Project: a garage conversion that became a home office
The kitchen table stopped being an office years ago, but the laptop is still on it. According to the ONS, 28% of working adults in Great Britain were hybrid working in early 2025, and most of the houses we work in were never designed for it. A garage conversion home office is the quickest answer we build: three to five weeks on site, usually no planning application, and a room that is warm in January. This is how a build like that runs, based on an attached single garage we converted on a Bristol semi.
The brief: a proper office, not a shed
The client wanted what most people mean when they say home office: warm, dry, quiet enough for calls, real daylight, plenty of sockets, and a door they could shut at six. Not a plasterboard box with a fan heater. An attached single garage on a 1930s or post-war semi is usually 15 to 18 square metres, roughly 2.5 by 5 or 6 metres, which is a generous room for one desk and a wall of shelving, or a smaller office with a store or WC at the back. The one in these photos finished at 12m².
Because we are carpenters first, the fit-out on a build like this is where the room stops looking converted and starts looking built: a fitted desk under the window, shelving on the party wall, a boarded-out store behind a flush door.
Insulation and damp: what turns a garage into a room
A garage is a shell with a slab in it. Turning it into a habitable room is mostly about the floor and the walls, and it is where a corner-cutting conversion goes wrong.
- The floor. Garage slabs sit lower than the house floor and almost never have a damp-proof membrane. We lay a new membrane and lap it into the wall damp-proof course, then insulation and a screed or insulated floating floor to bring the level up to meet the house. Approved Document L asks for 0.18 W/m²K on a new floor, and LABC's garage conversion guidance sets out how the membrane must lap with the existing walls.
- The walls. Many garages are single-skin brick. LABC's options are to tank the wall with a vapour-permeable membrane linked to a damp-proof course, or to build an insulated inner leaf. We usually do the latter with a studwork lining, insulation and a vapour control layer, aiming at 0.18 W/m²K, with acoustic insulation in the studs so a video call stays private.
- The roof. Flat garage roofs get insulation above or between the joists to 0.15 W/m²K, and we check the covering while we are up there.
- Ventilation and escape. Openable windows with trickle vents, an extract if there is a WC, and if the room is reached through another room, a window with a clear opening of at least 450 by 733 mm and a sill no higher than 1.1 metres.
A window where the door was, power, data and heat
Taking the garage door out is the noisy morning. Before the new wall goes in we check for a foundation under the old threshold; there often is none, and the infill wall is then carried on a lintel or a new footing agreed with building control. The infill is cavity walling with a damp-proof course lapped to the floor membrane, faced in brick to match, with a wide window whose head lines through with the neighbours' so the house does not read as a filled-in garage from the street. Some clients want French doors instead; the structure is the same.
Inside, the electrics are a dedicated circuit with sockets at desk height on two walls, a data cable run back to the router, and lighting on two switches. Our NICEIC-registered electrician certifies it under Part P. For heat we extend the central heating with a radiator where the boiler has the capacity, or fit an electric panel or underfloor heating in the new screed where it does not. This one is triple glazed, with pipe-fed heating run off the house system.
Planning, building regulations and sign-off
Most garage conversions do not need planning permission. Planning Portal's guidance is that permission is not usually required where the work is internal and does not enlarge the building. The catches are newer estates, where permitted development is often removed and a condition may require the parking space to be kept, and conservation areas. We check the original planning conditions on the house before we quote, and our garage conversion guide covers when not to convert at all.
Building regulations always apply. We submit a building notice or full plans, building control inspects at the membrane and insulation stage and the infill foundation, and you receive a completion certificate at the end. Keep it: a buyer's solicitor will ask for it. This job went through on a building notice.
Three to five weeks: how the build runs
Week one: strip out, garage door removed, foundation check, infill wall built and window fitted, floor membrane, insulation and screed down. Week two: roof insulation, studwork lining, first-fix electrics and heating, plasterboard. Week three: skim, second fix, floor finish, joinery, decoration and the building control final. Weeks four and five come into play where there is a WC to plumb, a knock-through into the hall, underfloor heating in a screed that needs to cure, or a garage that turns out to need a new roof deck.
The garage is sealed off from the house, so day-to-day life carries on. The disruptive days are the door removal and any knock-through, and we tell you the dates in advance. Our routine for keeping a home liveable during a build applies here as everywhere.
Guide numbers for a garage conversion home office
Typical UK cost in 2026 is from £10,000 depending on fit-out. MyJobQuote's 2026 guide puts the average at £14,500 for a standard conversion and a basic home-office fit-out at £8,000 to £12,000, with a WC adding £5,500 to £9,000. What moves the number on our builds: the floor level and how much has to be built up, whether the walls are single-skin, the glazing specification, plumbing, a knock-through into the house, and the amount of joinery. Set against a loft or an extension, it is the least expensive way to add a real room, and it is finished in weeks rather than months.
Every quote is detailed and itemised, the deposit is a modest booking deposit of around 10%, and we invoice against valuations of the work actually carried out. Garage conversions sit within our renovation work; Wilson & Cole Developments is FMB registered, with a 5.0★ Google rating from more than 25 reviews, and our written guarantees are described on our FAQ page. The office in this piece came in at £18,000 plus VAT.
Frequently asked questions
Do you need planning permission to convert a garage into a home office?
Usually not. Planning Portal's guidance is that permission is not normally required where the work is internal and does not enlarge the building. Exceptions are newer estates where permitted development has been removed or a condition requires parking to be kept, conservation areas and listed buildings. We check the house's planning history before quoting.
How much does a garage conversion home office cost?
Typically from £10,000 in 2026 depending on fit-out. MyJobQuote's guide puts the UK average at £14,500 for a standard conversion, with a basic home-office fit-out at £8,000 to £12,000. Floor build-up, single-skin walls, glazing, plumbing and joinery move the number. Our quotes are detailed and itemised.
How long does a garage conversion take?
Three to five weeks on site for an attached single garage. A straightforward office is nearer three; a WC, a knock-through into the house or underfloor heating in a new screed pushes it towards five. Building control inspections happen during the build and the completion certificate follows the final visit.
Do garage conversions need building regulations approval?
Yes, always, even when no planning permission is needed. Building control checks the floor damp-proof membrane and insulation, wall and roof insulation, the structure of the infill wall, ventilation, escape and the electrics, then issues a completion certificate that you will need when you sell.
Will a converted garage be cold or damp?
Not if it is built as a room rather than lined as a garage. That means a new damp-proof membrane lapped into the walls, an insulated floor brought up to house level, insulated and tanked or lined walls, roof insulation and heating sized for the room. Skipping any of those is where cold, damp conversions come from.
We have capacity this year. Let's talk before it's gone. Tell us about your garage and we'll call you back within one working day.
