Stairs Design

Why Stairs

1) Important consideration in a home2) Accommodate flow traffic3) Key to circulation—should be close to axis

of plan

Stair Groupings

Groupings by Material 1) Wood 2) Steel 3) Concrete

Stair Terminology

KICKER

Stair Term Definitions

Run (total run)--horizontal distance from end to end of the stairs

Rise (total rise)--vertical distance from finished floor to finished floor

Unit run--the design size of one horizontal step

Unit rise--the design size of the vertical distance between each step

Stair Term Definitions

Tread--complete horizontal size of the step, that is, the size of one unit run plus the nosing

Riser--the back portion between each tread, it is equal to the unit rise

Stringer, carriage, or stair jack--the saw tooth shape support for tread and riser

Kick block or kicker--used to keep the bottom of the stringer from sliding on the floor when a downward load is applied

Kicker

Stair Term DefinitionsHeadroom--vertical distance measured

from the tread nosing to the structure (wall or floor) above the stairs. Code required: 6’-8”min

Stair Term Definitions

Handrail--the support on the sides of the stair that you grab with your hand to aid walking up and down the stairs. Code required: 34”

Guardrail--the railing placed around an stair opening or balcony. Code required: 36”

Stair Term Definitions

Newel post--the vertical post used to support the handrail at its end, also the post intersecting the handrail and guardrail

Baluster--smaller vertical supports of the handrail or guardrail. Code spacing requirement: 4”-O.C. max 6” where a triangle is formed by the tread and riser.

Elevation of stairsWith newel post,

Balusters, andhandrail

BALUSTER

Stair Terminology

Nosing projection of

tread beyond riser

3/8” or less

Stringer Types Plain or Made On-

Site Stringer Closed/Housed or

Mill Made Stringer

Stair Terminology

Plain or On-Site Stringer

Notched out 2x12 to support the treads and risers

Closed/Housed or Mill-made Stringer

Stringer where ends of risers and treads are not exposed, usually routed so the treads and risers will fit into it

Types of Stairs

Basic types straight run right angle or “L” double “L” reverse or “U” winder spiral

Type of Stairs--Straight Run

Straight in design and does not change direction

Typical minimum width 3’-0”, sometimes where space can be justified 3’-6” or more

Type of Stairs--Right Angle or “L”

A 90 degree directional change occurs usually occurs near

the center

Platform at direction change intermediate landing

between floors

Type of Stairs--Double “L”

Same as L but with multiple platforms

Type of Stairs--Reverse or “U”

A 180 degree directional turn occurs, usually near center

Platform at direction change

Type of Stairs--WinderSteps continue in pie

shape fashion at landing area

Not desirable because steps are wedge shaped

The arc at the winders is 12” and the tread design not less than 10”

Handrail located where the tread is narrower

EQUAL

Type of Stairs--Spiral

Additional stair--not used as the main stairsUsed for unique design requirements

tight space aesthetics

Framing StairsNote

double header

double trimmer

stringers joist

hangers

Design Considerations

Stairs should be comfortable to climb30 - 35 degree angle is optimum

Design Considerations

Codes influence Sizes of Risers and Treads

Maximum angle 7 3/4” riser with 10” tread

Recommended (Common) Size Ranges riser = 7 to 7 1/2” tread = 10” to 10 1/2”

Design Rules

When: Unit rise = R Unit run = T

R+ T = 17” to 18”2R + T = 24” to 25”R (x) T = 70 to 75

Design Rule Example

If unit run is unknownunit rise = 7” (low limit of recommended)

(high) R + T = 18 (therefore) 7 + T = 18 (then) T = 11

(low) 2R + T = 24 (therefore) 2*7 + T = 24(then) T = 10

(high) 2R + T = 25 (therefore) 2*7 + T = 25(then) T = 11

(low) R (x) T = 70 (therefore) 7 * T = 70(then) T = 10

(high) R (x) T = 75 (therefore) 7 * T = 75(then) T = 10.7

Design Rule Example

If unit run is unknown unit rise = 7.5” (high limit or recommended)

(low) R + T = 17 (therefore) 7.5 + T = 17 (then) T = 9.5

(high) R + T = 18 (therefore) 7.5 + T = 18 (then) T = 10.5(low) 2R + T = 24 (therefore) 2*7.5 + T = 24(then) T = 9(high) 2R + T = 25 (therefore) 2*7.5 + T = 25(then) T = 10(low) R (x) T = 70 (therefore) 7.5* T = 70(then) T = 9.33(high) R (x) T = 75 (therefore) 7.5* T = 75(then) T = 10

Stair Calculations Necessary to determine exact riser height and total

run1. Determine vertical distance between finished floors

2. Divide vertical distance by approximate desired riser height to set approximate number of risers

3. Round to number of whole risers

4. Divide vertical distance by number of risers to get actual riser height

5. Number of unit runs = number or unit rise minus 1

6. Total run: use design rule to determine unit run size then multiply by the number of unit runs

Stair Calculations ExampleGiven: vertical distance = 102”(Total rise)

1--Approx # unit rise = 102 / 7.5 = 13.6

2--Round 13.6 to 14

3--Unit rise height = 102 / 14 = 7.286”

4--14 unit rise (-) 1 = 13 unit runs

5--Design rule: R + T = 17.286

(therefore) 7.286 + T = 17.286(then) T = 10”

6--Total run = 10 * 13 = 130” = 10’-10”

Solution: 14 R @ 7.286” and 13 T @ 10”

Stairs Layout Procedures

1) Calculate the how many and size of Risers and Treads

2) Create box showing total rise and total run

Total Run

Total Rise

Stairs Layout ProceduresDivide the total rise

into number of Risers (actual value of Riser)

Example: R=14, T=13

Line at any angle divided

Into equalParts, points

Transferred byParallel lines

Stairs Layout Procedures

Another approach to get equal risers

14 equal risers

Stairs Layout Procedures

Divide the total run into number of Treads (actual value of calculated Treads)

Line at any angle divided

Into equalParts, points

Transferred byParallel lines

Stairs Layout ProceduresAnother approach to get equal treads

13 Equal Treads

Stairs Layout Procedures

Draw grid using riser and tread divisions determined previously

Stairs Layout Procedures

Starting point: Head or Foot of Stairs

Follow grid and mark the design of stairs

Stair Design

Stairs Layout Procedures

Add actual tread boards and riser boards

Add stringer board

Material Sizes

Tread Thickness

Nosing ValueRiser Thickness

Stringer Size

Stairs Section Complete(Your drawing should look like handout)

Find the headroom location for structure

Locate headers to determine stairwell dimension

Add notes and dimensions

Place title and scale below drawing

Class Lab Work on

Stair Detail/Section Assignment