Designing a single storey extension

Find out how to design a single-storey extension that complements the existing property and creates the space you need

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The design of your single storey extension is the most important decision you will make during your project. It will dictate cost and appearance, so it pays to make sure you are happy with the design, that it is cost effective, and that it even raises the value of the property.

Single storey extension footprint

While usually determined by the space required within the property, the footprint is defined by factors such as the proximity to neighbouring boundaries, the position of existing windows, and its orientation towards light, views and garden area.

Planning constraints will also be a factor, although many smaller single-storey extensions will fall within the criteria for permitted development, and so will not need a planning application. It is essential at this stage to consider the roof design – in particular, the height of the ridge and the impact on existing first-floor windows.


Related articles: The ultimate guide to extending your home | Planning and costing your single storey extension | How to add a two storey extensionThe free Real Homes extension cost calculator

How to choose a roof for a single storey extension


A smaller, narrower extension can usually be covered by a mono or duo pitched roof, however, the spans that can be achieved are very limited. A very low roof pitch may be an option, but this may not work aesthetically and could cause problems when obtaining planning permission. Intersecting pitched roofs can work, but often a flat roof is the only solution for a larger extension.

In this instance, there are only a few design styles that really work, and the choice is between a contemporary flat-roofed “box”, usually featuring a lot of glass, an orangery-style extension, or a more traditional conservatory. Another option is a parapet roof – this has an area of pitched roof around the eaves, which conceals a flat roof over the extension and gives the appearance of a traditional pitched roof.

Doors and windows


There are few constraints on the position of doors and windows, unless they will impact directly on neighbouring boundaries. Their size, style and position should be determined by the extension’s architectural style – this being one of the most important defining features. The opportunity to bring light in from above the single-storey extension, such as with rooflights, should not be ignored.


Traditional single storey extension

Adding a single storey side and rear extension to a detached house to update a dated 1970s kitchen into a spacious kitchen-diner.

The design: A side and rear extension to a detached house

Simon smith traditionsl extension before


Simon smith traditionsl extension


‘The owners asked us to turn the small existing kitchen area into a space where they could cook and still feel connected to family life. With this in mind, we created a discreet side and rear extension that mimics the proportions of the original property and measures 14 metres in length. It forms an open-plan space that spans the front to the rear of the house, with a breakfast room to the front and a kitchen at the back.

‘There is a bespoke roof lantern to bring natural light into the extension, plus glazed double doors to the rear and side now connect the internal area to the tiered garden, improving access to the outside space.

‘As well as installing rooflights, we used reflective materials to maximise the daylight, which is important to the feel of the extended ground-floor space. While most of the ground floor is now open-plan, a separate central area, which receives the least daylight, has been used to create a utility room.’

Simon Smith


Garden room extension

Replacing a conservatory with a full width rear extension to a detached house in a Conservation Area.

The design: A full-width extension to a detached house

PD architects garden room extension before


PD architects garden room extension


‘Although the extension was quite large for a Conservation Area, and beyond the homeowner’s permitted development rights, the planning authority took the view that building a sympathetic design with the same footprint as the existing conservatory would be an improvement.’

‘Internally, the feature glazed gable, vaulted ceiling and rooflights help to provide a light, contemporary and luxurious feel in the new space, and shed ample light into the rooms behind. The extension was painted to merge old with new, and the existing natural slate roof was replicated on the extension to achieve a simple and consistent look.’

-Paul Day

The materials


Matching existing and new materials so they join seamlessly is often desirable, but is very difficult to get right. Choosing contrasting but complementary materials can work equally well, and is often a much easier alternative.


Single storey kitchen-diner extension

Adding a kitchen-diner extension with a level threshold leading out to the garden to a detached house.

The design: A single-storey kitchen-diner extension to a detached house

Apropos kitchen diner extension before

Apropos kitchen diner extension

‘The owner wanted a light, airy open-plan kitchen-diner and family living space. We designed an orangery to suit both the original style of the the L-shaped house and the previous extension. The new space has bi-fold doors to bring the outside in, plus a rooflight to add height and light to the kitchen area. The result is a highly functional, modern living space, perfect for a growing family to live and entertain in.’

-Paul Schofield


Contemporary single storey extension

Adding a rear and side-return extension to a terraced house to create a kitchen-diner with a seamless link to the outdoor area via folding-sliding doors.

The design: A single-storey rear and side return kitchen-diner extension to a terraced house

Riach architects contemporary extension before

riach architects contemporary single storey extension

‘We were asked by the owners to create a light-filled rear extension that would result in a family-sized kitchen, dining and garden room. The existing groundfl oor walls at the rear of the house were removed so that the first-floor accommodation appears to float above the new open-plan room, giving the period property a new contemporary facelift. Large, glazed folding-sliding doors link the new room to the garden for a practical, family-friendly space, with integral roof windows that serve to create a spacious and bright area.’

-Corin Rae

Open-plan extension

This 1920s mid-terrace house has had a single storey rear extension and a loft extension added to house a large, open-plan kitchen, dining area and living space for the whole family

The design:A single-storey rear infill and loft extension to a terraced house

Simon smith massive open plan extension before

Simon smith massive open plan extension

‘This large 1920s mid-terrace property was in need of a complete overhaul. It hadn’t been updated during the last 50 years, but was in a good structural state. All the services were in need of an upgrade, and the owners wanted to reconfigure each floor to optimise the flow between different areas and maximise space.’

‘The vision for the kitchen, dining and family living space at the rear of the house was achieved with an infill single-storey extension leading on to the garden, which created a safe place where the children could play and the adults entertain. The flat, modern rooflights bring natural light deep into the room.’

‘The aim was for the extension to flow seamlessly into the outdoor space. This was achieved with a threshold that sits flush with the patio level, and bi-fold doors that stack neatly to one side. Mood lighting highlights the tiered garden to create a stunning view from inside the house.’

-Simon Smith

Small scale extension

Adding a single storey extension to a semi-detached house and converting the loft to create an extra bedroom. The extension, plus a reconfigured ground floor layout, has made room for a family kitchen-dining area.

The design: A single-storey rear and loft extension to a semi-detached house

architect your home small rear extension before

architect your home small rear extension

‘This house was in need of a complete refurbishment, so the brief was to extend and reconfigure the existing ground floor to create a large family space, as well as adding an extra bedroom upstairs.’

‘Most of the additional space that the homeowner wanted downstairs was found by remodelling the existing rooms, and therefore the size of the extension itself was fairly small. Adding two sets of doors has enabled direct access to the garden from the extended dining and living areas.’

-Jude Tugman