Author Tom Norris
In my earlier blog, How Much For An Extension, I pointed out that the main factors influencing extension build cost per square metre were location, design and size.
Other factors, include the type of extension as some extension types work out significantly cheaper per sq metre than others.
Lets start off with listing the most popular types of extension. For example the most popular extension designs are:
The rear extension is definitely the most popular type of extension mainly because this is the only option for terrace houses apart from doing the loft.
In most cases this type of extension is a single storey extension and the average build size is around 5 metre x 3 metre.
Average build costs per square metre for this type of extension is £3,333 but this cost is subject to other factors such as location, design, and quality so don’t just jump in thinking this is how much your extension is going to cost.
Over the past 20 years side extensions have become the norm for extending period terrace properties with the long back addition. In many cases the garden is a little small on these types of property but the space down the side was rarely used and made an ideal extension area.
The main drawback is on the side extension is that you could only go out about 1.5 / 2 metre and in order to open plan or link the extension to the main back addition room a considerable amount of structural work is involved resulting in expensive costs for surveying, structural engineers reports and possible underpinning.
All of these costs and a restricted extension dept usually contribute to pushing the build costs per sq metre past £5,000. If you’re unlucky enough to have a chimney on the side return wall then the costs will be even higher as the chimney will have to be stripped out the whole way up including the roof stack.
For the uninitiated I can tell you that a wraparound extension is a common term used to describe a combination of a side and rear extension usually added to period properties with a back addition.
If you’ve ever visited a property that has had a wraparound extension added then you will no doubt agree that this is the Rolls Royce of extensions because if they are done well they provide absolutely fantastic living spaces for modern lifestyles.
When it comes to cost they clearly have a larger footprint which means that overall it will cost more. The good news however is that wraparound extension cost per square metre go down to around £4,250.
The 2 storey extension is most commonly added to the side of the property rather than the rear. Semi detached 1930’s properties are ideally suited for this type of extension.
Average size of a 2 storey extension to the side of a property is considerable as they tend to be the full length of the house by around 2.5 metre. Overall, around 40 sq metres / 400 sq foot.
You might be thinking that the build costs for a 2 storey extension of this size is going to cost a fortune but surprisingly it has one of the lowest extension costs per square metre.
For starters it may well be that one or both floors of the main building are in pebbledash making it cheaper and quicker to build a block wall with dash or render as the finish.
Extending a hipped roof is far cheaper than roofing with slate which is what is mostly required on older properties. Neither will you need roof windows that are usually installed on a single storey extension.
Build costs for the second floor are usually about 35% cheaper than the ground floor which means that your overall extension costs per square metre will be lower than that of a single storey extension.
If the extension was 40 square metres overall then that works out at 20 square metres at £3,333 per square metre and another 20 square metres at £2,166 per square metre.
Overall you end up with a square metre build cost of £2,749 making it an extremely good value for money extension.
This type of extension has becoming increasingly popular on the 1930’s type of property with garage. In some instances it is a simple matter of building up on the existing garage walls but this is not always possible as the garage walls on some properties are substandard with regard to wall thickness, 4.5” rather than a full 9” brick, and have foundations that are not strong enough to support two floors.
If this is the case it may well work out more expensive than doing a full 2 storey extension because the cost of removing the existing garage or bringing it up to scratch will involve additional works.
Generally speaking it is a great way of extending to get additional bedrooms or bathrooms and on a worst case scenario the build cost per square metre shouldn’t work out more than £3,000 per square metre.
Build Costs Summary:
Take the numbers with a pinch of salt as there many variables to consider. The build costs below are based on averages with regard to location, design and quality:
To find our more about extension costs and the various prices for different kinds of extension, check through this blog routinely as we are in the process of providing more costs for almost every type of house extension.
In the meantime the best way to get accurate extension costs is to Post an Enquiry here at Price Devils and get up to 4 comparative quotes from local builders.
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