If you are looking to add space to your home without extending, then a garage conversion is a great solution. A garage conversion offers little disruption (until it’s time to knock through) and makes much better use of often underused space.
You can often increase the sense of space and light in your home with a garage conversion and, when combined with a remodel of your existing ground floor, can transform how you live in your home.
A basic conversion of a single garage costs around £8,000 and a garage conversion done well can add up to 20% to the value of your home, according to a report by Nationwide.
In most cases, you will also be able to convert your garage under your permitted development rights (but do check with your local authority as these may have been removed or restricted).
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.
If you are looking for practical uses for your new space, check out these great garage conversion ideas.
Do I Need Planning Permission for a Garage Conversion?
Probably not. While it is best to check with your local authority, integral garage conversions do typically fall under Permitted Development, meaning planning permission is not required.
However, if you live in a conservation area or 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 (i.e, the garage has to remain as parking) before beginning works as an application will need to be submitted to remove the conditions.
(MORE: What are Planning Conditions?)
If the conversion falls under Permitted Development, applying for a Lawful Development Certificate (LDC) is a good idea, particularly if you aim to remortgage or sell in the future.
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.
How Much Does a Garage Conversion Cost?
A basic integrated garage conversion will cost from around £8,000 (or £400-640/m²), which is less than the value you could add to your home by converting the garage, so this project can make great financial sense.
You will need to be aware of the various factors that could affect the cost of your garage conversion, including:
- 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
Do I Need a Designer for my 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. You or your builder will need to adhere to the Building Regulations when converting an attached garage into habitable space. The Regs apply to various aspects of the construction, including:
- thermal performance
- fire safety
The LABC website is a good starting point for information regarding the Regs 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.
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Assessing the Foundations for a Garage Conversion
A key part of the project may involve blocking up the existing garage door opening; perhaps adding a new window or entry door in its place.
In order to add an infill wall, you’ll need to first 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.
What if the Garage Foundations are Inadequate (or Absent)?
There are typically two options if your existing garage foundations are found to be 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 build a new infill wall on top.
(MORE: Garage conversion ideas)
Ways to Insulate 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.
Wiring a Detached Garage
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.
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