House Extensions in Harrow
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At Bigness Group, we design and build high-quality house extensions in Harrow, helping homeowners transform their properties with more space, comfort, and value.
From detached homes in Pinner and Harrow-on-the-Hill to semis in Stanmore and Wealdstone, we deliver extensions that enhance modern living while respecting local character and planning guidelines.
We manage every stage — from design and planning to engineering and construction — ensuring a smooth, stress-free process and impeccable finish.
Design and Build Services
Our Harrow design-and-build team provides a complete, end-to-end service under one roof:
Full measured survey, design, and 3D concept plans
Planning and permitted development management for Harrow Council
Structural engineering and Building Control compliance
Kitchen, living, and interior integration
Dedicated project management and progress reporting
With one team responsible for every detail, we ensure your extension is delivered on time, on budget, and beyond expectations.
Types of Extensions We Build
We construct all major types of home extensions across Harrow, including:
• Glass Box Extensions – Contemporary builds with minimalist architecture.
• Modern House Extensions – Sleek designs that fuse architecture and innovation.
• Single-Storey Extensions – Expand your kitchen, dining, or family area with natural light.
• Double-Storey Extensions – Add bedrooms or offices above while extending living space below.
• Side-Return Extensions – Perfect for semi-detached and terraced homes.
• Rear Extensions – Create spacious, modern garden-facing living areas.
• Wrap-Around Extensions – Combine side and rear builds for full open-plan layouts.
• Conservatories & Orangeries – Glazed extensions for all-season comfort.
• Loft & Garage Conversions with Extensions – Add new rooms vertically or repurpose existing structures.
Construction Standards
Every Bigness project in Harrow follows a strict quality and safety process:
- Groundworks & Foundations – Engineered for Harrow’s mixed soil conditions.
- Steelwork & Framing – RSJs and supports for open-plan designs.
- Walls & Roofing – Brick match, render, or cladding to complement your home.
- Windows & Glazing – High-performance, energy-efficient installations.
- Interior Finishes – Electricals, plumbing, flooring, and bespoke joinery.
- Final Inspection & Sign-Off – Building Control certification and full warranty.
Local Knowledge
We have extensive experience working with Harrow Council’s planning and building control requirements, including conservation areas in Harrow-on-the-Hill and Pinner.
Our designs are tailored to meet both council guidelines and your property’s architectural identity, ensuring a seamless approval and build process.
Costs and Financing
Every extension is unique, but here’s a general guide:
| Type | Typical Cost Range (2025) |
|---|---|
| Single-Storey Extension | £45,000 – £85,000 |
| Double-Storey Extension | £75,000 – £130,000 |
| Wrap-Around Extension | £90,000 – £160,000 |
| Side-Return Extension | £40,000 – £75,000 |
💡 Factors include size, materials, access, and specification level.
We provide transparent quotes with detailed breakdowns and stage payments.
Financing options may be available through our partner lenders for eligible clients — ask our team for guidance on home improvement financing.
The Process
1. Consultation & Site Visit – We meet you on-site to discuss ideas, goals, and feasibility.
2. Design & Planning – We prepare drawings, handle permissions, and finalise the budget.
3. Construction Phase – Our project manager oversees all work, ensuring safety and communication at every step.
4. Completion & Aftercare – Once finished, we conduct final inspections and provide warranty documentation.
We also offer optional maintenance plans to keep your new space performing at its best.
Why Choose Bigness Group
Local expertise: deep knowledge of Harrow’s housing styles and planning rules.
Complete delivery: design, permissions, construction, and interiors handled in-house.
Certified quality: fully compliant with UK Building Regulations.
Transparent pricing: detailed quotes with no hidden costs.
Trusted reputation: proven record across North West London.
With Bigness Group, you’ll gain more than space — you’ll gain a carefully designed home extension that elevates your lifestyle.
FAQ
Do I need planning permission for an extension in Harrow?
Many smaller projects qualify under permitted development, but larger or multi-level builds require planning. We handle all applications for you.
How long does construction take?
Most single-storey builds take 8–14 weeks, while larger extensions average 12–20 weeks depending on complexity.
Can you work on sloped sites or limited access plots?
Yes — our engineers and site teams are experienced with challenging builds and restricted locations.
Do you handle kitchens and interior design?
Absolutely. We provide full interior and fit-out services for seamless integration.
Our Recent Projects in Harrow
Our recent work in Harrow includes a wrap-around extension in Stanmore, a double-storey build in Pinner, and a modern glass rear addition in North Harrow. Each project reflects our craftsmanship, structural precision, and design innovation — delivering light, flow, and value that homeowners love.
House Extensions in London by Borough
Bigness Group designs and builds professional house extensions across all London boroughs, including Harrow and the wider North West region. Our local experience ensures compliance with borough regulations, architectural harmony, and a flawless finish in every project.
Barking and Dagenham / Barnet / Bexley / Brent / Bromley / Camden / Croydon / Ealing / Enfield / Greenwich / Hackney / Hammersmith and Fulham / Haringey / Harrow / Havering / Hillingdon / Hounslow / Islington / Kensington and Chelsea / Kingston upon Thames / Lambeth / Lewisham / Merton / Newham / Redbridge / Richmond upon Thames / Southwark / Sutton / Tower Hamlets / Waltham Forest / Wandsworth / Westminster
Practical thinking for better-managed buildings.
Guidance, technical insight and practical perspectives on compliance, maintenance, building performance and long-term improvement.
