Garage Conversions: A Complete Design and Cost Guide

Carrying out a garage conversion is the perfect way to add extra space to your home without extending — plus, in many cases, it won't require planning permission. 

While trading in your garage for living space means forgoing a covered parking space, where extra rooms are needed this sacrifice is, more often than not, completely worthwhile. 

Garage conversions have other benefits when compared to extensions too. They are usually cheaper, quicker and easier to carry out so that, while they are not always necessarily a cheap project, they are most certainly one of the most cost-effective ways to add some square meterage to your home. 

If you're wondering if a garage conversion is right for you, our guide is here to answer all the questions most often asked by those considering this type of home project. 

We cover everything from garage conversion planning permission rules and building regulations information, to the ins and outs of the practical considerations of the project.  

Should I Convert My Garage?

Converting a garage it into habitable accommodation is one of the easiest ways to increase your living space, whether you have an integral or detached garage. 

The benefits of a garage conversion to consider, if you are still undecided, include: 

• You’ll be gaining extra room from the existing footprint of the garage without actually building an extension from scratch.
• A garage conversion won’t use up precious garden space.
• You won’t necessarily need to dig out new footings. It is always worth getting the existing footings checked out though, especially if you want to build a second storey on top of the garage at a later date.
• Many garage conversions won't require planning permission — in fact this type of project is often received favourably by planners.
• Garage conversions can be used for many different purposes — there are plenty of garage conversion ideas to consider — from an extra bedroom or a utility room, to spaces like games rooms and home gyms. 
• They work well as part of a whole house remodel. Look at ways of reorganising the floorplan for a layout that flows from one zone to the next.
• A garage conversion can add a considerable amount of value to your home.  

Can I Convert My Garage?

Before getting carried away it is important to check whether your garage is suitable for conversion. 

“You’ll need to consider how the garage is constructed and what you want to use it for,” says Jude Tugman, managing director at Architect Your Home (opens in new tab). “These criteria will impact on the cost of the conversion.”

Do you want more light, a quiet study, a utility area or an extra bedroom? Additionally, if you’re doing away with your main storage space for bikes and tools, you’ll need to work out where these items can be moved to.

Whilst a garage conversion is, in the majority of cases, a brilliant way to add space and value to your home, there are certain instances where it might not be a viable option or might cause more problems that it is worth. Consider whether this project is right for you by thinking about the following: 

• Will the work mean one or more existing rooms will frequently be rendered unusable by building work?
• Remember that you will be held responsible for the legality of work done on your property. Time and energy will be required supervising work, being present to allow tradespeople access and making design and other decisions
• Will planning permission be granted? Is the house listed or in a designated area? 
• Might the cost of reinforcing foundations, a new roof etc. mean you are paying more than you expected?

Will a Flat Garage Roof Need Replacing?

If, on inspection, you see that water is lying in pools on the flat roof, then this has the potential to cause problems in the new space beneath. The roof will need repairing and the underlying fabric of the structure checking for damage.

Occasionally it is necessary to replace the entire roof. This is sometimes a welcome discovery — swapping a flat roof for a pitched design can help tie the new space in with the rest of the house, aesthetically, although you may require planning permission to do so.

How Much Value Will a Garage Conversion Add?

Increasing your home’s usable floor area will likely boost its cash value, and a garage conversion can add as much as 15% according to estate agent Portico, but you need to consider the individual circumstances of your home. 

Does your home really need extra room? Do you have a drive to park on, or is there copious amounts of on-road parking? What is the price ceiling in your area? These factors will affect how attractive your home is to potential buyers and may affect the overall amount that converting a garage adds to the value of your home. 

Planning

Do Garage Conversions Need Planning Permission?

Do I Need Planning Permission? The short answer is: probably not. 

The majority of integral garage conversions tend to fall under Permitted Development, meaning planning permission is not required. However, it is still best to check with your local authority. According to architectural specialists Resi (opens in new tab), only 10% of garage conversions will require planning permission. 

If you live in a conservation area or in a listed building, you will almost certainly need planning permission. It is also worth checking for any planning conditions attached to the house or garage when constructed as in some cases garages will be required to remain as parking. If there are conditions, an application will need to be submitted to remove them.

In some areas, especially Conservation Areas, PD rights for garage conversions may have been removed. This may also apply to areas where on-road parking is an issue. 

If the conversion falls under Permitted Development, applying for a Lawful Development Certificate (LDC) is a good idea, particularly if you aim to re-mortgage or sell the house in the future.

Even if Permitted Development rights have been removed, you may still be able to convert a garage, but you'll need to make a householder planning application. 

If you are converting a separate, stand-alone garage as opposed to an integral one, then you may have to apply for a change of use.

Cost

How Much Does a Garage Conversion Cost?

When it comes to garage conversion costs, you will need to budget at least £1,000/m2 for a garage conversion. For this price you could expect to achieve construction, plus the design, planning, Building Regs and structural engineers fees — but not finishes and furniture. This could easily rise to between £1,500/m2 and £2,000/m2 depending on the level of work and the finish you choose.

“For a single garage conversion, you’ll need to budget around £20,000, with some variation due to your choice of materials and fittings,” says Rob Wood, managing director at Simply Extend (opens in new tab). “For a double garage, that figure would be more like £30,000.”

Of course, project costs will vary depending on structural changes, utilities and plumbing, which can push prices up (and if your project is in London you should always expect to pay at the top end of the range). 

It's also worth noting that at present construction material shortages are causing a spike in many building materials, from timber and steel to plaster. In fact, some estimates suggest that building quotes have increased 10% year on year to factor in these increases, as well as an increased workload for builders overwhelmed with new demand and less available labour. You should expect to wait several months before a contractor can start your garage conversion at present — you may find there's a good reason a builder has an immediate availability, and that they're a company to avoid. 

A final tailored quote would also take into account waterproofing, insulation and the integration of the conversion with the rest of your property.

Other factors that could affect the overall cost of your conversion include: 

• the foundations need reinforcing
• the condition of the existing structure
• the ceiling height needing to be raised (you need around 2.2-2.4m of headroom once the floor has been raised to 15cm above the external ground level)
• design fees
• planning applications
• the services of a structural engineer.

Design

Do I Need an Architect For a Garage Conversion?

This is very much a personal decision that should be based on the scale and complexity of the project. 

Using an architect, an architectural technologist or another type of design professional will mean expert design input and ideas that you might not have thought of. A design professional will also have useful trade contacts and will have experience in dealing with Building Control.

You will need to factor in architect's fees too — expect to pay from as little as £1,200 right up to £3,000 for design fees, depending on the complexity of the design.

Who Should Build My Garage Conversion?

Some people choose to come up with a design themselves and carry out a DIY garage conversion — a good option for those with limited funds and the spare time to get stuck in.

You could also use a recommended builder — most good builders will be able to take on a garage conversion.

Another option is to use a garage conversion specialist — these companies usually have a wealth of experience but, as with all of the above options, be sure to view completed projects and speak to past clients first. 

A garage conversion specialist should have plenty of experience in terms of dealing with any planning issues surrounding garage conversions, as well as building regulations.

Can I Add Another Storey to My Garage Conversion?

When converting an integral, single-storey garage into living space, it is worth considering the space above it — could adding a storey above be an option? This is well worth thinking about as a way of gaining extra first floor space without increasing the overall footprint of the house.

Clearly, creating a double storey extension means more work and expense, but the end value of the house should make it worthwhile. The existing foundations will almost certainly need to be checked and upgraded, and there will be further Building Regulations to consider. For example, the garage ceiling and new floor in the upstairs space will have to achieve a minimum of 30 minutes fire resistance.

Additionally, there will be thermal and sound insulating considerations to take into account.

How do I Make a Garage Conversion Blend In?

The best garage conversions, when finished, look like part of the rest of your house — not like a converted garage. 

One exception is in the case of partial garage conversions. This is where the front of the garage remains unchanged both internally and externally, while the rear section of the garage is incorporated into the house. This allows you to retain some storage space, while gaining a little extra living space — perfect for those after a utility room, a little extra kitchen space or a playroom.

Ensuring the materials used for the cladding and roof (where there is one) match or tie-in with those on the main house ensures a seamless finish, as does matching the window and door style.

Alternatively, you might wish to adopt a contemporary take on the design and highlight the garage as a new element of the house, choosing a modern cladding or render.

A new cladding will overcome any issues sur- rounding how the old opening for the garage door is concealed — a badly bricked up opening is a definite no no.

Building Regulations

What Are The Building Regulations For Garage Conversions?

A garage conversion will most certainly need building regulations approval. 

You or your builder will need to stick to the Building Regulations when converting an attached garage into habitable space. Regulations apply to various aspects of the construction, including:

• thermal performance
• acoustics
• fire safety
• ventilation.

The LABC website (opens in new tab) is a really good starting point for information regarding the Regulations surrounding garage conversions in England and Wales.

A building notice or full plans application will need to be submitted to building control as part of this process. Your local building control department will then register the conversion and carry out inspections throughout the project, then issue the final certificate on completion.

Do Garage Conversions Need Windows?

Garages don't always open onto hallways, and if this is the case for your build, you may be required to install a window that acts as a fire escape route under Building Regulations. This window is subject to certain criteria, including its height from the floor, how it opens and the size of the openable section:

• Width and height no less than 450mm
• Maximum 1100mm from the floor level
• Openable area of 0.33m2 at the bottom of the window 
• Generally side hung windows are required

If your garage conversion opens directly onto a hallway providing a direct protected route to an external door, or has access to the exterior from within the garage, the window won't be required. 

Bear in mind, windows within garage conversions under Permitted Development are largely only allowed in the section replacing the garage door. Any new windows added to the side of your home may require a planning application.

Key Works of a Garage Conversion

Making a garage into a liveable space isn't just a case of moving your furniture into it. Here's the basic process you can expect of jobs required during a garage conversion. 

• Level, insulate and damp-proof the floor. 
• Infill the garage door to create a solid wall if required
• Insulate the walls and the roof 
• Plasterboard and plaster 
• Decorate 

How Do I Brick Up My Garage Door?

One of the key elements of converting a garage is blocking up the existing garage door opening (with an infill wall) — perhaps adding a new window or entry door in its place.

The most common route would be to infill this using walling that matches the building, or using blocks before using house cladding or house rendering to unify the new wall with the existing structure. 

It may also be possible to retain a door, or use glazing in the infill to bring natural light into the space, also reducing the additional load on the existing foundations. 

Foundations

Do Garage Conversions Need Foundations? 

In order to add an infill wall in place of your garage door, you’ll need to establish whether the garage foundations were continued beneath this opening and/or the concrete slab is adequate to support the new wall. This may involve digging a small trial hole in front of the concrete slab to check.

If the existing concrete slab is 200mm or over, this is generally adequate to extend straight up with new brickwork.

"If the existing slab is not adequate there are typically two options," says Stuart Letts. "Either a 1m footing will have to be dug and filled with concrete or a 140mm x 100mm concrete lintel can be added into the wall on both sides below ground level. The new infill wall can then be built on top of that."

It will also be important to test foundation strength when extending over a garage, as this greatly increases the load exerting pressure on your foundations. 

Speak with your designer, builder or a structural engineer in order to ascertain the suitability of your foundations. 

There are two main routes for those who find their existing garage foundations are  inadequate. 

Either a 1m footing wall will have to be dug and filled with concrete, or a 140mm x 100mm concrete lintel can be added into the wall, below ground level, on both sides. You can then proceed to build a new infill wall on top.

Insulation

What Are Garage Conversion Insulation Requirements?

If you want your garage conversion be a comfortable space to spend time in you will need to ensure it is properly insulated. If the garage is integrated, it's likely to have been built to the same standard as the rest of the house in terms of its thermal performance, but this is not always the case. The garage's construction will inevitably dictate the work required. 

Adding external insulation is not usually recommended as, although it minimises the impact that extra insulation will have on internal spaces, it can cause issues externally with wall thicknesses.

The simplest method is to use insulated plasterboard, fixed to timber battens that are protected by a strip of damp proof course (DPC) placed between batten and wall. Alternatively, insulation can be placed between battens, before a fireproof plasterboard is fixed to them.

Insulating a roof typically becomes a consideration in detached and attached garages with no room above. 

Otherwise:

• In pitched roofs, go for two layers of 150mm glass fibre quilt, one between the joists, another over as usual. A gap of 50mm should be left for ventilation. 
• Flat roofs tend to need one layer between of rigid PUR insulation board and another below — the space in between flat roof joists however can’t be entirely filled. A 50mm air gap must be left above for ventilation. The second layer underneath will drop the ceiling height a bit. Typically 150mm deep flat roof joists will receive 100mm of PUR insulation between the joists and 50mm beneath them

Floor insulation is always absent in a garage and including some in the conversion should be part of the project, whenever it’s possible.

Garage floors are often lower than the house floor and so adding a damp proof membrane (DPM), insulation and a new screed, along with your final floor covering, is a good method for how to level a floor up to that of the rest of your house.

You can use the existing concrete floor as a base, adding a solid or liquid DPM, before fitting a layer of insulation on top — building control will advise on how much insulation will be required.

Finally, the new screed is poured, ready to take your new floor covering. Be careful not to cover up any existing air bricks.

This is a good time to think about include underfloor heating within your garage conversion.

When working with very large differences in floor levels, a new suspended timber floor is a good idea. Aim to create a void beneath of at least 150mm between the concrete and underside of the timber, placing insulation between the joists, with new air vents to provide ventilation.

Ventilation

How Do You Ventilate a Garage Conversion?

"Home ventilation is vital for a garage conversion, otherwise you're just building a box that's going to sweat." says Mike Taylor from Taylor + Co Architects. Installing an openable window is an easy way to purge ventilation. The opening should have an area of at least 1:20 of the floor area of the room it serves, whereas bathroom windows can be any openable size. Trickle vents should also be incorporated into the window framework to provide background ventilation. 

If your garage already has air bricks, these should not be covered up. Be mindful of Building Regulations regarding ventilation if converting a garage to include a bathroom, kitchen or utility room, as you'll likely need an extractor unit to ensure moist air can be removed from the room. You'll find all the information you need about ventilation in Building Regulations Part F. 

Services

Garage Conversion Electricity Requirements

Garages often house electricity meters and distribution boards, making it easy to install electrics there. However, new lights, sockets and electric radiators could put additional strain on older consumer units, which may need to be upgraded. If you're installing wiring for a detached garage, it can be run through an underground channel. 

An electrician will be able to test the existing wiring and ascertain what work will be required. 

If the garage is to be another habitable room in your house, its own miniature circuit breaker (MCB) is probably enough. Consider adding at least one new 20-amp circuit.

An additional mains supply can be installed, with the cost varying from £500 to £20,000. This will also require the installation of a separate consumer unit.

What Plumbing Does a Garage Conversion Need?

This depends on what you plan on using your garage conversion for. 

A survey should be carried out to locate the main outflows for water (as well as the waste pipe if you're installing a WC). Consider how far the garage is from the mains and waste pipes of the main house. The further the distance, the more digging pipes will add to your project's cost. 

Fire Regulations

What Are Garage Fire Door Regulations? 

You must consider fire safety and the regs under Building Regulations Part B when it comes to your garage conversion project.

“Attached garage conversions are usually accessed by a hallway door, providing a safe means of escape to outside, but if you can only enter this new room from another (outer) room, it defines it as an inner room,” explains building control officer Paul Hymers.

“Because a fire in the outer room could prevent your escape, the inner room will need an alternative escape route. That could be a door or window and so the role is often performed by the one replacing the garage doors at the front. Escape windows have minimum criteria. If you inner room is a kitchen, en suite, cloakroom WC or bathroom then it doesn’t need an alternative exit.”

In partial conversions, where only part of the garage is being used as habitable space, the wall separating the two should be fire-rated to 30 minutes.