Do I need planning permission for a garage conversion?

Most garage conversions do not need planning permission as they are internal alterations. However, you will need a Building Regulations application as the space must meet standards for structure, insulation, ventilation, fire safety and drainage. If the conversion materially changes the external appearance (e.g. new windows) or the property is in a conservation area, planning permission may be required.

What floor insulation do I need for a garage conversion?

The floor must achieve a U-value of 0.22 W/m²K per Part L. The most common approach is to overlay the existing slab with a DPM, 75–100mm PIR insulation (e.g. Celotex/Kingspan) and 18mm T&G chipboard. This raises the floor level by about 95–120mm. If headroom is limited, thinner high-performance insulation or excavating the slab may be needed.

How much does a garage conversion cost in the UK?

A basic garage conversion typically costs £8,000–£15,000 for an integral or attached garage, and £12,000–£20,000 for a detached garage. Costs vary by specification, location and whether plumbing is included. A conversion is usually the most cost-effective way to add habitable space to a property.

What happens to the garage door opening?

The garage door is removed and the opening is bricked up, usually with a window and/or entrance door. The infill must include DPC, cavity insulation and proper lintels. The brickwork should match the existing house as closely as possible. Full-width glazing is an alternative but requires structural assessment.

Does a garage conversion add value to a property?

Yes, a well-executed garage conversion typically adds 10–20% to a property value, far exceeding the cost of the work. However, losing a garage can reduce value in areas where off-street parking is at a premium. Check local market conditions and consider retaining a parking space on the former garage drive.

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Garage Conversion Calculator — Insulation & Compliance

Plan a UK garage conversion with Part L compliant floor insulation buildup, wall insulation, garage door replacement structure and electrics.

Garage type

Internal length

Internal width

Ceiling height

Door opening replacement

Include wall insulation

How We Calculate This

This calculator helps plan a garage conversion by quantifying insulation, plasterboard and other material requirements based on garage dimensions and configuration.

Part L compliance

All external walls must achieve U-value 0.26 W/m²K, floor 0.22 W/m²K. The calculator accounts for which walls are external based on garage type (integral, attached or detached).

Floor buildup

Existing slab + DPM + PIR insulation + T&G chipboard. The total raised height is flagged so you can check door thresholds and step heights.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.