How to Plan a Garage Conversion Step-by-Step (2026 UK)
A garage conversion is one of the cheapest ways to add a usable room in 2026 — typically £7,000–£20,000 for an integral single garage, because the walls, roof and foundations already exist. The work is mostly about insulation, damp-proofing, a new front wall and Building Regulations compliance. This 8-step framework takes you from feasibility check to sign-off, with the costs and the pitfalls at each stage.
Garage conversion — the short answer
- Typical cost: £7,000–£20,000 for an integral single garage.
- Planning: usually Permitted Development — get a Lawful Development Certificate for proof.
- Always needs Building Regs: structure, insulation, damp, fire and ventilation.
- Biggest hidden costs: floor build-up to remove the level difference, and bringing walls/floor up to Part L insulation.
- Timeline: 3–5 weeks on site once approvals are in place.
The single most overlooked detail is the floor level. Garage floors usually sit ~150mm below the house and slope to the door. Your insulated floating floor build-up has to correct that and meet Part L, which sets the finished floor height — get this designed before you commit, because it affects door heads, the step from the hallway and radiator positions.
8 Steps to Plan Your Garage Conversion
1. Check feasibility
Confirm the garage is suitable: floor level vs house, foundation depth, and whether the door opening can take a new insulated wall. Integral and attached garages convert easily; detached garages cost more as services must be run across.
2. Confirm the planning route
Most conversions are Permitted Development. Get a Lawful Development Certificate (£129) for proof. Conservation areas, flats, or homes with a condition removing PD rights need full planning (£258).
3. Commission structural & Building Regs
An engineer specifies the new front wall, lintel over any retained opening, and how to bridge the floor-level difference. Submit a Building Regulations application (£380–£580) — always required.
4. Solve insulation & damp
Plan a damp-proof membrane, insulated floating floor build-up, and insulated inner walls to meet Part L. The floor build-up sets your finished floor level — design it early.
5. Vet and hire a builder
Get 3 fixed-price quotes on the same scope. Check FMB or TrustMark membership, £2m+ public liability and references for similar conversions.
6. Sign a written contract
Fixed price, milestone payments, written variations process, completion date, and a 5% snag retention held for up to 3 months after handover.
7. Manage the build
Typically 3–5 weeks. Keep a signed variations log, take progress photos, and book Building Control inspections at floor, insulation and completion stages.
8. Sign-off and update records
Collect the Building Regs completion certificate, update insurance and EPC, and keep the LDC with your deeds. Release retention once snags are closed.
Common Questions
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