Extension build costs

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?

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 and that all the work is done by a main contractor.

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 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.

Standard construction, no significant structural issues, budget specification

£1,500.00 per m2

Standard specification some structural or site related complexity

£1,700.00 per m2

High quality materials or unusual specification challenging structural or site conditions

£2,100.00 per m2

(For loft conversions and internal work is cheaper and as such you should assume 60% of the above, however for basements the figures above need to be uplifted by a minimum of 50%)

Please note that these figures are illustrative only and do not include fees or VAT. They are not intended to be anything more than a helpful guide.