Calculating your Self-build Costs

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One of the most important aspects when planning your self-build or home renovation/extension project is working out how much it is going to cost. This figure will depend on the size and shape of the house, the level of your own involvement, where in the country you intend to build, and the materials you’re going to use. If you can make even rough decisions about these factors, then you can begin to work out how much it is going to cost.

As a very general rule of thumb, expect a building plot to cost between a third and a half of the end value of the finished house. The costs of building a house will then depend on the variables listed above. All building work is usually quoted on a cost/m2 basis. For example, a typical new four bedroom self-built home is around 200m2 (with 100m2 on two storeys) and usually varies between £1,000-£1,500/m2 (although self-builders can achieve costs of between £300£3,000/m2).

Renovation costs are more difficult to establish as they involve many variables, but allow at the very least £1,000-£1,300/ m2 for work. This, added to the cost of the plot/house and with a 10-30% contingency, should result in less than the final end value of the house.

The table below, based on information from the Building Cost Information Service (part of RICS, the Royal Institution of Chartered Surveyors), is updated monthly to help you work out a more accurate estimate (note, however, that these figures are for build costs only and do not account for VAT, which is not charged for self-build projects). There is a free online version at homebuilding. co.uk/calculator.

1

Identify your build route from the four options Your level of involvement in the project will influence the build costs. For simplicity, the four most common build routes have been identified below:

Build Route A: DIY + Subbies Building on a largely DIY basis, substituting around 30% of labour costs with DIY, and employing help with the rest of the building work. Materials purchased directly.

Build Route B: Subbies Building using tradespeople hired directly — you will be project managing, but there is minimal DIY involvement. Most or all materials purchased directly. l Build Route C: Builders/subbies Building using a main contractor or package supplier to complete the structure to a weathertight stage, with the remaining work undertaken by subcontractors and most materials purchased by self-builder direct from suppliers. l Build Route D: Main contractor Building using a main contractor. Building in this way requires the least involvement from the self-builder.

2

Identify your expected level of specification The standard of specification that you choose will have an enormous influence on your build cost. For estimating purposes, three general categories of quality have been identified: l Standard: This represents a basic build quality equivalent to that offered by most speculative developers. A house may include standard softwood joinery, studwork partitions, a contract kitchen, basic sanitaryware and radiator central heating. l Good: This is equivalent to that offered by quality developers. Features may include high-end off-theshelf softwood joinery, blockwork partition walls, contract quality kitchen and sanitaryware and underfloor heating (UFH) downstairs. l Excellent: A very high standard. This house may include hardwood joinery, blockwork partition walls, a bespoke kitchen and quality sanitaryware, and UFH, for instance.

3

Multiply the figure by your house size We have used gross internal floor area as a measure (it’s the most common in the industry). It’s the area of a building measured to the internal face of each perimeter wall for each floor level. It includes areas occupied by internal walls and partitions.