Relax... you have found a reliable extension builder in BT12. SM Plumbing & Heating is a friendly and reliable company based in BT12 who consider n...
From £1,536
Trusted and professional extension builder in BT12. Experienced in all extension buildering work and keeping within budget and on quote. Belfast Lo...
From £1,376
Trusted and professional extension builder in BT12. Experienced in all extension buildering work and keeping within budget and on quote. Extended l...

How much RSJs cost for supply and installation varies depending on the size, type and load-bearing properties, but in BT12 it ranges from £1,376 (Extended living by Gilbert-Ash based in BT12) to £1,568 (SM Plumbing & Heating based in BT7).
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 BT12 by posting a job with HaMuch and we will send it to extension builders in BT12.
"RSJ installation" - BELFAST, job posted 09/08/25
| Location in UK | Hourly Rate | Daily Rate |
|---|---|---|
| Install An RSJ near Belfast | £23 | £161 |
| Install An RSJ near Carryduff | £23 | £158 |
| Install An RSJ near Holywood | £23 | £159 |
| Install An RSJ near Lisburn | £24 | £164 |
| Install An RSJ near Greenisland | £23 | £153 |
| Install An RSJ near Comber | £22 | £160 |
| Install An RSJ near Hillsborough and Culcavy | £25 | £170 |
| Install An RSJ near Crumlin | £26 | £194 |
| Install An RSJ near Ballygowan | £24 | £183 |
| Install An RSJ near Saintfield | £23 | £162 |
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 - £16,793

Two storey extension - £86,940

Build a timber frame extension - £25,293

Build a swimming pool - £80,293

Single storey extension - £40,867

Side return extension - £33,550

Install an RSJ - £1,493

Outbuilding - £9,293

Build a Mansard loft conversion - £51,293

Loft conversion - £27,125

Build a kitchen extension - £41,293

Hip to gable loft conversion - £41,293

Granny annexe - £86,293

Garden office - £9,293

Convert a Garage - £15,293

Garage - £17,793

Build a flat roof extension - £21,293

Build a dormer loft conversion - £41,293

Concrete foundations - £5,543

Convert a bungalow loft - £28,293

Convert a basement - £29,550