Deciding to convert a garage into living space is a great way to add extra space to your home. It’s cost-effective and is one of the least disruptive improvement projects you can embark on — in fact, a good garage conversion can add as much as 10% to the value of your home.
But before you start, make sure you are well versed in the most common aspects of a garage conversion project.
Do I Need Planning Permission to Convert a Garage?
Not normally, no. In most cases, a garage conversion will fall under permitted development — particularly if you are not altering the actual structure of the building.
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.
If you live in a Conservation Area or your property is listed then you will almost certainly require permission.
If you live in a relatively new build, check that there is no condition attached to the garage stating that it has to remain as parking — if this was the case, an application would need to be submitted to remove this condition.
Do I Need an Architect?
This depends on the scale and complexity of the project, but you have multiple options when it comes to designing the space.
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. In addition, a design professional will usually have experience of dealing with Building Control and should have useful contacts when it comes to hiring trades.
In terms of 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. They can see the project through form conception to completion.
How Much Will a Garage Conversion Cost?
As a guide, a basic integrated garage conversion will cost from around £1,000 – £1,250 per square metre.
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
This is a great example of a seamless garage conversion — new render has been used to blend the conversion in. Back to Front Exterior Design
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Do I Need to Update 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 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.
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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.
How Should I Insulate the Garage?
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.
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
The concrete floor may or may not have been cast over a damp-proof membrane (DPM).
In recent decades, integral garages would normally have included a DPM and certainly the walls would have a damp-proof course (DPC). But without plaster and screed finishings to conceal them, the two elements would not meet as they would in the house.
Protecting the concrete floor with a polythene or paint-on DPM and dressing it up under your new finishings to the DPC layer will ensure that damp is not a problem.
Garage Conversions and Building Regulations
Garage conversions fall into ‘change of use’ and so will require building regulations approval.
Building Regulations apply to:
- 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.
Plumbing and Wiring
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.
Otherwise, 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 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.
Will Floors Need to be Raised and Insulated?
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.
How Do I Fireproof my Garage Conversion?
Part B of the Building Regulations concerns fire safety.
When it comes to garage conversions, you need to consider the following:
- “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
Garage Conversion Pros
- Design Control: Converting a garage means every step of the design process is under your control, subject to technical and legal restrictions
- Added Value: Moving house costs money that can’t be recouped. But converting a garage into a habitable room adds more value to your home than it costs in most cases
- Cost Effective Way to Add Space: Conversion costs for the average garage are between £5,000 and £8,000
- Local Amenities: Moving children from school and families from local facilities and communities is difficult and sometimes expensive. Remaining at your current address but with additional living space is a better solution for many
- Contract Control: One in 10 house sales falls through because one party changes their mind. If you choose conversion you’re the sole decision maker
- Council Tax: Moving from a three to a four bedroom house could put you up a council tax band. A garage conversion leaves council tax bands unaffected
Garage Conversion Cons
- Disruption: During garage conversion, one or more existing rooms will frequently be rendered unuseable by building work. Rooms adjoining the garage, and garden or yard space, will be most affected
- Control of 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
- Impact on Existing Buildings: Extending the garage will consume garden space. Light to existing rooms, access to the property, yard space and the exterior appearance of the building as a whole may all be affected
- Planning Uncertainty: Projects that require planning permission may not receive it. Application will involve a non-returnable fee, usually of about £150. This will be higher if you want to alter a listed building or you live in a conservation area
- Cost Uncertainty: Once investigations begin on your property, you might be required to pay for additional improvements or repairs