Cost per square metre is the quickest way to get a rough figure early on. You won't price a job properly this way, but it'll tell you within a few minutes whether something is worth looking at, and that's usually all you need at the start.
These are national average figures before adjusting for where you are. The first column is handing the whole job to a builder and letting them run it. The second is managing it yourself and bringing in your own trades, which is what Avalor works to.
| Type of work | Builder runs it | You run it |
|---|---|---|
| Cosmetic refresh | £250 to £875 | £200 to £700 |
| Light refurbishment | £750 to £1,440 | £600 to £1,150 |
| Full refurbishment | £1,440 to £2,375 | £1,150 to £1,900 |
| Loft conversion | £1,500 to £2,500 | £1,200 to £2,000 |
| Flat conversion | £1,440 to £2,500 | £1,150 to £2,000 |
| HMO conversion | £1,440 to £2,375 | £1,150 to £1,900 |
| New build | £1,730 to £3,075 | £1,385 to £2,460 |
The gap is roughly 20%. That's the builder's overhead and margin for pricing it, programming it, chasing the trades and carrying the risk when something goes wrong. It isn't free money. You're taking all of that on, and if you haven't done it before that's usually where the 20% goes.
The gap between light and full refurbishment is where most of the confusion sits. A light refurb is kitchen, bathroom, decorating, flooring, maybe some rewiring. A full refurb is the whole lot including a rewire, replumb, new heating, plastering throughout, and often some structural work. It's easy to price a job as light and find out halfway through it was always going to be full.
Where you are makes a big difference, mostly through labour. Inner London runs about 35% above the national average and outer London about 25%. The South East is around 10% above. Go the other way and the North East is about 10% below, with Wales, the north west outside the cities and the Midlands somewhere between 5% and 8% below. Access matters as much as the postcode, though. A terraced street with no parking and a skip permit costs more to work in than a house with a driveway, wherever it is.
There's a lot these rates don't include. Professional fees run around 12% of the build for most jobs, more if it's structural or listed. Contingency should be at least 10%, and I'd carry more than that on anything old where you don't know what's behind the walls. VAT is on top if you're not registered. So is finance, and so is stamp duty on the purchase.
A couple of things skew the rate itself. Small jobs cost more per square metre than big ones, because setting up, welfare, skips, scaffold and the builder's time don't get any cheaper just because the job is smaller. They just land on less floor area. Kitchens and bathrooms are also far more expensive per square metre than bedrooms, so a flat with two bathrooms in 60 square metres will cost more per metre than a big house with one.
Spending well above what the street supports is a common way to lose money on a scheme that looked fine on paper. You won't get it back at the sale.
Use the rate to sift. If something only works at the bottom of the range, it probably doesn't work. Once you're serious, get a builder in and price it properly.
Avalor prices this using BCIS benchmark rates, adjusted for your postcode and set to self delivery, so the figures assume you're running the job with your own trades rather than handing it to a builder. If you've got a real quote you can put that in instead.