Budgeting to build an extension

There are many variables involved in the cost of building an extension. This can make it difficult to give a straightforward answer to the question of how much it will cost. When asked we find it helpful to give an understanding of the breakdown of the parts that will make up your budget so that we can begin to apply it to your specific situation.

The type of extension, it’s floor area and what it will be used for, have the most significant impact on the construction cost. The next most significant considerations are the location of the project, the desired quality of the build, ground conditions and type of construction. Using the area of the extension it is possible to apply a square metre rate as a rough guide for this part of the budget. Depending on how the project is affected by these factors it could typically range from £2000-2750 per metre square.

Extensions often involve some degree of alteration to the existing part of the house and part of your budget should be dedicated to these costs. Excluding demolition, joinery and decoration, opening up a new doorway for example could add around £750 to your budget while combining two rooms with a large opening could add around £2500.

If an extension includes a new kitchen, bathroom or fitted joinery, you should allow a cost for each of these. Kitchens can typically range from £10,000 to £25,000 while bathrooms will usually be from £5,000 to £15,000. You may also wish to make allowances for landscaping, decoration and furniture if required.

There are ‘soft’ costs which need to be accounted for in preparing to build. This includes fees for the consultants who will support you, applications for approvals, surveys and insurance.

There are finally allowances which should be made for VAT at the prevailing rate and a contingency fund. The contingency should typically be 10-15% of the construction cost though this could be increased if market conditions are volatile at the time of building. You may also wish to allow for temporary accommodation and the cost of temporary storage for your belongings.

While this may seem a lot of issues to consider, beginning to budget for your project using this framework will start to build a comprehensive picture of the costs for you at the outset. We offer a service to our clients to support initial cost planning. Please contact us if you wish to arrange an initial consultation.