From £2,544
London, N4
Need an Extension Builder in N4? BM Lofts Limited has been helping local clients (5 mile radius) with their extension buildering jobs for many year...
From £2,536
Mel Massey Studio, based in Finsbury Park, North London, offers interior design, interior styling and project management. With over 10 years of exp...
From £2,456
London, N4
Michael Collins Builders are experts in domestic conversions and extensions - drawing on over 25 years experience in the trade. We have built up a ...
From £2,336
Our building services company Brothers Group have been helping customers in North, East and West London and the surrounding area by providing profe...
From £2,536
We make the adage ‘House is where the heart is’, a reality for the house-owners.We are an empathetic housebuilder that delivers elegance and du...
From £2,496
We pride ourselves on our ability to provide unmatched construction, renovation and refurbishment services to homeowners, designers and architects ...
From £2,600
Experienced extension builder ready to quote for your work. Five Star Builder is the best extension builder in N4. No obligation free quotes and ma...
From £2,456
DLER SINGH D S BUILDERS are here to help customers who need an Extension Builder in N4. We offer a competitive rate to complete all your extension ...
From £2,240
Maddison & sons pride ourselves on attention to detail at the highest level.With an extensive background As Mains Contractors in construction fabri...
From £2,512
Need an Extension Builder in N4? F has been helping local clients (5 mile radius) with their extension buildering jobs for many years. Get a quote ...

How much RSJs cost for supply and installation varies depending on the size, type and load-bearing properties, but in N4 it ranges from £2,240 (Maddison & Sons based in N16) to £2,600 (Five Star Builder based in N16).
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 N4 by posting a job with HaMuch and we will send it to extension builders in N4.
"RSJ re-installation" - N16, job posted 04/10/25
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 - £17,771

Two storey extension - £88,407

Build a timber frame extension - £26,271

Build a swimming pool - £81,271

Single storey extension - £60,424

Side return extension - £44,551

Install an RSJ - £2,471

Outbuilding - £10,271

Build a Mansard loft conversion - £52,271

Loft conversion - £36,293

Build a kitchen extension - £42,271

Hip to gable loft conversion - £42,271

Granny annexe - £87,271

Garden office - £10,271

Convert a Garage - £16,271

Garage - £18,771

Build a flat roof extension - £22,271

Build a dormer loft conversion - £42,271

Concrete foundations - £6,521

Convert a bungalow loft - £29,271

Convert a basement - £40,551