An attached garage conversion turns a garage built against the side or back of the house, but outside its main footprint, into a room that is part of the home. Compared with an integral garage, there is usually more to do: the garage often has its own flat or lean-to roof, half-brick walls with piers, and no proper way through into the house. A good conversion upgrades the roof, walls and floor to Building Regulations standards, infills the door opening and forms a new doorway into the house where the layout needs one.
How is an attached garage built, and why does it matter?
Most attached garages on inter-war and post-war semis were built as cheaply as the rules of the time allowed. Typical features are a single skin of brick (half a brick thick) strengthened with piers, a flat felt roof or a single-skin pitched roof with no insulation, a thin concrete floor laid straight on hardcore, and a gap between the garage and the house wall that has been bridged rather than properly tied. Linked garages on 1960s–80s estates often share a wall with the neighbour’s garage.
None of that is a problem for parking a car, but a bedroom, snug or office needs to be dry, warm and quiet. That is why converting an attached garage is closer to building a small extension than to fitting out a spare room, and why it usually costs and takes more than an integral garage conversion. It is also why so many attached conversions done years ago now show up with damp and mould, as our garage conversion problems guide describes.
What usually needs upgrading in an attached garage?
The roof
Flat garage roofs are commonly upgraded to a warm-deck build-up, with insulation laid above the deck under a new waterproof covering, or a cold-deck build-up with insulation between the joists and ventilation above. Single-skin pitched roofs can be insulated between and under the rafters with ventilation kept open. LABC guidance gives a target U-value of 0.15 W/m²K for the roof. More detail is on our garage roof upgrade page.
Older garage roofs and soffits are sometimes made of corrugated or flat cement sheets that may contain asbestos. These must be tested by a qualified surveyor and, if needed, removed by a suitably qualified asbestos contractor before any work starts. We never disturb suspected asbestos, and you should not break, drill or sand it yourself.
Single-skin walls and piers
A half-brick wall lets driven rain through and loses heat quickly. LABC guidance says single-leaf garage walls need treatment to make them weatherproof, often by building a new insulated inner leaf or a framed inner wall with a cavity and membrane. If piers are removed to gain space, the wall is weakened and should be tied to the new inner leaf with remedial wall ties. Existing walls are checked for stability and cracking first. Our garage wall insulation page explains the build-ups.
The floor and door infill
The floor gets a damp-proof membrane that laps with the DPC in the walls, rigid insulation and a screed or timber finish. The old door opening is filled with a new wall, usually with a window, on a new foundation or, where building control agrees, a suitable lintel or beam.
A new way into the house
Many attached garages are reached only from the drive or through a side door. Joining the room to the house usually means cutting a new opening in the house wall or widening an existing one. That is structural work: it needs a correctly sized lintel or beam, temporary support during the work, and approval from building control. It is not something to attempt yourself.
Shared and linked garages: sound and party walls
Where the garage wall is shared with a neighbour, building control may ask for a set level of sound insulation for the new room under Part E, especially if it is a bedroom. Work on or near a shared wall may also fall under the Party Wall etc. Act 1996, which can mean serving notice on your neighbour before work starts. We flag this on the first visit, and you may want independent advice on the notice itself.
Attached garages around Liverpool
Side and attached garages are everywhere in the city’s south and east suburbs. Inter-war and post-war semis in Childwall and Allerton often have side garages, while many 1960s–70s homes in Gateacre have attached or linked ones. Across the water, Bebington has plenty of semis with side garages too. Wherever the house is, we plan the roof, walls and floor together, as part of converting garages across Merseyside to a standard that lasts.
Do you need planning permission?
The Planning Portal says planning permission is not usually required when the work is internal and does not enlarge the building. Replacing a garage door with a wall and window counts as a change to the outside, though, so check if you live in a conservation area or if the house’s permitted development rights have been removed by a planning condition. Ask your own council: Liverpool City Council, Sefton, Knowsley, St Helens, Wirral or Halton. Raising the roof or building out further than the existing garage is a different matter and may need an application.
What happens when you get in touch?
- Questions. We call you back and ask about the garage type, the age of the house, what the room is for and any planning conditions you know of.
- Visit. We look at the roof covering, wall thickness and piers, the floor level, the door opening and where any shared wall or services run.
- Options and approvals. We explain layout options, likely drawings and the Building Regulations route; drawings are prepared by an architect or architectural technician where needed.
- Quote and build. You get a written quote, then work follows the agreed drawings with building control inspections at the usual stages and a completion certificate at the end.
What affects the cost of an attached conversion?
The biggest variables are the roof (repair and insulate, or replace), how much inner-leaf walling is needed, whether piers come out, the new opening into the house, sound insulation on a shared wall and any asbestos removal. Our cost guide sets out published figures and why they differ. For your own house, it starts with a visit from our garage conversion service.
Got a side or linked garage to convert?
Call 07777 659786 or leave your details. Tell us how the garage joins the house and what you would like the room to be, and we will call you back.
Frequently asked questions
Can a single-skin garage wall be used for a bedroom?
Not as it is. A half-brick wall lets driven rain through and loses heat fast. LABC guidance says it needs treatment to make it weatherproof, usually a new insulated inner leaf or a framed inner wall with a cavity and membrane. Building control checks the detail, and the wall itself is inspected for cracks and stability first.
Do I have to replace the flat roof on my attached garage?
Not always. If the deck and joists are sound, a flat roof can sometimes be upgraded by adding insulation and a new covering on top as a warm deck. If the deck is rotten, the joists are undersized or the covering contains asbestos, replacement is usually the better route. We look at it before recommending either.
My garage is linked to my neighbour’s. Can I still convert it?
Usually yes, but there is more to plan. Building control may ask for sound insulation on the shared wall, particularly for a bedroom, and work on or near that wall may fall under the Party Wall etc. Act 1996. That can mean serving notice on your neighbour, so it is worth getting advice early.
Is an attached garage conversion more expensive than an integral one?
It often is, because there is usually a roof to upgrade, single-skin walls to line and a new opening into the house to form. Published guides such as MyJobQuote show attached conversions in a higher band than integral ones. Our cost guide explains the ranges.
Can I take out the brick piers to make the room bigger?
Sometimes, but piers stiffen a single-skin wall. LABC guidance says that if they are removed, the wall should be tied to a new inner leaf with remedial wall ties. That is structural work that needs to be designed and agreed with building control, so please do not remove piers yourself.