Garage conversion ultimate guide

If you are one of the many households with a junk filled, unused garage, and you are looking for a relatively quick and affordable way to add more flexible space and value to your home, then a garage conversion may be the solution for you, subject to the below considerations.

Conversion suitability

If your garage is not used for parking, or you can park in your front garden, or if your road has lots of parking available, then it makes sense to consider converting it to habitable accommodation.

Conversion uses

As attached garages are typically to the side of the ground floor, the space lends itself to a range of different uses such as an extra living space, home office, gym, bedroom, or an annex for a relative. Detached garages are more suited to home office or gym use, though in some boroughs, planning permission for use as an annex for a relative may be possible. An annex could even be used to generate income by renting as a room to a lodger or as short-term holiday accommodation.

Value added

Garage conversions can add up to circa 10% value to your house, assuming the loss of the parking space will not devalue your property. An extra bedroom will normally add the most value, though the bedroom could also be used for other functions. It’s best to seek the advice of a local estate agent familiar with your street to get a better understanding.

Construction costs

Compared to loft conversions and extensions which typically start at circa £2,000 per square metre, garage conversions can typically start at circa £1,000 per square metre, depending on the amount of upgrading required, as they don’t require the new superstructure that extensions do or structural steel strengthening like loft conversions do.

Garage conversion timescales

An architectural designer should take a week or two to complete architectural drawings following an on-site measured survey. Either a planning application or lawful certificate application then takes up to eight weeks. If a structural engineer is required, then the calculations can take a further week or two. Construction of garage conversions can take as little as 6 weeks compared to lofts which start at circa 8 weeks or extensions which start at circa 10 weeks, owing to the reasons outlined above. The six weeks are typically divided into: a week for structural works such as walls/partitions/windows, a week for first fix plumbing/wiring, a week for insulating/plasterboarding, a week for plastering, a week for installing carpentry and plumbing fittings, and a week for decorating.

Planning permissions

Most of the time, garage conversions don’t require planning permission as they are covered by permitted development rights, though it is still prudent to apply for a lawful certificate to confirm this is indeed the case to avoid enforcement after construction. However there are many exceptions to the rule where planning permission will be required.

Annex use

Planning permission will always be required to include a bathroom or shower room to a detached garage, as permitted development does not allow this in outbuildings. In boroughs where unlawful “beds in sheds” are not typically a problem, planning permission may be granted for this on condition that the outbuilding is only used to accommodate a relative and not rented or sold as a separate dwelling. Similarly renting out or selling an annex created through conversion of an attached garage without planning permission will lead to enforcement as permitted development does not allow for the effective creation of a separate dwelling unit.

Planning conditions

Newer houses with garages built after permitted development started in the eighties, or extensions containing garages built at any stage can have a condition requiring use of the garage solely for parking, in which case planning permission for conversion will be required.

Conservation areas and listed buildings

In conservation areas there can be article 4 directions removing permitted development rights for the insertion of windows (normally required to replace the garage door), in which case planning permission for this will be required. Any changes to listed buildings will always require planning permission.

Height increases

Planning permission may also be required if raising the roof of an attached garage or detached garage if it would not comply with permitted development maximum dimensions for side extensions or outbuildings respectively, or if it would comply but an article 4 direction has removed these rights.

Building regulations requirements

Structural changes

Structural changes such as raising the roof or floor of a garage or removal of a load bearing wall to open plan usually require calculations from a structural engineer. When installing a window to replace the garage door, it will be necessary if the existing foundation is not continuous under the door to either install a new section of foundation or better a concrete lintel to support the new wall, to the inspector’s satisfaction.

Fire regulations

Fire regulations normally require provision of egress windows for attached garages converted into self-contained habitable rooms such as bedrooms or living rooms in case a fire starts in the room used to access it. A new smoke alarm will be required if the newly created habitable room is more than 7.5m from existing smoke alarms. If converting only part of a garage and retaining any portion as car/cycle parking or just storage, then a self-closing fire door in fireproof partition with a step down into the unconverted space will be required to prevent fire from flammable liquids spreading into the converted space.

Thermal upgrades

Thermal upgrades will be required to floors walls and roofs. Floors are usually upgraded with insulation and vapour control layer under either cement screed or chipboard flooring if a slimmer profile is required to match existing floor level in the house. Walls less than 20cm thick will require construction of an insulated inner stud-work partition with 50mm gap in between to stop damp ingress, whereas thicker walls can usually be upgraded by attaching insulated plasterboard. Flat roofs can be upgraded with insulation and a new waterproof membrane on top of the existing boards, while pitched roofs can either be upgraded with insulation on a new flat ceiling or between and under rafters if a vaulted ceiling is required. If the existing pitched roof as an older unbreathable tile underlay such as bitumen, ventilation will need to be added to the bottom and top of the roof slope to prevent condensation rotting the timbers.

Services

New underground drainage for a bathroom may be needed which can normally connect to fittings via a new short internal air admittance valve if no existing soil vent pipe is present nearby for connection. Heating will need to be installed which can normally be achieved with extra radiators connected to the existing boiler, though new bathrooms may require the upgrade of the existing boiler to a more powerful one. Electrics will need to be self-certified by a registered electrician.

Inspections

A council or private building regulations inspector will need to be engaged to inspect the works at various stages and to sign them off with a completion certificate at the end.

Conclusion

Garage conversions can be a relatively affordable and quick way to add space and values to your home, though the complex planning and building regulations issues are best left to an experienced architectural designer, who can prepare a good set of planning drawings and building regulations drawings. Draw and Plan have submitted many garage conversions over the last decade and are here to help you.