GSM Builders Ltd builds house extensions in Uxbridge and across UB8 and UB10 – Hillingdon, Hillingdon Hill, Cowley, Yiewsley, Ickenham and Harefield. From our yard in Hayes we are fifteen minutes away, and we know Hillingdon Council’s planning and Building Control teams well.
Want a number first? Use our free extension cost calculator for an instant 2026 range, then book a free survey for a fixed price.
Uxbridge housing and extension options
Uxbridge mixes large Edwardian and inter-war detached houses around Hillingdon Hill, Vine Lane and Uxbridge Common with 1930s semis in Hillingdon, Cowley and Ickenham and Victorian terraces near the town centre and in Yiewsley. On the detached houses we build wrap-around and double-storey extensions – a detached house can extend 4 m (8 m with prior approval) under permitted development. On the semis, 3–6 m rear extensions and side extensions over the passage are the norm; on the terraces, side-return extensions. Garages on the wider Ickenham plots convert into home offices and annexes.
Extension costs in Uxbridge (2026)
| Extension | Typical size | Indicative cost (ex VAT) | Build time |
|---|---|---|---|
| Single-storey rear, 3 m | 18–22 m² | £50,000 – £70,000 | 8–10 weeks |
| Single-storey rear, 6 m (prior approval) | 30–36 m² | £75,000 – £110,000 | 10–12 weeks |
| Side-return | 8–12 m² | £40,000 – £60,000 | 8–10 weeks |
| Wrap-around | 30–40 m² | £85,000 – £130,000 | 12–14 weeks |
| Double-storey rear | 40–50 m² | £110,000 – £160,000 | 14–18 weeks |
Larger detached plots in Ickenham and on the Hill often mean bigger extensions and higher specifications, so totals there sit at the upper end of the ranges. Full breakdown in our extension cost guide.
Planning permission in Uxbridge
Hillingdon Council is the planning authority. Most rear extensions are permitted development (3 m on a semi, 4 m detached; 6 m and 8 m with prior approval). The exceptions are the Old Uxbridge conservation area around the High Street and Windsor Street, Ickenham Village, Harefield and Cowley Church, where Article 4 directions apply and a householder application is needed. Newer estates around Brunel and the Hillingdon Hospital area often carry planning conditions restricting extensions. We check your address, advise the route and manage the application, and we recommend a Lawful Development Certificate on every permitted-development extension.
Ground conditions vary from London clay on the Hill to gravel near the Colne and the canal in Cowley and Yiewsley; our engineer designs foundations accordingly and Building Control inspects at every stage.
How we run an extension
- Free site visit and itemised quote
- Drawings and structural calculations for planning and Building Regulations
- Planning or prior approval submitted to Hillingdon Council and managed by us; Lawful Development Certificate where permitted development applies
- Party Wall notices served and surveyors coordinated
- Build with a dedicated site manager – foundations, drainage, steel, walls, roof, glazing, first fix, plaster, second fix, decoration
- Building Control completion certificate, snagging and a 12-month workmanship warranty
Why GSM Builders Ltd for an extension in Uxbridge
- Family-run building company based at Leven Way, Hayes – 15 minutes from Uxbridge
- One contract from drawings to completion certificate
- Written, itemised price with agreed payment stages
- Fully insured, Building Control certified, 12-month warranty
- Experienced with Uxbridge’s housing stock and its council’s planning rules
Nearby
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Uxbridge extension FAQs
How much is a house extension in Uxbridge?
A 3 m rear extension in Uxbridge typically costs £50,000–£70,000 excluding VAT and kitchen; a wrap-around £85,000–£130,000; a double-storey extension £110,000–£160,000. GSM Builders Ltd surveys and quotes free of charge.
Do I need planning permission for an extension in Uxbridge?
Not usually for a single-storey rear extension within permitted development limits. Homes in the Old Uxbridge, Ickenham Village, Harefield or Cowley Church conservation areas need a householder application, as do double-storey extensions and flats.
Can a detached house in Ickenham extend further than a semi?
Yes – detached houses can extend 4 m under permitted development and up to 8 m with prior approval, compared with 3 m and 6 m for semis and terraces.
Which parts of Uxbridge do you cover?
Uxbridge town centre, Hillingdon, Hillingdon Hill, Cowley, Yiewsley, Ickenham, Harefield and the Brunel area. Our base is in Hayes, 15 minutes away.
Start your Uxbridge extension
Send us your address and a few photos and we will book a free site visit.