What does the garage conversion cost calculator include?

It estimates the build cost of converting an integral or attached garage. Typical London figures are £1,200–£2,000 per square metre, so a single garage typically runs £18,000–£30,000. Statutory fees and professional fees are separate.

How accurate is the estimate?

It is an indicative London market range for budgeting, not a quotation. Only a contractor pricing a defined drawing package can give a firm number.

Garage Conversion Cost Calculator

What this estimates

This tool estimates the build cost of converting an integral or attached garage. As a London market range, expect £1,200–£2,000 per square metre, so a single garage typically runs £18,000–£30,000. That is a budgeting range, not a quotation.

Does the garage conversion figure include the application?

No. Most attached garage conversions are permitted development, so the cost to add is £274 for a lawful development certificate rather than £548 for a planning application. Building regulations always apply, because the floor, walls and any new opening all become new thermal elements.

Item	Amount	Basis
Lawful development certificate	£274	statutory, England 2026
Householder planning application, if needed	£548	statutory
Building regulations package	from £840	our fixed fee
External wall, new thermal element	0.18 W/m²K	Approved Document L
Ground floor, new thermal element	0.18 W/m²K	Approved Document L
Garage conversions in Bexley’s Datahub set	1,065	83% approved

Sources: fees from the Town and Country Planning (Fees for Applications) (England) Regulations 2012 as amended, 2026 rates; U-values from Approved Document L, Volume 1 (2021 edition, incorporating the 2023 amendments); the Datahub row from the Planning London Datahub, retrieved 15 August 2026, phrase-matched and comparable within Bexley only. Build costs the calculator returns are our own 2026 London range and are an estimate.

What moves the number?

Whether the garage door opening is infilled with a wall and window, which needs a steel beam and padstone design.
Floor build-up, because a garage slab is usually lower and uninsulated.
Damp-proofing, since garage walls are frequently single skin.
Heating and electrical extension from the existing house systems.
Whether a parking condition on the original permission has to be varied first.

What sits outside the build cost?

Statutory fees go to the council and are set nationally for England: a householder planning application is £548 determined in 8 weeks, larger home extension prior approval is £249 over 6 weeks, and a Lawful Development Certificate is £274. Building control is separate again at typically £500 to £1,200 in London.

How should you use the figure?

As a budget envelope before design, not as a target after it. Build cost should drive the design rather than follow it: a scheme drawn without a budget is a scheme that gets value-engineered after planning consent, which usually means a second application. Fix the range first, design to it, then price the defined drawing package with two or three contractors.

Ranges are indicative London market rates observed across domestic projects and are not a quotation. Statutory figures are the England rates in force in 2026 under the Town and Country Planning (Fees for Applications) (England) Regulations. Building control charges are set by each local authority or registered building control approver.