How much do trench foundations cost per metre?
Updated 6 October 2026 · prices for 2026
Typical cost of trench foundations for an extension
£3,240–£5,220
for a 10 to 20 m run, 600 × 1000 mm, including VAT (£2,700–£4,350 + VAT)
About £218 to £270 a metre before VAT. Dug by mini digger, soil taken away in skips, filled with C25 ready-mix 750 mm deep. Building control decides the final depth.
Trench foundations for a typical extension cost about £261 to £324 a metre including VAT (£218 to £270 before VAT) in 2026. That's a 600 mm wide trench dug 1 m deep by mini digger, the soil taken away in skips, and C25 concrete poured 750 mm deep. A 15 m run, the three walls of a modest rear extension, comes to about £4,509 including VAT (£3,758 before VAT). Short runs cost more per metre, because the digger, the low loader and the concrete part-load charge cost much the same for 10 m as for 20 m.
What's in the price
We priced a 15 m run. This is where the money goes, before VAT.
- Digging: about 14.5 hours on a 1.5 t mini digger, with two days' self-drive hire, the low loader there and back, and diesel.
- Skips: three 8-yard skips for the 9 m³ of soil, once it bulks up, about £1,150, and loading them.
- Concrete: 6.75 m³ of C25 ready-mix, about £1,090, and about 7 hours of labour to place it straight from the lorry. If it has to be barrowed in, allow nearer 13.
- Trench bottoms: levelled and compacted with a wacker plate before the pour.
Plant and skips are about 45% of the price, materials 30% and labour 25%. That's why groundworks are so sensitive to access and disposal.
Price per metre by run
| Run | Before VAT | With VAT | A metre |
|---|---|---|---|
| 10 m | £2,822 | £3,387 | £282 |
| 15 m | £3,936 | £4,723 | £262 |
| 20 m | £4,588 | £5,506 | £229 |
Pricing it as a builder
If you price foundations at a flat rate per metre, you'll lose on short runs and win on long ones. Price the fixed things once (the digger hire, the low loader, the part-load charge) and the rest by volume. On a 10 m run, concrete comes in under 6 m³, so a part-load charge of about £80 at cost goes on top.
Check three things on the site visit before you settle the price. Can a lorry get to the trench, or does the concrete need barrowing, a pump or mixing on site? Is there room for skips, or does the soil go by grab lorry? And is it clay, with trees nearby, which could mean digging deeper when building control looks at the trench? Each one moves the price more than the rate per metre does.
The foundation run is the new walls only. Where the extension meets the house, there's usually no new foundation along the existing wall. Check the drawings and the engineer's details.
Priced on its own, a job like this carries a small premium for travel, setting up, a minimum charge and part-used materials. Done as an extra while you're already on site, the same work usually costs a bit less.
How we priced it
We built the job in Bricken, the quoting app for UK builders, item by item. Merchant and hire prices for the concrete, skips and plant, typical hourly rates for each trade (£22 an hour for a groundworker, before markup), and a typical builder's markup of 30% on materials and plant and 35% on labour. Your groundworker will price it at their own rates, so get a few quotes.
Priced in Bricken at standard UK rates (a 10 m run for the low figure, 20 m for the high). Each figure is then multiplied by Bricken's regional factor, from 0.90 in the North East to 1.30 in inner London. The factors come from public 2025-26 build-cost guides and our own quotes. Where a region covers two areas, the low uses the lower factor and the high the higher. The factors are set for whole building jobs, so treat small differences as a guide.
Cost by region
| Region | 10 m run | 20 m run |
|---|---|---|
| London | £3,890£3,244 | £6,790£5,656 |
| South East | £3,630£3,028 | £5,850£4,872 |
| East of England | £3,410£2,839 | £5,480£4,568 |
| Midlands | £3,150£2,622 | £5,220£4,350 |
| North West | £3,080£2,568 | £4,960£4,133 |
| North East and Yorkshire | £2,920£2,433 | £4,960£4,133 |
| South West | £3,410£2,839 | £5,480£4,568 |
| Wales | £2,980£2,487 | £4,800£4,002 |
| Scotland | £3,240£2,704 | £5,220£4,350 |
What pushes the price up or down
Up
- Deeper trenches: clay, tree roots or soft ground can mean digging deeper. A 10 m run at 1.2 m deep with 950 mm of concrete priced at £2,922 before VAT, about £220 more than at 1 m.
- Digging by hand: when a digger can't get in. The 10 m run took about 35 hours by hand against 17 by machine.
- Concrete mixed on site: when a lorry can't get close. On 10 m it came to £3,299, about £595 more than ready-mix from the lorry.
- A concrete pump: when the trench is out of reach of the lorry's chute.
- London: skips cost about 30% more, and labour and parking more again.
Down
- Longer runs: the digger, low loader and part-load charge are mostly fixed, so 20 m costs £218 a metre against £270 for 10 m.
- Spoil kept on site: skips are the biggest single line, nearly 30% of the price on a 15 m run.
- Full concrete loads: a run that needs at least 6 m³ avoids the part-load charge on ready-mix.
- Sharing the digger: if the same hire also digs the floor and drains, each item carries less of it.
Questions
How deep do foundations need to be for an extension?
There's no single answer. Many extensions start at about 1 m, but clay soil, nearby trees and drains can push it deeper. The building control inspector looks at the open trench before the concrete goes in and decides.
How long does it take to dig and pour trench foundations?
Our 15 m run has about 26 hours of work in it, so about two days for a small gang, plus the building control inspection before the pour.
How much concrete do I need per metre of trench?
A 600 mm wide trench filled 750 mm deep takes 0.45 m³ a metre. A 15 m run needs about 6.75 m³; order a little over, as trenches are rarely exact.
Why are skips such a big part of the price?
Soil bulks up by about a third once it's dug. A 15 m trench at 600 × 1000 mm is 9 m³ in the ground and nearly 12 m³ in skips, which is three 8-yard skips.
Is VAT included?
The big figures include VAT at 20%. If your groundworker isn't VAT-registered, the price before VAT is closer to what you'll pay.
Related guides
How we price: each figure is a Bricken quote built from the sizes, at standard UK merchant prices and day rates, with a typical builder’s markup. Your builder’s price will differ: get quotes.