Name: Extension Builder
Brand: HaMuch
SKU: extension-renovation
Rating: 4.5 (2 reviews)

Find affordable W1J extension builders

Prices range from cheapest £26/hour and £26/day (London Design And Build ) to £83/hour and £508/day (Q Lofts and Extensions ) - average £45/hr and £277/day

HaMuch is Excellent

Local W1J extension builders & latest jobs

"Concrete foundation" - W1T, job posted 16/10/25

"Basement conversion" - LAMBETH, job posted 02/05/25

Quickly find an Extension Builder in W1J

Use these steps to find Extension Builders in W1J for FREE!

Post your job: Click "Get quotes" and briefly describe your job.
Enter your details: We’ll match you with Extension Builders in W1J. 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 W1J 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 Piccadilly
Extension Builders in Savile Row
Extension Builders in Mayfair
Extension Builders in St James's
Extension Builders in Regent Street
Extension Builders in Oxford Street
Extension Builders in City of Westminster
Extension Builders in Soho
Extension Builders in Whitehall
Extension Builders in China Town

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 - £26,224

Garden office - £10,224

Granny annexe - £87,224

Build a flat roof extension - £22,224

Convert a Garage - £16,224

Hip to gable loft conversion - £42,224

Convert a bungalow loft - £29,224

Build a dormer loft conversion - £42,224

Build a swimming pool - £81,224

Build a Mansard loft conversion - £52,224

Concrete foundations - £6,474

Underpin a building - £17,724

Two storey extension - £88,336

Convert a basement - £40,020

Side return extension - £44,020

Loft conversion - £35,850

Garage - £18,724

Single storey extension - £59,480

Outbuilding - £10,224

Install an RSJ - £2,424

Build a kitchen extension - £42,224

More extensions & conversions cost guides...

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