In this article we cover:
- Sample floor plans for granny flat conversions
- What statutory approvals you need to get
- What you need to apply for
- Fire safety considerations
- Design considerations: dos and don’ts
As well as being usually more economical to exploit any spare space in an existing property, many of us have a strong attachment to the family home or locality, so it often makes more sense to extend a home or convert an existing building instead of buying elsewhere.
When weighing up your options, a garage conversion could be a better option than a loft
conversion. After all, our vehicles are often parked outside all year round for convenience, so garages end up as rather expensive storage units. Ideal for repurposing.
Of the many reasons for altering a home or garage, the most common one is to gain additional
living space, followed closely by the need for a home office or studio. These are often converted
into a granny flat, i.e. an independent living space for an elderly relative.
But there are a few things to consider before you take the plunge. The most important first step
is to determine the intended use of the space and whether statutory approvals are necessary.
Statutory approvals
As a general rule, even if little or no actual building work is to be carried out, a garage which is to be converted from one use to another will require applications to be made to the planning and building control authorities and possibly also other agencies.
There is a lot of guidance available to read on the subject and in practice some of it can be quite
complex, with certain rules taking priority over others. The fastest way to get reliable answers is to ask a design professional such as an architect or chartered architectural technologist. They will help you to make decisions by telling you what is possible or allowable, will examine how the structure can be adapted for living purposes and can also try to keep any proposals within your planned budget (page opposite).
Probably the easiest garage conversion to gain approval for and to carry out the works, is one where the garage forms part of the overall dwelling and where alterations can be kept simple.
Probably the easiest garage conversion to gain approval for and to carry out the works, is one where the garage forms part of the overall dwelling and where alterations can be kept simple.
The only external changes may be the replacement of the garage door with a window and maybe the addition of another external entrance door.
One thing to keep in mind is that in the countryside, extra living space created by this method should remain dependent upon the existing dwelling and be physically linked internally, e.g. with a connecting internal door.
If, on the other hand, the annexe were to include a kitchen and bathroom in addition to a bedroom and living room and not be internally linked through to the remainder of the dwelling,
it would be regarded as a separate dwelling unit. In that case, you will need to go through a full planning application and other statutory requirements applicable to a new house.
Applications and approvals
Find out what the planners and building control authorities will have to say about your garage
conversion.
In our cities, towns and villages, the change of use of an existing building is usually encouraged in favour of new builds as this is considered to be a more sustainable form of development.
Generally, a garage for conversion in an urban area can be attached or detached and may have
more than one storey. In the NI countryside, planning policy categorises a separate domestic
garage as a ‘domestic ancillary building’ and in most cases, converting one into standalone
accommodation would not be permitted.
In ROI, the rules for garage conversions are similar. In both areas, subject to certain limitations,
there is the possibility for permitted development.
The planning authority will look at issues such as location, existing and intended use, whether the garage is attached to or detached from the dwelling, access, dimensions, external appearance, outdoor amenity space and local character. Rules for rural development will differ
to those for urban development.
Converting a garage for commercial purposes in an urban residential area or in the countryside
would not usually be permitted although there are some exceptions.
In some urban areas, the garage may have counted as parking space when the original planning permission was granted, so check what implications it may have if you remove this space
from the parking allocation.
Other agencies will be consulted as part of the planning application process. The local roads authority will look at such things as access to and from the public road, gates, parking, roadside
drainage, temporary works and street lighting.
The water authority will be interested in water supply, pollution and the impact on, or capacity of, any public wastewater system. Rivers and fisheries agencies will have an input on drainage, pollution, flood protection and so on.
Environmental agencies exist for conservation of the environment and natural heritage, so will want to check on likely impacts on local protected flora and fauna and their habitats and the treatment of any invasive species. The presence of listed buildings, conservation areas and archaeological sites may also influence the application.
If the planning requirements can be satisfied, the proposed design must also be able to conform
to the building regulations, which will cover things like structure, access, fire safety, acoustics, energy conservation, ventilation and drainage, etc. The provision of a separate septic tank for the new habitable space will require approval.
Fire safety
A garage attached to a dwelling should have had a separating fire-resisting wall built up to the underside of the roof.
This should be retained intact if the garage is to become a separate dwelling unit and it will be important to carefully check all fire-stopping and upgrade that if necessary.
If the conversion simply extends the use of the existing dwelling, fire separation will not
be necessary, but emergency egress measures will be required and fire, gas and smoke detection and alarms will need to be linked throughout the dwelling.
A separate dwelling unit should have its own fire safety system.
General design considerations
Find out whether the garage was originally built with approvals or as a later unapproved add-on,
as this could have implications for the adaptability of the construction for its new purpose.
The pre-design survey will assess its suitability and should also attempt to identify materials
which may be hazardous, e.g. asbestos; or defective, such as reinforced autoclaved aerated
concrete (RAAC).
Space: Available space will largely dictate what can be done. A single bedroom with an ensuite shower room might suffice with 15 to 20 sqm of floor space, but add an open plan living room with a compact kitchen and it would require around twice that. A single person bedsit should require about 30 to 35 sqm and a two person, one bedroom flat might need around 50 to 55 sqm of floor space.
A home office or studio could be smaller, although the planned activities or equipment sizes
and positions will need to be considered.
Access: Many attached garages are accessed from the dwelling through a utility room or similar. If so, a separate route might be needed, but if this removes the use of an existing room or renders it impractical, alternatives may be required. Any internal or external stairs, ramps, handrails and guarding serving the new habitable space must comply with the building regulations. A loft access hatch will need to be added if the garage roofspace is not accessible from the dwelling one, and no hatch exists on the garage side.
Insulation: To begin working out how internal spaces might be affected by the addition of insulation, allow insulation thicknesses of about 150mm for external walls, 300mm for ceilings
and 100mm for floors. Your designer will carry out heat loss calculations to refine these thicknesses to meet the building regulations. Insulation thickness will depend on its thermal conductivity and the target U-values. Newly insulated elements may require a vapour control layer (VCL) and/or a breather membrane.
Foundations: If it is suspected that existing foundations have been constructed to a lesser standard than required, it is imperative that trial pits are excavated adjacent to them for examination by a structural engineer, who can then decide whether additional loads can be applied or if strengthening is required.
Floors: Garage floors might not be insulated, however any attached garage should have been built with its floor at a lower level than that of the adjoining dwelling; so it is often possible to add insulation and a floating floor finish to the top of the existing floor to bring it up level with the dwelling floors. Add a damp proof membrane (DPM), just in case the one under the floor is
damaged or missing.
Walls: Some garages will have been built with single-skin solid external walls, possibly with piers. These walls will need to be insulated and an air cavity provided between the inner and outer wall leaves. If the wall is already a cavity wall, check the width of its cavity, whether it is insulated and if additional insulation needs to be added. If the cavity has insulation board fixed inside the cavity, with some free air space, it may be possible to have the space filled with injected bead and gel insulation.
Roofs: Check the weather resisting performance of all roofs before or during the design stage. If any leaks are suspected in a flat roof, a surveyor can carry out electronic leak detection tests and
have them repaired and retested as the survey proceeds. An older concrete or asphalt flat roof
or one with a built-up bituminous felt covering may now be near the end of its life. Pitched roofs
tend to last longer, but old felt underlay, battens, slates and tiles can deteriorate. Also check the
fastenings including nails, clips and hooks. In all roofs constructed with timber, get into the roof
void and check for rot or infestation. Only alter roof trusses under guidance from a structural
engineer.
