Cost of a side or rear house extension in the UK

WRITTEN BY Karen Lawrence

A well-designed extension can give you the home you want and the space you need - much cheaper than moving house. But how much does a home extension cost? It’s a common question, but one that’s very hard to answer without going into a lot more detail.
If you’re thinking about a side or rear extension to your property, here are a few rules of thumb to give you a starting point, and some ideas to help keep the costs under control according to your budget.

How much does it cost to add a side or rear extension in the UK?

Depending where you live, the cost of an extension can vary considerably according to the size, design, materials and standard of finish you want. In London and the South East – generally the priciest – the build cost for a single-storey extension, using standard off-the-shelf materials and fittings, might start at around £1,500 - £2,000 per square metre (m2) and rise according to specifications. In other parts of the country, you might find it’s a little cheaper, at around £1,200 - £1,500/m2.Don’t forget that you’ll also need to budget for fees such as an architect and structural engineer, planning and building regulations applications, and VAT.

Should I choose a side extension or a rear extension?

Your choice will be determined by the layout of your existing property, the space you have available and what you want to achieve. A side extension can be great value for money. As Tom Bentley, Operations Manager at Refresh Renovations UK, says;
“A side return extension is an excellent way of making use of ‘dead space’. That extra four feet may not seem like a big gain but it can dramatically transform a kitchen, especially if you add a glass roof to illuminate the space”.
On the other hand, a rear extension can give you even more added space, as well as the opportunity to open up the back of the house with glazed sliding or folding doors. Unless you have a very large garden, though, you’ll need to weigh up the loss of outdoor space against the increased internal floor area.

Will I need planning permission to add a side or rear extension?

If it meets certain conditions, your extension may be classed as ‘permitted development’ – which means you won’t need to apply for planning permission. This normally covers small extensions to the side or rear of a house, whose appearance is in keeping with the original building.
Your renovation specialist can give you further advice, but if your home is a listed building, or on designated land such as a conservation area or national park, you will need planning consent. 

What can you achieve with a basic budget?

If your budget is limited, a single-storey extension is usually the most affordable. Try to avoid moving services such as plumbing and drainage and keep structural work to a minimum; non-loadbearing walls are much cheaper and easier to remove, so you can still change your layout with careful planning.
You can maximise the extra space in your home, within your budget, if you choose simple finishes and fittings. Stick to painted walls and carpet or laminate floors and, if you’re re-fitting a kitchen or bathroom, look for value off-the-shelf ranges.

What can you achieve with a mid-range budget?

A mid-range budget will give you greater choice of finishes such as tiling or fitted joinery. Sliding or folding doors are a popular addition and can create a flexible indoor/outdoor space, ideal for entertaining and for young families.
Opening up rooms by removing structural walls is an option, and you can make the most of the available space by building a two-storey extension on the same footprint. This could give you an extra bedroom and en-suite bathroom as well as more living space, or alternatively allow you to make a design statement with a double-height feature.

What can you achieve with a high-end budget?

With a bigger budget, the sky’s the limit. An experienced architect can help make your dreams a reality by remodelling your entire home to incorporate a larger extension.
A bespoke staircase, linking old and new areas of the layout, can give an extension real ‘wow factor’. Building work is likely to change the shape and size of your outdoor space, so think about remodelling the garden at the same time. A professionally-designed terrace, outdoor kitchen and garden lighting will transform your outside space into a year-round feature.

You might be interested in reading this article: How much does it cost to create an indoor outdoor flow?

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*Costs are rough estimates and are subject to change. For a fixed-quote accurate to your specific project, please consult your local Refresh Renovations specialist. All Refresh Renovations franchises are independently owned and operated.