Many garage walls are a single skin of brick, often half a brick thick with piers for stiffness, and they let in wind-driven rain and lose heat quickly. For a habitable room, LABC guidance says they need weatherproofing, usually by building a new insulated inner leaf of blockwork or a framed inner wall with a cavity or membrane, and insulating to a U-value of 0.18 W/m²K. Walls shared with a neighbour may also need sound insulation. We check every wall before choosing the method.
Why garage walls need upgrading
A garage only has to keep the rain off a car. Many attached and detached garages were built with a single skin of brick or block and no cavity, insulation or vapour control. That is fine for storage, but in a heated room the inside face of the wall stays cold, warm moist air from the room condenses on it, and damp from outside can come straight through in heavy, wind-driven rain. It is the reason older conversions so often have mould behind furniture and a room that is never quite warm.
Upgrading the walls is a core part of every garage conversion we carry out in Liverpool, and the method depends on how your garage was built.
What types of garage wall do we find?
| Wall type | Where you often find it | Usual approach |
|---|---|---|
| Single-skin half-brick with piers | Attached side garages and detached garages, especially on inter-war and post-war semis | New insulated inner leaf or framed wall with cavity or membrane; piers checked and tied in if altered |
| Single-skin block, rendered or fair-faced | Some detached and rear garages | Similar to the above, with attention to render condition and weathering |
| Cavity wall built to house standard | Some integral garages, where the walls are part of the main house | Assessed case by case; may need insulation added to bring it up to the current target |
| Wall to the house | Integral and attached garages | Becomes an internal wall after conversion, so its role in fire separation and the wider fire strategy is reviewed with building control |
| Wall shared with a neighbour | Linked and semi-detached garages | Insulation plus any sound insulation building control requires; Party Wall Act considered |
How is a single-skin wall upgraded?
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 or membrane. In practice there are two common routes.
- New blockwork inner leafA new leaf of block is built inside the existing brick, on a suitable base, with a cavity and insulation between. The two are tied together, turning the old wall into something close to a modern cavity wall. Solid and robust, but it takes more floor space.
- Framed inner wallA timber or metal stud frame is set off the brick with a ventilated gap or breather membrane, insulation fitted between and over the studs, and a vapour control layer on the warm side before plasterboard. Usually slimmer and quicker to build.
Either way, the build-up is designed to meet the insulation target and to manage moisture: keeping rain that penetrates the brick away from the insulation, and stopping warm, damp room air reaching the cold outer skin. Building control confirms the specification for each job.
Insulated plasterboard fixed straight to a single-skin brick wall is a common shortcut. It can trap moisture against the brick and behind the board. We do not recommend it for this kind of wall.
Piers, ties and wall stability
The brick piers along a single-skin garage wall stiffen it. It is tempting to want them gone for a flat wall, but LABC guidance is clear that removing piers weakens the wall, which should then be tied to a new inner leaf with remedial wall ties. Existing walls are also checked for stability and defects such as cracks, leaning sections and failed pointing before the new work is built against them. Structural changes like these are designed and agreed with building control and carried out by experienced builders, never improvised.
Sound and shared walls
Linked garages and garages on semi-detached houses often share a wall with next door. When the garage becomes a bedroom, office or living room, building control may require a set level of sound insulation for the new room. That can affect the wall build-up: dense blockwork, acoustic insulation and resilient fixings for plasterboard are all options. The Party Wall etc. Act 1996 may apply to work on or near a shared wall, so you may need to serve notice and get advice. We flag this on the first visit.
Where the walls meet the floor, infill and roof
Wall insulation only works if it joins up with the rest of the insulated envelope. At the bottom, the floor membrane must lap the damp-proof course, and edge insulation stops a cold strip along the skirting; see floor insulation and levelling. At the old door opening, the insulation in the new wall should line up with the garage door infill. At the top, the wall insulation should meet the roof insulation without a gap, covered on our garage roof upgrade page. Gaps at these junctions are where condensation and mould tend to start.
Planning sockets, fixings and pipes
With a framed inner wall, sockets, switches and cables are fitted within the frame and must be planned so they do not break the vapour control layer more than necessary. The electrics are installed by a registered electrician; see electrics for garage conversions. If you plan heavy shelving, a wall-mounted TV, kitchen units or gym racks, tell us early so we can add solid fixing points before the wall is boarded.
Exposed and coastal houses
Single-skin walls facing the prevailing weather take a lot of rain. On houses near the coast, such as in West Kirby and Southport, we pay extra attention to the outer face: sound pointing, sound render where there is render, and a build-up that keeps penetrating damp away from the insulation. Older side garages on inter-war semis, for example around Bebington and Childwall, are often half-brick with piers and benefit from the same care.
How we approach your walls
- We call back to ask about the garage type and the age of the house.
- We visit and check every wall: thickness, piers, cracks, damp, render, which walls are shared, and how the garage joins the house.
- We agree the wall build-up with you, showing the effect on room size, and drawings are prepared by an architect or architectural technician where needed.
- After a written quote, work follows the drawings with building control inspections. Wall insulation is part of the completion certificate for the whole conversion.
If you are looking at the whole project, our page on converting garages in Liverpool and Merseyside explains how the walls fit with everything else.
Worried your garage walls are too thin to convert?
Most can be upgraded. Tell us about the garage and we will call you back to talk through the options. Call 07777 659786 or use the form.
Frequently asked questions
Can I just fix insulated plasterboard to a single-skin garage wall?
On a single-skin, half-brick wall that is rarely enough on its own. LABC guidance says these walls need treatment to make them weatherproof, often by building a new insulated inner leaf or a framed inner wall with a cavity or membrane. Boarding straight onto the brick can trap moisture behind it. We assess each wall and agree the approach with building control.
How much room will I lose when the walls are insulated?
Some, because the new inner leaf or framed wall, its insulation and the plaster all sit inside the existing brickwork. The exact amount depends on the method and on the U-value target. On a narrow side garage this matters, so we measure the finished room width at the planning stage and show you the effect before you commit.
What are the brick piers on my garage walls for?
Piers stiffen a thin single-skin wall, much like ribs. LABC guidance notes that if piers are removed, the wall is weakened and should be tied to a new inner leaf with remedial wall ties. Never knock piers off to gain space. Any change to them is designed and agreed with building control.
Does a wall shared with my neighbour's garage need anything extra?
Building control may require a set level of sound insulation where the converted room shares a wall with a neighbour. The Party Wall etc. Act 1996 may also apply to work on or near the shared wall, so you may need to serve notice on your neighbour and get advice before work starts.
What U-value do converted garage walls need to meet?
LABC's garage conversion guidance gives 0.18 W/m²K for external walls. Building control confirms what applies to each job. Reaching it on a single-skin wall usually needs a reasonable thickness of insulation in a new inner leaf or framed wall, which is shown on the drawings.
Why do some converted garages get mould on the walls?
Usually because the walls were left as a single skin, or insulated without dealing with damp and air movement, so warm moist air from the room meets a cold surface and condenses. Poor ventilation makes it worse. Our problems guide covers how this is diagnosed and put right in an existing conversion.