The Scottish Building Standards
TECHNICAL HANDBOOK
CONSERVATORIES
The Scottish Building Standards
TECHNICAL HANDBOOK
CONSERVATORIES
© Crown copyright 2006
Cover designed and produced by Astron
Text pages designed by Scottish Building Standards Agency
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
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
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 www.sbsa.gov.uk and any part may be
downloaded free of charge.
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 m2 but not more than 20 m2,
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 m2 (including any house roof
area to be drained via the
conservatory gutters and down pipe),
and
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 m2) facing that
boundary. (e.g. if a side of the
conservatory has an area of glass and
frame of 9m2, then the conservatory
must be at least, 9÷ 6 = 1.5 m from the
boundary which that glazing faces),
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.
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 m2 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.
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).
300
150
150
reinforcement
Junction Detail
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/mm2, 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.
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.
6a
CONCRETE FLOORS
•
An 80 mm thick layer of polyurethane or other equal insulation boarding (thermal
conductivity 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) 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.
dpc
min 150
GL
150mm concrete
80mm insulation
dpm
25mm sand blinding
min 150 compacted
hardcore
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
dpc
min 150
GL
min 150mm air space
dpm
50mm concrete
25mm sand blinding
min 150mm compacted
hardcore
Joist hangers
200mm joists and insulation
dpc
min 150
GL
dpm
min 150mm air space
50mm concrete
25mm sand blinding
min 150mm compacted
hardcore
Scarcement wall
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.
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 0.023 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
100
50
70
100
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 0.023 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
50
100 mm brick/block/stone
100 35
nom
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/m2K .
•
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 1/30th 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 1/5th 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 10000 mm2,
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.
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/m2K.
•
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
15
0 m roof
m
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.
10
DRAINAGE
Before
Before
ex rwp
rwp
re
trap
After
After
ex rwp
ex re
extended
svp
rwp
svp
rwp
re
renew in uPVC
lintol over pipe
section through wall
relocate trap
outwith base
11
ELECTRICS
•
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 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
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
equal
900mm
900mm
Single door
equal equal
900mm
Double doors
equal
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
cavity insulation
type
built-in full fill
injected fill (not UF)
injected fill (UF)
partial fill + 50 mm
clear
no cavity insulation
cavity
width
mm
roughcast
full height
roughcast
above facing
brick
50
75+
50
75+
50
75+
2
3
2
3
2
2
2
2
1
2
1
1
facing
brick
flush
joints
1
2
1
2
0
1
50
3
3
2
0
50
100
3
3
2
3
2
3
0
1
facing brick
recessed
joints
0
0
0
0
0
0
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 www.brepress.com
15
Sheltered
EXPOSURE ZONES IN SCOTLAND
Moderate
Severe
Very Severe
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
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 4.
2. 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 – 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 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 4.
2. 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.
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 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 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 4.
2. 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.
CONSERVATORIES
17/5/06
11:44
Page 1
www.sbsa.gov.uk
£5.00
B46427 05-06