Garage conversion
The
conversion of an attached garage into living accommodation is
treated as building work for the purposes of the building
regulations. An application must be made under the regulations
before work commences. The following points should be
considered.
Foundations
A foundation must be provided to carry any additional masonry
loads such as a new inner leaf wall to line existing external walls
or a garage door infill. The condition and suitability of the
existing foundation and floor can be assessed when the door infill
area is excavated. In most cases, the infill panel can be supported
on a new foundation complying with the Building Regulations or on
suitable beams or lintels spanning between the shoulders of the
existing foundations or brickwork either side.
Infilling the garage door opening
This is usually done with a new panel of cavity walling
incorporating a damp proof course (DPC) that is lapped to the
damp proof membrane in the floor and to the existing DPC at
junctions. The cavity should extend to at least 225mm below the
DPC. The masonry must be tied to the existing by tooth bonding or
proprietary stainless steel fixing profiles. Alternatively a
timber framed panel can be used instead of the inner blockwork skin
or both skins of masonry. All infill panels must be durable,
weather-proof and adequately thermally insulating.
Structural adequacy
If the existing wall is single leaf construction with piers, it
must be checked for stability and be free from defects. If
satisfactory it is likely the wall would be considered suitable
subject to issues raised under the headings of weather resistance
and sound proofing. The roof structure must also be assessed
for adequacy.
New floor
Various methods of forming a floor are acceptable. The four most
popular are:
- Solid – where levels are made up with a finishing screed and
sometimes concrete incorporating suitable insulation and a damp
proof membrane (DPM) between layers.
- Floating – where flooring grade tongued and grooved chipboard
is laid with glued joints on a vapour check (polythene sheet) on
foam insulant board over concrete as needed for levels and
incorporating a DPM.
- Suspended timber – the formation of a traditional floor with
joists bearing on wall plates on a damp proof course bedded on
honeycomb brick sleeper walls. This is insulated with a suitable
material between the joists and the under floor void needs to be
vented with air bricks to outside on two opposing sides (or
connected to an existing vented sub floor void).
- Battened solid – with this technique, the timber boarding is
fixed onto treated timber battens plugged and screwed into a
concrete slab beneath. Insulation can be placed between the battens
(fully filling the void) with a vapour check over. It is essential
that an effective linked DPM be incorporated with this system.
Weather resistance
A bare brick wall of single leaf construction must be treated to
provide adequate resistance to the passage of moisture. A
waterproofing material applied to the inner face and linked to
floor damp proofing may be an effective way to achieve this
although this does restrict the natural permeation of air through
the wall to the outside. The provision of a stud framed or masonry
inner leaf to create a cavity wall is another method however such
an element must incorporate a linked DPC and must be carefully
detailed to form a drained cavity at its base.
Insulation
A garage conversion creates new ‘thermal elements’ ie. walls,
floors and roofs that separate the heated space from an unheated
space or outside air. When insulating roofs, consideration
should be given to providing a vapour check and appropriate
ventilation to prevent a problem of condensation occurring within
the roof void.
Windows
These should meet
the minimum standards of thermal insulation required by the
regulations. If the new room can only be accessed via another room
then a suitable escape window will normally be required. This means
a clear opening with minimum height or width dimension of 450mm and
area of at least 0.33m² (ie. 450mm x 733mm). The windows
should provide for ‘purge’ ventilation by having clear openings
equal to at least one twentieth of the floor area of the room (one
tenth floor area if window opens by more than 15o and
less than 30o). The windows can also be used to provide
the necessary ‘background’ ventilation via trickle vents giving at
least 8,000mm² free area.
Sound proofing
This will be needed to any single leaf walls separating
neighbouring garages or properties. An adequate standard can be
achieved by forming a 100mm dense block work lining or an
independent studwork wall lined with 30mm total thickness of
plasterboard and with at least 35mm of mineral wool quilt between
studs. There should be at least 15mm clearance between studs and
wall. Additional thermal insulation will be needed where the wall
separates the new heated room from an unheated space (see
‘insulation’ above). Other methods can be used subject to the
agreement of the Building Control surveyor.
Electrical
Electrical wiring is controlled under the building regulations.
Where the work involves a new circuit or forms a new kitchen, bath
or shower room, it is classed as ‘notifiable’ under Part P of the
regulations. The most straightforward route to compliance is
by using an electrician who is registered under a
Government-authorised Competent Person Scheme.
Other considerations
Mechanical ventilation is required to serve any shower rooms,
bathrooms utility rooms or kitchens created by the garage
conversion. Extractor fans with an appropriate air change capacity
can provide this.
Further advice
You can obtain further advice on building regulations and garage
conversions from the building control section of your local
council.
Planning permission
The conversion of a garage into a room may require planning
permission, whether the garage is integral with the house or
detached. In many cases where the garage door is replaced with a
window and/or wall, planning permission may not be
required. However, where the conversion involves a new bay or
bow window projecting beyond the face of the building, planning
permission may still be required.
Planning permission for the construction of a garage may include
specific conditions that prevent its use for anything other than
the parking of a private car. In this case it is always
necessary to obtain planning permission for the conversion.
Consequently, you are strongly advised to check with the Council’s
development control section before starting work.