How Much Do Extensions Cost?

Build Cost Variations
Extension Costs By Project Type

Extensions can add around 25% to value of your property, and basement or loft conversion will typically boost the property value by 10% to 15%. But what will they cost? We asked the experts at The National Self Build & Renovation Centre for the facts and figures.

Providing costings for an 'average' extension can be tricky - since there really is no average! However, issues such as ground conditions, access to the site, location and proximity of services are a huge factor in the build budget; therefore in providing indicative costs, we have assumed that all of these issues are reasonable to deal with.

Build Costs

The biggest variance in terms of cost comes from the individual specification, and how the budget is managed. Whilst our costs provide an indication of the variation between build route and extension size, there is no accounting for a home owner suffering from 'decisionitis'! There are so many choices available and therefore many decisions to be made, which can affect your overall budget, by a considerable amount. Over-spending on material specification is one of the most frequent reasons why extensions go over budget. The costs indicated assume a good specification and standard and reflect the cost variation predominantly on build management route.