bldg tech handbook

8/7/2019 Bldg Tech Handbook

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The Scottish Building Standards

TECHNICAL HANDBOOK

CONSERVATORIES


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The Scottish Building Standards

TECHNICAL HANDBOOK

CONSERVATORIES


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Crown copyright 2006

Cover designed and produced by Astron

Text pages designed by Scottish Building Standards Agency


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Contents

1 Status of this document2 When you can use this document

3 Introduction

4 Foundations

5 Walls below floor level

6 Floors

6a Concrete floors

6b Suspended timber floors

7 Walls above floor level

7a Cavity masonry walls

7b Timber framed walls

8 Windows

9 Roofs

10 Drainage

11 Electrics

12 Connecting doors

13 Steps

14 Cavity trays

15 Exposure zones in Scotland

16 Design checklist

17 Worked examples for cavity trays


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This document provides guidance on how to meet the building regulations for simpleconservatories which are built onto existing houses.

The use of this document does not remove the need to obtain a building warrant for theconservatory, but all or some of this document may be submitted to the verifier as part of the

warrant application process. The checklist at the rear should be used to highlight to buildingstandards which parts of the document relate to the application.

If this guidance is followed it should be accepted by the verifier (local authority buildingstandards department) as indicating that the Building (Scotland) Regulations have beencomplied with. Consequently, it is expected that any requests by verifiers for furtherinformation will be minimal, thus saving time for both the verifier and the applicant. Inaddition, aset of drawings such as a location plan, a block plan and scaled floor plans andelevations, may also be required by the verifier.

It is quite acceptable to use alternative methods of compliance with the regulations. Thefunctional standards set out in schedule 5 to regulation 9 of the Building (Scotland)Regulations 2004 must be met. A Technical Handbook for Domestic buildings is published,providing detailed guidance on complying with the standards. It may be accessed on thewebsite of the Scottish Building Standards Agency at www.sbsa.gov.uk and any part may bedownloaded free of charge.

1 STATUS OF THIS DOCUMENT


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This guidance does not cover every conservatory, and for many it will be necessary to referto the Technical Handbooks. The document when used in its entirety will only apply toconservatories that:

1. meet the definition of conservatory

(A conservatory is a building attachedto a dwelling and having a doorseparating it from that dwelling andhaving not less than three quarters ofthe area of its roof and not less thanone half of the area of its externalwalls made of translucent material),and

2. are to be attached to the groundstorey of houses (but not flats ormaisonettes) and only when thosehouses have foundations of traditionalconcrete strips, or when the groundconditions allow for the use oftraditional strip foundations, and

3. have an internal floor area of morethan 8 m2 but not more than 20 m2,and

4. are connected to the mains drainagesystem, and the invert level at the

point of connection to the housedrainage system is not more than1000 mm, and

5. have an effective roof area of not morethan 35 m2 (including any house roofarea to be drained via theconservatory gutters and down pipe),and

6. are fixed directly to masonry walling atleast 100 mm thick, and

7. are at least 1 m from any boundary,and

8. are at a distance from the boundary (inmetres) of at least 1/6 of the area ofglazing and frame (in m2) facing thatboundary. (e.g. if a side of theconservatory has an area of glass andframe of 9m2, then the conservatorymust be at least, 9 6 = 1.5 m from theboundary which that glazing faces),

and

9. have glazing to all sides (excluding the

back/house wall), onto which the roofis fixed, and

10. will meet the thermal insulationrequirements whether theconservatory is to be heated or not,and

11. are not built on or above ground that iscontaminated, and

12. do not contain a chimney, flue pipe,fixed combustion applianceinstallation, washbasin, sink, bath,shower, urinal, watercloset orwaterless closet, and

13. are not built over any form ofunderground drain, other than a drainonly serving the dwelling on to whichthe conservatory is to be built, and

14. have a floor level the same as, or not

more than 600 mm below the floorlevel of the house, and

15. are not built over an existing rain waterdown pipe, and

16. are not built over any existing escapewindows.

2 WHEN YOU CAN USE THIS DOCUMENT


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A conservatory may need no permission at all, some permission, or indeed manypermissions of various types. If you are in doubt you should contact your localauthority building standards department for advice.

You may need to obtain, for example;a building warrant,planning permission,listed building consent,and any other permission relevant to the individual circumstances of a project.

This guidance concerns only building warrants and other regulatory bodies should becontacted for information on any other permissions.

All new building work in Scotland, to which the building regulations apply, must havea building warrant prior to work commencing, except where the regulations permit.

A building warrant must be obtained before you start any work where theconservatory is more than 8 m2 in floor area. A warrant is also required forconservatories below this size if they contain a chimney, fixed combustion appliance,washbasin, sink, bath, shower, urinal, watercloset, waterless closet, orare closer than 1 m to a boundary.

This document provides enough information to cover a large proportion of simpleconservatories. It does not seek to tell you all you need to build, but to give yousufficient guidance on what must be done to ensure compliance with the technicalstandards.

This guidance does not cover every conservatory, and for many it will be necessaryto refer to the Technical Handbooks. Professional advice may be required forconservatories of a more complex design than those covered in this document.

3 INTRODUCTION


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The area of ground where the foundations of the conservatory are to be poured mustbe stripped of all topsoil, soft subsoil and vegetable matter.

Foundations must be reinforced concrete strip foundations.

A check should be made of the house foundations prior to work starting and if thehouse foundations are not ordinary strip foundations, work must cease and theverifier must be informed. This guide is only for use where the ground conditionsallow the use of strip foundations.

The foundations must be poured at the same depth as the house foundations or withthe underside of the foundations at a minimum depth of 450 mm below ground level.

If the foundations are to be poured at the same depth as the house foundations theymust be poured over the scarcement of the house foundations, as shown in thefoundation detail. Within the foundation there must be 1 layer of A142 mesh laid with

a 50 mm bottom cover.

Foundations to intermediate sub-floor walls (if required) must be at least 400 mmwide and at least 150 mm deep.

The foundation must be at least 300 mm wider than the overall wall thickness.

Where steps in the foundations are required due to a sloping site, the steps musthave a horizontal overlap of at least twice the foundation thickness.

The concrete must have a strength grade of at least C20 (a cement/sand/aggregate

ratio of 1:2:4).

150

300

Junction Detail

150

reinforcement

4 FOUNDATIONS


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This document provides guidance on 2 types of floor:a. Concrete floors poured onto a prepared solum, andb. Timber floors suspended above a prepared solum.

The solum is the prepared area of ground inside the perimeter of the external walls.The preparation of the ground is similar in both floor constructions, as follows:

All topsoil, vegetable matter and loose sub-soil must be removed down to thefirm subsoil. This excavation of the soil must be taken down to at least 250 mmbelow the existing ground level to prevent frost heave.

A layer of hardcore, (small sized crushed rock or brick) at least 150 mm thickmust be laid on the prepared sub-soil. This layer must be compacted with aroller or vibrating plate in layers not more than 150 mm thick.

A layer of sand a minimum of 25 mm thick must be laid over the hardcore.

A layer of at least 1000 gauge damp proof membrane (dpm) must be laid on topof the sand. All joints must be sealed by either a welted or mastic sealed joint.The dpm must be larger in area than the area of sand, so that the dpm is takenup the inside of the walls below floor level by at least 150 mm.

Now follow the appropriate specification for either concrete or timber floors.

6 FLOORS


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An 80 mm thick layer of polyurethane or other equal insulation boarding (thermalconductivity of not more than 0.023 W/mk) must be laid over the whole floor.

Concrete must be laid over the insulation to give a smooth finish. The concrete must

have a strength grade of at least C20 (a cement/sand/aggregate ratio of 1:2:4) andbe at least 150 mm thick, with 1 layer of A142 mesh having 50 mm bottom cover.

When a concrete floored conservatory is to be built over sub-floor ventilators on thehouse, these ventilators must be ducted to the outside air through the concretefloor/hardcore using 100 mm diameter uPVC pipes.

The damp proof membrane to the floor must be linked to the damp proof course ofthe external walls.

GL

min 150 80mm insulation

25mm sand blindingmin 150 compactedhardcore

dpc 150mm concrete

dpm

6a CONCRETE FLOORS


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50 mm of concrete must be poured onto the dpm to give a smooth solum finish. Ensurethat the top of the concrete is slightly above external ground level.

The joists must be supported by joist hangers attached to the inner leaf of the external

wall, or where a wall scarcement detail is used, on a 100 x 25 mm timber wall plate ona dpc.

The joists must be nominally 200 mm x 50 mm and be of at least strength grade C16.

The joists must be at not more than 450 mm centres and must span not more than3 m, either between the external walls of the conservatory or between 1 external walland a sub-floor wall.

At least 200 mm thick mineral wool, must be laid between the joists, supported bynetting draped over and between the joists. The construction is now ready to lay thetongue and groove floorboards (min 16 mm thick) or tongue and groove chipboard (min

18 mm thick).

The underside of the joists/insulation must be at least 150 mm above the level of thesolum. 220 x 65 mm sub-floor ventilators must be installed in the perimeter wall at notmore than 1500 mm centres.

Any heating pipes below the insulation level must be insulated.

GL

200mm joists and insulation

min 150mm air space

min 150mm compactedhardcore

50mm concrete

25mm sand blinding

dpcdpmmin 150

GL

200mm joists and insulation

min 150mm air space

min 150mm compactedhardcore

50mm concrete

25mm sand blinding

dpc

dpmmin 150

6b SUSPENDED TIMBER FLOORS

Joist hangers

Scarcement wall


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External walls above ground level are commonly built to a variety of heights. Theconservatory does not have to be built with a wall above floor level. The windowsmay start at floor level.

This document provides guidance on 2 types of wall:a. Cavity masonry walls, andb. Cavity walls with masonry outer and timber framed inner leaves.

In all cases the following details must be incorporated:

the inner and outer leaves of the walls must be tied together using stainlesssteel wall ties with a minimum of 4 per square metre, and

cavity closers of mineral wool or timber wrapped in dpc must be provided atwall head, door jambs and corners of walls, and

the walls must be fixed to the house wall using a wall starter.

All gaps and junctions at the walls and floor must be sealed to limit air infiltration.

In all cases the external masonry must be of a quality suitable for the exposure thewall will face, or have a rendered finish.

Now follow the appropriate specification for either cavity masonry walls or timberframed walls.

7 WALLS ABOVE FLOOR LEVEL


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The walls must be either built of two leaves of at least 100 mm thick brick, block,stone or reconstituted stone with a clear cavity of at least 50 mm between. The wallscan be with or without a roughcast finish externally, and have either plaster,plasterboard, or facing brick finish internally.

The walls must be insulated by using 70 mm polyurethane or equal insulationboarding (thermal conductivity of not more than 0.023 W/mk) within the cavity, orbehind the plasterboard, or in a combination of both locations.

If the insulation is to be within the cavity, a clear 50 mm cavity must still bemaintained. This will result in an overall cavity of 120 mm, partially filled withinsulation.

100 50 70 100

dpc

mastic

cavity batt

brick/block/stoneclear cavity and insulationtwo leaves of

with a 50 mm

7a CAVITY MASONRY WALLS


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The walls must be of 100 mm thick masonry outer leaf, with or without roughcast,and a timber framed inner leaf. There must be a clear cavity of at least 50 mmbetween the two leaves.

The cavity must be vented to the outside air using proprietary perpend ventilatorslocated at the bottom of the timber frame, at not more than 1200 mm centres.

The timber frame must be constructed using studs with a nominal size of100 x 50 mm at a maximum of 600 mm centres, with a top and bottom rail. Dwangsshould be provided at mid height if the timber frame is greater than 1200 mm inheight.

The frame must be clad externally with plywood at least 12 mm thick and a breathermembrane. The frame must be finished internally with a vapour control layer andplasterboard at least 12 mm thick.

The insulation must be provided in two locations:100 mm thick mineral wool must be provided between the studs,and 35 mm thick rigid polyurethane insulation boarding or equal (thermal conductivityof not more than 0.023 W/mk) must be provided immediately behind theplasterboard.

10050 100

nom35

dpc

mastic

compressiblecavity batt

mm brick/block/stone

plasterboard with vapour barrier behind

insulation behind vapour barrier

mineral wool insulation between timber studs

12 mm plywood with breather membrane on cavity side

7b TIMBER FRAMED WALLS


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Conservatory windows must be of reinforced plastic profiles or of solid timber, or ofmetal.

There must be a certificate from a UKAS accredited scheme, (e.g. BBA) supplied aspart of the warrant application, certifying the complete conservatory framing toconfirm its fitness for purpose.

The units must be double glazed with a maximum U-value of 3.3 W/m2K .

All glazing which is closer than 800 mm to floor level must be made from safetyglass. The term safety glass includes laminated and toughened glass.

All glazing to doors must be made from safety glass.

All glazing to windows which is both within 300 mm of the sides of a door and closer

than 1500 mm to floor level must be made from safety glass.

Laminated glass is suitable in all circumstances. Toughened glass is suitable wherethe difference between floor level and the adjacent ground level is not more than600 mm. Both types of safety glazing must be marked with a BS kite mark whichconfirms that the glass is indeed safety glass.

The opening area of conservatory windows and doors must be at least 1/30th of thecombined floor area of the conservatoryand the room covered by the conservatory,or, the conservatory must be provided with windows and doors of at least 1/5th of thefloor area of the conservatory, whichever is the greater.

The window frames must be fixed to the house wall and the base wall as per themanufacturers instructions.

There must be provided 1 or more trickle ventilators (small closable ventilators whichcan provide minimum ventilation) with a combined open area of at least 10000 mm2,allowing a slow change of air within the conservatory without opening the windowsor doors.

All windows and doors must be draught stripped.

Opening windows must not be fitted at a height of less than 800 mm above floor level

where the difference between the floor level and the adjacent ground level is greaterthan 600 mm.

If the conservatory is to be built over a mechanical extract fan terminal the fan mustnot discharge into the conservatory, but fans may be ducted through theconservatory to the outside air.

If the conservatory is to be built over a window to a kitchen, bathroom, shower roomor utility room, a mechanical extract fan must be provided to those rooms, leading tothe outside air. The extraction rate of the fan should be 60 lts/s to a kitchen, 30 lts/sto a utility room and 15 lts/s to a bathroom or shower room.

8 WINDOWS


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The conservatory roof must be constructed from reinforced plastic, aluminium/steel ortimber rafters with double glazed units, or multi-skin polycarbonate sheets between therafters.

The double glazed units or multi-skin polycarbonate roof sheets must have a U-valueof not more than 3.3 W/m2K.

There must be a certificate from a UKAS accredited scheme, (e.g. BBA) supplied aspart of the warrant application, certifying the complete roof, to confirm its fitness forpurpose.

The roof must be fixed to the house in accordance with the manufacturers instructions.

Code 4 lead flashing must be raggled into the house wall 150 mm higher than the roofbar and dressed down either into the roof bar if the manufacturers system allows, or afurther 150 mm over the roof sheets.

The roof must be fixed to the top of the windows in accordance the manufacturersinstructions.

A cavity tray may be required to be installed in the existing wall, at the point where theconservatory roof meets the house wall. The need for a cavity tray will depend on theconstruction of the house and the amount of wind driven rain the wall above theconservatory will be exposed to. See section 14 to calculate if a cavity tray is required.

Conservatory

roof

150 mm

150mm

Cavity tray(if required)

25mm raggle

lead flashing

9 ROOFS


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The rainwater from the conservatoryroof must be drained to the main surface watersewer via the existing house drainage.

The rainwater must connect to the existing drain via 100 mm diameter half round

gutters (or of equivalent volume), a 68 mm minimum diameter rainwater down pipe(with handhole access), and 100 mm diameter underground grade pipes laid at a fallof 1 in 60. The drain must be surrounded by a 150 mm thick layer of pea gravel.

The underground pipes must be laid with a ground cover of at least 600 mm. If this isunachievable due to the depth of the existing pipes, the new pipe must have a coverof at least 50 mm concrete above the pea gravel.

Rodding access must be provided at all changes of direction.

Where the conservatory is to be built over an existing rodding access point, trap,gulley, manhole or other access point, that trap, gulley etc must be relocated and

sited outwith the area of the conservatory. This will allow the existing drain to beaccessed when necessary.

Drainage pipes may therefore remain below the conservatory if it is impractical toreroute the drain around the conservatory. If the existing pipe is of fireclay, the pipeto be below the conservatory must be removed and replaced in uPVC piping. Thepipe must be replaced from access point to access point so that there is not amixture of pipe materials in the same pipe run.

The conservatory foundations must be below the level of the drain, and the points atwhich the pipe passes through the external walls of the conservatory must beconstructed as shown in the diagram below.

Where the conservatory drain is to be connected to a drain carrying both rainwaterand wastewater, a ventilated trap must be provided to the new rainwaterunderground pipe as close as possible to the connection to the existing wastewater/rainwater pipe.

10 DRAINAGE


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ex rwp

rwp

re

ex reextended

rwp

svp

relocate trapoutwith base

renew in uPVC

ex rwp

re

rwpsvp

trap

Before

After

Before

After

lintol over pipe section through wall

10 DRAINAGE


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All electrical installations must be carried out in accordance with BS 7671.

It is recommended that a 30 mA RCD (residual current device) be installed to theelectrical circuit, to provide protection to socket outlets likely to feed portableequipment outdoors. (e.g. lawnmowers).

There must be a door in the external wall of the house between the house and theconservatory. This door, or doors, must provide thermal separation between thehouse and conservatory. The retention of existing external quality doors is deemed tomeet the thermal requirements.

6 WINDOWS

6 WINDOWS

10 CONNECTING DOORS10 CONNECTING DOORS

10 CONNECTING DOORS6 WINDOWS

11 ELECTRICS

12 CONNECTING DOORS


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Steps from the conservatory to the ground level, and steps from the house to theconservatory must be provided to ensure that occupants can enter and exit safely.No steps are required where the difference between the floor level of the

conservatory and the adjacent ground level is not more than 170 mm.

A ramp may be used instead of steps, but this is only specifically required where theconservatory is being built over an existing level or ramped access to the housewhich was required to be provided for accessibility purposes. In this case, theexternal door of the conservatory must be provided with a low level threshold to allowwheelchair users to pass. The addition of the conservatory must not make the levelof accessibility to the house any worse than it was originally.

The rise of each step must be uniform over the flight, must be not more than 170 mmor less than 100 mm high. The depth of the step must not be less than 250 mm. Theflight must have a pitch of not more than 34. The width of the flight must be at least

1000 mm.

The steps and top landings must be constructed of pre-cast step units supported on100 mm thick brick or block walls on either side. Paving slabs at least 50 mm thickand not larger than 600 mm x 600 mm may be used when supported on all sides, butthese are suitable for light domestic use only.

If the height from ground level to floor level is more than 600 mm, or if the externaldoors of the conservatory open outwards where the height from ground level to floorlevel is more than 170 mm, a landing must be provided at the top and bottom of theflight.

A barrier must be provided to the open sides of the steps and landing where they areat a height of more than 600 mm. The barrier must be at least 900 mm high and haveno gaps within it which would allow a 100 mm ball to pass through. Handrails mustbe provided on both sides of the steps where the steps are at a height of more than600 mm. The handrails must be at a height of more than 840 mm and not more than1000 mm above the pitch line of the steps.

The landing at the bottom of the flight can be any suitable clear space, (e.g. pavingslabs).

equalequal

landing more

than 170mmabove

ground level

900mm

equal

equal900mm

900mm

Single door

Double doors

13 STEPS


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Determining the need for the provision of a cavity tray

Correct installation of a cavity tray at the junction of external wall and conservatory roof willprevent the ingress of water into the conservatory through the existing external wall of thehouse.The following calculation confirms where cavity trays must be provided and is based uponwall construction and the exposure to wind driven rain of the existing house. If thiscalculation confirms the need for the installation of cavity trays, these must be provided.Designers and householders should be aware that without a properly installed cavity traysome water ingress may occur in severe weather conditions.

1. Determine the exposure zone number from the map (see over).

2. Add 1 to that number where conditions accentuate wind effects, such as on open hillsidesor in valleys where the wind is funnelled onto the wall, and subtract 1 from the number wherewalls are well protected by trees or buildings or do not face the prevailing wind.

The number arrived via steps 1 and 2 denotes the degree of exposure the house faces.

3. Check the house wall construction against the table below to find the degree of exposurethe house wall is designed to withstand.

If the house design number (step 3) is equal to or greater than the exposure number (steps 1and 2) no cavity tray is required.

Degree of exposure which various wall constructions are designed to withstand

cavity insulationtype

cavitywidth

mm

roughcast

full height

roughcast

above facing

brick

facingbrick

flushjoints

facing brick

recessed

joints

built-in full fill 50 2 2 1 0

75+ 3 2 2 0

injected fill (not UF) 50 2 1 1 0

75+ 3 2 2 0

injected fill (UF) 50 2 1 0 0

75+ 2 1 1 0

partial fill + 50 mmclear

50 3 3 2 0

no cavity insulation 50 3 2 2 0

100 3 3 3 1

When unfamiliar with the type of cavity insulation in the house, it may be necessary to cut ordrill a small hole in the wall for a visual check.

UF = Urea Formaldehyde injected foam insulation

From Thermal insulation: avoiding risks BR262, 2002, BREReproduced by permission of BRE PressCopies are available from www.brepress.com

14 CAVITY TRAYS


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Sheltered Moderate Severe Very Severe

15 EXPOSURE ZONES IN SCOTLAND


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The proposed conservatory is designed to meet the guidance contained in the sections ashighlighted with a cross ( x ) below

FOUNDATIONS

WALLS BELOW FLOOR LEVEL

FLOORS

CONCRETE FLOORS

SUSPENDED TIMBER FLOORS

WALLS ABOVE FLOOR LEVEL

CAVITY MASONRY WALLS

TIMBER FRAMED WALLS

WINDOWS

ROOFS

DRAINAGE

ELECTRICS

CONNECTING DOORS

STEPS

CAVITY TRAYS

16 DESIGN CHECKLIST


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CAVITY

Worked example 1.

The house is located on an exposed hill in Fort William, and the conservatory will not facethe prevailing wind. The house walls are roughcast over their full height, with a clear 50 mmcavity.

1. Fort William is in exposure zone 4.

2. Subtract 1 as the conservatory will face East and add 1 as the house is in an exposedlocation.

Degree of exposure the conservatory will face is 4 1 + 1 = 4

3. Check the house wall construction against the table to find the degree of exposure the

house wall is designed to withstand.

From the table a full height roughcast wall with a 50 mm clear cavity is designed to withstanda degree of exposure of 3.

As the degree of exposure the wall is designed to withstand is less than the degree ofexposure the wall faces, a cavity tray is required.

Worked example 2.

The house is located on a housing estate in Stornoway, and the conservatory will face theprevailing wind. The house walls are roughcast over their full height, with a clear 50 mmcavity.

1. Stornoway is in exposure zone 4.

2. Do not add or subtract anything as the conservatory will not be particularly sheltered orexposed.

Degree of exposure the conservatory will face is 4

3. Check the house wall construction against the table to find the degree of exposure thehouse wall is designed to withstand.

From the table a full height roughcast wall with a 50 mm clear cavity is designed towithstand a degree of exposure of 3.


17 WORKED EXAMPLES FOR CAVITY TRAYS


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Worked example 3.

The house is located on a housing estate in Oban, and the conservatory will not face theprevailing wind. The house walls are roughcast over their full height, with a clear 50 mmcavity.

1. Oban is in exposure zone 4.

2. Subtract 1 as the conservatory will face East.

Degree of exposure the conservatory will face is 4 1 = 3

3. Check the house wall construction against the table to find the degree of exposure thehouse wall is designed to withstand.

From the table a full height roughcast wall with a 50 mm clear cavity is designed to withstanda degree of exposure of 3.

As the degree of exposure the wall is designed to withstand is equal to the degree ofexposure the wall faces, a cavity tray is not required.

Worked example 4.

The house is located on a housing estate in Greenock, and the conservatory will face theprevailing wind. The house walls are facing brick with flush joints, with a clear 50 mm cavity.

1. Greenock is in exposure zone 4.

2. Do not add or subtract anything as the conservatory will not be particularly sheltered orexposed.

Degree of exposure the conservatory will face is 4

4. Check the house wall construction against the table to find the degree of exposure the

house wall is designed to withstand.

From the table a facing brick wall with a 50 mm clear cavity is designed to withstand adegree of exposure of 2.



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