FIREPLACE CONSTRUCTION

CHAKAMBA J

FIREPLACE CONSTRUCTION

• A FIREPLACE: is a space in a wall, or formed in a freestanding position, to accommodate an open fire from which the smoke and gases pass to the open air through a duct or flue. (Jack Stroud Foster)

• Is a special designed area where the combustion of fuel takes place. ( Mugari and Pekeyo)

FUNCTIONS OF A FIREPLACE AND FLUE

• Primary function• Is to regulate thermal comfort levels in a

building during cold winter months.• Secondary functions• To burn fuel efficiently and safely transfer the

heat generated into the room effectively.• Provides a focal point in the living room or

lounge.

FLUE

• A passage or duct within the chimney to carry smoke and gases (combustion fumes) away from the fire.

• Is the working part of the chimney, conveying the products of combustion safely to the atmosphere.

FUNCTIONS OF A FLUE

• To convey products of combustion into the atmosphere.

• To ventilate the room in which the fire is situated.

FUNCTIONAL REQUIREMENTS OF A FIREPLACE

1 Provision of adequate strength and stability• Must resist wind pressure and must be properly

bonded to the main wall.2 Weather resistance a properly constructed fireplace should prevent penetration of wind and rain especially where the stack passes through the roof. Flashings and damp proof courses are required at the junction of the two.

FUNCTIONAL REQUIREMENTS CONTI..

• The top of the stack must also be protected to prevent saturation of the chimney.

3. Thermal insulation provision of adequate thermal insulation to the flue avoids cooling of the flue gases and the consequent slowing down of the upward air flow and draught (condensation of flue gases).

FUNCTIONAL REQUIREMENTS CONT…

4. Fire resistanceA properly constructed fireplace should not end up igniting combustible materials within and outside the building.Material for the fireplace should be non- combustible (this is ensured by the provision of adequate thickness of non- combustible material around flues and fireplaces and by keeping all combustible materials a sufficient distance away from a flue or fire place).

REQUIREMENTS CONTI…

• Suitable materials for walls should be 100mm of brick, stone, concrete ( a temperature 70 degrees Celsius is considered to be a safe maximum which should not be exceeded).

• Outlet of a flue should be well above the roof, especially if the roof covering is combustible, in order to avoid danger from sparks.

DIAGRAM SHOWING FIREPLACES TERMINOLOGY

TERMINOLOGY OF VARIOUS COMPONENTS OF AN OPEN FIREPLACE

• Chimney- a structure, which contains the flue through which smoke and other gases may escape.

-A structure enclosing a flue.• Flue pipe- means a pipe forming a flue but does

not include a pipe built as a lining into either a chimney or an appliance ventilation duct.

• Chimney stack- a structure enclosing a flue which rises above the roof.

TERMINOLOGY CONTI…• Chimney breast – a structure enclosing a flue

from fireplace to the roof.• Constructional hearth – a hearth forming part

of the structure of the building.• Hearth – the platform on which the fuel is

burnt.• Superimposed hearth – a hearth not forming a

part of the structure of the building.• Fireback -

TERMINOLOGY CONTI…• Recess – is part or space set back from the line of

a wall or a room.• Throat – part of a flue immediately above the

fireplace opening. - a slot like opening part of the flue.• Party wall – it is a wall which separate two

families.• Mantel/Surround – part of a fireplace around an

opening often incorporated for aesthetic reasons or to increase the effective depth of the fireplace.

TERMINOLOGY CONTI..• Surround – is the finish to the fireplace and

generally consists of a precast ceramic tile slab or in-situ built brick, slate, or stone.

• R.C lintel – a horizontal member supporting the brickwork over the opening ( should be of precast or in-situ reinforced concrete).

• Gathering over – bringing together the sides of the smoke chamber by means of corbelling to form the flue.

-formed by corbelling brickwork to reduce the size of the throat to flue size.

CROSS-SECTION AND PLAN OF RECESS

TERMINOLOGY CONTI..

• Reduction of the fireplace opening to flue size.• Smoke shelf – is constructed between the throat

and flue, used to prevent downdraft and help divert cold air into smoke chamber.

• Rendering/ Pargetting a 10-13mm coat of plaster applied to the inside of the flue during construction.

• Flaunching/Weathering – a sloping of the chimney pot to shed off rain water.

• Chimney pot and cap – the termination of a chimney.

FIREPLACE TERMINOLOGY CONTI…

Damper1. Controls air flow/shut off when not in use

Smoke Shelf1. Prevent downdraft2. Help divert cold air into smoke chamber

Smoke Chamber1. Transition from the firebox to the flue2. Responsible for controlling & regulating burning and eliminating smoke & combustion gases

TERMINOLOGY CONTI…

• Withes – dividing walls between the flues of minimum thickness 100mm.

-properly bonded into the outer walling of the stack so as to obtain the greatest amount of stability.• Jamb- protruding vertical side of a fireplace

opening.

Apart from blockage of the flue by soot or debris, there are conditions which render a fireplace ineffective:

• Insufficient air entering the room to replace that passing up the chimney.

• Poor design of passages through which smoke passes ( throat, flue and the gathering ).

• Down-draught caused by the build-up of pressure at the chimney pot/top influenced by the building itself, neighboring buildings, trees and the general topography of the area.

PRINCIPLES OF FIREPLACE DESIGN

• To promote the efficient combustion of fuel the shape of the fireplace must be designed to allow an adequate but not excessive supply of primary air to the fire bed and secondary air to the flue.

• All fires require sufficient air for combustion purposes, and as air is drawn into the flue from the room, further air is needed to replace it.

REGULATIONS GOVERNING THE CONSTRUCTION OF FIREPLACES AND CHIMNEYS

• A brick flue should have a minimum size of 225 by 225mm or 175mm diameter.

• Every flue must be surrounded by at least 100mm thickness of properly bonded brickwork.

• Every chimney must be built on a suitable foundation forming part of the building foundation.

REGULATIONS CONTI..

• The inside of every chimney/ flue must be rendered or lined with non-combustible materials (fireclay, heavy duty asbestos, vitrified clay pipes).

-this is done to protect brickwork from acids and products of combustion.

CONSTRUCTION REQUIREMENTS OF:1. HEARTH• The construction begins with the constructional

hearth.• Every fireplace must have a hearth extending both

under and in front of the opening.• The hearth shall project not less than 500mm in

front of the jambs.• It shall extend not less than 150mm beyond each

side of the opening between the jambs.• The minimum thickness of the hearth shall be

125mm.

HEARTH

• Be constructed of such size as to contain a square of 840mm side, if there is no recess.

• Have no combustible material placed underneath the hearth within 250mm of the top surface unless there is a minimum separate air gap of 50mm, or it provided support to the edge of the hearth.

• Hearth in suspended timber ground floors may be supported by fender walls

HEARTH• In upper floor construction use reinforced

concrete.• If such a hearth is being supported by the wall, it is

a cantilevered slab, therefore, the reinforcements must be placed within the top part of the slab, about 25mm from the upper surface.

• If timber formwork is used between trimmer joist and the fireplace recess so that the concrete hearth may be cast in-situ, such timbering must be removed if it is within 250mm of the upper surface of the hearth.

HEARTH

FIREPLACE RECESS• The fireplace opening is the recess housing

the fire grate.• The jamb on each side of the opening is not

less than 200mm thick (of either bricks, in-situ concrete, or concrete or clay blocks).

• The back of the recess if a solid wall shall be not less than 200mm thick, or if a cavity wall shall be not less than 100mm thick, extending for the full height of the recess.

RECESS• With the exception of a cavity wall or an

outside wall with no combustible cladding where respectively two 100mm leaves or a single 100mm leaf will satisfy the regulations.

• No opening shall be made in the back of a fireplace recess which does not communicate with a flue.

• No combustible material other than timber supporting the sides of the hearth where it joins the floor shall be placed under the hearth.

THE LINTEL

• Should be constructed in such a way that it support the brick over the opening and it should be of precast or in-situ reinforced concrete to BS 1251.

LINTEL

CONSTRUCTIONAL REQUIREMENTS OF THE FIREBACK

• It is sloped forward in order to direct or transmit maximum heat into the room and raise the temperature of fire, thus assisting combustion.

• It must prevent the heat of the fire from damaging the wall behind it as such the space is left behind the fire back.

• The space behind the fire back is filled with a width as 1:2:4 mix of lime sand and broken bricks or a light weight aggregates ( this takes care of heat).

DIAGRAM OF A FIREBACK

FIREBACK

• The fire back should be preferable in two parts since the lower half will become hotter than the other.

• It should be lined rear with corrugated paper which will eventually smolders away leaving a small expansion gap.

THROAT• It should be 100mm wide, 200-250mm long and

150-200mm deep.• It is restricted in order to accelerate the flow of

flue gases and to ensure enough draught.• The throat restricts down-draught by reducing the

amount of air down the flue and it also reduce excessive heat loss into the flue.

• It is formed by corbelling brickwork to reduce size this called GATHERING.

• It can also be made from concrete or an adjustable metal throat restrictor.

SURROUND

• Is the finish to the fireplace and generally consists of a precast ceramic tile slab or in-situ built brick, slate, or stone.

• It is securely fixed to the brickwork of the chimney breast by lugs cast in the back at each side of the surround.

TYPES OF FIREPLACES1. Single Breast• Fireplace opening on one side of the wall by

inserting jambs or attached piers.• The opening can be formed internally or

externally.• If the breast is formed externally the

advantage is that the large room area is available into the room.

• The minimum depth of the fireplace opening 338mm.

SINGLE BREAST FIREPLACE

TYPES CONT…

2. Double Breast/ Back to back fireplace• It is usually formed on semi-detached type

dwelling.• The fireplaces are formed on the party wall

which is sometimes called a double breast party wall (the wall that separate two properties).

DOUBLE BREAST OR BACK TO BACK FIREPLACE

TYPES CONTI..

• 3. Interlacing fireplace/Side by side fireplace• These fireplaces are usually built on internal

walls and placed side by side.• This arrangement has a tendency to increase

the chimney breast and the projection of jambs into the rooms is reduced to give greater room area.

INTERLACING FIREPLACE

TYPES CONTI..

• 4. Angle fireplace• The fireplace is formed at an angle and

construction is complicated because it entails a number of twist of the flue in order to obtain the correct position.

ANGLE FIREPLACE

FLUES AND CHIMNEYS

FLUES AND CHIMNEYS• Flue is a passage for conveying the smoke or

discharge gases from an appliance to the external air.

• The minimum internal diameter of metal flue 175mm.

• Minimum cross sectional area of a brick flue is 225mm2

• The flue must be pargetted or rendered to ensure a smooth surface and seal any cracks in the joints.

FLUE CONTI..• Sides of the flue to be smooth to avoid the

accumulation of soot not to block the passage and reduce its size.

• The flue must be lined to provide a chimney that is resistance to acids and combustible products.

• Materials used for lining a flue are acid resisting clay pipes, rebated or socketed flue linings made from kiln, burnt aggregate clay flue linings and high alumina cement.

FLUES CONTI…• Substances obtained when burning coal-

carbon dioxide, sulphur dioxide and water.• Water + carbon dioxide = carbonic acids.• Water + sulphur dioxide = sulphurous acids.• When either the two oxides are mixed with

water acids can be produced.• These acids are not concentrated but

continuous application in the flue will eventually harm the bricks.

CHIMNEY FLUES

• Area through which the combustion gases and smoke travel

Flue liners• used to prevent deterioration to mortar joints• produces a better downdraft & requires smaller

flue (smoother surface)Unlined Flue• Chimney must be thicker walls than with chimney

with flues liners

MATERIALS USED AS FLUE LININGS

1.Parging with mortar• As construction progresses the sides of a flue

are rendered with the 12mm thickness of mortar mix 1:3 or 1:3:10 if you add a bit of lime.

2.Pipes either made from clay or concrete.• These must be placed with sockets facing

upwards to prevent dislodgement of components.

MATERIALS CONTI…

3.Precast concrete blocks (425×102×215)• These are sized to bond to the brickwork.• The block contain opening which were aligned

or lined to form smooth way.

DAMP PREVENTION OF THE CHIMNEY

• Chimneys are vulnerable to dampness because they are exposed at their junction within roof is exposed.

• At the point where the chimney meets the roof dampness can be prevented by:

a) Flashings are often used on pitched roof junction between roof and the chimney stack.

DAMP PREVENTION CONTI..

• Flashings- are pieces of metal specially made to waterproof the gap between the roof and chimney stack, roof and the vent pipe or a parapet wall.

• Building regulations make it mandatory that dampness must be prevented at valleys, chimney stack and roof junctions, parapet wall.

REQUIREMENTS FOR FLASHINGS

• The material selected for use as flashings must be rust proof.

• Dissimilar materials which may cause electrolytic corrosion should never be used.

• Certain situations like chimney stacks require double layered flashings, that is, under and cover flashings. The flashings should be properly secured and bonded in mortar.

• The material should be damp proof.

MATERIALS SELECTED FOR USE AS FLASHINGS

• Galvanized sheet metal.• Aluminium• Asbestos cement• copper

DAMP PREVENTION CONT…

• d.p.c;• cover flashings (lead or steel);• tilting fillet;• chimney back gutter;• stepped cover flashing;• line of soakers;• front apron;

FLASHINGS AROUND THE CHIMNEY STACK

DAMP PREVENTION CONTI…

• The flashing is stepped along the slope. On the upper end, a gutter and stepped flashing are provided while on the sloping lower end, a flashing apron is provided.

Chimney outlets or stacks

• The top of the chimney should not be less than one meter(1m) above highest point of contact between the chimney and the roof. If it is not within 600mm from the ridge.

• If roof pitch is not less than 10 degrees on either side of the ridge and the chimney passes within 600mm from the ridge, the top chimney may not be less than 600mm above the ridge.

CHIMNEY OUTLETS

• The chimney stack should not be less than (1m) above the top of a window or sky light which can not be opened.

CHIMNEY STACK OUTLETS

CHIMNEY POTS

CHIMNEY POTS

• These are structures put at the top of a chimney stack to lessen the possibility of down draught and also preventing the wind from blowing down the flue. To prevent rains from falling into the flue.

• It can be made from: clay, bricks, metal, concrete.• The chimney pot must be securely fixed at the top

of the chimney stack to prevent dislodgement by wind.

CHIMNEY POTS AND CAP CONTI..

• It may be circular or circular with a square base. A circular chimney pot is used with a circular flue lining. A circular with a square base used with a circular square lining.

• The chimney pot must be weathered to shed off rain.

• The chimney pot must project 100mm-175mm above flaunching or weathering.

ceramic or clay differently designed pots

CERAMIC CHIMNEY SYSTEMS

Cowl (Crow Guard)

-Decorative-Helps protect chimney from forming nests

TEE-CHIMNEY POT

• decorative; helps protect the upward flow of flue gases in windy or exposed areas

CAUSES OF SMOKING CHIMNEYS

• Failure to provide a restricted throat (poor design of the throat).

• A blocked flue.• Insufficient air supply.• Unsatisfactory gathering of the flue.• Overshadowing of the flue outlet by tall trees

or buildings.

SOLUTIONS TO SMOKEY CHIMNEYS

• Ensure that the chimney is swept regularly to remove excess soot.

• Open windows and doors of the room, if smoking ceases then the fire is starved from the air.

• Provide ventilators or under floor or ducts. If the height of the fire opening is too much reduce it by a permanent canopy.

SOLUTIONS CONTI..

• Determine the effect of increasing the height of chimney stack with pieces of sheet metal pipes of varying lengths.

• Where desirable results are achieved fit a long chimney pot.

By-laws controlling fireplace and chimney construction.

• are concerned with stability, fire hazards and escape of noxious fumes into the building, which might constitute a danger to health and property;

• for domestic fireplace construction, the assumption is that heat producing appliance will not exceed 30 kW (London) 45 kW (Building Regulations) output rating.

BY-LAWS CONTI…

• a resulting flue should not exceed 225 mm x 225mm;

• a chimney may be defined as a solid material surrounding a flue;

• flue is a duct through which smoke and other combustion products pass;

• a chimney is a single flue surrounded by at least 100 mm of brickwork;

BY-LAWS CONTI..

• a stack consists of two or more flues surrounded by the requisite amount of brickwork, if the withes of the stack are ½ brick in thickness;

• every flue must be surrounded by at least 100 mm thickness of brickwork, properly bonded and exclusive of the flue lining thickness;

• a gas flue thickness is reduced to 225 mm, exclusive of plastering, but the mortar joints must not project into the flue;

BY-LAWS CONTI…

• every chimney or stack consisting of two or more chimneys must be built to a height of at least 900 mm above the last point of contact emerging from the roof;

• in no case must a chimney or stack be built up to a height greater than 6 times its least width at the last point of leaving the roof;

• the top of a chimney carried up through the ridge must be at least 600 mm above the ridge;

BY-LAWS CONTI…

• but in all other cases at least 1 m measured from the highest point in the line of junction with the roof;

• every chimney must be built on a suitable foundation approved by the District Surveyor;

• the twelve highest courses of every chimney or stack must be built in cement mortar, or cement-lime mortar can be used, provided there is 1 part of cement to every 6 parts of sand;

BY-LAWS CONTI…• a chimney stack passing through a roof must be properly

protected against the adverse effects of moisture, achieved by inserting a damp course in the brickwork as the stack emerges from the roof;

• chimneys inclining at an angle less than 45 degrees to the horizontal must be provided with a soot door not less than 0.026 square metres in a proper frame.

• the inside of every chimney must be rendered or lined with non-combustible materials (e.g. fireclay, diatomaceous earth, heavy duty asbestos) as building proceeds.

BY-LAWS CONTI…

• non-combustible linings are purpose-made units either square or circular in section to fit 1 brick by 1 brick flue;

• the outer surface of every chimney within a building constructed of a material less than 200 mm thick must be properly rendered up to the level of the outer surface of the roof or gutter.

BY-LAWS CONTI…

• woodwork must not be placed under any fireplace opening within 225 mm (London) or 250 mm (Building Regulations) from the upper surface of the hearth except for fillets or bearers supporting the hearth, unless an airspace of not less than 50 mm between the underside of the hearth and any combustible material is provided;

BY- LAWS CONT…

• woodwork must not be built within 225 mm to any flue or to the inside of any fireplace openings;

• wooden pegs must not be driven into any wall or chimney nearer than 150 mm to any flue or the fireplace inside;

• if fireplace surrounding is constructed of wood or any other combustible materials, must be at 150 mm measured horizontally and 300 mm measured vertically from fireplace opening, being backed with solid incombustible material;

BY-LAWS CONTI…

• line the chimney with insulating brick (e.g. fosasil) or by the cavity provision where a chimney is adjacent to constructional steelwork or reinforced concrete;

• a flue must not be used for more than one fireplace unless: it is impracticable to meet building requirements erected before the by- laws were approved and enforced, or there are two fireplaces in the same room;

• jambs of every fireplace opening must be at least 200 mm wide;

BY-LAWS CONTI…

• the back of every fireplace opening in a party structure must be at least 200 mm thick from the hearth up to 300 mm above the top of the fireplace;

• all thickness may not be less than 100 mm where a chimney breast is not on a party wall (Hodge, 1987).

REFERENCE• Chudley, R. (1987). Construction Technology-V.L. 1 (2nd ed).

England: Longman Group UK Limited.• Chudley, R. and Greeno, R. (2001). Building Construction Handbook

(4th ed). Great Britain: Keywood Typsetting Services Ltd.• Grundy JT. (1984). Construction Technology-Vol 3. London. Edward

Arnold Ltd.• Hodge, J.C., (1987). Brickwork for Apprentices. London: Edward

Arnold (Publishers) Ltd.• Mugari, K. and Pekoyo, I. (2010). O’Level Building Today. Harare,

Zimbabwe: ZPH Publishers (Pvt) Ltd.• Nash, W.G. (1989). Brickwork 2. London: Stanley Thornes

(Publishers) Ltd.