The Scottish Building Standards TECHNICAL HANDBOOK CONSERVATORIES

Transcription

1 The Scottish Building Standards TECHNICAL HANDBOOK CONSERVATORIES

2 The Scottish Building Standards TECHNICAL HANDBOOK CONSERVATORIES

3 Crown copyright 2006 Cover designed and produced by Astron Text pages designed by Scottish Building Standards Agency

4 Contents 1 Status of this document 2 When you can use this document 3 Introduction 4 Foundations 5 Walls below floor level 6 Floors 6a 6b Concrete floors Suspended timber floors 7 Walls above floor level 7a 7b Cavity masonry walls 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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6 1 STATUS OF THIS DOCUMENT This document provides guidance on how to meet the building regulations for simple conservatories which are built onto existing houses. The use of this document does not remove the need to obtain a building warrant for the conservatory, 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 building standards which parts of the document relate to the application. If this guidance is followed it should be accepted by the verifier (local authority building standards department) as indicating that the Building (Scotland) Regulations have been complied with. Consequently, it is expected that any requests by verifiers for further information will be minimal, thus saving time for both the verifier and the applicant. In addition, a set of drawings such as a location plan, a block plan and scaled floor plans and elevations, may also be required by the verifier. It is quite acceptable to use alternative methods of compliance with the regulations. The functional 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 the website of the Scottish Building Standards Agency at and any part may be downloaded free of charge.

7 2 WHEN YOU CAN USE THIS DOCUMENT This guidance does not cover every conservatory, and for many it will be necessary to refer to the Technical Handbooks. The document when used in its entirety will only apply to conservatories that: 1. meet the definition of conservatory (A conservatory is a building attached to a dwelling and having a door separating it from that dwelling and having not less than three quarters of the area of its roof and not less than one half of the area of its external walls made of translucent material), and 2. are to be attached to the ground storey of houses (but not flats or maisonettes) and only when those houses have foundations of traditional concrete strips, or when the ground conditions allow for the use of traditional strip foundations, and 3. have an internal floor area of more than 8 m 2 but not more than 20 m 2, and 4. are connected to the mains drainage system, and the invert level at the point of connection to the house drainage system is not more than 1000 mm, and 5. have an effective roof area of not more than 35 m 2 (including any house roof area to be drained via the conservatory gutters and down pipe), and 9. have glazing to all sides (excluding the back/house wall), onto which the roof is fixed, and 10. will meet the thermal insulation requirements whether the conservatory is to be heated or not, and 11. are not built on or above ground that is contaminated, and 12. do not contain a chimney, flue pipe, fixed combustion appliance installation, washbasin, sink, bath, shower, urinal, watercloset or waterless closet, and 13. are not built over any form of underground drain, other than a drain only serving the dwelling on to which the conservatory is to be built, and 14. have a floor level the same as, or not more than 600 mm below the floor level of the house, and 15. are not built over an existing rain water down pipe, and 16. are not built over any existing escape windows. 6. are fixed directly to masonry walling at least 100 mm thick, and 7. are at least 1 m from any boundary, and 8. are at a distance from the boundary (in metres) of at least 1/6 of the area of glazing and frame (in m 2 ) facing that boundary. (e.g. if a side of the conservatory has an area of glass and frame of 9m 2, then the conservatory must be at least, 9 6 = 1.5 m from the boundary which that glazing faces), and

8 3 INTRODUCTION A conservatory may need no permission at all, some permission, or indeed many permissions of various types. If you are in doubt you should contact your local authority 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 be contacted for information on any other permissions. All new building work in Scotland, to which the building regulations apply, must have a building warrant prior to work commencing, except where the regulations permit. A building warrant must be obtained before you start any work where the conservatory is more than 8 m 2 in floor area. A warrant is also required for conservatories below this size if they contain a chimney, fixed combustion appliance, washbasin, sink, bath, shower, urinal, watercloset, waterless closet, or are closer than 1 m to a boundary. This document provides enough information to cover a large proportion of simple conservatories. It does not seek to tell you all you need to build, but to give you sufficient guidance on what must be done to ensure compliance with the technical standards. This guidance does not cover every conservatory, and for many it will be necessary to refer to the Technical Handbooks. Professional advice may be required for conservatories of a more complex design than those covered in this document.

9 4 FOUNDATIONS The area of ground where the foundations of the conservatory are to be poured must be 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 the house foundations are not ordinary strip foundations, work must cease and the verifier must be informed. This guide is only for use where the ground conditions allow the use of strip foundations. The foundations must be poured at the same depth as the house foundations or with the 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 they must be poured over the scarcement of the house foundations, as shown in the foundation 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 mm wide 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 must have 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) Junction Detail reinforcement

10 5 WALLS BELOW FLOOR LEVEL Walls below floor level must be built of two leaves of at least 100 mm thick brick or block with a compressive strength of at least 5 N/mm 2, with a 50 mm cavity between the leaves of masonry. The two leaves of masonry must be tied together using stainless steel wall ties with a minimum of 4 per square metre. The mortar to the masonry walling must be of a 1 part cement to 4 parts sand mix. The cavity will be 120 mm wide if the above floor walls are to be insulated within the cavity. The walls must be built centrally on the foundations. The walls must be of a material suitable for use underground such as common or engineering brick, or dense concrete block, and be built up to the level of the damp proof course (dpc), at least 150 mm above external ground level. Where the conservatory floor is of concrete construction, laid directly onto the ground, or when the conservatory has a timber floor and the floor joists are supported off joist hangers, both leaves must be 100 mm thick. Where the conservatory timber floor is supported on a wall scarcement, the inner leaf of masonry below floor level must be 215 mm thick. The cavity must be filled with lean mix concrete up to ground level, to prevent the cavity filling up with rain water, and weep holes (open perpend joints are the normal provision) must be provided at not more than 1200 mm centres. The walls must be attached to the house wall, typically using a proprietary wall starter bar bolted vertically to the house wall at the point were the conservatory wall abuts it. This starter bar must also be used for the walls above floor level. Sub-floor walls may be needed to support a suspended timber floor construction. These walls need only be 100 mm thick, but must be built in honeycomb construction or with crawl holes to allow the air below the floor joists to circulate freely.

11 6 FLOORS This document provides guidance on 2 types of floor: a. Concrete floors poured onto a prepared solum, and b. 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 the firm subsoil. This excavation of the soil must be taken down to at least 250 mm below the existing ground level to prevent frost heave. A layer of hardcore, (small sized crushed rock or brick) at least 150 mm thick must be laid on the prepared sub-soil. This layer must be compacted with a roller 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 top of 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 taken up the inside of the walls below floor level by at least 150 mm. Now follow the appropriate specification for either concrete or timber floors.

12 6a CONCRETE FLOORS An 80 mm thick layer of polyurethane or other equal insulation boarding (thermal conductivity of not more than 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) and be 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 the house, these ventilators must be ducted to the outside air through the concrete floor/hardcore using 100 mm diameter upvc pipes. The damp proof membrane to the floor must be linked to the damp proof course of the external walls. min 150 GL dpc 150mm concrete 80mm insulation dpm 25mm sand blinding min 150 compacted hardcore

13 6b SUSPENDED TIMBER FLOORS 50 mm of concrete must be poured onto the dpm to give a smooth solum finish. Ensure that 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 on a 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 than 3 m, either between the external walls of the conservatory or between 1 external wall and a sub-floor wall. At least 200 mm thick mineral wool, must be laid between the joists, supported by netting draped over and between the joists. The construction is now ready to lay the tongue 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 the solum. 220 x 65 mm sub-floor ventilators must be installed in the perimeter wall at not more than 1500 mm centres. Any heating pipes below the insulation level must be insulated. 200mm joists and insulation min 150 GL dpc dpm min 150mm air space 50mm concrete 25mm sand blinding min 150mm compacted hardcore Joist hangers min 150 GL dpc dpm 200mm joists and insulation min 150mm air space 50mm concrete 25mm sand blinding min 150mm compacted hardcore Scarcement wall

14 7 WALLS ABOVE FLOOR LEVEL External walls above ground level are commonly built to a variety of heights. The conservatory does not have to be built with a wall above floor level. The windows may start at floor level. This document provides guidance on 2 types of wall: a. Cavity masonry walls, and b. 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 stainless steel wall ties with a minimum of 4 per square metre, and cavity closers of mineral wool or timber wrapped in dpc must be provided at wall 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 the wall will face, or have a rendered finish. Now follow the appropriate specification for either cavity masonry walls or timber framed walls.

15 7a CAVITY MASONRY WALLS 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 walls can 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 insulation boarding (thermal conductivity of not more than W/mk) within the cavity, or behind 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 be maintained. This will result in an overall cavity of 120 mm, partially filled with insulation. dpc cavity batt mastic two leaves of brick/block/stone with a 50 mm clear cavity and insulation

16 7b TIMBER FRAMED WALLS 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 mm between the two leaves. The cavity must be vented to the outside air using proprietary perpend ventilators located 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 of 100 x 50 mm at a maximum of 600 mm centres, with a top and bottom rail. Dwangs should be provided at mid height if the timber frame is greater than 1200 mm in height. The frame must be clad externally with plywood at least 12 mm thick and a breather membrane. The frame must be finished internally with a vapour control layer and plasterboard 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 conductivity of not more than W/mk) must be provided immediately behind the plasterboard. dpc compressible cavity batt mastic plasterboard with vapour barrier behind insulation behind vapour barrier mineral wool insulation between timber studs 12 mm plywood with breather membrane on cavity side mm brick/block/stone nom 35

17 8 WINDOWS Conservatory windows must be of reinforced plastic profiles or of solid timber, or of metal. There must be a certificate from a UKAS accredited scheme, (e.g. BBA) supplied as part of the warrant application, certifying the complete conservatory framing to confirm its fitness for purpose. The units must be double glazed with a maximum U-value of 3.3 W/m 2 K. All glazing which is closer than 800 mm to floor level must be made from safety glass. 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 where the difference between floor level and the adjacent ground level is not more than 600 mm. Both types of safety glazing must be marked with a BS kite mark which confirms that the glass is indeed safety glass. The opening area of conservatory windows and doors must be at least 1/30 th of the combined floor area of the conservatory and the room covered by the conservatory, or, the conservatory must be provided with windows and doors of at least 1/5 th of the floor area of the conservatory, whichever is the greater. The window frames must be fixed to the house wall and the base wall as per the manufacturer s instructions. There must be provided 1 or more trickle ventilators (small closable ventilators which can provide minimum ventilation) with a combined open area of at least mm 2, allowing a slow change of air within the conservatory without opening the windows or 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 greater than 600 mm. If the conservatory is to be built over a mechanical extract fan terminal the fan must not discharge into the conservatory, but fans may be ducted through the conservatory to the outside air. If the conservatory is to be built over a window to a kitchen, bathroom, shower room or utility room, a mechanical extract fan must be provided to those rooms, leading to the outside air. The extraction rate of the fan should be 60 lts/s to a kitchen, 30 lts/s to a utility room and 15 lts/s to a bathroom or shower room.

18 9 ROOFS The conservatory roof must be constructed from reinforced plastic, aluminium/steel or timber rafters with double glazed units, or multi-skin polycarbonate sheets between the rafters. The double glazed units or multi-skin polycarbonate roof sheets must have a U-value of not more than 3.3 W/m 2 K. There must be a certificate from a UKAS accredited scheme, (e.g. BBA) supplied as part of the warrant application, certifying the complete roof, to confirm its fitness for purpose. The roof must be fixed to the house in accordance with the manufacturer s instructions. Code 4 lead flashing must be raggled into the house wall 150 mm higher than the roof bar and dressed down either into the roof bar if the manufacturer s system allows, or a further 150 mm over the roof sheets. The roof must be fixed to the top of the windows in accordance the manufacturer s instructions. A cavity tray may be required to be installed in the existing wall, at the point where the conservatory roof meets the house wall. The need for a cavity tray will depend on the construction of the house and the amount of wind driven rain the wall above the conservatory will be exposed to. See section 14 to calculate if a cavity tray is required. Cavity tray (if required) 25mm raggle lead flashing 150 mm Conservatory roof 150 mm

19 10 DRAINAGE The rainwater from the conservatory roof must be drained to the main surface water sewer 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 fall of 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 is unachievable due to the depth of the existing pipes, the new pipe must have a cover of 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 be accessed when necessary. Drainage pipes may therefore remain below the conservatory if it is impractical to reroute the drain around the conservatory. If the existing pipe is of fireclay, the pipe to be below the conservatory must be removed and replaced in upvc piping. The pipe must be replaced from access point to access point so that there is not a mixture of pipe materials in the same pipe run. The conservatory foundations must be below the level of the drain, and the points at which the pipe passes through the external walls of the conservatory must be constructed as shown in the diagram below. Where the conservatory drain is to be connected to a drain carrying both rainwater and wastewater, a ventilated trap must be provided to the new rainwater underground pipe as close as possible to the connection to the existing wastewater/ rainwater pipe.

20 10 DRAINAGE Before Before re ex rwp trap rwp svp After After ex re extended ex rwp rwp re renew in upvc rwp svp relocate trap outwith base lintol over pipe section through wall

21 11 ELECTRICS All electrical installations must be carried out in accordance with BS It is recommended that a 30 ma RCD (residual current device) be installed to the electrical circuit, to provide protection to socket outlets likely to feed portable equipment outdoors. (e.g. lawnmowers). 12 CONNECTING DOORS There must be a door in the external wall of the house between the house and the conservatory. This door, or doors, must provide thermal separation between the house and conservatory. The retention of existing external quality doors is deemed to meet the thermal requirements. 6 WINDOWS 6 WINDOWS 10 CONNECTING DOORS 10 CONNECTING DOORS 10 CONNECTING DOORS 6 WINDOWS

22 13 STEPS Steps from the conservatory to the ground level, and steps from the house to the conservatory 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 the conservatory is being built over an existing level or ramped access to the house which was required to be provided for accessibility purposes. In this case, the external door of the conservatory must be provided with a low level threshold to allow wheelchair users to pass. The addition of the conservatory must not make the level of 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 mm or less than 100 mm high. The depth of the step must not be less than 250 mm. The flight must have a pitch of not more than 34º. 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 on 100 mm thick brick or block walls on either side. Paving slabs at least 50 mm thick and not larger than 600 mm x 600 mm may be used when supported on all sides, but these are suitable for light domestic use only. If the height from ground level to floor level is more than 600 mm, or if the external doors of the conservatory open outwards where the height from ground level to floor level is more than 170 mm, a landing must be provided at the top and bottom of the flight. A barrier must be provided to the open sides of the steps and landing where they are at a height of more than 600 mm. The barrier must be at least 900 mm high and have no gaps within it which would allow a 100 mm ball to pass through. Handrails must be provided on both sides of the steps where the steps are at a height of more than 600 mm. The handrails must be at a height of more than 840 mm and not more than 1000 mm above the pitch line of the steps. The landing at the bottom of the flight can be any suitable clear space, (e.g. paving slabs). landing more than 170mm above ground level 900mm Single door 900mm equal equal equal equal 900mm Double doors

23 14 CAVITY TRAYS 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 will prevent the ingress of water into the conservatory through the existing external wall of the house. The following calculation confirms where cavity trays must be provided and is based upon wall construction and the exposure to wind driven rain of the existing house. If this calculation 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 tray some 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 hillsides or in valleys where the wind is funnelled onto the wall, and subtract 1 from the number where walls 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 exposure the house wall is designed to withstand. If the house design number (step 3) is equal to or greater than the exposure number (steps 1 and 2) no cavity tray is required. Degree of exposure which various wall constructions are designed to withstand facing cavity insulation cavity roughcast facing brick roughcast brick type width above facing recessed full height flush mm brick joints joints built-in full fill injected fill (not UF) injected fill (UF) partial fill + 50 mm clear no cavity insulation When unfamiliar with the type of cavity insulation in the house, it may be necessary to cut or drill a small hole in the wall for a visual check. UF = Urea Formaldehyde injected foam insulation From Thermal insulation: avoiding risks BR262, 2002, BRE Reproduced by permission of BRE Press Copies are available from

24 15 EXPOSURE ZONES IN SCOTLAND Sheltered Moderate Severe Very Severe

25 16 DESIGN CHECKLIST The proposed conservatory is designed to meet the guidance contained in the sections as highlighted 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

26 17 WORKED EXAMPLES FOR CAVITY TRAYS CAVITY Worked example 1. The house is located on an exposed hill in Fort William, and the conservatory will not face the prevailing wind. The house walls are roughcast over their full height, with a clear 50 mm cavity. 1. Fort William is in exposure zone Subtract 1 as the conservatory will face East and add 1 as the house is in an exposed location. Degree of exposure the conservatory will face is = 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 withstand a degree of exposure of 3. As the degree of exposure the wall is designed to withstand is less than the degree of exposure 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 the prevailing wind. The house walls are roughcast over their full height, with a clear 50 mm cavity. 1. Stornoway is in exposure zone Do not add or subtract anything as the conservatory will not be particularly sheltered or exposed. Degree of exposure the conservatory will face is 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 withstand a degree of exposure of 3. As the degree of exposure the wall is designed to withstand is less than the degree of exposure the wall faces, a cavity tray is required.

27 Worked example 3. The house is located on a housing estate in Oban, and the conservatory will not face the prevailing wind. The house walls are roughcast over their full height, with a clear 50 mm cavity. 1. Oban is in exposure zone 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 the house wall is designed to withstand. From the table a full height roughcast wall with a 50 mm clear cavity is designed to withstand a degree of exposure of 3. As the degree of exposure the wall is designed to withstand is equal to the degree of exposure 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 the prevailing wind. The house walls are facing brick with flush joints, with a clear 50 mm cavity. 1. Greenock is in exposure zone Do not add or subtract anything as the conservatory will not be particularly sheltered or exposed. 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 a degree of exposure of 2. As the degree of exposure the wall is designed to withstand is less than the degree of exposure the wall faces, a cavity tray is required.

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