How much will it cost?

"How much will it cost to build?" This is one of the most common questions asked by anyone considering a self build. Unfortunately it is also the most difficult to answer. It is complicated, mainly because there are so many variables: house size, location, design, ground conditions, trees, access, labour and material costs, local wildlife and the weather, to name just a few.

Set your budget first and then explore what you can realistically afford to build.

It is probably a better idea to come at it from another angle – set your budget first and then explore what you can realistically afford to build. This approach still won’t cover many unforeseen problems but you can allow for this with a contingency of 10-15% of your build budget. This will also give designers, package companies and builders something concrete to work with, and they can tailor the design and spec accordingly. You will soon know if your plans are realistic. And there is the option to tweak them to reduce the costs.

Your budget

Your budget will be based on available savings, the likely profit from the sale of your existing home and what you can expect to raise on a mortgage. Traditionally, around a third of the total budget was spent on a plot, with the remainder covering construction. At today's prices, however, land is like to be 40-60% and in popular areas like London and the South East the ratio can be even higher.

It makes financial sense to build a house that reflects the value of the plot

Whatever your budget, it makes financial sense to get the balance right so that the house reflects the value of the plot: spend too much on a house on a cheap plot and you risk not getting your money back when you come to sell; invest too little, and you haven’t realised your plot’s potential. Of course this may be perfectly acceptable if you intend to live there for any length of time.

Getting out of the ground is usually the biggest unknown with any build. Ground conditions will dictate your foundation options, and heavy clay soil or nearby trees may result in needing deeper footings. In some cases, specialist foundations may even be required. All of this will impact significantly on your budget.

Get specialist help to cost your build


Costing a build is bit like the chicken and egg scenario. Which comes first - the budget or the house design?

Costing a build is complicated and you're almost certain to require specialist help. Estimating software is a useful tool to plan your budget. Most just require you to input data from your drawings to calculate the costs, based on a recognised price list. There is the flexibility to experiment with different materials, specifications and layouts to compare costs. For example, the cost savings of replacing clay tiles with concrete ones can be done at the click of a mouse. Be warned, though: most software is expensive for a one-off build and is probably better suited to serial selfbuilders or small developers.

A cheaper option is to get quotes from a builders’ merchant, based on your drawings. These will usually need to be approved for Building Regulations to make it worth their while.

Make sure that you are comparing like for like when getting quotes from different companies

Package companies can also provide accurate costings, especially if your house is based on one of their standard designs. Make sure that you are comparing like for like when getting quotes from different companies. A turn-key option, where they do virtually everything, will ensure the most accurate quote – and also the most expensive

Conventionally, construction estimates are provided by a quantity surveyor, though the service is unlikely to be cost-effective for a project as small as a single family home. In practice, it will come down to the negotiating skills of your project manager. A good builder will also produce a detailed quote, depending on the amount of detail contained in the specification. It is not uncommon for the spec to run to many pages.

Selfbuilders can make significant savings by agreeing in advance to supply the required materials. The VAT can be reclaimed for these later, after the build. Remember to ask if the builders’ quotes include plant and equipment hire, such as WCs and scaffolding.

One of the biggest causes for budget over-runs is indecision

Most builders are happy to comply with their clients’ wishes but every change to what’s agreed in the contract will come at a price. This can be a nasty shock when presented with the total bill later on.

Finally, right from the outset, allow for fees and associated charges that may not be immediately apparent. These include associated costs of acquiring planning permission such as wildlife surveys, Building Control, warranties and insurance, and design fees. Remember also to allow for charges if your plot is not connected to mains utilities. This can be expensive. A sewage treatment plant will be required if living off mains drainage.

You will also need to factor in the costs of your accommodation during the build. The longer the build, the more this will cost.

Further reading

For more detail, read Guide to Budgeting Your Build »


Gerald Cole's blog page Topping Out: Six hidden costs - Self build's worst budget busters »