What’s it going to cost? Part 1 – pricing the build

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Speaking at the London Homebuilding & Renovating and Home Improvement Show last month, after each seminar the same question was raised, ‘How can I accurately cost a renovation or extension?.??

Working out how much to budget is never easy. Factors such as personal taste for the fittings and the varying prices in different styles and quality, as well as unforeseen costs emerging once a renovation is underway can all pose a challenge to setting a definitive financial plan.

However, you can get a rough guide for a final price. Work it out by starting a list or spreadsheet on all expected costs, and then add twenty per cent to this total for contingencies.??

Start with the build and labour costs, as this will be the most expensive part. From previous extension work undertaken and current research, I expect quotes in the region of £1000 per m2 for building work. So if extending by twenty square metres the rough cost will be £20,000. Builder’s merchant Jewson has a handy online Build Cost Calculator that refines the price area-by-area of the UK. Using this calculator for Greater London the cost for a one-storey extension, standard build, hiring builders and subcontractors for a twenty square metre extension worked out at £954 per m2 – total cost £19,080. Prices do vary slightly around the country with the build cost in Yorkshire at £912 a square metre – an overall cost of £18,240.

After working out the build costs, list every detail you plan to include in your project, from bi-fold doors, windows, internal doors, radiators, wiring, and tiles – everything on your wish-list. Bear in mind that there could be unforeseen costs, such as rot, crumbling walls, eroded pipes, so a contingency budget to fall back on is a must. A builder will be able to advise on how to tackle any problems, but it is worth obtaining several quotes from different trades to make it easier to compare like-for-like before you make a final decision.