House Extensions in Harrow

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:

1. Groundworks & Foundations – Engineered for Harrow’s mixed soil conditions.
2. Steelwork & Framing – RSJs and supports for open-plan designs.
3. Walls & Roofing – Brick match, render, or cladding to complement your home.
4. Windows & Glazing – High-performance, energy-efficient installations.
5. Interior Finishes – Electricals, plumbing, flooring, and bespoke joinery.
6. 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:

💡 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.