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Building a Two Storey Extension

By: Chris Hogan MSc - Updated: 12 Oct 2012 | comments*Discuss
 
Extension Two-storey Single-storey

It’s not rare for a renovation project to feature an extension and it's becoming increasingly common for people to go for a two-storey extension rather than the usual single-storey.

Economics of a Two-Storey Extension

A renovation project will often be on an older property which may not have the right space and the right layout for modern family living. An extension is a good way of putting that right and going for the two-storey option makes good economic sense too. The reasons are building costs and the vagaries of the UK property market.

A large proportion of the cost of an extension goes into the groundworks and foundations and then on the roof, particularly if it is a decent apex roof rather than a flat one. To add the required courses of blocks and bricks for the second storey and then fit them out isn't such a huge increase in the cost. Some costs, like hiring, erecting and dismantling scaffolding, will probably come in at double the cost for a single-storey extension.

Double the Space for a Third More

This is balanced out by other costs which will be largely the same whether the extension is two-story or one like ground clearance. Examples are planning, building control and landscaping once the project is over. This isn't to say that a two-storey extension won’t cost more than a single-storey one, it will, and quite a bit.

But it won't cost twice as much, that's the point, so the cost per square yard is a good deal lower. Depending on the design and specification of the extension you might find that a two-storey extension costs somewhere between 25% and 33% more than a single-storey one with the same footprint.

Property Price Hike

A two-storey extension will also add proportionally more to the price of the property. This is because of the slightly odd way of categorising houses in the UK, where the number of bedrooms is given more importance than almost anything else.

So if you can add a two-story extension with an extra bedroom to a property it will shift the property into the next price bracket. You won't get the same price increase by building putting a conservatory or a single storey kitchen and dining room extension.

There are other knock on benefits as well. With any building project you get disruption; noise, dust and dirt. Again there is a disproportional effect; you won't get twice as much disruption from a two-storey extension build, more like 50% more. Unfortunately the disruption will be on both levels of the house, so it will be harder to keep the dust and dirt out of the house.

Planning for Success

Finally, don't forget to look closely at the planning issues. You may be prevented from building a two-storey extension, in which case this is all academic. Take a look at the area, your street in particular, and see if a two-storey extension has been grafted on to any other property.

If it has then you are likely to be alright. If not, pay close attention to how it will look from your neighbours' points of view and make sure you take that into account in your plans.

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