Cobin Contractors is a House extension specialist in Leeds. From single-storey kitchen extensions to full double-storey builds, all structural steelwork is handled in-house. Serving Leeds, Harrogate, Baildon, Ilkley and surrounding areas.
Note on the Government’s 2026 PD consultation: In 2026 the UK Government consulted on increasing standard Permitted Development depth limits from 4m to 5m for detached houses and from 3m to 4m for semi-detached and terraced properties. If enacted, this would allow more kitchen extensions to be built without the Prior Approval neighbour consultation process. We track planning policy changes and will advise on the current position at your survey.
Cobin Contractors offers transparent pricing ranges for each extension type. All figures are based on a standard specification build. Premium finishes, complex structural work and difficult site access will affect the final cost.
| Extension Type | Cost Range (£) | Build Time | Planning Permission |
|---|---|---|---|
|
Rear extension — single storey
Most popular. Kitchen, dining or living room. |
£36,000 – £60,000 | 8–12 weeks | Usually PD |
|
Kitchen extension (open plan)
Includes RSJ installation and wall removal. |
£42,000 – £75,000 | 10–14 weeks | Usually PD |
|
Double storey extension
Ground + first floor. Maximum space gain. |
£72,000 – £130,000 | 16–22 weeks | Planning Needed |
|
Side extension
Side return or infill. Works well on semi-detached. |
£30,000 – £55,000 | 8–12 weeks | Depends On Size |
|
Wraparound extension
Rear + side combined. Most complex build type. |
£60,000 – £110,000 | 14–20 weeks | Usually Needed |
|
Loft conversion
Dormer, hip-to-gable or Velux. |
£40,000 – £75,000 | 10–14 weeks | Usually PD |
|
Garage conversion
Attached or integral garage to habitable room. |
£18,000 – £35,000 | 4–6 weeks | Rarely Needed |
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.
Full county coverage
Wider regional coverage
House extension costs typically range from £1,800 to £3,000 per square metre for a standard build. A single storey rear extension of 20m² would cost between £36,000 and £60,000 depending on specification, finish and complexity. Kitchen extensions and those requiring load bearing wall removal or RSJ steel beam installation sit toward the higher end of this range. We provide fixed written quotes after a site survey — no guesswork. Read our full house extension cost guide for West Yorkshire.
Many house extensions in West Yorkshire fall under Permitted Development Rights and do not require a planning application. A single storey rear extension can typically extend up to 4 metres for detached houses and 3 metres for semi-detached or terraced properties without planning permission. However, all extensions require Building Regulations approval regardless of whether planning permission is needed. We assess Permitted Development eligibility at the start of every project and handle all submissions.
A standard single storey extension takes 8–14 weeks from breaking ground to completion in West Yorkshire. Double storey extensions typically take 14–20 weeks. These timelines start after planning and Building Regulations approval — which can take 8–12 weeks for projects requiring planning permission. We produce a detailed build programme at the start of every project. Read our guide: how long does a house extension take?
Yes — and this is a key difference from most extension builders in West Yorkshire. Cobin Contractors handles all structural steelwork in-house, including RSJ steel beam installation, load bearing wall removal and structural calculations. We do not subcontract structural work to third parties. This means faster timelines, single-point accountability and Building Control approval without coordinating between separate contractors. Visit our structural steelwork page for more detail.
Almost every house extension that involves removing or altering a wall, spanning a new opening or adding significant load to an existing structure will require structural calculations. These are a requirement of Building Regulations approval. We have structural engineering capability within our team — calculations, RSJ specification and pad stone design are part of our standard service.
