House Extensions
London & Hertfordshire
Transform your home with a professionally designed and built house extension. TCM Building has delivered over 200 extensions across London and Hertfordshire — from simple rear additions to complex double-storey projects.
The Most Popular Way to
Add Space & Value
A house extension is a permanent structure added to an existing residential property to increase its floor area. Unlike a loft conversion or basement conversion, a house extension typically extends the footprint of the property outwards — to the rear, side, or both — creating new ground-floor or multi-storey living space.
For homeowners in London and Hertfordshire, a house extension is often the most practical alternative to moving — avoiding stamp duty, estate agent fees, and the upheaval of relocation, while creating a home that is precisely tailored to your family's needs.
TCM Building manages the entire process from initial design through to final decoration, including all structural engineering, planning applications, and specialist trades. You deal with one team, one contract, and one point of contact throughout.
Which Extension Is Right for You?
Rear House Extensions
A rear extension is the most common type of house extension in London and Hertfordshire. It extends the back of your home into the garden, typically creating a larger kitchen, open-plan kitchen-diner, or additional living space. Under Permitted Development rights, a single-storey rear extension can extend up to 3 metres on a semi-detached or terraced house, and up to 4 metres on a detached house — without planning permission.
How We Deliver Your Extension
Free Consultation & Site Visit
We visit your property, discuss your vision, assess feasibility, and take initial measurements. No obligation, no charge.
Design & Planning
Our in-house design team produces architectural drawings. We advise on Permitted Development vs. planning permission and submit applications on your behalf.
Structural Engineering
A qualified structural engineer calculates all load-bearing requirements, foundation specifications, and steel beam sizes.
Detailed Quotation
We provide a fully itemised, fixed-price quotation with no hidden costs. You know exactly what you're paying before work begins.
Construction
Our dedicated site team carries out all works — groundworks, brickwork, roofing, glazing, plastering, and first-fix services — under one contract.
Finishing & Handover
We complete all second-fix works, decoration, and snagging. We don't leave until you're completely satisfied.
Do You Need Planning
Permission?
Many house extensions in England can be built under Permitted Development rights, meaning no formal planning application is required. However, the rules are complex and depend on your property type, location, and the size of the proposed extension.
TCM handles all planning applications and Building Regulations submissions on your behalf. We have an excellent track record of securing planning approval.
House Extension Cost Guide
Prices vary based on specification, materials, and site conditions. These figures are indicative guides for London and Hertfordshire. We provide a fixed-price quotation after the free site visit.
| Extension Type | Size | Typical Cost | Build Time | Planning |
|---|---|---|---|---|
| Single-Storey Rear | Up to 30m² | £35,000 – £65,000 | 10–16 weeks | Often PD |
| Single-Storey Rear | 30–50m² | £65,000 – £90,000 | 14–18 weeks | Often PD |
| Side Return | 15–25m² | £40,000 – £80,000 | 12–18 weeks | Often PD |
| Wrap-Around | 40–70m² | £80,000 – £150,000 | 20–28 weeks | Usually required |
| Double Storey | 40–80m² | £60,000 – £140,000 | 16–24 weeks | Required |
PD = Permitted Development. All prices are indicative and exclude VAT. A fixed-price quotation is provided after the free site visit.
The TCM Difference
Building an extension is one of the largest investments you'll make in your home. Choosing the right contractor is critical. Here's why over 200 London and Hertfordshire homeowners have trusted TCM with their extension projects.
We manage all trades — structural engineers, bricklayers, roofers, plumbers, electricians — under one contract. No coordination headaches.
Our detailed quotations are fixed-price. No surprise invoices, no scope creep. What we quote is what you pay.
Every project has a dedicated site manager who is your single point of contact from groundworks to handover.
We are independently verified on Checkatrade with a 5-star rating from over 100 verified reviews.
All structural work is backed by a 10-year workmanship guarantee, giving you complete peace of mind.
"TCM built a stunning rear extension and side return for us. The whole process was seamless — from the initial design meeting to the final handover. The quality of the brickwork and the bi-fold doors is exceptional. We couldn't be happier."
Ready to Get Started?
Book a free, no-obligation site visit. We'll assess your property, discuss your vision, and provide a detailed quotation.
You love your home, but you're running out of room. Maybe your family's growing, or you just need that extra living space you've always wanted. Moving house can be a huge headache, with all the costs and disruption. What if you could create the perfect new space right where you are? That's exactly what a house extension offers. It's about expanding your existing property, whether that's a single-storey rear addition for a bigger kitchen, a double-storey extension for extra bedrooms, a clever side return, or a comprehensive wrap-around. We also handle extensions over garages, making the most of every inch. An extension isn't just about adding square footage; it's about transforming your daily life. Imagine a brighter, more functional kitchen, a dedicated home office, or a spacious new master suite. It's an investment that significantly boosts your property's value and, more importantly, your quality of life.
You're starting to feel the squeeze at home, aren't you? Maybe the kids need more space, or you're dreaming of a bigger kitchen for entertaining. You know something needs to change to make your home work better for you, but you're not quite sure what the best path forward is yet.
What You Need to Know
Tailored Design & Planning Expertise
Every home is unique, and so is every extension project. We work closely with you to design a space that perfectly fits your needs and lifestyle. Our team guides you through planning permission or Permitted Development regulations, ensuring a smooth process from concept to completion.
Structural Integrity & Safety First
Building a safe, durable extension means getting the structure right. Our experienced structural engineers ensure your new space is built to the highest standards, providing peace of mind that your investment is sound and secure for years to come.
Fixed-Price Quotes, No Surprises
Worried about hidden costs? We provide clear, fixed-price quotes upfront, so you know exactly what to expect. This transparency means you can budget confidently, without any unwelcome surprises along the way.
Seamless Project Management
From the initial design to the final touches, we manage every aspect of your extension project. Our dedicated project managers coordinate all trades, keeping you informed and ensuring your build stays on schedule and within budget.
Everything Else You Should Know
Understanding House Extension Costs
How much does an extension really cost? It's a common question, and the answer depends on several factors like size, materials, and complexity. We provide detailed, transparent quotes, breaking down all expenses so you can make informed decisions. We'll discuss your budget early on to ensure your dream extension is also financially viable.
Navigating Planning & Regulations
Do you need planning permission, or does your project fall under Permitted Development? Understanding the rules can feel overwhelming. We're experts in local regulations for Borehamwood and Hertfordshire, guiding you through the entire process to ensure your extension complies with all legal requirements.
Extension vs. Moving: What's Right for You?
You're weighing up your options: extend or move? Extending your home can save you stamp duty, solicitor fees, and the stress of finding a new property. It allows you to create a bespoke space tailored to your exact needs, often at a lower overall cost than relocating.
Common Extension Mistakes to Avoid
Building an extension is a big undertaking, and it's easy to overlook crucial details. We help you avoid common pitfalls like underestimating budgets, neglecting proper planning, or choosing the wrong builder. Our expertise ensures a smooth process and a high-quality finish.
House Extension FAQs
Get Your Free Extension Quote Today
Call us or submit an enquiry and we'll arrange a free site visit at a time that suits you.
Where We Deliver House Extensions
TCM Building & Maintenance is based in Borehamwood and serves Hertfordshire, North London, and the surrounding area. Each location page covers planning authority details, property types, and local considerations specific to that area.
Our home base. Fast response times across the whole town.
Serving Radlett's conservation areas and Green Belt properties.
Covering Bushey, Bushey Heath, and the surrounding Hertsmere area.
Serving Potters Bar, Brookmans Park, Northaw, and Cuffley.
Full coverage across Watford and the Three Rivers district.
Experienced in St Albans conservation areas and listed buildings.
Covering Hatfield, Welham Green, Birchwood, and Old Hatfield.
Specialists in the WGC Conservation Area's Arts and Crafts properties.
Serving all parts of the London Borough of Barnet.
Covering Edgware, Canons Park, Burnt Oak, and Queensbury.
Serving Stanmore, Harrow Weald, Belmont, and the surrounding area.
Not sure if we cover your area? Call 07305 121634 — we serve a wide area across Hertfordshire and North London.