​The average price of building 20sqm extenson will cost between 25000£ to 35000£, so the basic price is 1250£ to 1750£ per square metre. The price bracket reflects the variance of materials used, the complexity of design and the quality of finishes. 

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How long do home extensions take to complete? 

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The length of time it takes to build an extension will obviously depend on the scale of the build, without even including any time spent drawing up plans and obtaining planning permission (which can take several months in and of themselves). A rough time-frame would be between three and four months, from the start of the project - clearing the space and digging the foundations, adding the finishing touches, and dealing with any snags you encounter. Delays are common, and are often due to bad weather, changes in the plans, and hold-ups in materials being delivered. With multiple trades working on an extension, backlogs can also occur; for example, plastering can only be done after the electrics and plumbing are in place, so a delay to one will create a knock-on effect for other work to be finished.

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Double vs single storey extension costs

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Many sources claim that a second storey will be priced at only half or two thirds of the cost of the first floor (so if the single storey extension is 20msq and costs £25,000, the second floor could be an additional £12,500, for a total of £37,500). However, the majority of extension builders will price a job based on the total square meterage - so a two-storey extension with both floors of 20msq floor space will be £50,000.

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While it may seem intuitive that the ground floor is the more labour intensive element because of the groundwork and foundations that must be completed, there are a number of additional costs involved in a second storey that are not applicable to a single storey project. Using scaffolding, working at height, increased structural integration with the original building, changing the roof - all of these factors serve to ultimately balance out the cost.

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Masonry vs timber frame extension costs

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Masonry, or “brick and block” construction has been the most common way of home-building in the UK for nearly a century, but timber frame projects are becoming more and more common.  Masonry construction sees the structural element built from blocks, with brick or another form of exterior cladding added around it, whereas timber frame uses wood to construct core panels that are assembled on site.

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Both have benefits and drawbacks in terms of speed of construction and their structural benefits, but in terms of cost, as stated above, the two methods are fairly equivalent.

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Bathroom and kitchen costs

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The two biggest additional factors that can impact the overall cost of an extension is if you plan to install a kitchen or bathroom in the new space.  The price of new kitchens and bathrooms vary widely depending on your requirements and the quality of the products you choose to buy.  The  typical price range for fitting a bathroom may range from £3,000 to £12,000, while a kitchen could cost anywhere from £7,000 to more than £25,000.

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