How do I calculate the cost of a self build?

You will need to do your sums carefully before embarking on a self build.

Traditionally, around a third of the budget was spent on the plot with the remainder covering construction. At today’s land prices though, 40-60 per cent is more likely to account for the plot and in popular areas the percentage can be even higher.

Estimating the build cost will depend on the house size, the form of construction, the complexity of the design, the materials selected, local labour rates and the specific conditions of the site such as poor ground conditions which can demand specialist foundations. In other words, it’s complicated.

Specialist price books detailing the costs of every aspect of construction and updated annually, are available, and Mark Brinkley’s The Housebuilder’s Bible is an essential guide specifically for selfbuilders.

Estimating software such as EstimatorXpress from HBXL or the online costing service Cost My Self Build is a good way to plan the cost of your project. Easy to understand building diagrams help you input your project’s dimensions to calculate the cost, and because it’s linked directly to a builder’s merchant’s price list, the estimates are totally accurate.

Custom build companies will also provide basic estimates for their standard designs. Some builder’s merchants will supply free estimating services based on detailed house plans.

Traditionally, construction estimates are provided by a quantity surveyor, though the service is unlikely to be cost-effective for a project as small as a single house.

In practice, arriving at a precise budget will depend on negotiations with your designer or project manager and your contractor. Don’t expect to tie everything down before you start.

Every build has its own peculiarities and this is why a contingency of at least 10-15 per cent of your budget is necessary.