Garage Conversion Cost UK: Pricing Guide 2024

Quick Answer: A standard UK single garage conversion (around 15-18m²) typically prices between £12,000 and £25,000, while a double garage (28-36m²) ranges £20,000-£40,000 depending on region, insulation depth and services. Building Regulations approval is almost always required under the Building Regulations 2010 (Schedule 2) because a change of use from non-habitable to habitable space triggers Part L (energy), Part F (ventilation), Part B (fire safety) and Part C (moisture).

Summary

Garage conversions are one of the most reliable margin jobs a small UK builder can take on. Unlike extensions they rarely require planning permission (most fall under permitted development, provided the garage is attached and there's no alteration to the external footprint), they bring fast turnaround, and the customer usually has a clear budget benchmark in mind. The work is well-suited to a small team — one builder, an electrician, a plumber, a plasterer and possibly a heating engineer — over a 3-6 week programme.

The reason garage conversions go wrong on price is almost always the same: builders quote on the visible scope (block up the door, plaster it, put a door in) and miss the regulatory work underneath. Floor build-up to match house finished floor level, damp-proof course continuity, sub-floor insulation to Part L1B u-values, mechanical ventilation, and a fully compliant electrical install all need to be priced in. Getting any one of these wrong turns a £15,000 quote into an £18,000 job and the difference comes off your margin.

This guide covers every line item a UK garage conversion should contain, with current 2025-2026 trade day rates, materials cost ranges, regional pricing variation, and a fully worked example so you can benchmark your quote against the market.

Key Facts

• Typical floor area — single garage 15-18m² (5m × 3m typical), double garage 28-36m² (5.5m × 5.5m typical)
• Average duration — 3-4 weeks for a single, 5-6 weeks for a double, including drying time for screed and plaster
• Building Regulations — full plans submission or building notice required; change of use triggers Part L1B (energy), Part F (ventilation), Part B (fire), Part C (moisture)
• Planning permission — usually not required if the conversion is internal and doesn't alter the external appearance; check Article 4 directions in conservation areas
• Floor level — original garage slab is typically 100-150mm below house finished floor; build-up required to match house level
• Insulation u-values (Part L1B 2021) — floor 0.18 W/m²K, walls 0.18 W/m²K, roof 0.16 W/m²K, glazing 1.4 W/m²K
• Builder day rate — £200-£300/day (£25-£37/hour), £180-£250/day for North/Wales/Scotland
• Electrician hourly rate — £35-£50/hour, day rate £280-£400, NICEIC/NAPIT registered required for certified install
• Plumber hourly rate — £40-£60/hour, £320-£480/day, Gas Safe required if extending gas heating circuit
• Plasterer day rate — £180-£250/day, output approximately 30-40m² of plastering per day on flat walls
• Damp-proof course — must be continuous with existing house DPC; gap between garage and house at the join is the most common point of failure
• Garage door infill — typically 100mm blockwork inside, 102.5mm brick outside to match house, with insulated cavity; 1.5-2 days work for a bricklayer plus mortar drying time
• Ventilation (Part F) — habitable rooms need 8,000mm² background ventilation (trickle vents) plus extract if used as kitchen/utility
• VAT — standard rated at 20%; conversions of garages attached to a dwelling do NOT qualify for the 5% reduced rate (which only applies to dwellings unoccupied 2+ years)
• Margin — target gross margin 20-30% on a sub £25k job; net margin after overheads typically 12-18%
• Preliminaries — 8-12% of trade cost (skip hire, scaffold if needed, welfare, site protection)
• Contingency — 5-10% — recommended on every garage conversion because slab condition and DPC continuity are unknowns until you open up

Quick Reference Table

Detailed Guidance

Floor Build-Up — The Hidden Cost Most Builders Miss

The original garage slab is almost always 100-150mm below the finished floor of the adjacent house. You have two routes: build up off the existing slab, or break out and re-cast at the correct level. The build-up method is normal and cheaper, but it eats the headroom (usually 200-220mm) and on garages with low door heads or existing ceiling beams it can leave you under the 2.3m minimum recommended ceiling height for habitable rooms.

A typical build-up stack is: existing concrete slab → DPM (1200 gauge polythene, lapped 150mm and taped, dressed up walls to meet the DPC) → 100mm rigid PIR insulation (achieves around 0.18 W/m²K) → separation layer → 65-75mm sand/cement screed or 50mm liquid screed. Materials run £35-£55/m² for the insulation and DPM and £25-£35/m² for the screed. Labour for laying and screeding is one to two days depending on size.

The trap is the DPC. The existing house has a horizontal DPC at brick course 2-3 above ground level. The garage was never required to maintain this — it had no DPC, or one that stops at the corner where it meets the house. When you convert, the new floor DPM must marry up with the house DPC continuously, or you'll get rising damp on the new internal walls within 6-18 months. Budget half a day of the brickie's time to expose the joint and lap it correctly.

Blocking Up the Garage Door

A standard UK garage door opening is 2.1m wide × 1.9-2.1m high. Filling it is straightforward — 100mm thermalite or dense block inner leaf, 100mm cavity with 90mm full-fill insulation, 102.5mm facing brick outer leaf to match the house. The cost driver is matching the existing brick: if the house is built in a common stock you're fine, but a non-stock brick (handmade, blend) can add £200-£400 to the brick bill alone for sourcing.

You'll usually want a window or a smaller door in the new wall — for natural light (Part L1B has glazing area requirements) and for ventilation. A 1.2m × 0.9m UPVC window with a concrete lintel above is the most common spec. The lintel needs to be sized by a structural engineer if there's any load above (rare on a single-storey garage but always check). Total time for blocking up with window is 2-3 days for a bricklayer plus a labourer, with a day of drying before the inside can be lined.

Insulation and Achieving Part L1B U-Values

Part L1B of the Building Regulations 2010 (as amended 2021) applies to material change of use, which a garage conversion is by definition. The relevant target u-values are: floor 0.18 W/m²K, exposed walls 0.18 W/m²K, roof 0.16 W/m²K, windows 1.4 W/m²K, doors 1.4 W/m²K.

For walls, you typically have a single-skin garage wall (100mm block, no cavity). To meet 0.18 W/m²K you need around 80-100mm of PIR internally, on battens, with a vapour control layer behind the plasterboard. That eats roughly 110mm off each internal wall — significant when the garage is already narrow. Some builders use 50mm PIR-backed plasterboard direct-bonded for speed, but on a single-skin garage wall this won't achieve 0.18 W/m²K and your building control officer will fail it. Don't try to skip this — budget the full depth and price it in.

For roofs, if the garage has a pitched roof with a roof void you can insulate at ceiling level (cheaper, around £15-£20/m² for 270mm mineral wool). If it's a flat roof or warm roof construction, the cost rises to £45-£60/m² for the insulation board and the works.

Electrical Work

A garage conversion needs a full domestic electrical install: sockets to BS 7671:2018+A2:2022 (18th Edition Amendment 2), lighting circuits, smoke alarm interlinked with the house system (Part B), and possibly a consumer unit upgrade if the existing CU has no spare ways. Notification to Building Control via a registered competent person (NICEIC, NAPIT, ELECSA) is mandatory under Part P.

Typical scope for a single garage conversion: 6-8 double sockets, 2 lighting points, isolation switches, RCBO protection, smoke alarm interlink, possibly a ring main for an extra room. Two-day job for an electrician plus a half-day for second fix and testing. Material cost £350-£600, labour £600-£1,000. If a new dedicated circuit needs running back to the consumer unit and the CU is full, add £450-£800 for a CU upgrade.

Heating

If the property has wet central heating, the simplest spec is to extend the heating circuit with one or two radiators sized to the room heat loss (calculate using a Mears or similar online calculator, or do a proper Part L SAP-aligned heat loss assessment). Typical room heat loss for a 15m² well-insulated converted garage is 1.0-1.4 kW, so a 600 × 1000mm double-panel double-convector radiator does it.

Watch the boiler. A 24kW combi running an existing 3-bed house may not have headroom for an extra room without lengthening warm-up times. Most cases are fine; flag it as a "boiler check" line in your quote and price a £180 service visit as part of the works. Don't get drawn into a boiler upgrade for free.

Frequently Asked Questions

Do I need planning permission for a garage conversion?

Usually no, provided the conversion is internal and doesn't alter the external appearance significantly. Filling the garage door with brick and adding a window normally falls under permitted development. However, you should check for: an Article 4 direction in conservation areas; properties where permitted development rights have been removed by a planning condition (common on newer estates); flats and maisonettes (PD doesn't apply). When in doubt, apply for a Lawful Development Certificate (around £103 fee) to get written confirmation.

Why is the floor the most expensive single item?

Because it's a stack of compliance items: DPM, insulation depth, screed, plus the labour to break out the threshold and tie in to the house DPC. The slab itself is fine — it's everything you have to put on top to satisfy Part L and Part C that drives cost. A floor build-up done properly takes 2-3 days of labour spread over a week with drying time.

What's the difference between a builder's notice and a full plans submission?

A building notice is a faster, less paperwork route — you give the local authority 48 hours' notice and they inspect as the work proceeds. A full plans submission means you submit drawings and specs upfront, get approval, then build. For garage conversions either works. Use a full plans submission if you want certainty before you start, or if you're using an approved inspector rather than local authority. Build over notices are not appropriate — they're for drainage works.

How do I price the unknowns?

Build a contingency line of 7-10% into the quote (£800-£2,000 on a typical job) and have a conversation with the client about it upfront. The unknowns are: condition of the slab (cracks, settlement), DPC continuity, whether the existing electrical supply can take the new circuits without a CU upgrade, the state of the wall plate if there's a pitched roof. Pricing for these as contingency rather than absorbing them into your margin protects you.

Regulations & Standards

• Building Regulations 2010 (as amended) — primary statutory instrument, requires approval for material change of use

• Approved Document L1B (2021) — energy efficiency in existing dwellings, target u-values

• Approved Document F (2021) — ventilation requirements

• Approved Document B (2019) — fire safety, including smoke alarm interlinking and means of escape

• Approved Document C (2004) — site preparation and resistance to contaminants and moisture

• Approved Document P (2013) — electrical safety, notification requirements

• BS 7671:2018+A2:2022 — IET Wiring Regulations, 18th Edition Amendment 2

• BS 5250:2021 — management of moisture in buildings

• Gas Safety (Installation and Use) Regulations 1998 — for any gas works

• VAT Notice 708 — buildings and construction, confirms standard rating for garage conversions

• Approved Document L1B Conservation of fuel and power - existing dwellings (2021)

• Planning Portal - Garage Conversion

• HMRC VAT Notice 708 - Buildings and Construction

• LABC - Garage Conversions Guidance

• NICEIC - Part P Notification Process

• single storey extension pricing guide — pricing model for ground-floor extensions

• building regulations part l — energy efficiency requirements detail

• dpc continuity on conversions — avoiding rising damp at conversion joints