Name: Extension Builder
Brand: HaMuch
SKU: extension-renovation
Rating: 4.63 (8 reviews)

Find affordable W12 extension builders

Prices range from cheapest £33/hour and £253/day (Mr) to £50/hour and £325/day (Ferdas Design & Build Ltd) - average £44/hr and £281/day

HaMuch is Excellent

Local W12 extension builders, reviews & latest jobs

"Side return extension" - NW10, job posted 14/08/25

"Loft conversion" - W12, job posted 21/04/25

"Loft conversion" - W12, job posted 20/04/25

"Loft conversion" - W12, job posted 23/10/24

"Flat roof extension for a period mews terraced house. We'd like a bedroom extension with full bathroom and a roof top terrace. Footprint is roughly 8.5m x 6m." - W6, job posted 06/10/24

"Mansard loft conversion" - SHEPHERD'S BUSH, job posted 26/09/24

"Garage" - W3, job posted 18/06/24

"Basement conversion" - W4, job posted 07/08/23

Quickly find an Extension Builder in W12

Use these steps to find Extension Builders in W12 for FREE!

Post your job: Click "Get quotes" and briefly describe your job.
Enter your details: We’ll match you with Extension Builders in W12. We’ll notify you via text or email when an Extension Builder is available to quote.
Select your Extension Builder: Compare Extension Builders interested in working with you. You can use HaMuch to safely message local W12 Extension Builders or phone them directly - you’re in control!

What are the best ways to avoid problems when paying the Extension Builder?

The most important thing is do avoid handing over cash or paying large sums in advance. Be wary of paying cash for a cheaper job, i.e. to avoid VAT, you may be going down a slippery slope of not doing things properly which may eventually mean your job is also not done properly.

Agree when you intend to pay, ideally after you are satisfied with the completed job. If it is a big job agree a schedule of staged payments which is fair to both parties.

To avoid bad tradespeople and to ensure you can find them should they not answer a mobile;

Get proper contact details and check them yourself
Check if the company is verified on the Companies House website
Get phone details, ideally a land line or 0800 number and check it
Get a physical office address

Before the job starts should I agree standards of quality and behaviour?

Get quotes in writing by email or in person if possible. Getting quotes online or by text is ok (make sure you accept the offer by replying). For large projects make a written agreement, schedule of works and snagging plans as part of a working document. Also;

Agree expected quality of workmanship and materials in advance
When will work start and when will project be finished, what happens if project over runs ?
How long is the guarantee on work and materials eg 12 months
Discuss onsite behaviour in advance (no smoking, swearing or using mobile phones for non-work purposes)
Agree that your Extension Builder will remove all debris and rubbish and what level of tidying up you want after job

Local Extension Builders in London Boroughs

Local Extension Builders in London Boroughs
Borough in London
Extension Builders in Shepherd's Bush
Extension Builders in Hammersmith
Extension Builders in Notting Hill
Extension Builders in Kensington
Extension Builders in West Kensington
Extension Builders in Kensington
Extension Builders in Acton
Extension Builders in Chiswick
Extension Builders in Maida Vale
Extension Builders in Earl's Court

Job estimates from extension builders near you

Whether you’re looking to extend your kitchen with a side return extension or you want to convert your basement into a liveable space, read our cost guides to get an idea of how much each project costs before getting a more accurate quote from our database of reliable tradespeople.

Build a timber frame extension - £26,216

Garden office - £10,216

Granny annexe - £87,216

Build a flat roof extension - £22,216

Convert a Garage - £16,216

Hip to gable loft conversion - £42,216

Convert a bungalow loft - £29,216

Build a dormer loft conversion - £42,216

Build a swimming pool - £81,216

Build a Mansard loft conversion - £52,216

Concrete foundations - £6,466

Underpin a building - £17,716

Two storey extension - £88,324

Convert a basement - £39,930

Side return extension - £43,930

Loft conversion - £35,775

Garage - £18,716

Single storey extension - £59,320

Outbuilding - £10,216

Install an RSJ - £2,416

Build a kitchen extension - £42,216

More extensions & conversions cost guides...

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