GSM Builders Ltd designs and builds house extensions across the London Borough of Hillingdon – Hayes, Uxbridge, Ruislip, West Drayton, Ickenham, Eastcote, Northwood, Yiewsley, Cowley and Harefield. Our yard is at Leven Way, Hayes UB3, so every Hillingdon address is within 20 minutes of us. That means quick site visits, accurate quotes and a team that already knows Hillingdon Council’s planning department, Building Control and the local ground conditions.
Extensions that suit Hillingdon’s houses
Hillingdon is overwhelmingly a borough of inter-war housing. The 1930s semis and terraces of Hayes, Ruislip Manor, Eastcote, Yiewsley and West Drayton were built with small rear kitchens, separate dining rooms and long gardens, which makes them ideal for extending. The most common projects we build here are:
- Single-storey rear extensions of 3–6 m for an open-plan kitchen, dining and family room, usually with roof lights or a lantern and sliding doors
- Wrap-around extensions that use the side passage of a semi to add a utility room and downstairs WC alongside the new kitchen
- Double-storey rear or side extensions adding a bedroom and bathroom above – the most cost-effective way to go from three bedrooms to four
- Side-return extensions on the Victorian and Edwardian terraces around Uxbridge town centre, Hillingdon Hill and Hayes Town
- Garage conversions on the wide-fronted houses of Ickenham, Northwood and Ruislip
House extension costs in Hillingdon (2026)
The table gives realistic ranges for a standard specification across Hillingdon. Prices exclude VAT, kitchen units and professional fees; see our full West London extension cost guide for what drives them.
| Extension | Typical size | Indicative cost | Build time |
|---|---|---|---|
| Single-storey rear, 3 m | 18–22 m² | £50,000 – £68,000 | 8–10 weeks |
| Single-storey rear, 6 m (prior approval) | 30–36 m² | £75,000 – £105,000 | 10–12 weeks |
| Wrap-around | 30–40 m² | £85,000 – £125,000 | 12–14 weeks |
| Double-storey rear | 40–50 m² | £110,000 – £155,000 | 14–18 weeks |
| Garage conversion | 12–16 m² | £15,000 – £25,000 | 3–4 weeks |
Planning permission in Hillingdon
Hillingdon Council handles planning for the whole borough. Most single-storey rear extensions of up to 3 m on a semi or terrace, or up to 6 m under the larger home extension prior-approval route, can be built without a full planning application. Double-storey extensions and wrap-arounds normally need one. Hillingdon’s householder application fee is £258 and decisions take around eight weeks; prior approval is £120 and 42 days.
Three local factors to be aware of. First, Hillingdon has more than 20 conservation areas – including Old Uxbridge, Ruislip Village, Eastcote Village, Harmondsworth Village, Harefield and Ickenham Village – where Article 4 directions can remove permitted development rights. Second, many post-1980s estates in Hayes, West Drayton and Yiewsley carry planning conditions restricting extensions or requiring garages to be kept for parking. Third, homes under the Heathrow flight paths in Harmondsworth, Sipson, Harlington and Hayes benefit from acoustic glazing and upgraded insulation, which we specify as standard there. We check all three for your address before we quote, and we submit and manage the application for you.
We also recommend a Lawful Development Certificate (£129) for every permitted-development extension, so you have proof it was lawful when you sell.
Building Regulations and ground conditions
Every extension needs Building Regulations approval, either through Hillingdon Building Control or an approved inspector – we work with both. Much of the borough sits on London clay, and the shrinkable clay near mature trees in Ruislip, Northwood and Ickenham often means deeper foundations than the standard 1 m. Our engineer designs the foundations and steelwork, Building Control inspects at each stage, and you receive a completion certificate at the end. Where the extension runs along a boundary, we serve the Party Wall notices and work with your surveyor.
Why Hillingdon homeowners choose GSM Builders Ltd
- We are a Hillingdon company. Based in Hayes, working in the borough every week – not a London-wide firm sending a crew from the other side of the M25.
- One contract, one team. Drawings, structural calculations, planning, Building Control, all trades and decoration.
- A written, itemised price with agreed payment stages and no hidden extras.
- Fully insured, with a 12-month workmanship warranty and Building Control certificates on every project.
- Fast response. Site visits within days and same-day attendance if something needs attention during the build.
Areas of Hillingdon we cover
Hayes · Hillingdon · Uxbridge · Ruislip · West Drayton · Harmondsworth · Sipson · Ickenham · Eastcote · Northwood · Yiewsley · Cowley · Harefield · Harlington
Related services in Hillingdon
Loft conversions · Kitchen fitting · Property refurbishment · Renovations · Roofing · All house extension services
Hillingdon extension FAQs
Do I need planning permission for an extension in Hillingdon?
Often not. Single-storey rear extensions up to 3 m on a semi or terrace (4 m detached) are permitted development, and up to 6 m (8 m detached) with prior approval from Hillingdon Council. You will need a full application for double-storey extensions, wrap-arounds, flats, listed buildings and homes in conservation areas with Article 4 directions such as Old Uxbridge, Ruislip Village and Eastcote Village.
How much does a house extension cost in Hillingdon?
A 3 m single-storey rear extension in Hillingdon typically costs £50,000–£68,000 excluding VAT and the kitchen; a 6 m extension £75,000–£105,000; a double-storey extension £110,000–£155,000. GSM Builders Ltd provides free itemised quotes.
How long does an extension take to build?
A single-storey rear extension takes 8–12 weeks on site, a wrap-around 12–14 weeks and a double-storey extension 14–18 weeks, after 2–4 weeks for drawings and any planning or prior approval period.
Does GSM Builders Ltd handle planning and Building Control?
Yes. We prepare the drawings and structural calculations, submit the planning or prior-approval application to Hillingdon Council, arrange Building Control inspections and hand you the completion certificate. We also serve Party Wall notices where needed.
Which parts of Hillingdon do you cover?
All of the borough: Hayes, Hillingdon, Uxbridge, Ruislip, Ruislip Manor, Eastcote, Ickenham, Northwood, West Drayton, Yiewsley, Cowley, Harefield, Harmondsworth, Sipson and Harlington. Our base is in Hayes UB3.
Start your Hillingdon extension
Send us your address and what you have in mind. We will visit, measure up, check the planning position with Hillingdon Council and give you a written quote – free and without obligation.
