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Window extensions

Single Storey Extension Guide

The Sterlingbuild Guide to Single Storey Extensions

Single storey extensions are still the go-to choice for most homeowners when expanding their property. Here are the important things you need to consider along with our recommendations of the best products to complete your new space.



Why you should build a single storey extension

Move or improve? A question many homeowners have asked themselves upon realising they have outgrown their living space. When all costs related to upscaling and upheaval are considered, it is understandable that many decide to stay put and extend their homes, saving a lot of time and money in the process.

Single storey extension are the most popular type of home extension. This will usually take the form of a rear extension or side extension. 

Rear extensions have become increasingly popular in recent years as the benefits of sacrificing a few metres of garden space to make way for an enlarged, open-plan living area have become abundantly clear.

VELUX flat roof windows for single storey extension
aluminium bi-folding doors for single storey extension or kitchen extension

Single storey extension ideas

Whether your single storey extension is covered by a flat roof or pitched, in order to create a new space that is light, welcoming and spacious for friends and family, the right choice of rooflights or pitched roof windows can make the world of difference.

With the sun being the most powerful source of energy we have, it makes sense for us to make maximum use of it. A VELUX extension using VELUX’s roof windows will keep your room warm and reduce the need for artificial light during the day, while also saving you on energy bills. ECO+ and VELUX's sister company, RoofLITE, are also smart, value for money single storey options. ECO+ have both roof windows and flat rooflights to cover all roof size and pitch requirments.   

Popular open-plan living designs that involve extending the dining room out towards the garden are tailor-made for the installation of REAL aluminium bi-fold doors.

Pitched roof or flat roof?

The type of roof that you choose will define the overall look of your extension and will be the cornerstone of your new living area. Flat roofs are generally cheaper than pitched roofs as there is likely to be less building work involved. Flat roof windows are available in a variety of styles, including showstopping lanterns and pyramids, a speciality of UK manufacturer Korniche.      

However, though usually more expensive to construct, pitched roofs allow for a bigger space as the ceiling can be higher underneath and the appearance of the roof is known to blend in more effortlessly with the existing building. 

Another benefit of choosing a pitched roof for your extension is that it allows for greater insulation than a flat roof. 

If you need to work out the pitch of your current roof for the purpose of building an extension, guidance can be found in our Flashings Buying Guide.

VELUX pitched roof windows with pine finish for single storey extension
VELUX white velux windows for pitched roof and single storey extensions

How much does a single storey extension cost?

The cost of a single storey extension will depend on the scale of your project and where abouts you live in the country.

A basic extension would typically cost around £1,000 per square metre meaning a 3 x 5 metre single storey extension, for example, would set you back £15,000.

While the bulk of outgoings will go on building materials and features, approximately 10% or 15% of your budget is likely to spent on professional fees such as an architect and building regulations.    

Important things to consider

Planning permission for extensions is first thing to think about, whether you think you need it or not. The Planning Portal can provide a full picture on the limits and conditions to your conversion.

If objections are received to your expansion by neighbours, a Neighbour Consultation Scheme will take place to see if you can proceed with your home improvements.

You will also need to consider the Party Wall Act that covers the construction of a new building on or at the boundary of two properties. It is therefore worth informing your neighbours of your plans before the council does- their early approval could save you a lot of money!

Contact a ‘building control body’ (BCB) to check a full list of building regulations appropriate to your property. This can be done via

Visit our Loft Conversion Guide for guidance on who can help with your extension.

VELUX flat rooflights for home extensions