For many households, the garage is the biggest under-used space they own. It's often full of bikes, boxes and garden furniture rather than a car, and it already has walls, a roof and a foundation. Converting it into a bedroom, playroom, home office or larger kitchen can add useful living space for less disruption than a full extension. But a garage was never designed to be lived in, so turning it into a warm, dry, compliant room takes more than plastering the walls and swapping the door for a window. This guide walks through the process from checking permissions to the details Building Control will look at.
Is a garage conversion right for your home?
Before getting into the detail, it's worth asking a few practical questions:
Do you need the parking? On narrow Cornish streets and busy estates, losing a garage can put pressure on parking, and some planning conditions require garages to stay available for cars.
Is the structure sound? Look for cracking, damp and roof problems. Older garages, particularly detached ones, may have shallow foundations or single-skin walls that need more work.
How will it connect to the house? An integral garage that opens into a hallway usually makes a more natural room than a detached garage across the drive.
Is the head height adequate? Raising the floor to meet the house level and fit insulation reduces ceiling height, which can be tight in some garages.
Do you need planning permission?
In many cases, converting an integral or attached garage doesn't need a planning application, because the work is mostly internal and replacing the garage door with a wall and window can fall under permitted development, provided the materials are similar to the existing house. However, there are important exceptions:
Removed permitted development rights. Many newer estates in Cornwall were approved with conditions that remove permitted development rights or require garages to be kept for parking. Check the planning history of your property, as this is one of the most common reasons a conversion needs permission.
Listed buildings and conservation areas. External changes may need consent, and listed buildings need listed building consent for most alterations.
Detached garages. Converting a detached garage into living space used as part of the house may be fine, but creating a separate dwelling or holiday let needs planning permission.
Flats and maisonettes don't have the same permitted development rights as houses.
If you're unsure, a Lawful Development Certificate from Cornwall Council gives formal confirmation that the work is lawful. Our guide to planning permission in Cornwall explains the options.
Building Regulations: what will be checked
Converting a garage into a habitable room almost always needs Building Regulations approval, even when planning permission isn't required. Our guide to Building Regulations in Cornwall explains the process. For a garage conversion, the main areas are:
Floor. Garage floors are usually lower than the house and have no insulation or damp-proof membrane. The floor is typically raised with a new membrane, insulation and screed or a timber floor, bringing it closer to the house level.
Walls. Single-skin garage walls need upgrading to stop damp coming through and to meet insulation standards, usually with an insulated inner lining and a vapour control layer. Cavity walls may be easier to improve.
Door infill. The new wall under the window, where the garage door was, needs suitable foundations, which may mean digging down beside the old door opening. It must also include a damp-proof course and insulation.
Roof and ceiling. Insulation is needed in the ceiling or roof, and flat roofs on attached garages are often replaced or upgraded at the same time.
Ventilation. Habitable rooms need background ventilation, usually trickle vents in windows, plus an opening window large enough for rapid ventilation. Any kitchen or shower area needs mechanical extract.
Fire safety. Depending on the layout, the room may need an escape window, a fire door onto the hallway and a mains-powered, interconnected smoke alarm. If part of the garage is kept for storage, the wall and door between it and the house need suitable fire separation.
Energy and heating. Windows, doors and insulation must meet current energy standards, and heating is usually an extension of the house system or electric underfloor heating.
How much does a garage conversion cost?
Every garage is different, so treat any figure as general guidance only. As a broad indication, converting a single garage into a simple habitable room often costs in the region of £15,000 to £35,000, while double garages, conversions that include a shower room or kitchen, structural work or high-specification finishes can cost considerably more. The main factors are:
The condition of the existing structure and foundations
How much work the floor, walls and roof need to meet the regulations
Whether new plumbing, drainage or heating is required
Window and door specification, and the quality of finishes
Design, structural engineering, planning and Building Control fees
A detailed, itemised quote based on a site visit is the only reliable way to budget.
Garage conversion FAQs
How long does a garage conversion take?
Once approvals are in place, a straightforward single-garage conversion often takes a matter of weeks on site, though more complex jobs with plumbing or structural work take longer.
Will converting my garage add value?
It can, if the new room is well built and useful, but losing parking can matter to some buyers. Make sure you keep the completion certificate and any planning paperwork.
Can I convert half my garage and keep the rest for storage?
Yes, this is common. The dividing wall and any door into the house must provide suitable fire separation and insulation.
Is a garage conversion better than an extension?
It's often quicker and less disruptive because the structure already exists, but an extension can create more space and a better layout. It's worth comparing both.
Plan your garage conversion
Cornish Building Company carries out garage conversions as part of our property renovation and home extension work across Cornwall. Call us on 01208 816991 or contact us to arrange a visit and talk through your options.
