House Extension Costs: What You Really Need to Know Before Starting

When you think about adding space to your home, house extension costs, the total price of expanding your living space through structural additions like side extensions, rear extensions, or loft conversions. Also known as home extension, it’s one of the most common ways UK homeowners gain extra room without moving. But here’s the thing—most people underestimate what goes into that number. It’s not just bricks and mortar. It’s permits, structural support, plumbing reroutes, and sometimes even temporary relocation while work happens. And if your foundation is already showing signs of stress, like a small crack or uneven floor, that’s not just a side note—it’s a major factor that can double your bill.

That’s why you can’t just Google an average cost and call it done. A simple single-storey rear extension might start around £30,000, but if your house is on clay soil, or the existing foundation has settlement issues, you’re looking at £50,000 or more before you even pick flooring. foundation repair, fixing structural weaknesses in a home’s base to prevent further damage or collapse often comes up unexpectedly during extensions. If your walls are cracking or doors stick, you’re not just adding a room—you’re fixing a problem that’s been growing for years. And if you skip that step, your new extension could end up pulling away from the old house. It’s not a myth. It happens all the time in older UK homes where the original structure wasn’t built to handle modern loads.

Then there’s the building extension, the physical addition to a home’s footprint, often requiring planning permission and structural engineering input. Not every extension needs planning approval, but most do. The rules vary by location, property type, and how close you are to a neighbor’s boundary. And if you’re in a conservation area or have a listed property? Good luck getting approval for a glass box extension. You’ll need to match materials, roof pitch, and even window styles. That drives up cost fast. Even something as simple as choosing between timber framing and steel beams changes the price by thousands. And don’t forget the hidden stuff—electrical rewiring, new heating connections, insulation upgrades. All of it adds up.

What you’ll find in these posts isn’t just a list of prices. It’s the real talk behind them. You’ll see how a horizontal foundation crack can turn a £40,000 project into a £100,000 nightmare. You’ll learn why waiting six months after a new build before extending isn’t just advice—it’s a safety rule. You’ll find out what actually adds value when you sell, and what’s just a waste of money. Some posts break down costs for loft conversions, others show you how to spot when a DIY foundation fix is dangerous. None of it is fluff. Every article here comes from real jobs, real homes, and real mistakes people made before calling a pro.