Garage conversions: how to cost, design and plan your project

A garage conversion is a great way to bring more room into your home. Use our guide for all the costing, planning and design advice you need

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

A garage conversion is a sound option for households in need of more living space. Not only is it often more affordable than extending a house, but the build time can be as short as a few weeks, and the options for how you use the space, endless. 

Whether you've felt the need for a home gym, office, cinema or other type of area over the past few months, garage conversions can be a great alternative to moving house altogether, or to extending into your garden space. You might pay anything from £5,000 upwards, but you can expect to increase the value of your property in the long run, making this a worthwhile project to pursue.

In this guide, we go through everything you need to know ahead of getting started. From costs, to the different types of garage conversions and all the planning stages to consider – including information on planning permission – so use the jump links below to help you navigate this feature with ease and to get your project off the ground.

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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.

Garage conversion costs

How much a garage conversion costs depends on your project, but what it will set you back will usually be significantly lower than the costs associated with a house extension. Reason being that you will be saving money on laying new foundations and building new walls; your garage may even have power and 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.

Before you begin planning a garage conversion, first consult an estate agent about whether this could have a negative impact on your property's price. If you'll be living in your home for years to come, it may well be worth proceeding whatever they say, but if garages are highly sought after in your area, think carefully before converting your garage.

Planning a garage conversion

Before you start work on the conversion, consider what you’ll do with everything currently kept in the garage. If you store a lot of garden gear in it, you may need to factor a shed or another type of garden storage into your plans; if it’s where you keep your chest freezer, you’ll need to work out where it can be moved to – or whether you can live without it. 

If you really have no room anywhere else for these things, perhaps a partial garage conversion (or a conversion that has lots of storage space set aside within it) will work better for you.

What are the different types of garage conversion?

It's important to know about the different types garage conversions to ensure that you get the best use out of yours. Here are the four main types:

  • Full Integral single garage conversion: the most common type and also very cost-effective, an integral garage is attached to your property within the main walls and access will be via an area of the home. Usually a utility room/ through the kitchen.
  • Partial garage conversion: this is an ideal and speedy option if you really need to keep some storage space and if you're on a tight budget. It will usually be the rear part of the existing garage that gets converted into the new living space to allow for normal use of the front, dividing both areas by a partition wall.
  • Double garage conversion: much like the name suggests, it's simply double, so you will in essence be getting more room. Many often dedicate half the space to parking and storage as with a partial design.
  • Detached garage conversion: this is a matter of converting a single or double garage that is separated from the main property. It asks for more design, including insulation, work and planning permission may be likely so this is often more costly but the results can be exceptional. Plus, if it is close enough to the house, you may be able to fit an integrated passageway to improve ease of access.

Do you need planning permission for a garage conversion?

In the majority of cases, the work involved in converting a garage will be classed as permitted development

However, if you live in a Conservation Area, a location where development can be restricted to protect the appearance of the surroundings, or on a new estate with strict guidelines (some new homes are built with a condition that the garage remains as parking, so you'd need to apply to change its use), it’s worth checking what’s allowed. 

Detached garages are much more likely to require planning permission for a change of use.

Use our guide to planning permission for more details.

Do you need insurance to convert a garage?

Yes: if you are project managing the garage conversion yourself, it is highly sensible to arrange conversion insurance. If you fail to insure yourself properly, and there is any loss or damage caused during the works, it's unlikely that your home insurer will cover you will your home is undergoing alteration or renovation.

Conversion insurance will cover the work being carried out and the existing structure: in other words, your house. It should also cover materials, plant tools and equipment (stolen or damaged during works, these can cost thousands to replace). 

This type of insurance should also cover public liability and employer's liability – should any of the workers be injured on site, for example – do check as this is an important element needed to protect yourself. 

Ensure that the conversion insurance is ready to go from the moment work starts until the very end of the job when the new room is in use. 

Architect or garage conversion specialist?

Using an architectural designer or a specialist garage design and build contractor, will help put your ideas into fully formed plans, and give you much needed expert design input. If the garage is attached or integral to your home, they will also help you consider the best position for access, and put plans in place to redirect this if required. 

To find an architect, visit architecture.com or use an architectural technologist (see ciat.org.uk). The starting point for your design is to draw up a floorplan. Expect to pay from as little as £1,200 right up to £3,000 for an architect's services, depending on the complexity of the design.

Specialist garage conversion companies can save you time in putting together applications and will be experienced in getting the best from this type of project, but any good builder will be able to do the job. 

Ideally, work with someone who has been recommended and is a member of an accredited body, such as The Federation of Master Builders. Find reliable contractors with the help of our guide.

mews house garage conversion, Dublin

TAKA Architects transformed a mews house in Dublin, moving the cramped kitchen from the rear of the building into the garage and replacing the original garage door with a striking steel screen with vertical fins which incorporates space for planting

(Image credit: TAKA Architects/ Alice Clancy)

Planning a garage conversion: the DIY route

If you're on a budget, some people choose to come up with a design themselves and carry out all the work they can on a DIY basis – a good option for those with limited funds and the spare time to get stuck in.

You can do most of the work yourself, which is ideal if you’re on a tight budget, but your work will be regularly inspected by building control officers and anything that’s not up to scratch will have to be undone at your own expense. Get an idea of what's involved in project managing an extension with the help of our guide.

Get written quotes (not estimates) from three different companies, with a clear specification of what’s included. Using an architect can give a more creative result.

spare bedroom in a garage conversion

Converting an unused garage in a high value area such as London and adding extra living space can be a sure way of adding significant value

Garage conversion structural essentials

When planning a garage conversion, there are some important structural considerations that you need to tackle early on.

Replacing the garage door

The garage door will have to be replaced with a new wall and/or window. This may mean new foundations, but there are other options, including having lintels set just below ground level that bear on sound masonry or existing foundations each end. Expect to pay, including a small window, around £1,300 for this.

If you live in a conservation area you might find that your local council want you to retain the original door. There are ways to do this, including building a false interior wall behind the doors which, ideally, will have glazed sections. This isn't a bad place to site a kitchen sink, for example (see below for inspiration).

Garage converted into a home office seen from the exterior by Bliss Interiors

(Image credit: Bliss Interiors)

Upgrading the garage roof

The garage roof will almost certainly need to be upgraded to ensure it is water-tight. Use new tiles and materials that match those of the main roof. If you can swap a flat roof for a pitched one it will make the conversion less obvious from outside, and the new raised pitch may have space for rooflights. Doing much more than general repairs to the roof will have to be approved by your local building control department.

Internal wall work

An internal structure of stud walls built inside your garage will have insulation added to increase energy efficiency. Expect to pay around £750 per stud wall.

Upgrading external walls

External garage walls will usually be single course brickwork, which won’t meet building regulations for moisture and insulation. This can be solved by adding an interior, insulated stud wall built off a damp-proof course on a couple of courses of bricks. ‘Set 75mm clear of the original wall, this stud wall can easily accommodate services and insulation prior to plasterboarding,’ says Designer Nigel Lewis of Space & Style Home Design.

Ventilating, heating and insulating a garage

Ventilation: Shower rooms and kitchens must meet building regulation requirements with extractor fans, but you might also like to include an extractor if you’re planning on using the room as a home gym. Otherwise, an opening window and background ventilation in the form of air bricks or trickle vents will be needed.

Insulation: Building regulations require walls, windows, the floor and roof to be insulated to a certain level. It’s important to get this right — poorly done, it will result in a cold, damp room. 

With pitched roofs, insulation may be two layers of 150mm glass fibre quilt, one between the joists, another over; flat roofs tend to need one layer between the joists of rigid PUR insulation board and another below, with a 50mm air gap above for ventilation. The second layer underneath will drop the ceiling height, however. 

Dry-lining the walls and fitting sealed double-glazed windows are also probable requirements. New windows won’t usually need planning permission but will need to be energy-efficient and double-glazed to be approved by building control. They may also need to be able to be opened right up, too, to comply with fire safety regulations (see above). Match the style to the house’s existing windows to help the conversion fit in.

If floor height is an issue (particularly if you've had to lower the ceiling to insulate it, fitting multi-foil laminate insulants rather than using polystyrene floor insulation can help reduce the thickness of the under layer. 

Heating: If your boiler won’t cope with another radiator, or it’s not practical to run the new pipework, consider electric underfloor heating, which is relatively easy to install.

Bear in mind that bedrooms, home offices and playrooms will need more insulation and better heating than a utility room, while a home gym or shower room will need better ventilation than a living room.

Electrics and plumbing in a garage conversion

Plumbing: If you're planning on installing a toilet or shower, double check the location of the existing water and soil pipes – doing so may help you keep garage conversion costs down, if you can put your fittings in a convenient place. 

Bear in mind the extra costs involved in installing a radiator – and the extra strain put on your boiler. Factor in between £1,000 and £3,000 for gas and plumbing works.

Electrics: Ask your electrician or builder if rewiring the garage for lights and electric radiators will mean that your mains (fused at 100 amps) will be put under strain, too. They may suggest installing an additional mains supply and separate consumer unit, which can add significantly to costs. 

Another option is to put the garage on the existing consumer unit, perhaps with its own miniature circuit breaker. Consider adding a minimum of one new 20-amp circuit, too.

If yours is a detached garage conversion, wiring can be run through an underground conduit, although a new connection may be needed if it is to be a separate dwelling, an annexe, perhaps. A good electrician will always be able to advise.

Expect to pay around £100 to have a new electrical socket fitted; this price will be negotiable the more electrical work you are having done.

Kitchen diner in a garage conversion

This garage conversion is now a spacious kitchen diner

(Image credit: Clear Architects)

Fire safety for integral garage conversions

What if you have an integral garage but without an internal door to it from the house. Can you fit one if you're not converting it?

The answer is yes, but two fire safety requirements apply:

The door needs to be an FD30S fire door with a self-closing device fitted. Thirty-minute fire-resisting doors are best bought as a set with the frame because the latter is made from thicker timber than standard and is rebated to fit the necessary intumescent (which means it swells when heated) smoke seal to the sides and the head. Hence, you can’t use normal door frames for this purpose.

Internal doors to garages are the only doors in homes that need to be self-closing. Those with a checking action that pauses in the almost-shut position before fully closing are best, avoiding crushed fingers. The floor within the garage must be at least 10cm lower than the finished floor within the house to prevent fuel spillage running into the house. If it isn’t 10cm lower, the door sill will need to be raised by brick or concrete block to create this 10cm step over, or the floor of the garage should be sloping outwards to beneath the garage car doors.

Garage conversion build schedule

  • Check structure is suitable for conversion
  • Produce design drawings
  • Confirm whether planning permission is required
  • Apply if consent is required
  • Produce detailed design and building regulations drawings
  • Arrange conversion insurance to cover the new works and the existing structure; most home insurers will exclude loss or damage while the property is undergoing alteration or renovation.
  • Notify local authority Building Control of commencement
  • Strip garage back to retained structure
  • Structural alterations, including knocking through to house
  • Damp-proof new floor, if necessary
  • Insulate walls and new floor, plus the roof if single storey
  • Pour new floor, if required
  • Install new window and doors
  • First fix joinery, wiring and plumbing
  • Plaster and dry-line
  • Fit new doors, skirting, architrave, fixed floor finishes and light fittings
  • Decorate

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