Beginner’s Guide to Garage Conversions

Chris Bates looks at how a garage conversion could be a cheap and easy way to add space and value to your home
Chris Bates, Editor of Build It magazine
by Chris Bates
1st June 2020

What do you use your garage for? If it’s turned into more of a store room (or a junk yard for that old exercise bike) than a safe spot to park the car, then maybe it’s time to consider making better use of what could be a valuable asset.

A garage conversion is one of the speediest and most affordable routes to adding floor space: a typical scheme creating a new home office or playroom can often be completed in little more than a week.

Plus, of course, you won’t need to resort to moving to get a house that suits your family’s needs; so you’ll save on fees for stamp duty, solicitors etc. What’s more, unlike a conventional home extension, it won’t eat up any of your garden amenity.

A garage conversion can also increase your home’s value. Virgin Money reckons you can net around a 10%-20% return by taking on a well-considered project that enhances the usability of your home.

Designing your space

The first step with any garage conversion is to conduct an assessment of the existing structure, in particular the soundness of the foundations, walls and roof.

This will go a long way to revealing the extent of works required to create a comfortable living environment – so it’s a key part of the design stages. If the building is in an especially dilapidated state, it may be cheaper to knock down and replace.

Read more: How Much Living Space Do I Need in My Home?

Getting the right result will depend on the scale of the scheme, how you want to use it and integrate it into the property, and what your budget will stretch to.

For higher-end projects, working with an architect could help to identify creative ways to maximise the potential of your garage and establish a space that flows naturally into your home.

Another popular route is to use a company that specialises in the design and build of garage conversions.

The results can be fantastic – if not quite so avant garde – and many will take your scheme through planning and building control as part of their fee. Plus their experience on-the-ground can help to ensure a smooth project and a predictable budget.

Garage conversion during construction
Work gets underway, with alterations made to the original structure as a disused garage is converted into a liveable space
Retro kitchen garage conversion
The stylish final result is a retro-inspired kitchen with family breakfast area. Image: David Giles

If it’s integrated or attached, the garage should be fairly easy to work into the main accommodation. You could knock through the wall to join up with an existing zone, for instance – perhaps enlarging a hallway or creating a front-to-back kitchen-diner.

A detached structure, meanwhile, lends itself to segregated uses, such as an annex or quiet home office. A single garage will offer around 15m2 of floor space; more than enough for a playroom, separate drawing room, guest bed, or even an accessible downstairs shower and WC.

Read more: How to Create a Home Office in Your Garden

At around 30m2, a double garage gives you more flexibility. It could house a bigger living room, ensuite bedroom, well-sized kitchen-diner or an annex.

Alternatively, you could retain a single parking space by erecting a suitably insulated and fire-rated partition, and fit-out the rest for habitation.

Planning permission

With many garage conversions – particularly integral or attached spaces – most of the work is internal (with the exception of changing the frontage and adding a window or two).

This is likely to be considered permitted development (PD), so it won’t usually need formal planning consent.

In some cases, such as in conservation areas, PD rights for this change of use may have been removed – so consult the local authority before you begin. For peace of mind, you could apply for a lawful development certificate.

Children playing in living space basement

Hut Architecture re-designed a compact mid-terrace property in Bethnal Green for a growing family. Infilling an existing basement courtyard allowed for more family space. [Photography: Heather Hobhouse]

Some modern builds are subject to restrictive covenants requiring the garage to be retained as parking, which would need to be discharged (check the deeds to find out if this applies). You’re also more likely to need formal permission to change the use of a detached garage.

You may still be able to pursue a scheme even if PD rights have been removed – but you’ll need to put together suitable drawings and apply for householder planning consent. This costs £234, plus any design fees.

A full application will also be necessary if you want to significantly alter the external appearance, such as making big changes to the windows, using new materials or adding an extension. Among the other permissions you might need to secure are listed building consent (if you live in a listed building) and party wall agreements with any adjoining neighbours.

Building regulations

As this type of conversion involves a change of use, a garage conversion will always be subject to the Building Regulations.

For straightforward schemes, the building notice route may be sufficient, whereby you or your contractor informs the local authority of your intent to start work 48 hours prior to commencing on site.

With more complex projects, you may prefer to have full structural plans drafted. This gives you peace of mind that building control has inspected the drawings and confirmed that – if it’s constructed as per the approved schematics – your conversion will conform to the regs.

In addition to structural safety, key areas your building control officer or approved inspector will look at are damp proofing, ventilation, insulation and energy efficiency, fire safety (including escape routes), electrics and plumbing.

Key works

Before the project can start in earnest, the walls and roof must be made sound and watertight. Thereafter, most of the work will take place inside the existing garage.

The first job will be stripping out the main structure, at which point you’ll get the clearest view yet of what’s in store – including where you’re most likely to encounter unexpected problems (such as patchy foundations or hidden issues in the walls) that could add to costs.

Here are some of the main considerations:

Floor slab

An existing concrete floor might well be strong enough to cope with general domestic use. However, it may need to be levelled (consider a self-levelling liquid screed), damp-proofed with a suitable membrane (lapping into the walls’ DPC) and insulated to achieve adequate thermal performance.

Garage floors tend to be lower than those in the main house, so it may be possible to incorporate all of this and still achieve a step-free threshold between the two zones.

Builders working in basement conversion

Waterproofing a basement ensures that the integrity of the structure. All basements should be constructed to cope with groundwater levels up to the full retained height of the area.

In principle, a cavity drain membrane system allows moisture or running water to travel behind the membrane within a controlled drainage system. A cavity drain system requires minimal preparation and disturbance to an existing structure.

Read more: Basement Waterproofing System

Infilling the door

The most common route is to replace the main garage door with conventional walling matching the rest of the building, such as a masonry infill fully toothed and bonded into the existing brickwork.

The design stage assessment should identify whether the foundations need upgrading to take the new loads. Planning allowing, you could add windows or a glazed access door and introduce more daylight into your new space, which may also help reduce the loads imposed.

If your budget will stretch, you could even have a little fun with the design – perhaps by going for a fully glazed wall.

Wall insulation

Integrated garages are usually built to the same standard as the main house, so the walls may not need upgrading.

Attached or detached garages of single-skin construction can be insulated internally; usually by erecting stud walling using timbers deep enough to accept sufficient insulation (plus an air gap).

Buildings with cavity walls can have insulation blown into the gap, thus preserving the internal floor space.

If you’re going for a part-conversion, retaining a parking space, you’ll need to erect a fully-insulated internal dividing wall that is designed to provide 30-minute fire protection.

This can be done in blockwork, or switch to timber studwork lined with pink fireline plasterboard on the garage side.

Roof insulation

The simplest way to insulate a garage roof is at loft level. With a pitched covering, 270mm of mineral wool should be sufficient – 100mm between the joists, and the rest on top.

Warm roof setups, which are insulated at rafter level, are also possible and can enable the use of rooflights to bring in more natural brightness.

Flat roofs will need to be fitted with rigid insulation between and under the ceiling joists, with a ventilation gap above to prevent condensation. If you want to preserve floor-to-ceiling height, go for slim multifoil or PIR (polyisocyanurate) products.

Windows & doors

The fenestration you specify will need to hit the required whole-unit U-values (1.6 W/m2K for windows; 1.8 for doors), match your security expectations, provide adequate ventilation and suit the style of your home.

If you’re keen to keep costs down, aim to work to standard-sized units.

Casements, sashes and doorsets can be incorporated by punching a suitable hole in the wall and adding lintels as required. The same is true of openings between the main house and garage.

For larger spans enabling a more open-plan feel, a reinforcing steel beam may be needed. This kind of work may require calculations from a structural engineer.

Contemporary kitchen garage conversion by Cue & Co
Now a light, airy scheme, this garage conversion has made space for a stunning kitchen by Cue & Co
Garage conversion regulations
Developers may impose a restrictive covenant on integrated garages that will need to be bought out before conversion

If you’re creating a habitable room that doesn’t offer a direct protected route to an external door, or its own door leading to outside, then you’ll need to provide an escape window.

This must have a width and height of no less than 450mm, a clear openable area of at least 0.33m2 and should be sited so the bottom of the openable area is no more than 1,100mm from finished floor level.

Heating & electrics

The most straightforward way to get this infrastructure in place is to engage professionals qualified to self-certify their work under Part P of the Building Regulations.

You’ll almost certainly need new electrical circuits and heating loops, which will put additional loads on your consumer unit and boiler. If these systems need upgrading, this could easily add upwards of £2,000 to your overall project budget.

Efficient LED downlights are a good choice for illumination, as they can be easily integrated into the new ceiling structure.

Heating-wise, plumbing in a suitably-sized radiator will be the cheapest solution – but slimline underfloor heating is a sleek alternative that can maximise the floorplan and free up wall space. If you’re planning a kitchen or bathroom, you’ll need to account for hot and cold water supplies as well as drainage.

Ventilation is another key issue. Openable windows, fitted with trickle vents, will be sufficient in most cases – but if you’re incorporating a bathroom or kitchen, you’ll need a powerful enough extractor fan to manage moisture build-up.

Garage conversion costs

Provided the structure is in reasonable condition, this type of project should be more cost-effective than adding an extension or carrying out a loft conversion.

A 15m2 integrated garage in good condition could be renovated for as little as £6,000 (£400 per m2). It’ll cost significantly more to convert a detached building, partly because it’s trickier to bring in services – expect to pay from around £15,000 (£1,000 per m2) to renovate a standalone single garage.

Even this should prove cheaper than most single-storey extensions, which will typically start from around £1,200 per m2.

Ultimately, costs will depend on the kind of space you’re creating and the quality of finish you want to achieve.

Kitting your conversion out with a kitchen, bathroom or utility could add another £2,000-£3,000 in plumbing and electrical work – plus whatever you choose to spend on furniture and fittings.

Main image: Urban Front’s Milano up-and-over garage door in RAL 1031, with matching Milano pivot entrance door featuring an 11v handle

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