London mews house garage conversion by Trewhela Williams. Photo by Lorenzo Zandri.
Many UK houses constructed after the First World War were built with garages, either integral to the house or detached. However, as the majority aren’t fit for parking modern cars, the space is better used for other purposes. Additionally, the rise in property values and the expense of building a new extension make garage conversions a cost-effective way of adding useable floor area.
A garage conversion is ideal for creating additional bedrooms, home offices, gyms, or utility rooms, tailored to your specific needs. It can also significantly enhance your home's market value, making it a sound investment.
Converting your garage is a practical solution for adding extra room. The process is often quicker, more cost-effective, and less disruptive than other home improvements. While you will lose a covered parking space, the additional living area usually outweighs this downside.
Garage conversions can:
Guest bedroom garage conversion by Mark Lewis Design. Photo by Rory Gardiner.
Before embarking on your garage conversion project, assess whether your garage is suitable.
The first thing you should check is your title deeds. Some properties, particularly leaseholds, may be subject to legal constraints prohibiting the use of the garage for anything other than parking a private vehicle. If this is the case, seek legal advice from a conveyancing solicitor to see if the clauses can be changed.
If there are no legal obstacles, you can then evaluate the building’s suitability. You’ll need to consider:
A well-executed garage conversion may increase your home's value by up to 15%.
However, consider factors such as local parking availability, in cities a private garage can fetch a premium, and the market value ceiling in your area to gauge the potential return on investment.
Do this by evaluating similar properties in your area to understand the potential value increase. A conversion that adds a unique feature, such as an ensuite bedroom or a home office, can make your property more attractive to homebuyers.
However, consider factors such as local parking availability – especially in cities where a private garage can fetch a premium – and the market value ceiling in your area to gauge the potential return on investment.
Also evaluate similar properties in your area to understand the potential value increase. A conversion that adds a unique feature, such as an ensuite bedroom or a home office, can make your property more attractive to homebuyers.
If your garage serves a single dwelling house (as opposed to a flat), isn’t listed, or on designated land (conservation areas and other protected places), your garage conversion will likely fall under Permitted Development (PD) rights, meaning planning permission is unlikely.
It’s important to understand the specifics of what is allowed under PD rights, as there are limits to the type of work that can be done without planning permission.
Preparing plans and applying for a Lawful Development Certificate (LDC) will remove any uncertainty and help you re-mortgage or sell the house in the future once the work is complete.
In some designated areas your local authority may remove permitted development rights under an Article 4 Direction to further control development.
If you do not have PD rights, you will need to seek planning permission.
Engaging an architect early in the process will prevent delays and ensure your project adheres to all necessary regulations.
READ: Do Garage Conversions Need Planning Permission?
Architect Paul Westwood has converted a disused garage into a garden home office. Photo by Chris Wharton.
Construction costs will vary depending on location, structural changes, utilities, and plumbing.
A straightforward 12 square metre integrated garage conversion, which is within the footprint of the house and has existing first floor accommodation above, could cost as little as £600 per square metre, depending on the interior finishes. Costs for adjoining or detached garage conversions are more difficult to estimate. For early-stage budgeting, you should allow approximately £1,300 per square metre for a basic conversion. More radical conversions can easily exceed £2,000 per square metre.
Factors affecting conversion costs include:
Deciding between engaging an architect or just a builder will depend on the project's complexity. Professionals can provide valuable design insights and ensure compliance with building regulations.
For more complex or design-focused projects, engaging an architect (and structural engineer if there are new structural works) will add to the overall expense, but their expertise can ensure the space is designed and utilised effectively, saving on costs in the long run.
An architect is essential for complex projects where design and integration with the existing structure are critical. They can provide detailed plans and manage the project from start to finish. General builders are suitable for straightforward conversions where you have a clear idea of what you want and structural changes are minimal. They can complete the work more quickly and cost-effectively.
For anything other than a simple room conversion, commissioning a set of plans will help provide design and cost certainty.
Drawing up a set of plans before starting your project will provide a clear framework, will ensure all design and structural elements are considered, and help identify potential issues early. Having a set of plans will also help builders provide accurate estimates and streamline the construction process, while ensuring compliance with planning and building regulations.
If you need more space, adding a second storey to your garage conversion might be an option. This will involve more extensive work, including checking and possibly reinforcing the existing foundations, but can add significant value to your home.
A double-storey conversion provides additional living space without further expanding the footprint of your home, ideal for properties on confined plots. It can significantly increase the overall value of your property, particularly if it includes high-demand features such as additional bedrooms or bathrooms.
Note that increasing the height of your existing garage is likely to require planning permission.
Two-storey garage extension by modernist architect Henry Winter. Photo by The Modern House.
Garage conversions offer a lot of design flexibility and can be both contemporary and traditional. There is lots scope to create something architecturally interesting that enhances the visual appeal and functionality of your home.
For detached garages, there is more potential to change the appearance of the building, especially if it’s located in a discreet place. This could include new cladding and glazing, and changes to the roof form.
For listed buildings or homes in heritage settings, the scope for innovative design is likely to be restricted. Here, local authorities may insist that your garage conversion matches the appearance of the existing building and wider street scene by stipulating that front-facing exterior materials and glazing should match original features. If the garage has original timber doors or is part of a street scene with a particular type of doors, such as a row of mews houses or townhouses on a mid-century modern housing estate, they will insist on these being maintained.
READ: Garage Conversion Ideas: UK Architect-Design Inspiration
The slab level of attached garages is often lower than the finished floor level of the main house. This makes it easier to insulate the floor, as insulation can be added on top of the existing slab to create step-free access between the two structures.
However, as garages aren’t built as habitable spaces, the ceiling heights can be quite a lot lower than the main house. This can present challenges when raising the floor level, as headroom could be restricted.
When conversion works create inadequate head height, consider the following options:
If the garage has a pitched roof with a flat ceiling, additional headroom can be achieved without changing the exterior of the garage by modifying or removing the ceiling joists and opening up into the roof void.
Garage conversions that create new living space, be it a bedroom, playroom, or home office, must comply with building regulations covering aspects such as structural integrity, energy efficiency, fire safety, ventilation, electrics, and plumbing.
You can seek building regulations approval through your local building control department or an approved inspector who are certified private build control companies.
For a simple garage conversion, submitting a building notice is normally sufficient to gain compliance. This involves notifying building control and signing off the design and construction as the work progresses.
For more complex projects, a full plans application is recommended. This involves the preparation of detailed architectural and structural plans which are signed off by building control before work begins on site. The site works, built in accordance with the plans, are then signed off in stages. Agreeing the technical design upfront provides comfort through greater design and cost certainty.
This will largely depend on the specifics of the design and existing building.
If the design involves structural steelwork, then it’s likely you’ll need new foundations to ensure it’s adequately supported. The same applies to building a new storey on top. The additional weight will significantly increase the load on the existing foundations, usually resulting in underpinning and other structural works.
If you’re infilling the existing garage door opening with masonry, you’ll need to check whether the existing foundations or concrete slab is suitable to support the new load. The general rule of thumb is a 200-millimetre thick concrete slab is normally strong enough to support masonry. If the existing concrete slab isn’t suitable, you can build a new foundation within the opening.
Installing floor to ceiling glazing within the existing garage door opening can reduce loads on the existing foundations and give sense to spaciousness. Architect, VATRAA. Photo by Jim Stephenson.
Most concrete garage floors are strong enough for general domestic use. However, they are often built with a slight slope to allow rainwater and fuel leakages to drain out and therefore require levelling. This can be done with a screed (liquid self-levelling screeds are ideal) or by building a floating timber floor.
One method of insulating the existing slab is to build a floating screed floor. This involves laying a damp proof membrane (DPM) over the levelling screed, then rigid foam insulation, a vapour control layer (VCL), and then a sand and cement screed, normally about 75 millimetres thick, to receive the floor finish.
Garage floors tend to be lower than those in the main house, so the added build-up described above is often possible. However, if the level change isn’t sufficient, building a floating timber floor is a practical solution. The overall build-up is thinner than a floating screed floor and involves laying a DPM, then installing timber battens with insulation between. A VCL is laid over the top and then sheet subflooring – chipboard or plywood – is fixed over the top ready for the final floor finish.
Conversely, if the existing garage floor level is much lower than the main house, building a new suspended timber floor to bring the level up is a sensible solution. However, this will only work if there is sufficient floor-to-ceiling height. Otherwise, steps between the garage and house will need to be incorporated into the layout.
When considering different floor build-up options, you should also think about how you’re going to heat the new space and whether you’re going to install wet underfloor heating.
A floating screed floor works particularly well with wet underfloor heating, where pipes are clipped on top of the VCL before the screed is poured. The thermal mass of the screed acts as a perfect medium to store heat and radiate it out into the room.
Alternatively, instead of pouring a screed, you could install underfloor heating tiles. Slowly increasing in popularity in the UK, they are more sustainable than wet screeds, can reduce the overall floor build-up thickness, and speed up the installation process.
There are also wet underfloor heating systems integrated into timber subflooring, which work with suspended or floating timber floors. However, they are less effective than a heated screed due to the limited thermal mass.
Garages, designed as non-habitable spaces, need to be properly insulated to make them comfortable spaces to spend time in.
If your garage is detached, and planning rules allow, adding external wall insulation (EWI) offers optimal energy efficiency and scope to reimagine the exterior design through new cladding. For integral garages, internal wall insulation (IWI) is likely to be your best option as it won’t impact the rest of the house.
If the garage has uninsulated cavity walls, insulate internally or fully fill the cavity with blowing wool (or similar) and install EWI. Cavity insulation plus internal wall insulation is not recommended as there is an increased risk of penetrative damp and condensation-related issues.
The most common method is to infill the garage door opening with low-level masonry that matches the rest of the building and install glazing above. For stability, the masonry needs to be fully bonded to the existing wall. This can be done by ‘toothing’ the brickwork or using wall starter ties.
Alternatively, you could install glazed doors or full-height glazing to introduce more daylight into your new space and reduce the load on the existing foundations.
Using materials that are similar in appearance to the existing house will help your proposals meet PD rights, should they apply.
Works to garages in heritage settings, like conservation areas, will face more scrutiny from your local authority. This is not to say architectural expression will be completely stamped out, but if you want to do something a little different, you’ll need to enlist the services of a skilled architect.
Garage door infill using painted brickwork, timber-panelled entrance door and sash windows by McLaren Excell. Photo by Rory Gardiner.
Many post-war detached garages have poorly constructed flat roofs which are prone to leaking.
If your garage roof needs repair, consider upgrading to a warm flat roof for superior waterproofing and thermal performance. This involves stripping the roof structure back to the joists, installing a plywood deck, and insulating over the top. The roof can then be finished with a single-ply membrane, or for improved aesthetics, a sedum roof.
Alternatively, consider replacing it with a pitched roof, subject to planning permission. Pitched roofs typically require less maintenance than flat roofs and offer the potential to increase the internal ceiling height or create a usable roof space.
For existing pitched roofs, you can create a cold roof by insulating at ceiling level, or a ventilated warm pitched roof by insulating between and the rafters, leaving an air gap above, and a second layer of insulation below. Alternatively, for optimal thermal and acoustic performance, consider an unventilated pitched roof. This, however, requires completely stripping back the roof to the rafters.
Garage conversions must meet Part B of the Building Regulations.
For attached garage conversions, the best approach is for the new living space to be accessed via your existing protected hallway, providing a safe means of escape out of the building. If your new garage room is accessed directly off another room, it becomes an ‘inner room’ and you’ll need to provide an alternative means of escape to the outside. This can be a door or window.
Escape windows should be no higher than 1.1 metres from the finished floor level, at least 450 by 450 millimetres, covering 0.33 square metres in area, and positioned to allow the occupants to move away from the building. A mains-linked smoke alarm may need to be fitted in every access room serving an inner room.
Providing an alternative means of escape only applies if the inner room is a habitable space – living rooms, bedrooms, home offices, etc. Non-habitable spaces – kitchens, bathrooms, utility rooms, storage rooms, etc. – do not need an alternative exit.
All structural elements should be at least 30-minute fire protected. If the garage room is attached to the main house, the dividing wall should be at least 30-minutes fire-rated with a 20-minute fire-rated door.
All heating, hot water, and electrical works need to be carried out by certified tradespeople and conform to Part P of the Building Regulations.
As a minimum, you’ll need new electrical circuits and heating pipes when creating a simple garage conversion. These will put additional loads on your consumer unit and boiler, respectively. Adding a bathroom or converting a large garage space will increase the loading further still. If your existing systems have insufficient capacity to serve the new space, you’ll need to upgrade these, which could add significant costs to your overall budget.
To minimise electrical loads, opt for a simple layout that incorporates energy-efficient LED lighting. For heating, installing radiators is the most economical solution. Alternatively, air-to-air heat pumps, effectively air conditioning units that heat and cool, can be a cost-effective solution for self-contained spaces. To free up wall space and maximise the available floor area, install wet underfloor heating. Electric heating mats can be used in small areas such as bathrooms, but they’re inefficient and expensive to run when heating larger spaces.
If you’re installing a kitchen, utility room, WC, or bathroom in your garage conversion, you’ll need to allow for below-ground drainage and hot and cold water supplies. These will need to meet Part H of the Building Regulations.
Your architect or builder will need to locate the existing water supply, waste pipes, and foul drainage so the new services can be planned accordingly. Positioning new drainage connections close to existing provisions will simplify the building work and reduce costs.
New connections into existing sewers need careful management, not only in terms of practicality but also consents. If the sewer only serves your property, it’s classified as private and any new connections just need to meet building regulations. However, if the sewer is shared with other properties, it’s classified as a public sewer and you’ll need prior consent from your local water company. This requires submitting separate technical information to meet their requirements.
Garage converted into a kitchen-dining space by Trewhela Williams. Photo by Lorenzo Zandri.
Good ventilation is vital to prevent moisture build-up, and your garage conversion will need to meet Part F of the Building Regulations.
General air circulation in habitable rooms should be provided by adequately sized openable glazing. The opening area needs be at least 1/20th of the floor area of the room. There is no prescribed opening size for non-habitable rooms like bathrooms, which need to be mechanically ventilated.
Unless there are heritage dispensations, background ventilation will need to be provided by trickle vents within the windows and doors, or by a mechanical ventilation heat recovery (MVHR) system.
To meet building regulations, a kitchen, utility room, WC, or bathroom will require an extractor fan.
If you’re installing a wood-burning stove with an output of 5kW or more, you’ll need additional ventilation, either by installing air bricks or an outside air kit. Note that Parts F, J, L, and G of the Building Regulations all apply to stove installations. A HETAS certified engineer will be able to advise on how much ventilation is needed as well as ensuring the overall installation meets regulations.
The information provided in this article is intended for general guidance and educational purposes only. For specific expert advice on your project, choose a skilled residential architect featured on Designs in Detail.
About the author
Aron Coates, an architect with over two decades of experience, draws upon a wealth of residential architectural expertise, encompassing projects ranging from the restoration of historic structures to the design of contemporary homes.
