From £18,004
At Ferdas Design & Build Ltd we have been fitting bespoke bathrooms since 2013. We pride ourselves on being the go-to bathroom fitters for discerni...
From £17,812
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...
From £17,892
Need an Extension Builder in SL9? Samuele Paolini has been helping local clients (5 mile radius) with their extension buildering jobs for many yea...
From £17,780
Member since August 2026
Relax... you have found a reliable extension builder in SL9. ABC Associates STRUCTURES 4 U is a friendly and reliable company based in SL9 who cons...
From £17,692
Need an Extension Builder in SL9? VA Structures has been helping local clients (10 mile radius) with their extension buildering jobs for many years...
From £17,780
Trusted and professional extension builder in SL9. Experienced in all extension buildering work and keeping within budget and on quote. DC Build & ...
From £17,932
DP Services is a fully insured friendly local company which has been trading since 2002 and delivers high quality building work in domestic extensi...
From £17,652
I am a qualified, builder, electrician and plumber. I have been working in the construction industry for over 23 years and have built everything fr...
From £17,804
Hi we have 15 years of experience in building and construction industry our specialization is bathrooms and renovations please have a look at the w...
From £17,924
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...

Underpinning ranges from £17,652 (Ali & Sons Builders based in SW11) to £18,004 (Ferdas Design & Build Ltd based in W3), but the final cost will depend on the method of underpinning used, how much of your foundations need underpinning and where you live.
Comparing extension builders estimates for underpinning gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
Get quotes to underpin your home in SL9 by posting a job with HaMuch and we will send it to extension builders in SL9.
| Location in UK | Hourly Rate | Daily Rate |
|---|---|---|
| Underpin A Building near Gerrards Cross | £43 | £282 |
| Underpin A Building near Rickmansworth | £42 | £278 |
| Underpin A Building near Hillingdon | £63 | £276 |
| Underpin A Building near Slough | £42 | £272 |
| Underpin A Building near Watford | £43 | £278 |
| Underpin A Building near Hazlemere | £40 | £272 |
| Underpin A Building near Chesham | £42 | £277 |
| Underpin A Building near Windsor & Maidenhead | £42 | £272 |
| Underpin A Building near Windsor | £41 | £271 |
| Underpin A Building near Maidenhead | £41 | £273 |
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.

Underpin a building - £17,827

Two storey extension - £88,491

Build a timber frame extension - £26,327

Build a swimming pool - £81,327

Single storey extension - £61,544

Side return extension - £45,181

Install an RSJ - £2,527

Outbuilding - £10,327

Build a Mansard loft conversion - £52,327

Loft conversion - £36,818

Build a kitchen extension - £42,327

Hip to gable loft conversion - £42,327

Granny annexe - £87,327

Garden office - £10,327

Convert a Garage - £16,327

Garage - £18,827

Build a flat roof extension - £22,327

Build a dormer loft conversion - £42,327

Concrete foundations - £6,577

Convert a bungalow loft - £29,327

Convert a basement - £41,181