House Extensions FAQ: Costs, Timelines & Our Fixed-Price Guarantee

Are you starting to feel like your home is bursting at the seams? Perhaps that "open-plan" kitchen you fell in love with five years ago now feels more like a crowded corridor, or your growing family is making the living room feel like a permanent obstacle course of toys and school bags. If you’re considering moving just to gain an extra room, you’re likely facing the daunting prospect of stamp duty, estate agent fees, and the sheer stress of the Dorset property chain.

But what if you didn't have to leave the neighbourhood you love? For many homeowners in Bournemouth, Poole, and Christchurch, the answer lies in extending rather than moving. However, we know that the world of construction can feel like a minefield. You probably have a dozen tabs open right now, trying to decipher conflicting advice on costs, planning laws, and how long you'll be living with a skip on your driveway.

At The Big Conversion Company Ltd., we believe in transparency from the very first conversation. To help you navigate your journey, we’ve compiled this comprehensive FAQ guide, addressing the most common concerns we hear from local homeowners in 2026.

How much does a house extension cost in Bournemouth & Poole in 2026?

This is usually the first question on everyone's mind, and for good reason. With the cost of materials and skilled labour evolving, you need an accurate benchmark to set your budget.

Currently, for a professional, high-quality extension in the BCP area, you should expect to budget between £2,200 and £3,300 per square metre.

To put that into a real-world perspective:

• A standard 25m² kitchen extension: Typically costs between £60,000 and £85,000.
• A smaller 15m² side-return extension: Usually ranges from £35,000 to £50,000.
• A large double-storey extension: Can range from £100,000 to over £160,000, depending on the complexity and whether you are adding new bathrooms or bespoke glazing.

It is important to remember that these figures are "all-in" for a professional build that complies with all current building regulations. While you might find lower quotes, they often exclude essential elements like VAT, structural engineering fees, or internal finishes. If you want a more tailored estimate for your specific project, our house extension calculator is a great place to start.

How long does the actual building work take?

One of the biggest pain points for homeowners is the fear of a "never-ending build." You want your new space, but you also want your privacy and your driveway back.

A typical single-storey extension usually takes between 10 and 14 weeks from the moment we break ground to the final coat of paint. Here is a rough breakdown of how those weeks are usually spent:

1. Weeks 1-3 (The Groundworks): This involves excavation, pouring foundations, and installing underground drainage. It’s the "messy" phase, but it’s the most critical for the structural integrity of your home.
2. Weeks 4-7 (The Shell): This is when you see the most visible progress. The walls go up, the roof structure is built, and the building becomes "watertight" with the installation of windows and doors.
3. Weeks 8-11 (The First Fix & Plastering): Our electricians and plumbers move in to install wiring and pipework before the walls are plastered.
4. Weeks 12-14 (The Second Fix & Finishes): This is the exciting part where flooring is laid, kitchen units are fitted, and the space finally starts to look like a home.

While we always aim for the 10-14 week window, factors like bespoke structural glazing (which can have long lead times) or particularly complex structural alterations can extend this slightly. However, we provide a clear schedule before we start so you can plan your life accordingly.

What exactly is the "Fixed-Price Guarantee"?

We’ve all heard the horror stories: a project starts at £50,000 and somehow ends up costing £75,000 because of "unforeseen extras." At The Big Conversion Company Ltd., we find that approach unacceptable.

Our Fixed-Price Guarantee is designed to give you total financial peace of mind. Once we have conducted a detailed site survey and provided you with a formal quote, that price is locked in.

• No Hidden Costs: If we find a standard structural issue that we should have reasonably anticipated during our survey, we absorb the cost. You don't pay for our oversight.
• Transparent Budgeting: Your quote will be itemised, so you know exactly where every pound is going: from the steel beams to the skirting boards.
• Stability: In a world where material prices can fluctuate, your contract price remains stable, allowing you to manage your finances without the stress of "bill shock" halfway through the project.

You can read more about how we structure our transparent pricing on our price page.

Do I need planning permission for an extension in Dorset?

The short answer is: not always. Many house extensions fall under Permitted Development (PD) rights. This means that as long as your extension meets specific criteria regarding its height, depth, and the materials used, you may not need to submit a full planning application to BCP Council.

However, there are several "ifs" and "buts" to consider:

• If you live in a Conservation Area (like parts of Talbot Village or Westbourne), PD rights are often restricted.
• If your property is a Listed Building, you will almost certainly need consent.
• Even if you don't need planning permission, you always need Building Regulations approval. This ensures the work is safe, energy-efficient, and structurally sound.

We handle the heavy lifting here. We work closely with local building inspectors in Bournemouth and Poole to ensure every stage of your build is signed off correctly, providing you with all the necessary certificates when the project is complete. This is vital for when you eventually decide to sell your home.

Will I have to manage the builders and trades myself?

Not at all. We know that you have a job, a family, and a life to lead. You shouldn't have to spend your lunch break chasing a plumber or wondering why the skip hasn't been collected.

When you work with us, you are assigned a dedicated project manager. They are your single point of contact for everything. They coordinate the groundworkers, the bricklayers, the carpenters, and the decorators. They ensure that materials arrive on time and that the work stays on schedule.

This "turnkey" approach is what sets a professional home renovation apart from a DIY-managed project. It not only saves you stress but also ensures a much higher standard of finish, as our teams are used to working together seamlessly.

How much value will an extension add to my property?

While the primary reason to extend is to improve your quality of life, it’s also a significant financial investment. In high-demand areas like Southbourne, Lilliput, or Christchurch, a well-designed extension can add between 10% and 20% to the overall market value of your home.

In 2026, the most "value-adding" extensions are those that create:

1. Larger Kitchen/Diners: The heart of the home remains the biggest selling point.
2. Home Offices: With hybrid working now the norm, a dedicated, quiet workspace is highly prized.
3. Additional Bedrooms: Especially if they include an en-suite.

If you find that an extension might be too large for your current garden space, you might also want to consider a loft conversion. These are often equally effective at adding value while keeping your outdoor space intact. You can check the potential costs for those using our loft conversion calculator.

What are the first steps to getting started?

If you're ready to stop dreaming and start building, the process is simpler than you might think. We always recommend starting with a clear vision of what you want to achieve. Is it a sun-drenched playroom? A sleek, modern kitchen? Or perhaps a wraparound extension that completely transforms the footprint of your ground floor?

Once you have a rough idea, contact us to arrange a site visit. We’ll walk through your home with you, discuss what’s possible under local regulations, and provide you with that crucial fixed-price quote.

Choosing to extend your home is a big decision, but it’s one that pays dividends in the comfort and happiness of your family. By choosing a team that understands the local landscape of Bournemouth, Poole, and Christchurch: and one that stands by its prices: you can enjoy the transformation of your home without the traditional headaches of construction.

Are you ready to create the space you've always wanted? If you'd like a clear, no-obligation quote for your project, visit our Home Extension quote page to get started.