Specialist structural steelwork contractors in West Yorkshire. RSJ steel beam installation, load bearing wall removal and structural alterations — all steelwork handled in-house. Leeds, Harrogate, Baildon and Ilkley. Free quotes within 24 hours.
Universal beams specified to structural calculations. All sizes and spans across West Yorkshire.
Full project management — engineer calculations, temporary propping, steel installation, Building Control.
Chimney breast removals, goalpost frames, opening enlargements and structural modifications.
Cobin Contractors does not work that way. RSJ steel beam installation, load bearing wall removal, goalpost frames and structural calculations are performed by our own in-house team. The same people building your extension are the same people installing the steel. That means single-point accountability, no scheduling gaps between contractors, and faster Building Control sign-off.
Sources: structuralengineercalcs.com (Feb 2026), myjobquote.co.uk (Jan 2026), procalculator.co.uk (Dec 2025).
| Extension Type | Size | Cost Range (£) | Duration | Design |
|---|---|---|---|---|
|
Double storey rear — small
Typical semi-detached rear extension. 2 rooms added: extended kitchen + bedroom above. |
15–25m² | £55,000 – £80,000 | 10–14 weeks | Included |
|
Double storey rear — medium
Most common format. Open-plan kitchen-dining below, master suite above. |
25–40m² | £80,000 – £130,000 | 12–16 weeks | Included |
|
Double storey rear — large
Large rear opening with goalpost steel frame. Typically in detached properties. |
40–60m² | £130,000 – £180,000 | 14–20 weeks | Included |
|
Double storey side extension
Side return format. Common on Victorian and Edwardian semis in Leeds and Harrogate. |
15–25m² | £55,000 – £95,000 | 10–14 weeks | Included |
|
Wrap-around double storey
Combined side + rear over two floors. Highest ROI format for terraced and semi homes. |
40–60m² | £110,000 – £180,000 | 16–22 weeks | Included |
|
Architectural + structural package only
If you already have a builder and need just the design and calculation pack. |
— | £3,500 – £7,500 | 4–8 weeks | Separate |
A double storey extension is not a two-week job. We break every project into eight clear phases — each with a defined output, defined sign-off and a named person responsible on our team.
We build two-storey extensions across Leeds, Harrogate, Bradford and the wider Yorkshire region. Every build is managed from our West Yorkshire base — no remote site managers, no weeks between visits.
Harrogate town, Pannal, Starbeck and surrounding villages.
Harrogate town, Pannal, Starbeck and surrounding villages.
Harrogate town, Pannal, Starbeck and surrounding villages.
Harrogate town, Pannal, Starbeck and surrounding villages.
Harrogate town, Pannal, Starbeck and surrounding villages.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
A typical double storey rear extension (25–40m²) in West Yorkshire costs £80,000 to £130,000 turnkey in 2026 — including design, structural engineering, planning submission, foundations, steelwork, shell and standard finishes. A wrap-around (40–60m²) runs £110,000 to £180,000. Yorkshire rates typically run £15,000–£25,000 below equivalent London projects. Every Cobin quote is fixed-price before work starts.
