Convert an existing single or double garage into a home office, study, gym, playroom or annex. Common across Borehamwood, Mill Hill, Hadley Wood and Barnet's wider 1930s and post-war suburbs where original garages no longer fit modern cars.
What's Involved
- Insulation (floor, walls, ceiling) to Building Regs Part L
- New flooring — concrete slab leveled or new screed
- Walling out the existing garage door — new external wall to match the house
- New window(s) where the garage door was
- Electrics — sockets, lighting, possibly a sub-circuit
- Heating — usually extending the existing central heating
- Plaster, paint, internal carpentry
- New door opening from the house if not already present
Cost Range
- Basic single garage conversion (existing door from house): £14,000–£20,000
- Single garage + new opening from house: £18,000–£26,000
- Double garage conversion: £25,000–£40,000
- Garage + adjacent rear extension combined: £45,000–£75,000+
Planning
Most garage conversions fall under permitted development — the building footprint isn't changing, only the use. However, conservation areas and houses with Article 4 directions may need planning permission. Building Regs sign-off is always required.
Frequently Asked Questions
Do I need planning permission?
Usually no — most garage conversions fall under permitted development since the footprint isn't changing. Conservation areas may need consent. Building Regs sign-off is always required.
How long does it take?
Single garage: 3–4 weeks on site. Double garage: 4–6 weeks. Most conversions don't need scaffolding or major external work.
Will it add value to my house?
Typically yes — adding habitable floor area to a house adds value. A converted garage usually adds £20,000–£40,000 of value in Barnet/Hertsmere, often a 30–60% return on the cost.
Can it include a bathroom?
Yes — adds £3,500–£6,000 depending on drainage run. Common for granny-annex conversions and where the garage is at the side of the house away from existing bathroom services.