A two storey extension could be the perfect way to transform your home. It is the best way of increasing living space and bedroom accommodation at the same time. It may also prove more cost-effective than building a single storey extension. A two storey extention spreads the cost of the foundations and the roof – bringing down the average construction cost per metre squared.


How much will a two storey extension cost?


Unlike material prices, labour costs vary across the UK. You might pay £70-£120 per day for a bricklayer in many rural areas up to £200-£300 per day in central London.

If you have time and good DIY skills, doing some of the work yourself will reduce costs. There are big savings to make through DIY, but it can prove a false economy if you take on too much work yourself.

The cost of project management is another big factor. A building contractor will charge 15-20 per cent on top of the net cost of labour, materials and overheads. If you get competitive tenders for the contract, you may be able to squeeze this margin. When there is less work around, this margin could reduce, as builders may take work on just to keep trading.

If you have the time and confidence, project manage the work yourself. You could save some of the 15-20 per cent margin.

Remember to consider value added tax, or VAT, which is at 20 per cent of the labour, materials and services. If your individual subcontractors turn over less than the VAT threshold, they won’t charge you any VAT on labour. This can result in a big cost savings.

As a starting point for budgeting purposes, base your costs on a figure of around £1,250 per m², plus VAT. If you are working on a DIY basis, then you will save as much as the labour you are willing to put in.


Adding value with a two storey extension


If space is the reason you want to extend your home, look at local houses with the footprint your home will have after the extension. Adding an extension may cost more than the value it will add to the property in the short-term. But yet, it can still work out as much less expensive than moving to a larger property. Remember to factor in estate agent fees, legal fees, Stamp Duty and removals fees if moving is an option.

Properties are generally valued on the basis of price per m². To get an idea of local property values, find several properties that are similar to what you propose to build. Then divide the asking or sale price by the area of the property. This will give you an average value per m².

If you compare this with the average cost per m² of your extension, you can work out whether your proposals will increase the value of your property. Be aware that there is a limit to how much value you can add to your home, known as the ceiling value.


Planning permission and permitted development for two storey extensions


Many two storey extensions can be built under permitted development rights, without the need for a planning application as long as you stay within these restrictions.

  • Your extension can’t be taller than the highest part of your roof
  • It must not extend beyond the rear wall by more than three meters
  • It has to be at least seven meters away from the boundry.
  • It has to be built in materials to match the original structure.

For homes in conservation areas, further restrictions apply.

  • You have to apply for planning permission on all extensions over one storey
  • You can’t add any exterior cladding without permission
  • No side extensions without planning permission

Where to add a two storey extension


The rear of a property is usually the best position to add a two storey extension on a terraced house or semi-detached property.

Where a property has a large outdoor area, as many houses on a street corner do, there may be the potential to extend over two storeys at the side. In some instances, an extension can wrap around multiple sides of an existing property.

If there are roof height restrictions, you could still extend into the roof space to form a one-and-a-half-storey extension. It may also be possible to dig down into the ground and build two storeys without effecting room height. This could result in a basement level or split-level design, and can work well on a sloping site.

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