From £1,864
Experienced extension builder ready to quote for your work. M & J Building Contractors is the best extension builder in Cornwall. No obligation fre...
From £1,968
Cornwall, EX22
We are experienced, creative, skilled craftspeople and builders. We design, construct and install interior projects for any space in your home. Fro...
From £1,552
Eastman Landscapes is a trusted extension builder serving customers in Cornwall and the surrounding area. Contact us to today to get a competitive ...
From £1,896
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...
From £1,960
Need to find an Extension Builder near you for all your extension buildering work?
SCP CONSTRUCTION provides a local, trusted extension bui...
From £2,288
Need to find an Extension Builder near you for all your extension buildering work?
BURGESS CONSTRUCTION provides a local, trusted extension...
From £1,936
Relax... you have found a reliable extension builder in Cornwall. Garage Door Repairman is a friendly and reliable company based in Cornwall who co...
From £1,848
RJ WEVILL BUILDER are here to help customers who need an Extension Builder in Cornwall. We offer a competitive rate to complete all your extension ...
From £2,264
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...
From £2,344
Reliable and experienced extension builders with competitive rates and good at keeping within budget. Happy to provide examples of extension builde...

How much RSJs cost for supply and installation varies depending on the size, type and load-bearing properties, but in Cornwall it ranges from £1,552 (Eastman Landscapes based in PL15) to £2,344 (A J HEARD BUILDERS LTD based in EX20).
Comparing extension builders estimates for fitting an RSJ gives you an idea of who will be better value but the best way to compare costs is to get actual quotes.
Get rates and quotes to install an RSJ in Cornwall by posting a job with HaMuch and we will send it to extension builders in Cornwall.
| Location in UK | Hourly Rate | Daily Rate |
|---|---|---|
| Install An RSJ near Bideford | £22 | £174 |
| Install An RSJ near Barnstaple | £25 | £196 |
| Install An RSJ near Newquay | £32 | £230 |
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 - £17,292

Two storey extension - £87,688

Build a timber frame extension - £25,792

Build a swimming pool - £80,792

Single storey extension - £50,840

Side return extension - £39,160

Install an RSJ - £1,992

Outbuilding - £9,792

Build a Mansard loft conversion - £51,792

Loft conversion - £31,800

Build a kitchen extension - £41,792

Hip to gable loft conversion - £41,792

Granny annexe - £86,792

Garden office - £9,792

Convert a Garage - £15,792

Garage - £18,292

Build a flat roof extension - £21,792

Build a dormer loft conversion - £41,792

Concrete foundations - £6,042

Convert a bungalow loft - £28,792

Convert a basement - £35,160