Costs of Building an Extension

Target Costs

It would not be unreasonable to target costs for the total build of an Extension, excluding professional fees and local authority charges, at around £1,200 to £1,800 per square metre, i.e. say £110 to £170 per square foot.

Again this depends on what is included, building complexity, local conditions, the range of building material costs, whether you want a plain wall envelope, a glulam post & beam structure, or a traditional green oak frame building, and so on.


Programming & Tragetting Costs

Current Cost Indications

Our currently suggested basic extension building costs, as noted above, are somewhat higher than those suggested by other people to allow for the higher specifications demanded by Planning & Building Regulations under the new rules since October 2010,


Overlooking Construction Costs


No Costs Allowed

Things often overlooked by DIY home extenders – whether or not they are doing any of the work themselves – are the costs of architectural design, engineering, preparing and producing the Building Regulation drawings, local authority fees for planning and building regulation submissions, and connection charges for sewage, water, electricity, gas, telephone and so on.

Elemental Extension Prices

Costs of Design & Planning for project  £1,500 - £4,000

Other Indicative House Extension Prices per m2 /metre squared

  • Skeleton Shell with Roof Covering     
  • Fixtures & Fittings                                     
  • Internal & External Decoration                   


£   700 - £   850 /metre squared
£   500 - £   650 /metre squared
£     10 -  £     15 /metre squared


On-Line DIY Pricing Help

Working out whether you can afford the home extension, loft conversion, or even new home you would like can be tricky. /metre squared

On the one-hand you don’t want to impose unnecessarily on potential suppliers or abuse their goodwill in quoting for your project. On the other hand you need to get a reasonably good idea of how much things will cost in order to work out your budgeting.

Fortunately this Timber Frame D-I-Y Pricing Guide can help you with your budgets.  While this is primarily intended for new Self-Build Houses, adding around 15% to the result will give you a good initial indication.

You can also get a Timber Frame House Design Guide in the same place.

Create Your Own Estimate On-Line

When you have a little better idea of what you are looking for, you can also create one or more of your own building budget estimates for your timber frame and design drawings on-line at Free On-Line Estimate

Online Help with Building Cost Estimates

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