Garage conversions: a complete guide to plan, design and cost your project

Garage conversions are a brilliant way to create more living space at home. Find costing, planning and design advice in our ultimate guide

Garage conversions: by OB Architecture
(Image credit: Martin Gardner)

A successful garage conversion will let your household enjoy more living space, in a what could be as little as a few weeks, or just a couple of months. Because whether you're dreaming of a home office, gym, cinema or even gaming room, the quicker it's sorted and the more cost-efficient it is, the better. 

Garage conversions are the ultimate answer to home improvement. This project will let you keep precious garden space, unlike a rear, kitchen or side return extension and, better still, converting a garage is significantly cheaper than extending a house. You can look to pay anything from £5,000 upwards –, while you can expect to increase the value of your property too, which will make moving house a doddle in the long run.

In this two page guide, we go through everything you need to know ahead of getting started. On this page, we've covered everything to do with costs, and on page two we'll cover more on garage conversion types, all planning stages including planning permission and more.

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Do garage conversions add value?

A garage conversion could add up to 20 per cent to the value of your home, while you'll gain valuable extra living space that's less prone to planning complications. So if the cost of the project is less than the extra value added to your property, this works out as a cost-effective way to add more space. Plus, if have a double garage, you could convert just half the space. Doing so means you will gain living space and continue to benefit from a parking space.

Should I convert my garage?

If you can't decide whether to convert a garage or not, consider these pros and cons: 

Profit vs spend: a garage conversion should add more value to your home than it costs to build. But always ask a trusted local estate agent first. 

Space vs spend: garage conversions can cost as little as £5,000, way less than you could ever hope to extend out for.

Moving costs vs spend: depending on how ambitious your plans are, it will be cheaper to convert a garage than to move house for more space.

Spend vs spend: converting a garage to add an extra bedroom might push you up a council tax band. Check the added cost before you proceed.

How much does a garage conversions cost?

Garage conversion costs are significantly lower than those associated with an extension because you will save money on laying new foundations and building new walls; your garage may also have power and perhaps even plumbing already, both of which will reduce your bill even more.

You can expect to pay between £5,000 and £7,000 upwards (depending on spec); that's around £1,000 to £1,250 per square metre – if the walls and floor are stable, there is a watertight roof, and the ceiling height is sufficient to leave around 2.2m to 2.4m of headroom after building up the floor by 15cm above external ground level. 

Dining area with Philip Starck Ghost Chairs in a converted garage

Part of this former garage has been transformed into a dining room that opens on to the outdoor space

(Image credit: ZazuDesigns)

If the structure is attached to the house, rather than integral, and needs structural repairs, it may be more cost-effective to demolish and replace it.

Compared to the cost of a single storey extension, which will be upwards of £13,000, it's a cost-effective way to gain more space indoors.

Design costs

Design fees for a garage conversion range from £1,200 to £2,500, plus £300 to £400 for a structural engineer. A typical single conversion (18 square metres) could cost as little as £5,000 without fitting costs, but expect to pay around £17,100 to £23,900; for a double (36 square metres), £31,300 to £43,300, plus VAT, is more likely, depending on personal specifications.

For an accurate estimate of how much your garage conversion project will cost, use our extension cost calculator.

Factors that might affect garage conversion costs

Typically, a garage conversion will cost more if the original structure is unsound. If you are going to spend a lot of money stabilising the building, knocking the original garage down and building from scratch might be cheaper.

Another factor to consider is the perceived value that it will add to your home. Check the value of houses in your area, if there is little off-road parking, homes with garages might be valued higher than those without. Unless the added space is vital, don’t run the risk of reducing the value of your own home.

A partial conversion should cost less, but not by much. Fewer materials will be needed, but services, such as electrics and plumbing, will still have to be installed and budgeted for.

Interior fit-outs

Garage conversion costs need to incorporate the interior fit-out, the cost of which really does depend on exactly how you'll be using the room. However, you can use these figures below as a rough guide. If the room is to be just an extra living space, perhaps as a play room, make sure you future-proof the wiring and lighting in case you want to convert it into a TV room in years to come.

  • To add a kitchen in a garage conversion, budget from around £5,000 to £20,000, depending on the specification; if you go high end, costs can increase significantly.
  • For a bathroom, factor in from around £4,500 to £11,000 for the plumbing and fittings.
  • For a shower room, utility or boot room, perhaps with a big sink for washing dogs, plan for between £4,500 and £11,000.
  • For flooring, budget in the region of £25 to £100 per square metre.
  • Set aside from around £85 per square metre for plaster or dry-lining walls plus paint.

a conversion of a integral garage

Berry Construction converted an integral garage in London into a valuable double bedroom (which can be seen below) with en suite shower. The project cost around £40,000

(Image credit: Berry Construction)

Adding heating

Your plumber should be able to extend your existing central heating system, which will mean a couple of day's work, at around £150 per day, excluding materials. 

If you are opting for underfloor heating in this room only, electric underfloor heating will be a less expensive option to install (a DIYer can fix it in place, but it needs to be connected to the mains by a qualified electrician; day rates are around £150 per day). If your garage conversion is part of a larger renovation, water-fed underfloor heating will be cheaper to run over time, if more expensive to install initially. This may also mean you need a new boiler to meet the underfloor heating's demand; the Energy Saving Trust estimates the cost of a gas boiler replacement at around £2,300.

Professional project fees

Remember to factor in professional fees, such as those from an architect. Expect to pay an architect for design fees at around three to seven per cent of the build cost; planning drawings and construction drawings could each come in around £2,000 upwards. You may also need a structural engineer to size roof joists and foundations, particularly if you are building on top of the garage, too. Factor in £500 to £1,000.

Dining room in a garage conversion

This open plan kitchen diner was once a garage beneath a pretty coach house in Devon.

Planning permission fees

It's likely you can convert a garage under permitted development rights (see the next page for more). As a safeguard for the future, it's worth applying for a certificate of lawful development from your local authority in any case, at a cost of £86. Do remember, the removal of permitted development does not rule out the potential of a garage conversion, but you’ll need to ensure the design is sensitive to the setting and apply for full planning permission, which costs £172 in England. Listed properties will need listed building consent, too.

When you will need planning permission:

  • If you live in a listed building;
  • If the garage conversion increases your home beyond permitted development rights;
  • You are converting the space for business;
  • Your council has restrictions on reducing parking.

Even if these restrictions apply, you should be able to convert the garage interior as long as the exterior is untouched.

Building regulation fees

As a ‘change of use’, a conversion is subject to building regulations approval, so your local authority will need to be notified. But you’ll need building regulations consent and sign off for the various elements of your garage conversion, as with other home alterations. To comply, it must: 

  • Be structurally sound and have a damp-proof course. 
  • Have the walls, the floor and the roof insulated to be energy efficient. 
  • Have all new and existing electrics tested to ensure safety. Future-proof the space by allowing plenty of electrical points and a phone point, even if they won’t be used now.
  • Be moisture proofed, with good ventilation. 
  • Fire-proofed, with escape routes (in case of fire), that comply too.

Once the building inspector is satisfied, the completion certificate will follow within 28 days. You can use the council’s building control service or an approved independent inspector, costing around £300. Always check that your local council is happy with your plans before starting work. For details, see planningportal.gov.uk.

Party wall agreement fees

If the work affects a structure shared with an adjoining property, the Party Wall act will also apply. Expect to pay around £700 to £1,000 for a party wall agreement with your neighbours – although if you are able to persuade them to sign a waiver, you'll save yourself this cost.

Sometimes there are legal restrictions on alterations to a property, too, so check the deeds to your home to see if permission is required from a previous owner.

Planning a garage conversion >>