A garage conversion is a great way to add some much needed living space to your home without having to extend or move. It’s a cost-effective project and can add as much as 10% to the value of your home.
You can often convert a garage without needing planning permission, but it still requires careful planning to make the most of the additional space and how it flows with your existing home.
This beginner’s guide to garage conversions explains everything you need to know about converting your garage into a usable room, from costs and Building Regulations through to effective heating and plumbing choices for the new space.
Do I Need Planning Permission to Turn a Garage into a Room?
Probably not. In most cases, a garage conversion will fall under permitted development — particularly if you are not altering the actual structure of the building. Although it is worth checking that there are no planning conditions attached to the garage (ie, that it has to remain as parking) — if conditions are attached, you will need to apply to have them removed.
However, 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.
You will almost certainly need planning permission to convert your garage if your property is listed or you live in a Conservation Area.
(MORE: What are Planning Conditions?)
How Much Does a Garage Conversion Cost?
A basic integrated garage conversion will cost from around £1,000 – £1,250/m² (around £5,000-£8,000 in total).
Factors that will affect cost:
- the foundations need reinforcing
- the walls, floors or roof are in dubious condition
- the ceiling height will need 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
Benefits of a Garage Conversion
- Often, a garage conversion adds more value to your home than it costs
- It’s cost-effective — the average garage conversion will cost between £5,000 and £8,000
- You can stay at your current address with the benefit of additional living space
- Extending from a three to a four bedroom house could put you up a council tax band. A garage conversion leaves council tax bands unaffected
Designing a Garage Conversion
Who you choose to design your garage conversion depends on the scale and complexity of the project, but you have multiple options:
Architect or Architectural Designer
Using an Architect or an architectural designer 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.
In terms of design fees, expect to pay from as little as £1,200 right up to £3,000, depending on the complexity of the design.
Can I Design it Myself?
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 could also use a recommended builder — most good builders will be able to take on a garage conversion.
Garage Conversion Specialists
These companies will have plenty of experience in terms of dealing with any planning issues surrounding garage conversions, as well as building regulations.
Does a Garage Conversion Need Building Regulations Approval?
Yes. Garage conversions fall into ‘change of use’ and so will require building regulations approval, in terms of:
- moisture proofing
- escape routes
- structural soundness.
You must notify your local council of the forthcoming project by submitting a building notice or full plans application.
Once you have finished, a building inspector will come to visually inspect the windows, doors, fireproofing measures and foundations before they will offer a certificate of completion.
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Will I Need to Assess the Foundations?
Your foundations will need assessing in cases where you are:
- filling in the space left by a garage door
- adding new windows and doors
- building up and above the garage
You can either contact a structural engineer to investigate for you or dig a trial hole and ask building control to come and view the foundations.
Some garages were built with a continuous foundation across the front, in which case, it may be fine to build on.
What if the Garage Foundations are Inadequate (or Absent)?
You will probably need to build new foundations to support the infill wall, the depth of which will depend on the soil conditions and any windows and doors you plan on including.
(MORE: Garage conversion ideas)
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What Insurance Do I Need if I am Converting a Garage?
If you are carrying out garage conversion works and are managing the project yourself you should arrange conversion insurance to cover the new works and the existing structure. This is because most home insurers will exclude loss or damage whilst the property is undergoing alteration or renovation.
Site insurance caters for both the existing element of the property that’s being converted and all the new conversion works that go into the process. The existing structure is usually your house – so if the is damaged during the works the site insurance will cover it and completely replaces the requirement for buildings insurance, which is not suitable.
All the works, including any temporary works, materials, plant tools and equipment need to be covered. Public liability and employers liability is automatically included to ensure you are adequately protected.
Conversion insurance needs to be in place from the moment you plan to start works on the property and should continue to the point the project is completed and taken into full use.
Insulating a Garage Conversion
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 the Roof
In terms of roof insulation, you will only need to look at this if there is no room above the garage already.
- In pitched roofs, go for two layers of 150mm glass fibre quilt, one between the joists, another over as usual
- 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
Insulating the Floor
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 way to bring the levels 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.
Plumbing and Wiring a Garage Conversion
- Make a thorough survey of the plumbing and wiring in the house and garage. Any wall you plan to pierce for doorways or windows needs special attention
- Locate the main outflows for water, and, if you plan to install a toilet, the soil outflow
- Check the garage for wiring in the walls and ceiling. Rewiring the garage for lights and electric radiators will place additional strain on the household mains, which is fused at 100 amps.
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.
It is possible to locate the garage on the current consumer unit. If it doesn’t have its own miniature circuit breaker (MCB), consider replacing the consumer unit or upgrading it.
If the garage is to be another habitable room in your house, its own MCB is probably enough. Consider adding at least one new 20-amp circuit.
What if the Garage is Detached?
Wiring to a detached garage can be run through an underground conduit. If it is to be a separate dwelling, a new connection may be required, depending on likely power usage; consult an electrician.
Fire Safety in a Converted Garage
When it comes to garage conversions, you will need to consider fire safety.
“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.
Disadvantages of Converting a Garage
- During a garage conversion, one or more existing rooms will frequently be rendered unusable by building work
- The householder will be held responsible for the legality of work done on their property. Time and energy will be required supervising work, being present to allow tradespeople access and making design and other decisions
- Projects that require planning permission may not receive it
- Once investigations begin on your property, you might be required to pay for additional improvements or repairs.