How to use the extension cost chart
We’ve put together a breakdown of benchmark costs for popular types of extension project. The prices in the table are indicative of what you can expect to pay to engage a main contractor to complete the works for each of our five extension scenarios. It is possible to reduce costs by undertaking some of the project management or building works yourself – check out the box (above) for a quick guide.
Most home extensions in the UK are built with cost-effective cavity wall masonry, which is familiar to every trade out there, so our benchmark figures relate to this construction method. We’ve assumed a standard quality and performance level for a bespoke home project (better than Building Regulations, but not high-end).
These figures include allowances for all the infrastructure required for each project type – including electric circuits, hot and cold water supplies and extending the central heating system. They also factor in a basic level of fit-out, such as second fix electrics (switches, sockets etc), plasterboard and final decoration.
A number of big-ticket fit-out items are omitted from the table, including floor finishes, sanitaryware, kitchen fit-out and landscaping. This is simply because they represent massive variables depending on your design tastes and specification choices. For instance, home extenders could spend anything from £5,000 to £50,000+ on a new kitchen. Other possible cost uplifts include clearing the site and any requirement to move drainage or other services.
Design fees would be in addition to the build costs quoted below. These depend on the scale and nature of your project, and whether you’re using an architect to draw up and submit your plans. Other potential professional fees that may apply include surveys, structural engineering, party wall agreements and project insurance.