Extension Builder Cost in Hillingdon

Building an extension in Hillingdon is a significant investment, with costs varying based on size, design complexity, materials, and planning requirements. As a Greater London location, Hillingdon extension costs typically run 25–35% above the national average. BizHub365 connects homeowners with experienced local extension builders who understand Hillingdon's planning regulations and can deliver quality work on budget. Whether you're adding a single-storey kitchen extension or a two-storey addition, our network of vetted tradespeople helps you compare quotes and find the right builder for your project.

Extension Builder Prices in Hillingdon

Service	Typical Cost	Unit
Single-storey extension (up to 20m²)	£20000 – £35000	per job
Single-storey extension (20–40m²)	£35000 – £55000	per job
Double-storey extension (up to 30m²)	£55000 – £95000	per job
Double-storey extension (30–50m²)	£95000 – £160000	per job
Loft conversion (standard)	£30000 – £55000	per job
Building Regulations approval	£800 – £2000	per application
Architect/designer fees	£1500 – £5000	per job
Structural works (foundation/party wall)	£5000 – £15000	per job

Prices are indicative averages for Hillingdon. Actual quotes will vary based on job specifics.

What Affects the Cost?

Extension costs in Hillingdon depend on several key factors: the size and complexity of your design, materials chosen (brick, rendered block, timber), ground conditions and foundation requirements, proximity to party walls (which require legal surveyor involvement), whether planning permission is needed, existing roof/structural modifications, and the specification of finishes inside. Extensions requiring specialist structural work, underpinning, or complex party wall solutions cost significantly more. Labour availability and material prices also fluctuate seasonally, with spring and summer typically busier and potentially more expensive.

Money-Saving Tips

Keep your design simple and rectangular where possible—complex shapes increase labour and material costs. Obtain multiple quotes from different builders to compare pricing and experience. Consider timing your project for autumn or winter when builders may offer better rates, and get planning and Building Regulations sorted early to avoid costly delays and rework.

Frequently Asked Questions

Do I need planning permission for an extension in Hillingdon?

Most single-storey extensions up to certain sizes and setbacks qualify for Permitted Development rights and don't need planning permission. However, two-storey extensions, loft conversions, and extensions in conservation areas typically do require planning approval. Hillingdon Council has specific rules; always check with them or your builder before starting work.

What is the typical timescale for a Hillingdon extension?

A straightforward single-storey extension usually takes 8–12 weeks from start to completion. Double-storey extensions take 14–20 weeks. Add 4–8 weeks for planning and Building Regulations approval beforehand. Delays can occur due to poor weather, supply chain issues, or unforeseen structural problems.

Are Building Regulations mandatory for extensions in Hillingdon?

Yes. All extensions must comply with Building Regulations, even those that don't need planning permission. Your builder should handle the application and inspections. Failure to comply can affect future house sales and may result in enforcement action by the council.

What is a party wall agreement and do I need one?

If your extension is near or affects a shared boundary wall with a neighbour, you legally need a Party Wall Award from a surveyor before work starts. This costs £800–£2,500 but protects both parties. Your builder or surveyor can advise whether one is required for your specific project.

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