Is it cost-effective to include a basement in a self build?

After learning about the Build It Education House, I now want to incorporate a basement into the design of my new self build project. I would like to know if the addition of a basement will add considerably more to the cost of the scheme if it is planned in the initial design stage?

A basement will of course add to your build costs, but it can be a great way to maximise space on a plot. e decision is all about calculating whether it represents value for money on your project – and it’s absolutely the right route to plan it at the design phase.

e technology behind waterproofing systems has massively improved, so much so that it is now possible to create a waterproof basement shell very affordably. But there are several key factors that might increase costs. ese include features such as: poor ground conditions, a compact plot, or a sloping site.

In the case of the Education House (www.buildit.co.uk/ ourhouse) it cost us £78,000 to create a waterproof and insulated basement shell, ready to kit out, with an insurance-backed guarantee behind the waterproofing. Our contractors estimated it would have cost £48,000 to build the engineered foundations we would have otherwise required for a standard two-storey house. So subsequently, we gained 80m2 of floor space for just a £30,000 extra spend (plus the costs of fit-out).

If you work out the cost per m2 of habitable space for the watertight shell of our basement, this comes to £975 per m2. So in the right circumstances, you can achieve a subterranean storey for about the £1,000 per m2 mark (plus fit-out costs). But it very much depends on the ground conditions, structural system, waterproofing requirements etc; and some basements will cost much more. So, you should investigate the soil conditions early and get the project fully costed before you make your decision.

I think what the Education House shows is that, with the right plot, it absolutely makes sense to add a basement. And you can always kit it out six months or a year after you’ve finished the main above-ground storeys if your budget won’t stretch initially!