Garage Conversions in West Sussex
The cheapest room you will ever add
You already own the floor, the walls and the roof. That is the whole argument. A garage conversion buys you a room without buying a footprint, and it does it without foundations, without a scaffold on most jobs, and usually without waiting on a planning officer.
It is the shortest job we do that genuinely changes how a house works. A family that has run out of ground floor gets an office, a bedroom, a utility, a playroom or a shower room out of a space that currently holds a lawnmower and eleven paint tins.
Guide price: £8,000 – £15,000 + VAT. An August 2026 guide rather than a quotation, and the VAT is not in it — twenty per cent is added to whatever the final figure turns out to be. Where your job lands inside that band is decided by the five things below.
Book a free site visit and you get a straight answer on which end of the band your garage is. Over 100 projects completed, with £2m public liability cover and employers' liability behind it.
Five things decide the price, and you can see four of them yourself
1. The slab, and what is under it. Garage floors are normally laid lower than the house floor, and older ones frequently have no damp-proof membrane and no insulation at all. Making it habitable means building up: membrane, insulation, then screed or a floating deck. The floor rises. The ceiling does not. Head height is the first thing we measure and occasionally it is the thing that kills the idea.
2. Whether the walls are one skin or two. An integral garage under the first floor is usually built like the rest of the house. A detached or side garage is often half-brick — a single skin, with no cavity and no insulation. That gets an insulated inner lining built off the slab, and you lose a hundred-odd millimetres of width on each wall you line. Measure your garage internally before you fall in love with a furniture layout.
3. The roof over it. Some garage roofs are sound and simply need insulating. Some are a tired flat roof that has to be rebuilt as part of the job. Some are corrugated sheet that may contain asbestos, which is a survey and a licensed removal, priced separately and never bundled in quietly.
4. What lives in there now. Consumer units, gas meters, boilers and stopcocks have a habit of being fixed to garage walls. Every one of them either stays accessible or gets moved by the right trade, and moving a utility meter runs to the utility company's timetable rather than ours.
5. What you want at the end of it. A dry, plastered, heated, decorated room is one number. The same room with drainage run for a shower and a WC is another, because the waste has to reach an existing drain and the fall has to be found. Tiling and sanitaryware sit with bathroom installation; wardrobes and desks built into the space sit with fitted storage and joinery.
The front wall is the bit people underestimate
Filling the door opening is not simply bricking up a hole. There is often no proper foundation beneath where the up-and-over door sat, so a new footing goes in first. Then the infill has to look like it belongs, on the elevation everyone in the street sees.
Old brick has weathered for forty years. New brick has not, and it will not match by trying harder. So the honest conversation happens at the quotation stage: a window wide enough that the brickwork below reads as a plinth, a render band that ties into something already there, or accepting a visible difference that will close up over a decade. We would rather have that conversation with you than present you with it afterwards.
Do you need planning permission?
Usually not. Nothing gets bigger — you are changing the use of a space inside a building that already exists and filling one opening in it. The national position did not shift in 2025 or in 2026 either, whatever you may have read elsewhere.
Two things change that answer, and we check both before quoting.
The first is a condition attached to the original planning permission for the house or the estate, requiring the garage to be kept available for parking. These are common on newer developments and they sit in the planning history, where most people never look.
The second is where the house sits. In a conservation area or inside the South Downs National Park the controls over the outside of a building are tighter, and the garage front is about as public as an elevation gets. We check the address rather than assume the estate is all one answer.
Building Regulations definitely do apply
Planning permission and Building Regulations are separate systems and a garage conversion is notifiable work. What that means in practice:
- Insulation. Where we build new thermal elements the limiting standards in Approved Document L Table 4.2 apply: 0.18 for a wall, 0.18 for a floor, 0.15 for a roof and 1.4 for a window. Those figures come from the edition in force today: Approved Document L Volume 1, 2021, as amended in 2023. The Future Homes Standard does not land until 24 March 2027 and is directed at buildings newly erected, so it changes nothing here.
- Damp. The membrane under the new floor gets lapped up and tied into the wall construction. A garage slab that has coped for thirty years with a concrete floor and an open door behaves differently once it is sealed, carpeted and heated.
- Ventilation. Background ventilation and, in a wet room, extract.
- Escape. A room that will be slept in needs a way out that does not depend on the rest of the house, which usually means the window size and the opening light are specified rather than chosen.
- Electrics and heating. Extending a circuit and adding a radiator to an existing system are both fine until the boiler or the consumer unit says otherwise. We check both at the site visit, not at second fix.
What is in the price and what is not
In: clearing and preparing the slab, membrane and insulation, screed or floating floor, new footing and infill to the door opening, window, insulated wall lining or cavity treatment, ceiling insulation and plasterboard, plaster, electrics and heating extension, skirting and architrave, one coat of mist and two of finish, any access equipment the job needs, and dealing with Building Control from application to final inspection.
Out unless it is written into your quotation: the council's Building Control charge itself, which you pay them direct and which changes often enough that we would rather you rang them for today's figure than trusted one printed here; the structural engineer, on the same basis; asbestos survey and removal; skips and waste removal; moving a gas meter or an electricity meter; a new consumer unit; drainage for a shower or WC where no drain is within reach; floor coverings; fitted furniture; anything structural in the wall between the garage and the house — that is steel beams and load-bearing alterations.
If you need the parking as well as the room, the answer is usually not a garage at all: see garden rooms and annexes. If you need more space than the garage footprint holds, it is our house extensions service.
How you pay
Fortnightly valuations against measured progress. A deposit of 5%. 5% retained until practical completion. Fuller bands live in our price guide, which carries an August 2026 date and quotes every figure before VAT, as this page does.
Call 07470 078236 or send a photograph of the garage on WhatsApp and we will answer it the same day where we can. Rated 5 stars on Yell.
The guarantee
All workmanship guaranteed for 24 months from completion. Manufacturer warranties on all materials and installed products passed to you in full — many run to 10 years or more. Structural work is signed off by Building Control and covered by our £2m public liability insurance. We're working towards an insurance-backed guarantee scheme and will offer it as soon as we're eligible.
Questions we get asked
Will it look like a converted garage? Only if it is done badly. The tells are a floor level that steps down, a window that is too small and too high, and an infill panel that is obviously an infill panel. All three are decisions taken at quotation stage.
Can I keep part of it as storage? Yes, and plenty of people do — a partition with a door to the outside keeps the mower and the bikes. It costs a little more, because you are building a wall and insulating one side of it.
Does it add value? We are builders, not valuers, and anyone who gives you a percentage is guessing. What we can say is that it adds a usable room for less than any other route to one.
Is my garage too damp? Damp in a garage is normal and not necessarily a problem — it is an unheated building with an opening in one end. What matters is where the water is coming from, and that is a site visit rather than a guess.
Will I lose the parking? Yes, on the drive-in space. Check whether your permission requires it before you commit.
Next step
Send a photograph of the garage from outside, one from inside, and the internal length and width. That is enough for a sensible first conversation. Book a free site visit and we will measure the head height properly and tell you what it will take. See also how we run a job.
Swanbourne Construction Ltd was formed in 2025 to bring James's building work in West Sussex, which goes back to 2001, under one accountable, fully insured limited company.