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 ‘normal’ extension can be difficult – since there really is no normal! 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 rough 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 alterations during the build. 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.

Build Routes

Executive

This for the cash-rich/time poor individuals who are looking to employ a range of professionals and tradesmen to undertake their extension project. They are less driven by cost, and will only get involved in the high-level decision making and specification.

Executive Build Costs

As a rough guide, a single storey extension costs around £1,450 per sq.m with this route; a two storey costs around £1,200 per sq.m.

Project Manager

This is where the homeowner engages a professional project manager to help them keep costs and project time to a minimum by allowing the project manager to purchase materials, employ reputable contractors, as well oversee site supervision and day-to-day management of the project, to ensure the project runs smoothly and quickly.

Project Manager Build Costs

As a rough guide, a single storey would costs £1,100 per sq.m with this route; a two storey extension would cost £1,150 per sq.m

Self Project Management

This where the homeowner is the ‘site agent’, responsible for the employment of contractors, on-site co-ordination and supervision, and the purchase and provision of materials. It is a predominantly organisational role, but in cutting out the fees of a professional project manager, it keeps costs down and allows the homeowner to maintain control of the budget. Those choosing this route may also choose to do a bit of work on site themselves in order to further reduce costs. However, it requires a lot of time.

Self Project Management Build Costs

As a rough guide, a single storey extension costs about £1,000 per sq metre with this route; a two storey extension costs about £900 per sq metre.

Trader

This is where homeowners undertake as much of the construction work themselves in order to reduce costs, and source and buy the materials themselves, rather than allowing contractors to supply them, to ensure they get the best deals. This method can also be the most rewarding, and can lead to serial self building, as new skills are learned quickly, although it is very time-consuming.

Trader Build Costs

As a rough guide, a single storey extension costs about £800 per sq metre with this route; a two storey extension costs about £700 per sq metre.

We have known of this route also getting the costs down to £500 per sq.m but this would involve the doing virtually all the building work from start to finish.