How much does the inclusion of a basement add to the cost of a newbuild house?
It is difficult to provide exact figures. However, the cost of including a basement as a proportion of overall project cost is lowest where land costs are high and on sites with ground conditions that would require deep foundations even if a basement were not included in the design (e.g. sloping site, poor ground).
A detailed cost-benefit study is available from the Basement Information Centre entitled "Basements 1 - Benefits Viability and Costs." The study found that a typical three bedroom house with a storey wholly below ground might cost 11.5% more than an equivalent house without a basement, while a house with a partial basement might cost just 4.1% more.
Obviously, the additional cost of including a basement should be weighed up against the benefits that the inclusion of a basement provides. These are explored on the basement advantages page of this website.