees. A

roof may have a single pitch, like a skillion, a double pitch, like a gable, or an unequal

pitch, where both sides of the roof have different angles.

Coupled roof: This is where pairs of rafters are attached on opposite sides of a ridge

and the feet are fixed to the wall plate. There is no tie between the feet, allowing the

rafters to spread under load. It is restricted to small span gable roofs, which may be

simply coupled.

Close-coupled roof: This is the same as the coupled roof except there is a tie, such as a

ceiling joist, placed between the feet of the rafters. This method is used for most roof

construction, especially for gables with a wide span.

Cut roof: Also known as a conventionally pitched roof, has all of its members cut and

assembled individually. These roofs are made up of separate rafters, ridge, purlins,

collar ties, struts, etc.

Free roof: This refers to any roof, which does not have enclosed walls under it. It is

typically used for a freestanding carport, portico, covered walk-way, lichgate, etc.

Gablets: These are simply small versions of gables. They may be used on the ends of

ridges for ventilation, over a dormer window or as an adornment to the main roof

surface.

Monoslope roof: Also known as a ‘Monopitch’ roof, it is any roof with a continuous

slope, which has no ridge. Skillion and lean-to roofs are monoslope roofs.

Open roof: Any roof, which is not enclosed underneath. Verandah, free roofs and garage

roofs are typically not lined or framed with a ceiling and therefore classified as open

roofs.



Shell roof: Made from a thin self-supporting and curved structural membrane used over

long spans. Precast, prestressed concrete is commonly used for this construction.

Southlight roof: Generally refers to the vertical glass of a sawtooth roof, which faces

south to allow glare-free light to enter the building.

Umbrella roof: This is a roof placed over a structure, but does not form part of the

structure.

THE ROOF

The roof, and roof covering, makes up a large part of the external fabric of the building.

It may be designed and constructed to create a picturesque roof scape using a variety of

materials or they may be very plain and use only one type of material.

The design of roofs has changed dramatically from the early part of the 20th century

where common features included ornate gables, gablets, turrets, spires, crested ridge

capping, finials, vents, and complex chimneys decorated with terracotta pots.

These steeply pitched and highly decorative roofs have given way to the modern low

pitched, plainly coloured roofs of today commonly seen in most new housing

developments.

Roofing materials such as glazed and unglazed terracotta, slate and ‘fibro’ have been

generally superseded by concrete tiles and ‘Colorbond’ roof sheeting.

As with most styles in building, the older types of design eventually become

incorporated into contemporary design, or make a comeback, therefore methods of

development and construction of roof types should not be forgotten.



TYPES OF ROOFS

There are many styles of roof, most of which are made up from variations on specific

types. Some of these roof types are described below:

A-frame:

This is a steeply pitched roof,

which forms a shape similar to the

letter ‘A’. More commonly used

in snow areas to allow the snow to

slide off easily, rather than have it

add excessive load to the roof frame.

Dutch gable:

This is a hip type roof with small

gables or gablets at either end of

the ridge. It may also be referred to

as a ‘half-hipped roof’ or a ‘Gambrel’.

Gable:

This is a roof with a double pitch

and vertical ends. It may also be

used as an add-on to a main roof in

the form of gablets over entries or

simply decorating the main roof

surface in the form of a dummy gable.

Gambrel roof:

This is similar to the Dutch gable

having gablets at either end of the

ridge on a hip roof. In recent times

the size of the gablet has increased

providing a more distinctive style of roof surface.



Hip or Hipped:

This is a roof with four sloping

sides on a rectangular base. The

ends are triangular in shape and the

sides form a trapezoidal shape.

Hip & valley:

This is basically a hip roof, which

is ‘T’ or ‘L’ shaped on plan. The

ridge lines are the same height for

the main and extended roof

sections.

(Broken) Hip & valley:

Again it is similar to the hip &

valley type except the ridge(s) of

the extended sections are not at the

same height as the main roof. This

creates a shortened or broken hip

used to link the minor ridge to the

major ridge.



Jerkin head: This is a roof, which is hipped

from the end of the ridge half way

down to the eaves, and gabled from

half way to the eaves. It is also

sometimes called a ‘Hipped gable’

or a ‘Clipped gable’.

Monoslope:

Also known as a ‘Monopitch’ roof,

it is any roof with a continuous

slope, which has no ridge. Skillion

and lean-to roofs are monoslope

roofs.

Student Notes.

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Skillion Roof Construction

This type of freestanding roof/ceiling frame is usually constructed by having the wall

frame at one end of the building higher than the other end. Internal walls running

parallel to the end walls would be built at different heights, depending on their location

in the building. Walls

running at 90° to the end walls would taper in height to fit under the sloping

rafters/joists. This type of roofing system may also have its ceiling lined on-the-rake or

be fitted as a false ceiling and placed level, as shown below:

The simplest method of marking the skillion rafters/ceiling joists is to scribe them over

the supporting plates in position. Once cut they are spaced at the maximum centres, to

suit the battens and roof sheets, and then fixed into position by double skew nailing to

the plates.

They are also connected to the plates with patent metal connectors to prevent wind

uplift forces.



Lean-to Roof Construction

This type of roof system is constructed against an existing wall or other roof structure. It

is mainly used for simple extensions, carports, awnings, verandah etc. and provides an

alternative to re-pitching the existing main roof to cover the extra room or space. The

ceiling finish may be one of the following:

i) The rafters and the covering may be

left exposed for a carport, verandah,

awning, etc;

ii) The ceiling may be fixed to the

underside of the rafters, making it a

raking ceiling; or

iii) A separate ceiling frame or false

ceiling may be installed to give a level

ceiling line.

Fig. 21 various methods used to line a lean-to roof/ceiling



Practical Week 1: In groups of three, students to set out and construct a skillion roof to the bases within

the workshop. The extension wall frame should already be constructed and stored

within the workshop area. Using materials available and specification on plan, students

to mark a pattern rafters, set out required amount of rafters erect and brace roof, cut in

raked plates, outriggers for barge rafter.

30

00

2300 or 3000



WEEK 2:

Gable Roofs

The gable roof is classified as being double-pitched and one of the simplest roof forms,

due to the fact that all rafters in the roof are exactly the same length and have the same

bevels.

Gables are best suited for use on buildings or structures with a simple quadrilateral

shape, which is typical of the freestanding car garage, most outbuildings, lichgates (or

lychgate), portico’s, etc.

They may also be used in a modified form, such as a gablet, to enhance the surface of

any other roof type or may also be used as a means of providing light and ventilation to

a room or roof space. Many modern roof designs use dummy gables to enhance plain

designs or to break up large areas of straight roof surface.

In a conventionally pitched gable roof there are many individual members, which have

specific structural roles to perform. Each member is reliant on the next to form an

unyielding structure and at the same time provide a framework for the roof covering.

PARTS, PROPORTIONS and DEDINITIONS

Span: This is the horizontal width of the roof, measured overall the wall plates.

Half span or Run of rafter: This is the horizontal distance measured from the centre of

the ridge to the outside of the wall plate. It is also the plan length of the rafter.

Centre line length of rafter: This is measured along the top edge of the rafter taken

from the centre of the ridge to plumb over the outside of the wall plate. It is equal to the

length of the hypotenuse of the right- ngled triangle formed by the rise and half span.

Hypotenuse: This is the sloping length of a right-angled triangle.

Rise: This is the vertical distance between the ‘X-Y’ line and where the hypotenuse

meets the centre of the ridge.

X-Y line: This is an imaginary horizontal line, which passes through the position where

the outside of the walls is plumbed up to meet the hypotenuse or top edge of the rafter.

It is used to identify the centre line positions to calculate rafter set out length and the

rise of the roof.

Plumb bevel: This is the angle found at the top of the right-angled triangle, formed by

the rise, half span and top of rafter edge. This bevel is used for the angled cut on the top

end of the common rafters.



Level bevel: This is the angle found at the bottom of the right-angled triangle, formed

by the rise, half span and top of rafter edge. This bevel is used for the angled cut on the

foot of the common rafters, where they rest on the wall plates.

Eaves width: This is the horizontal distance measured between the outside face of the

wall frame, for a timber-framed cottage, or the outside face of the brickwork, for a brick

veneer and cavity brick cottage, to the plumb cut on the rafter end

Eaves overhang:

This is the distance measured along the top edge of the rafter from the position plumb

up from the outside of the wall frame, where the X-Y line passes through the

hypotenuse, to the short edge of the plumb cut on the end of the rafter.

Birdsmouth: This is a right-angled notch taken out of the lower edge of the rafter,

where it rests on the top wall plate. The purpose of the birdsmouth is to locate the

bottom of the rafter over the wall plate and to provide an equal amount left-on so the

top edges of the rafters will all be the same. This is only necessary when rough sawn

timber is used. The depth of the notch should not be greater than ²/3 the width or depth

of the rafter, to prevent it from being weakened.

Height of the roof:

This is the vertical distance taken from the top of the wall plates to the top of the rafters

where they butt against the ridge.

Note: this should not be confused with the ‘Rise’ of the roof.



Diagram Illustrating members/ proportions of a roof



STRUCTURAL ROOF MEMBERS:

COMMON RAFTERS

These are the main sloping members, which all have the same length, running from the

wall plate to either side of the ridge. They are spaced at 450 to 600 mm centres for tiled

roofs, and up to 900 mm centres for sheet roofs. They support the roof battens, which in

turn support the roof covering.

The rafters may be set out using a variety of methods, which include use of the steel

square, full size set out and by calculating length. Since the rafters are all the same

lengths, they are usually set out from a pattern. This pattern has the cutting length,

plumb cuts and birdsmouth marked on it to allow for consistent accuracy during

repetitive mark transfer.

Note: Section size, timber species and stress grades for rafters may be obtained from AS

1684.



ROOF PITCH

All pitched roofs are based on the same simple geometric shape, the right-angled

triangle. In the case of the gable roof this shape is found on one side formed by the rise,

run or half span and centre line length of common rafter top edge.

The right-angled triangle shape contains one 90° angle and two complimentary angles,

which make up another 90°. Therefore, the angles within a right-angled triangle will

equal 180°.



Roof Pitch

The pitch or slope of the roof surface is calculated using the degree method.

Pitch is measured at the foot of the rafter in degrees. Roof pitch or Slope given in

degrees off plan

Notes:

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1000

700

Calculation of Common Rafter Set out Lengths

ROOF CALCULATION METHODS

The common method used to calculate the rise, centreline setout lengths as follows.

Step 1:

To Calculate the Rise/metre run using the degree

This method involves the same process as for calculating the drop-off,

i.e. (used during wall framing storey rod practicals)

(Note: Use the TAN button on a scientific calculator)

TAN θ = Rise/ per metre run

Eg. Tan 35˚ = 700mm / 1000mm Run.

RISE

θ

Run

Centreline set out length



Students to complete the following exercises:

Calculate the rise/per metre for the following, and sketch a triangle showing the rise

and half span (half span 1000) Scale 1:20

Example 1: 25 degrees





Step 2:

Method to Calculate the Actual Rise of a roof. (If required)

TAN θ = Rise/ per metre run x Actual Half span

Eg: = (Tan 35˚) x Say 2500

= 0.7 x 2.5

= 1.75

Step 3:

To Calculate Centreline Setout Length Common Rafter.

(Note: Use the COS button on a scientific calculator)

Centreline set out length for the original example using 35˚Pitch

Eg: Half Span ÷ COS θ

= 1000 ÷ Cos 35

= 1.221

1000

700

2500 (Actual Half Span)

1750

(Actual Rise)

1000

700

Centreline set out length = 1.221




Calculate the centreline set out length/per metre run for the following and sketch a

triangle showing the rise, half span and centreline setout length

Scale 1:20

Example1: 28 Degrees


Example3: 38 degrees



Step 4:

Therefore to Calculate the Actual centreline setout length for an actual roof.

Method 1:

Example 1: Say roof pitch 35˚, and actual Half span of 2500

Answer = (1000 ÷ Cos 35˚) x Actual Half Span (2500)

= 1.221 x 2.500

= 3.052

Method 2: (Most Common)

Answer = Actual Half Span ÷ Cos 35˚

= 2500 ÷ Cos 35˚

= 3.052

Step 5:

Calculation Method for the order lengths for Common Rafter.

This step includes calculating the setout length of the rafter including the eave width.

Example:

Say roof pitch 35˚, actual half span of 2500, eave width of 450mm

Answer = (Half Span + Eave width) ÷ Cos 35˚

= (2500 + 450) ÷ Cos 35

= 3601

Add a allowance of say 100mm (W) and round up to nearest .3 incrament.

Eg. = 3601 + 100

= 3701

Order 3900 lengths



Pattern rafter setting out points illustration



Students to Complete

Calculate the set out lengths for the given exercises.

No Pitch Rise/m Half Span Centreline setout length C/L ridge - BM

Set out length C/L Ridge- Fascia Note: Eaves 450mm

Add (W) W = 100

Order length

Formula = Half Span ÷Cos θ

Formula = (Half span+Eave width) ÷ Cos θ

1 30˚

2.000

2 16.5˚

3.200

3 15˚

2.400

4 18.5˚

2.700

5 22˚

3.650

6 28˚

3.900

7 20˚

1.800

8 19.5˚

1.650

9 24˚

2.180

Note: Eave Width 450mm, Rafter size 100 x 50mm



Students to Label and Identify members



SETTING OUT AND CUTTING RAFTERS

The common rafters for a gable roof are all the same length, have only two bevels and

may be set out from one pattern rafter. The length of this pattern rafter may set out by

calculation, as previously mentioned in calculating roof pitch, or be set out using a steel

roofing square, which will also have the two bevels required for the rafter.

THE STEEL SQUARE

A common method used to set out the length of a rafter is to use the steel roofing square.

This is a very versatile tool as it may be set up with the plumb and level bevels within

the 90° triangle formed by the square and the adjustable fence or buttons. Again, the

pitch of the roof is set up on the square using scaled measurements, which in this case

are usually half the full size proportions.

Example 1:

If the pitch or 30° it is firstly changed to a rise

per metre run, which equals 577 to 1000 mm,

then these measurements are halved to

become 288.5 to 500 mm.



Setting up the square

STEP 1: The proportion for the rise,

i.e. 288.5 mm, is placed on the tongue of the square and the run or half span, i.e. 500

mm, is placed on the blade of the square.

STEP 2: A timber fence may be used to link

the measurements and form the right-angled

triangle.

The timber fence sits on the top edge of the

rafter to be set out. This allows it to slide

along the rafter edge travelling in increments

of 500 mm, until the desired distance is

reached.

STEP 3: An alternative to the timber fence is

the use of patent type steel buttons or clips.

They are attached to the tongue and blade

measurements and then the square is used the

same as for the timber fence.

Note: When the square is turned upside down it

may be used to set out risers and treads for

stairs.

Using the steel square to set up a pattern rafter

Once the pitch of the roof has been determined, set the scaled dimensions on the square,

select a straight length of timber to use as a pattern rafter.



Forming bevels on the square

Once the scaled measurements are set on the square, with the fence or buttons fixed in

place, the plumb and level bevels will automatically be formed in the complimentary

angles of the square.

When the square is laid over the edge of a rafter these bevels may be easily transferred

as the square slides along the rafter.

Example 1:

Set up a steel square with a pitch of 30° and set out a pattern rafter, which has a run or

half span of 2700 mm and an eaves width of 400 mm.

STEP 1: Set the fence or buttons on the steel square to suit the scaled proportions,

which will provide the pitch and bevels for the roof,

i.e: Rise per metre run = 1.000

TAN 30˚ = 0.577m (Therefore 577 mm: 1000 mm)

• Divide both measurements by 2

= 577 = 288.5 mm, and 1000 = 500 m



STEP 2: Place the square over the rafter with the fence on the top edge.

Mark a plumb cut line across the face to represent the centre line of the ridge. Measure

back half the thickness of the ridge and mark a firm plumb cut line on the face. This will

be the cutting line for the top of the pattern rafter.



Measure down the top edge of the rafter from the centreline setout point and mark the

set out lengths for the Birds mouth



Roofing Calculations: Example 1

Calculate the set out length and order length for the common rafters for the gable

roof shown below.

Work out how many rafters would be needed for the roof.

Calculate the length of ridge. Specification Pitch = 280 Span = 4.600 Eaves width = 0.480 Gable overhang = 0.480 Length of building = 5.600 Ridge 150 x 25 F8 Oregon Rafters 100 x 38 F8 Oregon @ 0.450 cc’s

6.600

6.200

0.480

0.480



Question1: Calculate the Centreline set out length of Rafter from above the birdsmouth to the centre of the ridge.

ANSWER Question2: Calculate the set out length of Rafter from the inside edge of Fascia to the centre of the ridge.

ANSWER Question 3: Calculate the Order length of Rafters

ANSWER Question 4: Calculate the total number of Rafters required

ANSWER Question 5: Calculate the order length of Ridge required

ANSWER



Practical Week 2: Mark out temporary pattern rafter.

Setting out with a pattern rafter

A straight length of timber is selected for the pattern rafter, it is set out by measurement

or using the steel square. It is then cut to form a finished rafter with a plumb cut at the

top, plumb cut at the bottom and the birdsmouth checked out. A short length of batten is

then nailed directly above the plumb cut at the top and the birdsmouth at the bottom.

The pattern rafter is now ready for use.

Lay the rafters to be cut on top of a pair of saw stools with the spring uppermost. The

pattern rafter is then laid over each rafter, making sure the top edges are hard up under

the short batten, and then the plumb cuts and birdsmouth positions are transferred by

marking with a pencil.

Note: The purpose of positioning each rafter hard up against the short battens is to ensure

all the top edges will be in-line to maintain a straight roof surface.

Although the plumb cut at the bottom of the rafter may be marked and cut at this time, it

is usually better to leave the ends and cut them to a string line once the roof frame is

complete. After the first pair of rafters is marked and cut, they should be tried in place

to ensure the length and bevels are correct before proceeding with the remainder.

Exercise No1: Set out Steel Square to suit roof pitch.



Exercise no2: Students to individually mark-up pattern rafter to set given pitch and

project size

Step 1. Set out pattern rafter for gable roof with Centreline length, Cut length,

bidsmouth, and overhang

Step 2. Cut pattern rafter at centreline length and Bidsmouth check out.

Step 3. Attach cleats, each student to mark out and cut 4 rafters to their cut length and

Birdsmouths.

Specification

Rafters 90 x 35 mm 2.4 lengths

Stand up height 70mm

Eave width 300mm



WEEK 3:

Gable Roofing:

GABLE ENDS

There are three main methods used to finish the ends of gables:

1. Flush gable with no eaves;

2. Flush gable with raked eaves; and

3. Boxed gable.

Flush gables (no eaves)

The end of the gable is flush or in-line with the outside face of the end wall. The end of

the roof has no overhanging eaves, only a barge fixed

flush with the outside of the end wall. This finish may

be applied to timber framed cottages, where the walls

are clad with boards or sheeting, or to brick veneer

and cavity brick cottages, where the brickwork runs to

the underside of the roof covering. The triangular

section formed between the top of the standard wall

frame and the underside of the rafters is framed

With stud material, spaced at the same centres as the

wall frames, fixed on flat or on edge.

Fig. 43 Flush gable

Fig. 44 Framed flush gable



Flush gables with raked eaves

The gable finish for this type is similar to that of a

gable with no eaves. The main difference is the end

of the roof frame is extended past the end wall to

form an eaves overhang, which is lined on the rake.

The ridge and top wall plates may be extended to

provide support for the gable rafters. Where the

overhang is particularly wide or the length of the

gable rafters is excessive, the purlins may also be

extended to provide additional support. Fig. 45

Flush gable with raked eaves

Where the raked ends are required to adjoin

level side eaves, the ends of the eaves are usually boxed to allow the raked section to

terminate neatly

Fig. 46 framing for eaves lined on-the-rake



Boxed gable

A boxed gable occurs where it is desirable to

have level eaves on both sides and ends of the

roof. The face of the boxed gable may be clad

with the same material as the end wall, but may

also be featured by cladding with an alternative

material finish.

The fascia may be returned level around the

corner or the barge may extend to the outside

of the gutter and have a small timber ‘bellcast’

added to the top edge. Fig. 50 Boxed gable

The end of the boxed gable is framed up with gable studs, eaves trimmers and a full

width bottom chord or tie, to allow for fixing of the cladding and eaves soffit lining.

Fig. 51 framing for a boxed gable



Students to Identify Labelled Members

Legend

1

2

3

4

5

6

7

8

2

3

1

4

5 6

7

8



Students to Complete. Roofing Quiz/Calculations

1. What is the name of the two bevels used on a common rafter?

a) b)

2. Determine the rise per metre run from the following?

a) 28 degrees.= ………………………………………

Workings.

b) 31 degrees. = …………………………………………

Working

c) 25 degrees. = ………………………………………..

Workings

3. Calculate the centre line length of the common rafter for the following gable

roof?

Specification. Half Span = 3700mm

Roof Pitch = 27 degrees

Workings.

4. Calculate the centreline length plus overhang length of the common rafter for the

following gable roof?

Specification. Span = 7250mm

Roof Pitch = 30 degrees

Eave Width = 450mm

Workings.



ERECTION PROCEDURE for the GABLE ROOF

After the ceiling frame is totally complete and the rafters have been set out and cut,

follow the steps below:

Fig. 65 Completed ceiling frame

STEP 1

Measure the length of the ridge and cut to length or join lengths together if required.

Note: Allow extra length for gable overhang as required.

Lay the ridge on flat and place the top edge flush with the ends of the ceiling joists.

Using a square, transfer the rafter positions onto the edge of the ridge and square them

down the face of one side.

Fig. 66 Setting out rafter positions on the ridge board



STEP 2

Erect a pair of rafters for each end

Of the roof. Nail the feet of each pair to

the plate with the plumb cut ends

butted together.

Place a temporary nail at the top of

each pair of rafters for stability.

Lift the ridge up between the rafters

until it is flush with the top edge, or

to a marked straight line, then nail

through from one side into the end of

one rafter with 2/ 75 mm nails.

Align the opposing rafter and skew

nail from the opposite side using 2/ 75 mm nails.

Fig. 67 Fixing the first pairs of rafters to the ridge

STEP 3

Plumb one end and attach a temporary brace, to prevent racking, and then attach a

string line along the top of the ridge to ensure it remains straight while the remaining

rafters are nailed into position.

Note: Provided all rafters are exactly the same lengths and the side wall plates are

straight, then the ridge should automatically finish straight.

Fig. 68 Fix off the remaining rafters



STEP 4

Fit permanent wind bracing. This may be in the form of opposing timber braces onto an

internal wall or metal speed bracing over the surface of the rafters.

Fig. 70 Types of permanent wind bracing

STEP 5

Cut and fix gable studding into place to suit wall stud spacings and sheet cladding joins.

A pair of rafters and a bottom chord or tie forms the boxed gable frame. The studs are

cut around the rafters and tie.

Raked eaves on a gable end have the addition of a raking plate on either side, fixed

under the line of the rafters. Outriggers are supported on these raking plates with short

trimming rafters cut between them, for rafter continuity.



Initial basic Roof Bevels development drawing. Note: Drawing to be added to in coming weeks.

Students to complete on A3 paper Scale 1:100

BASIC HIP ROOF BEVELS

1. LEVEL BEVEL RAFTER2. PLUMB BEVEL RAFTER3. EDGE BEVEL CREEPER4. EDGE BEVEL PURLIN

5. PLUMB BEVEL HIP6. LEVEL BEVEL HIP7. EDGE BEVEL HIP8. FACE BEVEL PURLIN



Roofing Calculations: 2

Calculate the set out length and order length for the common rafters for the gable roof shown below.


Calculate the length of ridge.

Specification Pitch = 200 Span = 3.800 Eaves width = 0.450 Gable overhang = 0.450 Length of building = 4.600 Ridge 150 x 25 F8 Oregon Rafters 100 x 38 F8 Oregon @ 0.600 cc’s

4.600

3.800

0.450

0.450








ANSWER



Practical Week 3 Setout and construct a Flush Gable roof.

In three group’s students to set out top plates for a flush gable roof, using previous

weeks cut rafters, erect a gable roof, install wind brace to ridge, and set-out and install

gable to gable ends. Note: Studs to be cut around rafters at top and secured as required.

No ceiling joists to be installed



WEEK 4:

Technical Information 1684.2

7.2.11 Rafters

7.2.11.1 General

Rafters shall be single length members or joined over supports.

Rafters in cathedral roofs shall be designed to carry both roof and ceiling loads.

Purlins that support ceiling loads and roof loads shall be designed as rafters/purlins

with ceiling attached.

7.2.11.2 Birdsmouthing

Rafters may be birdsmouthed to a depth not exceeding one-third of the rafter depth

(see Figure 7.28).

7.2.12 Ridgeboards

7.2.12.1 General

Ridgeboards shall be provided to locate and stabilize rafter ends. Opposing pairs of

rafters shall not be staggered by more than their own thickness at either side of their

ridge junction.

The size of ridge boards shall be determined from Table 7 .6.

Junctions of ridge board and hip or valley rafters shall be strutted where the hip or

valley rafters exceed 5 m span, or where underpurlins are supported off hip or valley

rafters.

Where a ridge board is required to be strutted along its length but there are insufficient

strutting supports, the ridge board shall be designed as a ridge beam for a non-coupled

roof, or alternative provisions shall be made for the full support of the roof loads.

NOTE: An example of an alternative would be the provision of a tie-bolt truss.



7.2.12.2 Joints in ridgeboards

Ridge boards may be joined using a scarf joint at the abutment of a rafter pair or,

preferably, nail-spliced (minimum of 6 nails per side of splice) using full depth

fishplates on both sides of the ridge board

(See Figure 7.8).

NOTE: Full-length ridgeboards should be used wherever possible.

Additional Method of Joining Ridge boards

Notes:

……………………………………………………………………………………………………………………………………

……………………………………………………………………………………………………………………………………

……………………………………………………………………………………………………………………………………

……………………………………………………………………………………………………………………………………

……………………………………………………………….



7.2.10 Underpurlins

7.2.10.1 General

Underpurlins shall be in single lengths where possible and shall be in straight runs at

right angles to the direction of rafters. Where two or more rows of underpurlins are

required, they shall be spaced evenly between the ridge and the wall's top plates.

Normally spaced at 2100mm centres, butr will depend on the section size and stress

grade, including the section size and stress grade of the rafter.

7.2.10.2 Joints in underpurlins

Where underpurlins are joined in their length, the joint shall be made over a point of

support, with the joint halved, lapped, and nailed (see Figure 7.6).

Alternatively, underpurlins shall be lapped a minimum of 450 mm and spliced with 6

through-nails or 3/ No. 14 Type 17 screws or 2/MIO bolts through the splice. Laps shall

be made over a support.



7.2.10.3 Cantilevered underpurlins

The ends of an underpurlin may project (cantilever) beyond a support by up to 25% of

the maximum allowable span of the underpurlin, provided the actual backspan is at

least three times the cantilever length.

7.2.10.4 Support of underpurlins

Underpurlins shall be securely fastened to hip or valley rafters in accordance with one

of the following options:

(a) Underpurlins supporting hip or valley rafters:

(i) They shall not cantilever more than one-eighth of their allowable span.

(ii) They shall be fastened to the hip or valley using one of the following means:

(A) Cutting the underpurlin to and around the hip or valley and providing

support directly below via a roof strut.

(B) Proprietary framing anchors and blocking that provide 3 way support

(see Figure 7.7) or by a method providing equivalent support.

(C) Proprietary joist hangers.

(D) Using a proprietary/patented tension rod system (equivalent to the

old BARAP system).

(b) Underpurlins supported by hip or valley rafters shall be fastened to the hip or

valley using one of the following means:

(i) Proprietary/patented framing anchors and blocking that provide three-way

support.

(ii) Proprietary/patented joist hangers.

Where underpurlins are not strutted at the junctions with hip or valley rafters and the

allowable underpurlin cantilever is exceeded, the underpurlins shall be deemed to be

supported by the hip or valley rafters to which they are attached.



7 .2.15 Roof strutting

7.2.15.1 Roof struts

Where necessary, struts shall be provided to support roof members, such as

underpurlins ridgeboards and hip and valley rafters. Struts shall be supported off walls,

strutting beams, combined hanging/strutting beams, or combined counter/strutting

beams.

Struts shall not be supported on hanging or counter beams.

Except as provided for in Clauses 7.2.15.2, 7.2.15.3 and 7.2.15.4, struts shall be either

vertical or perpendicular to the rafters or at an angle between vertical and

perpendicular to the rafter. They shall be birdsmouthed or halved to underpurlins as

shown in Figures 7.9 and 7.10.

Alternative strutting methods

Studs supporting struts shall be determined in accordance with Clause 6.3.2.2, or top

plates shall be stiffened in accordance with Clause 6.2.2.3, as appropriate. (Refer Wall

Framing Notes) Struts that are not vertical shall be restrained by blocks or chocks, as

shown in Figure 7.10.



Supporting struts over internal walls

It is preferable to position struts directly over studs, however as this is not always

possible the load must be distributed in an alternative way. This may be achieved by

strengthening the plate either between or over the studs with additional blocking. Also,

where struts are placed at a low or flat angle, it will be necessary to fit a block, referred

to as a chock, behind the foot of the strut to prevent it from sliding under load.



7 .2.15.3 Fan struts

A pair of struts (fan or flying struts) may be used in the same line as, or perpendicular

to, the underpurlin with their supports opposing each other. The pair of struts shall be

at the same angle, and not greater than 45° to the vertical, as shown in Figure 7 .12.

Maximum fan strut length shall be 4.5 m with maximum 3.0 m spacing between the

struts and underpurlin connection.

Alternative Methods to support Roof strut and Loads



Scissor struts

These struts consist of deep-sectioned timber members supported over external walls

and bolted where they cross in the centre of the roof space.

They are designed to transfer the roof load to the external walls where there are no

internal walls for support or the internal walls are non-load-bearing. Note :( Requires

Engineer Certification)

If there is internal support available, but would cause an inclined strut to be too flat to

be effective, then a half scissor may be used.



COLLAR TIES

They are light sectioned horizontal members used for additional support, like

spreaders, to prevent the rafters from sagging at the purlin position.

These are fixed to alternative pairs of rafters, i.e. at 900 to 1200 mm spacings, and

placed on top of the purlins running parallel to the ceiling joists. They may be half

scarfed around the face and edge of the rafters and

nail fixed with 2/75 mm nails.

Alternatively, they may be run past the face of the

rafters and be bolted to them at both ends using a

single 10 mm Min. mild steel, cuphead bolt.

Fig. 41 Collar tie fitted to rafter over purlin

Note: The size of collar ties depends on the stress grade and length of timber used. As a

guide, they are normally 75 x 50 or 125 x 38 F5 to F7 up to 4200 mm long, and 100 x 50 or

125 x 38 F5 to F7 over 4200 mm long. Refer to AS 1684 for specific details.

Fig. 42 Placement of collar ties in the roof frame



Member section sizes AS1684.2



Students to name the parts of the Gable roof Indicated.



Roofing Calculations: 3

Calculate the set out length and order length for the common rafters for the gable roof shown below.


Calculate the length of ridge.

Specification Pitch = 330 Span = 8.600 Eaves width = 0.450 Gable overhang = 0.450 Length of building = 17.600 Ridge 145 x 35 MGP 10 Radiata Pine Rafters 90 x 45 MGP 10 Radiata Pine @ 0.450 cc’s (Max Length 5700)

17.600 8.600

0.450

0.450








ANSWER



Practical Week 4 Set out and Construct Raking Gable roof Including Underpurlins Struts, Collar Ties.

Fascia and Raking Eaves

Using Existing Rafters from previous week set plates to suit 600mm centres on existing

bases. Position rafters, mark out and construct gable end with raking plate and studs to

suit. Cut in trimmers to support barge rafter with a gable end overhang of 300mm

Students to position internal wall plates for internal wall strutting, re-position under

purlins, cut in struts to suit (Note: See following Page).

Fix off Fascia board as required and install eave sheets.



Roof Strut Installation

Diagrams illustrating methods of marking Inclined and Vertical Struts in one step.

Inclined Strut:

Note Clamp Strut material to Inside face of Under purlin

Vertical Strut:

Note: Clamp Strut plumb to top of wall plate in line with inside face of underpurlin



WEEK 5:

Intoduction Hip Roofing

These roof types are similar to the gable roof as they have two equal sloping surfaces

joined on a common ridge, but they have the addition of two sloping surfaces on either

end. The framing members are similar also with the addition of several new members

such as hips.

The common plumb and level bevels will now make up 2 of the 8 bevels required to

pitch these roof shapes.

A hip roof has four sloping or pitched sides and a rectangular

base. The hip ends are triangular in shape and the sides have

a trapezoid shape. The inclined rafters at either end of the

ridge will brace the roof.

Fig. 1 The hip roof

A hip & valley roof is simply a modified or extended hip roof. The shape and pitch of the

surfaces are basically the same, however the base shape changes from a simple

rectangle to a ‘T’ or ‘L’ shape, on plan. The hip & valley roof

has an additional ridge, which joins the main roof ridge at

the same height, which creates a single valley for an ‘L’

shaped roof. It may also join the roof surface at the same

height or at a lower level on a side or end, without

connection to a hip, creating two valleys for a ‘T’ shaped

roof.

Fig. 2 The hip & valley roof



PRINCIPLES of ROOFING

There are three main principles related to roofing, which are critical to the accurate

construction of roofs in general:

1. All ridges must be level and parallel to wall plates;

2. All rafters must be placed at 90° to the wall plates, regardless of the roof shape;

and

3. All external and internal corners must be bisected to allow for correct placement

of hips and valleys, regardless of the angle.

PARTS, PROPORTIONS and DEFINITIONS

Span: This is the horizontal width of the roof, measured overall the wall plates.

Half span or Run of rafter:

This is the horizontal distance measured from the centre of the ridge to the outside of

the wall plate. It is also the plan length of the rafter.

Centre line length of rafter:

This is measured along the top edge of the rafter taken from the centre of the ridge to

plumb over the outside of the wall plate. It is equal to the length of the hypotenuse of

the right-angled triangle formed by the rise and half span.

Rise: This is the vertical distance between the ‘X-Y’ line and where the hypotenuse

meets the centre of the ridge.

X-Y line: This is an imaginary horizontal line, which passes through the position where

the outside of the walls is plumbed up to meet the hypotenuse or top edge of the rafter.

It is used to identify the centre line positions for the purpose of calculating rafter set out

length and the rise of the roof.

Eaves width:

This is the horizontal distance measured between the outside face of the wall frame, for

a timber-framed cottage, or the outside face of the brickwork, for a brick veneer and

cavity brick cottage, to the plumb cut on the rafter end.

Eaves overhang:

This is the distance measured along the top edge of the rafter from the position plumb

up from the outside of the wall frame, where the X-Y line passes through the

hypotenuse, to the short edge of the plumb cut on the end of the rafter.



Birdsmouth: This is a right-angled notch taken out of the lower edge of the rafter,

where it rests on the top wall plate. The purpose of the birdsmouth is to locate the

bottom of the rafter over the wall plate and to provide an equal amount left-on so the

top edges of the rafters will all be the same. The depth of the notch should not be

greater than ²/3 the width or depth of the rafter, to prevent it from being weakened.

Height of the roof:

This is the vertical distance taken from the top of the wall plates to the top of the rafters

where they butt against the ridge.

Note: this should not be confused with the ‘Rise’ of the roof.

Roof bevels for Hip Roofs

(1) Plumb bevel:

This is the angle found at the top of the right-angled triangle, formed by the

rise, half span and top of rafter edge. This bevel is used for the angled cut on the

top end of the common rafters.

(2) Level bevel:

This is the angle found at the bottom of the right-angled triangle, formed by the

rise, half span and top of rafter edge. This bevel is used for the angled cut on the

foot of the common rafters, where they rest on the wall plates.

(3) Edge bevel creeper:

This is the angle found at the top corner of a right-angled triangle, formed by the

proportionate size of the true length of hip and the half span. This bevel is used

for the angled cut on the top edge of the creeper rafters, where they cut against

the hip.

(4) Edge bevel purlin:

This is the angle found at the bottom corner of a right-angled triangle, formed by

the proportionate size of the true length of hip and the half span. This bevel is

used for the angled cut on the top edge of the purlin ends, where they join under

the hip.



(5) Plumb bevel hip:


proportionate size of the plan length of hip and the rise. This bevel is used for the

angled cut on the face of the hip rafters, where they cut against the centring and

crown end rafters.

(6) Level bevel hip:

This is the angle found at the bottom of the right-angled triangle, formed by the

proportionate size of the plan length of hip and the rise. This bevel is used for the

angled cut on the foot of the hip rafters, where they rest on the wall plates at the

external corners.

(7) Edge bevel hip:


proportionate size of the true length of hip and the plan length of hip. This bevel

is used for the angled cut on the top edge of the hip rafters, where they cut

between the centering and crown end rafters.

(8) Face bevel purlin:


proportionate size of the true length of common rafter and the rise. This bevel is

used for the angled cut on the face of the purlins, where they join under the hip.

Note: The hip bevels may also be used for the cuts on the valley



STRUCTURAL ROOF MEMBERS

Apart from the fascia and trimmers, all the roof framing members would be considered

to be of structural significance. Each member relies on the next for strength and

support, which is why the roof frame must be correctly constructed with neat fitting

joints and securely fixed connections.

The detail below shows the various members contained in a hip and a hip & valley roof

frame:



ROOF PLAN LAYOUTS

The following rules should be adopted, when determining the position of plan roof

members:

1. All angles formed by the external wall plates must be bisected;

2. Only one member is drawn from any one corner;

3. Hips are formed where the wall plates create an external corner;

4. Valleys are created where an internal corner is formed by two plates;

5. Rafters are always set at 90° to the wall plates; and

6. A ridge will always be level and parallel to the external wall plates.

PLANNING the ROOF SHAPE

STEP 1 Select the largest rectangular area and mark its outline STEP 4 Draw in ridge positions for each

extension.

STEP 2 Lightly draw the outline

of a hip roof on this area. STEP 5 Remove any unwanted lines

STEP 3 Bisect all other external

and internal corners. STEP 6 Firm in the roof plan to ensure correct intersection connections.



Students to complete the ROOF PLANS and ELEVATIONS

Exercise 2



COMMON RAFTERS

These are the main sloping members, which all have the same length, running from the

wall plate to either side of the ridge. They are spaced at 450 to 600 mm centres for tiled

roofs, and up to 900 mm centres for sheet roofs. They support the roof battens, which in

turn support the roof covering.

The number of common rafters in a hip roof are restricted to the length of the ridge with

the rafters on either side, at the end of the ridge, being referred to as centering rafters.

The rafters may be set out using a variety of methods including use of the steel square,

full size set out and by calculation.

Since the rafters are all the same lengths, they are usually set out from a pattern. This

pattern has the cutting length, plumb cuts and birdsmouth marked on it to allow for

consistent accuracy during repetitive mark transfer.

Note: The common rafters for the hip roof are set out the same as the gable roof. Section

size, timber species and stress grades for rafters may be obtained from AS 1684.

RIDGE

Usually a deep and narrow member, it is the highest member of the roof, which runs

horizontally for the length of the roof, less twice the half span, plus one rafter thickness.

(Hip Roof)

It must be level and parallel to wall plates for its length with the rafters being nail-fixed

onto it on opposite sides. The ridge on a hip roof may be joined in length as for a gable

roof.

The ridges are butt jointed together at the same height to form a hip & valley ‘T’ or ‘L’

shape. The length of the ridge forming the ‘T’ or ‘L’ shape will be equal to the length of

the wall plate extension, plus half the thickness of a rafter, less half the thickness of the

ridge.

Note: Refer to AS 1684 or Timber framing manual for tie-down details.



CENTERING RAFTERS

These are simply common rafters, which are used to position the ridge and form the

first part of the apex cluster. They are called centring rafters because they centre the

ridge and provide the basic pitch of the hip roof.

CROWN END RAFTERS

The crown end rafters are cut and fitted against both ends of the ridge to form the

sloping end sections. They act as opposing braces making the hip roof a strong self-

braced frame.

The length of the crown end is similar to the common rafter, apart from the top end

deduction, i.e. it is shortened by half the rafter thickness as opposed to the half ridge

thickness of the common rafter.



The diagram below illustrates the centreline set outs/cluster position and shortening

distances required to set out a hip roof construction.

1: Note the length of Ridge required

2: The shortening length for the centring rafters are shown

3: The crown end rafter shortening distance can be determined





Pattern Rafter set out Crown End Rafter



Hip Roof Rafter and Ceiling Joist Set out, Marking out the Top Plates & Ridge

For Hip Roofs Top Plates

Step 1 Determine the roof span and measure out from the comers marked "A" the

distance A-X This represents half span. Mark these positions on the top plates.

Step 2 Mark out the thickness of the. Crown end rafters and centering rafters. These are

located centrally over the half span "X" lines.

See fig 9·

Step 3 From these positions commence setting out rafter spacing’s towards the building

corners. Do not be concerned if the end spacing is shorter.

Step 4 Common rafter positions along the ridge board can be equally spaced but do not

exceed the maximum spacing specified in the plans.

Step 5 Mark the positions for the ceiling joists and ceiling trimmers by placing a J or T

next to each rafter.

Ridge To mark rafter positions on the ridge, lay the ridge across the ceiling joists or top

plates and transfer the applicable rafter positions directly across, Square these marks

onto both sides of the ridge.

Centre line length of ridge

= Length of building- Width of building

Cut length of ridge

- (Length of building- Width of building) + Rafter thickness



Hip Roof

FIG 9 Set out crown end rafters and centring rafters first. These are all measured half

span from the comers.

NOTE:

Centre line length of ridge

= Length of building- Width of building

Cut length of ridge

= (Length of building- Width of building) + Rafter thickness



Class exercise

Students to complete the drawing below to represents the centre lines for the

intersections of hips, ridge, centring and crown end rafters.

Using a scale of 1:2, Show how those members meet at the ridge and name them.

Specification. Hips and ridge 150 x 25.

Rafters 100 X 50.



Class exercise: Complete the part drawn side elevation of a ridge board. Drawing to show. 1. Centre line set out length of ridge in mm 2. Actual cut length of ridge in mm 3. Position of all remainder rafters 4. Name all rafter types. Specification. 140 x 25 mm Ridge board 90 x 45 Rafters @ 600 centres Hip roof pitched at 35 degrees Length over wall plate = 6500 Span or overall wall plate = 4900 Eave width = 600mm

Scale 1:10.

Side Elevation of 140 x 25 mm Ridge Board.



Students to complete the following exercise setting out location of Rafters for a hip roof. Mark out the wall plates to show the correct position of all rafters and ceiling frame members to suit a hip roof pitched at 25 degrees. Specification: Legend: 100 X 50 Rafters at 600centres CR = Centring Rafter 100 X 50 Ceiling Joists at 600 centres CE = Crown End 100 X 50 Ceiling Trimmers at 600 centres. R = Rafters J = Ceiling Joists SCALE 1:20 T = Ceiling Joist trimmers



Practical Week 5: Hip Roof Practical

Step 1. Students to cut in and set out new top plates on bases to work shop, rafter

set out to suit hip roof layout. Rafters 450 centres

Step 2.Cut in ridge board, crown end rafters and common rafters to suit.

Step 3.Construct hip rafters in preparation for installation.

1/90 x 35 +1/42 x 35 Rip screwed together at 3.6m long Total 4 hips per group.

Step 4. Mark out top plates for hip location and cut corners as required.

Note: PREPARING the EXTERNAL CORNERS

The external corner of the wall plates is cut square to receive the square-edged plumb

cut of the hip. The thickness of the hip is marked on the corner of the plates, then the

distance from the corner to the square mark is measured, equal to ‘X’, and deducted

from the centre line length to establish the cutting position.

Note



WEEK 6:

Hip Roofing Continue,

HIPS

The hips are deep-sectioned members, which run from the external corners of the wall

plates to the end of the corner formed between the centring rafter and the crown end

rafter. The hips bisect the 90° external corners at 45°, when viewed on plan or are

placed at the appropriate bisected angle for external corners other than 90°, as would

be the case for a semi-octagonal ended hip roof.

Note: Refer to AS 1684 or Timber framing manual for tie-down details.



Calculation of Hip Rafter Length

Two methods Used

Method 1:

The length of the hip is calculated using the same method as for common rafters. A new

‘true length per metre run’ must be established as the pitch is lower due to the hip being

placed at 45° to the plates.

Example 1:

Calculate the length of the hip for a roof with a pitch of 30° and a half span of 3400 mm.

STEP 1: Rise per metre run = Tan 30

= 0.577m

This is the rise per metre run for all members, i.e. common rafters, hips, etc., which runs

at 90° to the walls plates.

The next step is to establish the run or plan length of the hip, which is at 45° to the wall

plates.

This requires a constant to be calculated based on a metre run.

Note: The rise remains unchanged, i.e. 0.577m

Fig. 32 Plan length of hip per metre run

STEP 2: Calculate a constant per metre run

= a² = b² + c²

= a² = 1.0² + 1.0²

= a² = 1.0 + 1.0

= a² = √ 2

Therefore: ‘a’ = 1.414m



STEP 3: Calculate the true length per 1.414 of run

= a² = b² + c²

a² = 1.414² + 0.577²

a² = 1.999 + 0.333

Therefore, ‘a’ = √ 2.332

= 1.527m

Therefore, for every 1.0m of run or half span the true

length of the hip will be 1.527m

(Note: This is centreline setout length)

To calculate the actual Centre Line set out length of Hip

For example 1

STEP 4: Find the centre line length of the hip,

i.e. Centreline of Ridge to Birdsmouth

= half span x true length hip/metre run

= 1.700 x 1.527

= 2.596m

Step 5: Find the actual set out length of hip including eaves,

i.e Centreline ridge to inside edge of Fascia,

= (Half span + Eave width) x true length hip/metre run

= (1700 + Say 450 wide eave) x 1.527

= 2150 x 1.527

= 3.283



Centreline set out

length C.R = 2.483

Centreline set out length Hip

C/L Ridge to Fascia

Method 2:

Using Pythagoras and the set out lengths of Common rafter the actual hip length can be

calculated.

Example: Using previous exercises span, pitch and eave width.

i.e Span = 3400, Pitch = 30 degrees Eave width = 450mm

Step 1: Calculate the actual set out length of Common rafter,

From centreline of ridge to inside of fascia.

Formula = Half span + Eave width ÷ Cos 30

= (1700 + 450) ÷ Cos 30

= 2150 ÷ Cos 30

= 2.483

Step 2: Calculate set out length of hip,

From centreline of ridge to inside of fascia, using Pythagoras

a²= b²+ c²

Centreline set out length of hip (C/L Ridge to Fascia)

= √ Set out length of common rafter² + (Half span + eave)²

= √ 2.483² + 2.150²

= √ 10.785

=3.283

(Same as previous example)

Illustration 1.



1414

532

Calculate the centreline setout length Hip Rafter


Calculate the centreline set out length/per metre run for the following hip rafters and

sketch a triangle showing the rise, plan length hip

Scale 1:20

Example1: 28 Degrees

ie: Tan 28° = 532mm / meter run, Plan length Hip = 1.414

Centreline set out length hip = √ Rise² + Plan Length Hip²

= 1.511


Example3: 38 degrees



Example 4: Calculate the Actual centreline length for a hip no eaves

Roof Pitch = 28 Degrees

Span = 3500

Workings:

Example 5: Calculate the actual centreline length of a hip and cut length including eaves

Roof pitch =21 degrees

Span = 5000

Eave width = 450mm

Workings:



Hip Roofing Calculations: 1

Calculate the set out length and order length for the common rafters for the Hip roof shown below.

Calculate the setout lengths and order lengths for the hip rafter.


Calculate the length of ridge. Specification Pitch = 280 Span = 3.800 Eaves width = 0.450 Length of building = 4.600 Hips & Ridge 150 x 25 F8 Oregon Rafters 100 x 38 F8 Oregon @ 0.600 cc’s

4.600

0.450

0.450

3.800







ANSWER Question 5: Calculate the cutting length of Ridge required

ANSWER



Question 6: Calculate the Order length of Ridge

ANSWER Question 7: Calculate the length of the hip rafter from inside the fascia to the centre of the ridge?

ANSWER Question 8: Calculate the order length of hip rafter?

ANSWER



DEVELOPING BEVELS on the STEEL SQUARE

This method allows all the roof bevels to be produced on the steel square, shown as

proportional lengths, and then some of the set positions may also be used to step out

the lengths of the rafters.

For example, when the steel square has the plumb and level bevels for common rafter

set it may be used to set out the common rafters and all the hip and valley creepers.

Also, when the steel square has the plumb and level bevels for hip rafter set it may be

used to set out the length of the hip and valley rafters.

Setting out these lengths will depend on the measurement used on the blade of the

square, as this measurement is divided into the run or plan length to determine the

number of times the square is moved along the rafter.

PRODUCING BEVELS

The 8 bevels are produced based on the rise per metre run proportions, which is

dependent upon the pitch of the roof. The proportions are calculated and then reduced,

proportionately, to fit onto the blade and tongue of the square. The position of the

proportions on the square will be the same as they occur in their actual position in the

roof, based on the right-angled triangle proportions previously stated in the Geometric

method.

Example 1: Set the bevels on the steel square based on a hip roof, which has a pitch of 30°, and a

metre run

1. Plumb and 2. Level bevel common rafter

These bevels are formed in a 90° triangle consisting of the rise and run or half span.

(Proportions of both these lengths may also be used)

STEP 1: Rise per metre run Tan 30° = .577

To fit the measurements onto the steel square,

divide both by 2

STEP 2: Divide rise by 2 = 577 ÷ 2 = 288.5

Divide run or ½ span = 1000 ÷ 2 = 500



3. Edge bevels Creeper and 4. Edge Bevel Purlin

These bevels are formed in a 90° triangle consisting of the true length common rafter

and run or half span. (Proportions of both these lengths may also be used)

STEP 1: Calculate true length C.R = a² = b² + c²

=√ Rise² + Run²

= √577² + 1000²

= √0.333 + 1.0

= √1.333

= 1.155m

To fit the measurements onto the steel square, divide

both by 3

STEP 2: Divide T.L.C.R by 3= 1.155÷ 3 = 385

Divide ½ span = 1000÷ 3 = 333

5. Plumb and 6. Level bevel hip rafter

These bevels are formed in a 90° triangle consisting of the rise and plan length of hip.


STEP 1: Plan length hip = √Run² + Run²

= √1.0² x 1.0²

= 1.414m

To fit the measurements onto the steel square,

divide both by 3

STEP 2: Divide rise by 3 = 577÷ 3 = 192

Divide plan length hip = 1414 ÷ 3 = 471



7. Edge bevel for hip

These bevels are formed in a 90° triangle consisting of the plan length hip and true

length hip. (Proportions of both these lengths may also be used)

STEP 1

Calculate true length hip = a² = b² + c²

=√ Rise²+ Plan length Hip²

=√577² + 1414²

=0.333 + 1.999

= √ 2.332

= 1.527m

To fit the measurements onto the steel square, divide both

by 4

STEP 2 Divide PL Hip by 4 = 1.414÷ 4 = 354

Divide TL Hip by 4 = 1.527÷ 4 = 382

8 . Face bevel purlin

These bevels are formed in a 90° triangle consisting of the rise and true length C.R.


STEP 1 Calculate true length C.R = a² = b² + c²

= √577² + 1000²

= √0.333 + 1.0

= √1.333

= 1.155m

To fit the measurements onto the steel Square, divide

both by 3

STEP 2 Divide rise by 3 = 577÷ 3 = 288.5

Divide TLCR by 3 = 1.155÷ 3 = 578



19

2

19

2



Alternative Method for setting out Roof Bevels.

Roof bevels can be set out geometrically on paper :

Completion of Hip Roof bevel Development from week 3:

OF

FS

ET

PLAN LENGTH HIPHALF SPAN

PL

AN

LE

NG

TH

HIP

OFFS

ET

T.L. HIP

RIS

ER

ISE

T.L.RAFTER

4

8

2 5

1

3

6

7

PLAN LEN

GTH

HIP

PROJECTED PLAN LENGTH HIPHALF SPAN

BASIC HIP ROOF BEVELS

1. LEVEL BEVEL RAFTER2. PLUMB BEVEL RAFTER3. EDGE BEVEL CREEPER4. EDGE BEVEL PURLIN

5. PLUMB BEVEL HIP6. LEVEL BEVEL HIP7. EDGE BEVEL HIP8. FACE BEVEL PURLIN

HA

LF S

PA

N



Onsite methods used to establish hip rafter lengths. There are four methods used:

1. Scribing; 2. Measured in-situ; 3. Calculation; and 4. Steel square set out

The two main methods used on site today constructing roofs are Method 1 and 2

Method 1: Scribing

STEP 1 The top end is prepared using the plumb cut for hip on the face and the edge cut

for hip from both sides of the centre, on the top edge. The amount to be ‘left-on’ the hip,

which is equal to the amount left-on the common rafters, (SUH) is gauged from the top

edge at the top end of the hip. This marking is repeated at the approximate position of

the birdsmouth.

STEP 2 The top cut end of the hip is laid between the centering and crown end rafters

with the left-on’ gauge mark being placed in-line with the top edge of the rafters. The

lower end of the hip is laid on top of the prepared external wall plates with at least part

of the ‘left-on’ gauge mark directly above the corner.

STEP 3 Place a rule or spirit level plumb against the external plate corner and scribe a

plumb line up to the ‘left-on’ gauge mark. Mark a 90° line from this intersection to form

the birdsmouth for the hip.

Note: SUH

Note: SUH can be

measured up from

bottom



Method 2: Measured in-situ

This method involves a direct measurement being taken in-situ and transferred onto

the hip rafter.

STEP 1 The top end is prepared using the plumb cut for hip on the face and the edge cut

for hip from both sides of the centre, on the top edge.

STEP 2 The amount to be ‘left-on’ the hip, which is equal to the amount left-on the

common rafters, is gauged from the top edge of the hip above the approximate position

of the birdsmouth.

STEP 3 A measuring tape is held at the intersection of the centering and crown end

rafters and extended down to the square cut at the external corner of the wall plates.

STEP 4 Lay the tape along the side of hip from the plumb cut at the top to the gauged

‘left-on’ position marked at the approximate birdsmouth position. Mark the length and

set out the birdsmouth, using plumb and level bevel hip, ready to cut.

Fig. 30 measuring the length of the hip in-situ

Fig. 31 marking the face of the hip



Practical Week 6: Students to set out Steel Square for hip rafters, construct hip roof with crown end and

set out mark and cut hips into position.

Development and Setting out Plumb and Level Bevel Hip Rafter

Steel Square Method.

This method is similar to setting out the common rafter with the steel square, except the

proportions on the square are changed. The tongue will have the rise per metre, Say i.e.

577 mm, but the blade will have the constant for the plan length of hip, i.e. 1414 mm.

Example Only

These two measurements are scaled down to fit onto the square:

577 = 192 mm and 1414 = 471 mm

3 3

Proportions for the Steel Square

Note: Students to set Steel Square to

their given pitch

Ensure corners of wall plates are cut to

suit hip roof



WEEK 7:

Hip Roofing Member Revision

Students to identify and name members in table below.

Roof members

1

2

3

4

5

6

7

8

9

10

11 12

13

14

15



Class Practical Steel Square Set out Exercise

Students to complete additional steel square set out exercise. To be used in workshop

tasks

Specification: Pitch = 35 Degrees

Step 1. Calculate Rise/ m run. =

Step2. Run =

Step 3. Calculate True length common rafter / m run. =

Step 4. Plan Length Hip. =

Step 5.Calculate the true length hip / m run. =





Calculation and Marking out creeper Rafters.

These are basically common rafters, which are shortened by equal amounts to fit

against the face of the hips at the maximum rafter spacing. The lower end is identical to

the common rafters but the top end has a compound cut, i.e. face and edge cuts, which is

formed by the plumb bevel for common rafter and the edge bevel for creeper.

They are usually set out from a pattern rafter and cut in pairs to fit on either side of

the hips.



Determining the length of the first creeper

Creeper set out Method.

One of the common methods is using the set out from the centring rafter and crown end

towards the outside of the wall plate corner. And mark lengths on the Pattern Rafter.

The long point of the creeper is set out first by measuring the rafter spacing on the

plates. Measuring from face of the hip, along the outside of the wall plate to the long

point side of the first creeper. This distance will be referred to as Distance ‘X’.

To calculate the set out length of the first creeper, (shortest creeper)

divide Distance X ÷ Cos° (Pitch of roof)

Eg1: Say distance X = 140mm ÷ Cos 35 = 171mm

Once the position of the outside face and long point for the first short creeper is

established, the remainder of creepers are set out towards the crown end and centring

rafters. To establish the length of the remainder creepers the rafter spacing distance is

used.

“DISTANCE X”



Calculating second creeper length and remainders we use the rafter spacing distance

Eg2: Rafter spacing Say

= 450mm therefore the set out length would be equal,

= Rafter spacing ÷ Cos° longer than the previous creeper.

= Rafter spacing 450mm ÷ Cos 35 = 549mm longer than the first creeper mark.

Note: Each creeper will be 549mm longer than the last.

.

Distance X

Rafter Spacing



PATTERN RAFTER SHOWING CREEPER POSITIONS



Additional Roof Members

PURLINS

Purlins, also known as underpurlins, are fixed to the underside of the rafters parallel to

the ridge and wall plates. They provide continuous support under the rafters similar to

bearers under joists in a floor frame. They are normally spaced at 2100 mm centres,

but this will depend on their section size and stress grade, including the section

size and stress grade of the rafters.

They are placed in a continuous line around the four sides of the hip roof and joined at

external corners, under the hips.

The ends of the purlins, under the hip, have a compound cut consisting of the face bevel

purlin and edge bevel purlin. The ends may be cut tight against the face of the hip on

either side or have a notch taken out of the edge of both lengths so they fit tightly under

the bottom edge of the hip for extra support

.







Calculate the length of ridge. Specification Pitch = 300 Span = 8.400 Eaves width = 0.450 Length of building = 12.000 Hips & Ridge 145 x 35 MGP 10 Rafters 90 x 45 MGP 10@ 0.600 cc’s

12.000

0.450

0.450

8.400








ANSWER






ANSWER



Practical Week 7. Approx 6 Hrs. Mark out pattern rafter for creeper rafter

lengths, each student to cut creepers for one corner. Each group to erect the hip roof

including creepers, underpulins, collar ties.



WEEK 8:

Student Exercise Steel square set out exercise

Students to develop the steel square bevels for a hip roof with a pitch of 28 degrees

Steel Square Set Out

Step 1. Calculate rise = Tan ø =

Step 2: Run / I/2 Span = 1000

Step 3. Calculate TLCR =

Step 4. Plan Length Hip = 1414

Step 5. Calculate TLHR =

Mark out Steel square, Set out points to develop the roof bevels.

Bevel 1 Bevel 2

Plumb bevel common rafter. Level bevel common rafter

Bevel 3 Bevel 4

Edge bevel creeper Edge bevel purlin



Bevel 5 Bevel 6

Plumb bevel hip Level bevel hip

Bevel 7 Bevel 8

Edge bevel hip Face Bevel Purlin



Student exercise : Creeper Rafter Length Calculations.

For the following exercises Students to calculate the setout lengths for the creeper

rafter.

Specification: Roof Pitch 38 degrees

Rafters 90 x 45 at 600centres

Hip Rafter 140 x 35

Question 1. Calculate the long point length of the first creeper rafter shown above?

Workings =

Question 2. When setting out the remainder creeper rafters lengths, how much longer

would they be?

Workings =







Calculate the length of ridge. Specification Pitch = 240 Span = 7.400 Eaves width = 0.450 Length of building = 15.000 Hips & Ridge 145 x 35 MGP 10 Rafters 90 x 45 MGP 10@ 0.450 cc’s

15.000

0.450

0.450

7.400








ANSWER






ANSWER



BROKEN HIP and VALLEY ROOFS

These roofs are created when a hip roof is built on an irregular shaped base having a

number of different spans. When the wall frame plan resembles a ‘T’ or ‘L’ shape, each

span will have its own hip roof.

Where these hip roofs connect with one another a ‘Broken hip’ is created, which ties the

higher ridges to the lower ridges.



TYPICAL BROKEN HIP and VALLEY ROOF SHAPES



Broken Hip & Valley Member Names and Positions



VALLEYS

A valley is formed where a secondary

ridge abuts a main ridge or is cut into the

surface of one or more sides at a lower

level than the main ridge.

This occurs in an ‘L’-shaped hip or gable

roof, which will have one valley, or in a

‘T’-shaped hip or gable roof, which will

have two valleys.

The valley is set out, cut and fitted in a

similar way to the hips with valley

creepers cut onto either side, similar to

hip creepers.

A typical detail is shown below for an

‘L’-shaped hip roof outlining the valley

members and the detail of the apex

cluster:



Hip and valley roofing

Methods used to establish valley length

Generally, the same methods may be used as for the hip length, however the method

shown here is the simplest for marking the valley length.

Fig. 48 scribing the length of the valley in-situ



Measuring and setting out Valley Creepers

Setting out Valley creeper rafter lengths from the Birds mouth.

(Note: Similarity between hip and valley creepers.)

Step1.

Establish rafter set out on plates, Crown End

rafters and centring rafters positioned and

marked first.

Step2.

Mark out Valley creeper positions

Step3.

Distance X is measured off the wall plate to the

first valley creeper (Longest)

Step4.

Distance X is divided by Cos˚

Step5.

The setout length is marked on the pattern

rafter from the birdsmouth down the rafter first to

establish Point 1. (ie. overhang side)

Step6.

Set out the remainder creepers from Point 1. By

using the rafter spacing (Point 2.)Calculate the

diminishing amount by, rafter spacing's divided

by Cos˚. (Note: Similar process to hip creepers.)

Step7.

On the pattern rafter from point 1 use the diminishing

calculated amount to set out for Creeper no2 travelling up the

rafter and repeat until all creepers are marked. This will give you pattern rafter with all

creeper cut lengths for that span at roof.

Valley creeper spacing

Valley c

reeper

spacin

g





Hip and Valley Roof Construction



VALLEY BOARDS and GUTTERS

Valley gutters may be galvanised iron,

Zincalume® or Colorbond® protective finish. They are

available in 1.8 to 2.4m standard lengths.

The valley gutter must not be rigidly fixed down to the

valley boards as it requires some allowance for movement

due to expansion when heated up. Failure to allow for

movement may result in the valley gutter buckling, in

extreme conditions.

The best and simplest method of fixing valley gutter into

place is to drive 75 mm nails into the valley boards on

either side of the valley gutter and then bend them over the

gutter’s edge. This provides secure fixing to prevent the

gutters lifting but allows for sliding length-ways at joins,

when the gutters expand.

The bottom end of the valley gutter should extend 50 mm,

± 15 mm, into the eaves gutter to prevent water splashing

over the back edge of the eaves gutter.

The tiles in an open valley, as shown in the section through

roof valley, should have a horizontal distance of 125 m

between the valley tiles. This allows leaves, sticks, debris, etc. to wash down into the

gutter.



Practical Week 8 Set out and construct a Hip and Valley Roof.

Students to construct an extension to the existing bases to suit a hip and valley roof ie

3000 x 2300. Set out location of rafters, position centring, crown end common and hip

rafters to suit. Cut in new valley rafter and mark out valley creepers to suit.



WEEK 9:

SCOTCH VALLEY CONSTRUCTION This method is used as an alternative to conventional construction to form a valley. The

valley board is replaced with a ‘Lay board’, which is laid on top of the rafters to form a

fixing platform for the feet of the minor span valley creepers.

The scotch valley is mainly used where an addition is added to an existing building. It

provides a quick and very efficient method of construction, requiring little or no

disturbance to the existing roof.

The existing rafters remain in place to

support the lay board, which in turn

supports the feet of the valley creepers.

This system may also be adapted for use

where dormer windows are built into

existing roofs

Fig. 140 Application of the scotch valley



Method of Construction

The following method is applied to roofs having the same pitch.

STEP 1 Locate the height of the minor

span ridge on the common rafters of the existing main

Fig. 142 obtaining ridge height STEP 2 Position the ridge and rafters to

form the minor roof.

Fig. 143 framing up the minor span

Ridge Length Minor Span = (Length of wall plate

+ Half span minor roof – half thickness of ridge

Angle cut to ridge

= Level bevel

Common Rafter

Mark out the layboard

thickness above the

existing roof line onto the

ridge and first rafter minor

span marking the internal

corner/face with similar

thickness material as

Minor span

rafter



Edge Bevel Creeper (Saw

set at 90°

Edge Bevel Purlin

(saw set to pitch of roof ie

35° When cutting the foot cut to the valley

Creeper. Set the saw at the angle of the roof

pitch ie 35° (See next Page)

STEP 3 Measure the length of the lay board, then cut and fix into position.

Fig. 144 Measuring the lay board

STEP 4 Measure the length of the longest creeper.

Use plumb bevel common rafter for the top of the creeper and level bevel common rafter

and edge bevel creeper for the compound foot cut.

The remainder of the creepers can be set out

using the steel square or by calculating a

Deduction from long point to long point.



Scotch Valley Completion,

Fig. 145 Cutting and fixing the valley creepers

Practical week 9 Students to construct a scotch valley roof.

Using existing base frames, students to construct a T shape building to create a scotch

valley to middle of frames, approx extensin built to two sides of frames 1800 x 1085.

Rafters to scotch valley to be spaced at 350 centres. Construct a hip roof to the main

structure of roof using existing hip roof components.

When cutting the foot cut to the valley

Creeper. Use the Level bevel common rafter

and Set the saw at the angle of the roof

pitch ie 35°



WEEK 10: Notes and Practical

Broken Hip and Valley Roofing









Practical week 10: Allow 7 Hrs

BROKEN HIP & VALLEY ROOF

Working in the groups you have been allocated to for the pitched roof practical and re-

using the scotch valley plates, roof rafters already cut you will set out and construct

the BROKEN HIP & VALLEY ROOF. Including Fascia and Valley boards.

SPECIFICATION:

Roof Pitch: You will use the same roof pitch as your previous projects.

Rafters: 90 x 35 spaced @ 350 c/c

Hips & Ridge: 135 x 35 radiata pine



WEEK 11 & 12:

Individual Mini Broken Hip & Valley Assessment

Students are required to construct a Mini Broken Hip & Valley roof to the given,

Specification and Pitch.

Assessment to be completed over a 12 Hour period, 2days Including written assessment

Work to be completed within the designated work shop.

All work to be completed by individual candidate.

Requirements of assessment completion.

All students to complete task items listed below:

Construct base frame as per plan provided and braced.

Calculate bevels required to given pitch prior to commencing in work shop.

Set out, complete pattern rafter for entire job including Centreline length,

Common rafter length, this will be submitted with roof on completion with roof

model.

Construct Gable roof as required to given pitch including Raking eave and flush

Gable overhangs as specified.

Roof model to be pulled apart and materials stored or disposed of as per

instructions prior to leaving

Students to clean work area on completion and return equipment as required.

Additional Information

Student to sign Assessment sheet and bevel calculation sheet prior to

comencement and return to teacher.

Student to supply and wear all PPE equipment throughout assessment, and

establish individual safe working platforms to complete tasks.

Roof models will be assessed on completion, to ensure accuracy an allowance of

only 2mm Gap on plumb cuts will be permitted.

I understand and agree to the above conditions of the assessment:

Candidate Name: Date:

Signature:

Assessor Name: Date:

Signature:



Students to develop the steel square bevels for a hip roof to suit their given pitch.

Steel Square Set Out

Step 1. Calculate rise = Tan ø =

Step 2: Run / I/2 Span = 1000

Step 3. Calculate TLCR =

Step 4. Plan Length Hip = 1414

Step 5. Calculate TLHR =

Mark out Steel square, Set out points to develop the roof bevels.

Bevel 1 Bevel 2

Plumb bevel common rafter. Level bevel common rafter

Bevel 3 Bevel 4

Edge bevel creeper Edge bevel purlin



Bevel 5 Bevel 6

Plumb bevel hip Level bevel hip

Bevel 7 Bevel 8

Edge bevel hip Face Bevel Purlin



Mini Broken Hip Roof Assessment Plan Layout

Documents

Construct Pitched Roofs Trade Notes - TAFE NSW · TYPES OF ROOFS There are many styles of roof, most of which are made up from variations on specific types. Some of these roof types