From £17,508
Whites Carpentry & Building prides in delivering an excellent extension buildering service and value for money in PO20 and the surrounding areas. ...
From £18,596
We are a Small Family run business with over 30 years experience in the building trade, Carpentry is my main trade, with NVQ Level 2.
From £17,644
We are a small family run business with over 20 years experience in brickwork, bathroom/kitchen fitting, roofing, landscaping, fencing, tiling and ...
From £17,492
Member since August 2026
H P Building Services Sussex is a one-stop solution for all your extension buildering needs. Establish over 10 years ago and covering 20 miles arou...
From £17,612
Futureways Design and Build are here to help customers who need an Extension Builder in PO20. We offer a competitive rate to complete all your exte...
From £17,252
Park Building Services Ltd is a trusted extension builder serving customers in PO20 and the surrounding area. Contact us to today to get a competit...
From £17,940
Need to find an Extension Builder near you for all your extension buildering work?
Main Construction provides a local, trusted extension bu...
From £17,700
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...
From £17,876
Giles Dixon is an experienced Project Manager with over 30 years experience, having worked from the ground up starting in 1984 as an apprentice ele...
From £17,628
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...

Underpinning ranges from £17,252 (Park Building Services Ltd based in PO9) to £18,596 (R&B Property Improvements based in PO9), 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 PO20 by posting a job with HaMuch and we will send it to extension builders in PO20.
| Location in UK | Hourly Rate | Daily Rate |
|---|---|---|
| Underpin A Building near Chichester | £34 | £242 |
| Underpin A Building near Bognor Regis | £35 | £247 |
| Underpin A Building near Arun | £35 | £241 |
| Underpin A Building near Havant & Waterloo | £35 | £248 |
| Underpin A Building near Havant | £35 | £249 |
| Underpin A Building near Littlehampton | £35 | £244 |
| Underpin A Building near Rustington | £36 | £246 |
| Underpin A Building near Waterlooville | £36 | £250 |
| Underpin A Building near Horndean | £35 | £253 |
| Underpin A Building near Portsmouth | £36 | £250 |
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 - £17,725

Two storey extension - £88,337

Build a timber frame extension - £26,225

Build a swimming pool - £81,225

Single storey extension - £59,496

Side return extension - £44,029

Install an RSJ - £2,425

Outbuilding - £10,225

Build a Mansard loft conversion - £52,225

Loft conversion - £35,858

Build a kitchen extension - £42,225

Hip to gable loft conversion - £42,225

Granny annexe - £87,225

Garden office - £10,225

Convert a Garage - £16,225

Garage - £18,725

Build a flat roof extension - £22,225

Build a dormer loft conversion - £42,225

Concrete foundations - £6,475

Convert a bungalow loft - £29,225

Convert a basement - £40,029