Planning permission gets quite a bit of consideration when people look at garage conversions. Building regulations are equally important. They ensure the conversion is safe and meets the required standard.
Most garage conversions require building regulations approval and this is true even if planning permission is not required.
Normally a garage is unheated and poorly insulated. To be able to make it a habitable room the building has to meet a number of technical standards.
This guide explains everything regarding what is checked by building control. It also explains the key rules for structure, damp, insulation, ventilation, fire safety, sound and electrics.
The Quick Answer
Most garage conversions will require you to get building regulations approval first. This is entirely different from planning permission.
Building control check the work for structure, damp-proofing, insulation, ventilation, fire safety, sound insulation and electrical safety.
You can either apply by way of Full Plans application or Building Notice.
Building control fees tend to be between £300 and £1,200. The price is determined by the size and complexity of the conversion.
Building control will inspect the work at various stages and if they find everything in order, you will receive a certificate of completion.
Keep this Certificate in a safe place. You’ll require it when you decide to sell the property or get a mortgage.
Building Regulations vs Planning Permission
Planning permission and building regs are not the same and you should know about both of them before start the garage conversion job.
Planning permission is about use and appearance of the property. In case of garage conversions, most work is internal and generally do not require planning permission.
Building regulations are about the actual building construction. They check if the new room is safe and up to standard for living.
You may modify your garage without planning permission, but you will need building regulations approval.
The two processes have to be treated separately.
The Application Process: Building Notice or Full Plans
There are two main ways of applying for building control approval.
Building Notice
The simple way is to use a Building Notice as there is less paperwork from the start. You tell building control you are going to start work and inspections are made as the work progresses.
This can be good for a simple garage conversion.
The main disadvantage is that your plans are not reviewed in detail before your work begins so you’re not so sure at the beginning.
Full Plans Application
A Full Plans application involves more detail where you have to submit drawings and specifications before the actual work starts. Building control checks them against the regulations. They will then approve the plans or tell you what needs to change in the plans.
This whole process takes more work at the start but gives you more certainty to carry on the job.
It is also the better choice for conversion projects that need things like structural changes, an additional en suite or a self-contained annexe.
You can apply for Full Plans application through your local authority’s building control team or you can also use a private approved inspector.
The fees are broadly similar for both Building Notice and Full Plans application. A standard garage conversion fee will be in the range of £300 to £1,200 for building control.
Part A: Structure
Any structural changes need to be checked properly.
This can include:
- Removing or changing the garage door opening
- Installing a new lintel
- Removing internal walls
- Building a new wall where the garage door was
The new lintel must be capable of bearing the weight above it and suitable foundations are also needed for the new wall because the original opening for the garage door was not intended to support a full masonary wall.
The places where the work involves load bearing elements, a structural engineer will be required.
Part C: Resistance to Moisture
Garages are not usually built to the same damp proofing standards as living areas. They are also not meant to be heated or utilised as a living space.
Building control will check a few things including:
- The wall damp proof course (DPC) shall be continuous and minimum 150mm above external level of ground.
- New wall insulation must not span the DPC. A bad installation will create a cold bridge and enable damp to rise.
- The floor should have a proper damp-proof membrane. This needs to be properly tied into the existing DPC before the insulation and new floor finish are added.
These things matter. Insulating over an existing damp problem does not solve it.
Part L: Conservation of Fuel and Power
Part L is about the energy efficiency.
That’s where a lot of the insulation work comes into play. Conversion against specific U-value targets is checked by building control The U-value is a measure of heat transfer and a lower number means less heat is transmitted through the material.
| Element | Target U-value |
|---|---|
| Roof | 0.15 W/m²K |
| Walls | 0.18 W/m²K |
| Floor | 0.18 W/m²K |
| Windows and doors | 1.4 W/m²K |
In practice the garage will have to be well insulated.
This can be insulation between or under the roof rafters. An insulated stud or block wall may need to be built inside the existing garage walls.
The floor will also need insulation below the new floor finish.
A standard garage does not normally have this level of insulation already in place.
Part F: Ventilation
A converted garage needs proper ventilation.
This helps control condensation and keeps the air fresh.
You will normally need:
- Trickle vents in new or replacement windows for background ventilation.
- Openable windows to provide purge ventilation when you need to clear moisture or pollutants from the room.
- Mechanical extract ventilation in a kitchen or bathroom. An extractor fan may be required even if the room has an opening window.
Part B: Fire Safety
Fire safety requirements depend on how the new room connects to the house and whether it will be used as a bedroom or not.
An escape window may be needed when the room can only be reached through another room.
The clear opening must be at least 0.33m². The minimum width and height are 450mm and the bottom of the opening should be no more than 1,100mm above the floor.
An FD30 fire door may also be needed where there is an internal doorway between the garage and the house.
FD30 means the door gives 30 minutes of fire resistance.
This is especially true for integral and attached garages, as the new room is directly attached to the main house.
You will also need mains powered interlinked smoke alarms. These should be incorporated into the rest of the property’s alarm system.
Part E: Sound
Sound insulation can be included in the building regulations work and this requirement is particularly relevant if your garage is attached to another property.
It is often so with semi-detached and terrace houses. It can also apply to detached garages that are close to a boundary.
The building control will check that the party wall is of the required standard of airborne sound insulation.
The target is normally a weighted sound reduction index of 45 dB.
It is worth including the wall construction in your building regulations application. This lets the design be checked before the wall is built.
Part P: Electrical Safety
All new electrical work must meet Part P requirements.
This includes:
- New sockets
- New lighting
- New circuits
- Changes to the consumer unit
The work must be carried out or checked by a qualified electrician that needs to be properly certified.
This applies to a small home office conversion as well as a garage with a full kitchen.
Part K: Protection From Falling, Collision and Impact
Part K covers things related to protection from falls, collision and impact.
This can be a applicable to new glazing. Low level windows and glazing may require appropriate safety glass or other protection if they are close to doors.
The goal is to reduce the likelihood that someone walks into the glass or falls into it.
Inspection Stages and the Completion Certificate
Building control does not just inspect the finished room.
They will normally visit at different stages of the work.
This can include:
- Foundations and groundwork
- Damp-proofing
- Insulation
- Final completion
The exact inspection stages depend on the type of project you are doing. Once the work has been checked and it meets the regulations, you will receive a completion certificate.
Keep this document safe as a buyer’s solicitor may ask for it when you are selling your home. Not having the certificate can delay or complicate the sale of your home in the future.
What Happens If You Skip Building Regulations?
Building regulations must be addressed before you can start a garage conversion.
If the work has already been done without approval, you can request retrospective approval which is also called a regularisation certificate.
The process can be so much easier than obtaining approval prior to the work starts.
Building control may want to look at areas already finished. They may need to remove plasterboard, flooring or other finishes to inspect the work which can add cost and cause a lot of disruption.
Selling the property without approval or regularisation can be more difficult too.
You might have to get indemnity insurance. Some buyers’ lawyers may still view the lack of approval as a risk so in our opinion, the safer and easier route is to get the work approved from the beginning.
A Note on Upcoming Changes
Building regulations are updated frequently and the amendments to energy and construction standards in England will come into force from 24 March 2027.
If you are converting a garage around this date you must check with your local building control team.
They can confirm what version of the regulations applies to your project and application.
Sources
This guide draws on the following primary sources. It is intended as a general guide and not a substitute for professional building control advice for your specific property.