Per Square Metre.
As the year passes, it’s time to share my updated building cost data before December sneaks up on us. I mentioned it briefly in a newsletter earlier this year but now feels like a good time to dive into the details. I’ve been tracking and refining this data over the past few years, and I plan to update it annually.
I’ve been following half a dozen model projects—mainly small to medium extensions, which are the bread and butter of my work. These are the most typical, repeatable projects I take on, so the data is more easily averaged and helpful in estimating costs.
This data allows me to confidently estimate building costs in the early stages of a project. For those who don’t know, the industry standard for estimating building works is per square metre rates, which multiply the internal floor area to give a rough cost for extensions or refurbishments.
Now, the good news: building costs have actually fallen in real terms over the past year. For example, the cost of a three-metre single-storey rear extension to a terraced house has risen slightly, from £73,177 to £74,003—but that’s still £2,200 below the inflationary increase for the period. Remember, though, that you’ll need to add VAT on top of that, plus a kitchen.
Just this week, I had a chat with a builder whose house extension I designed in 2017. At the time, he quoted £1500 per square metre plus VAT, excluding glass (bi-fold doors, etc.) and the kitchen.
“What’s the rate now?” I asked.
“£3000 plus…” he replied, shaking his head.
Other builders I speak to are quoting around £2500 per square metre, which gives me confidence that my figure of £2694 per square metre is about right. If you look at the graph below, you’ll notice how prices skyrocketed during the pandemic. It looks like we’re heading for a near-doubling of building costs over this ten-year period. Extraordinary, but it does align with some opinions that housing costs double every decade. Sadly, incomes aren’t keeping pace.
These rates cover the new-build elements of a project, but estimating the cost for remodelling existing parts of the house—especially where there’s structural work, new utilities, or electrical adjustments—can be trickier. On my projects, these parts typically involve a new loo, utility room, or similar updates. After some analysis, I use a rate of £1250 per square metre for this type of building work.
I’ve also factored in the cost of kitchens, bathrooms, doors, and windows—these are typically the big-ticket items that go beyond the basic square metre rate. My rates include standard doors, windows, and bathrooms, plus decoration at a standard specification, so clients can have a clearer idea of overall costs from the outset.
You can download the full datasheet here, with all the details.
This week’s web links include a champagne alternative and a trip to Italy.
You will always find me at carl@carlarchitect.co.uk
All the best
This Week’s Links:
Do house prices double every ten years?
10 picture-perfect stays in Puglia this season
Is open-plan living a thing of the past?
Foster + Partners showcases models of 14 skyscrapers that “challenge convention”
I recently bought a ten-quid bottle of Crémant de Loire at Sainsbury’s. A million miles better than Prosecco and not a million miles from a quid bottle of Champagne in my opinion.
Main Image credit: Estimated building costs (DALL-E)