15 single storey extension ideas under £100,000

Find inspiration for your own home transformation with these beautiful single storey extensions, all of which cost less than £100k

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Budgeting £100,000 on building a single storey extension? And why not, adding an extension is an effective way of increasing the size of your home, as well as it's value, and is likely a cheaper solution than moving house. 

If you've read our guide to building a single storey extension and are looking for inspiration for your own project, you're sure to find it with our selection of the best extensions; all of which come in under £100k.  

Find more tips on building an extension under £100,000 and check out our kitchen extensions under £100,000 for more design ideas, too.

1. A £55,000 oak and steel finish extension

The design brief: The family that owns this 1930s semi-detached house in Manchester wanted a larger kitchen, laundry space, a bigger dining area and a downstairs WC. Lisa Raynes of Raynes Architecture relocated the kitchen to where the dining room was and designed a single-storey oak-clad, steel- framed extension across the back to create a living/dining space, featuring an overhang with lighting over the bi-fold doors.

The cost: The project cost £55,000 for design, materials, construction, and underfloor heating.

Raynes architecture extension

2. A £46,500 extension with matching facade

The design brief: The owners of this Surrey home wanted a single-storey extension to form part of a new open-plan kitchen area. Urban Jungle Construction created the design, at the front of the property. It had to incorporate the side-supporting wall and not compromise the property’s external Victorian appearance. Reclaimed bricks were sourced to match the original brickwork, and new bargeboards templated and made to match the existing external decoration.

However, to keep the look simple, the owner didn’t want a new final, nor to use white in the soldier course of brickwork around the new window. Inside, new steels were inserted into the ceiling cavity rather than below it, to create a level internal ceiling.

The cost: The project cost around £46,500 for materials and construction.

Urban Jungle Construction

3. A £70,000 side return extension

The design brief: To create a room of dimensions more appropriate to the size of this detached villa in Salisbury, Wiltshire, architect Haydn Bennett designed a single-storey side return extension to fill in the corner between the house’s front main section and the narrower rear wing.

Part of the wall containing the window was removed, and although a new window provides light and a garden view, there was limited room for it. To keep the space bright, a strip of roof glazing was incorporated between the house wall and extension roof, extending to create a back door canopy. Oak beams project to carry the roof overhang.

The cost: The project cost £70,000, including materials and construction.

Hayden Bennet extension

4. A £92,400 kitchen extension

The design brief: Architects Jeff Kahane + Associates designed a new kitchen extension for this north London Victorian terraced house. Permission was obtained to retain and extend the roof terrace, and the materials used echo the industrial style of the kitchen. The owners preferred spray-finished timber doors and windows to bi-fold doors, and steel sheet balustrade panels minimise the shading of the neighbours’ terrace.

The cost: The project cost £92,400 for materials and construction.


5. A £95,260 barn-inspired extension

The design brief: The owners of this listed Suffolk cottage called upon Hartog Hutton to advise on extending their home to accommodate a growing family. Using black weatherboarding and an oak frame, the extension replaced a dilapidated single-storey barn attached to the house, adding two bedrooms, a bathroom, store rooms and a garage. Welsh slate for the roof was a requirement of being a listed building, while the pitch had to replicate the existing shallow one.

The cost: The project cost £95,260 for materials and construction.

Hartog Hutton cottage extension

6. A £60,000 contemporary kitchen diner extension

The design brief: Architects Dittrich Hudson Vasetti were called in to improve a Bristol home with an existing lean-to kitchen extension, the proportions of which were too small for the house. The owners wanted a new space for cooking, eating, entertaining and relaxing, and a separate utility room.

Building into the side return created a dining area open to a new contemporary kitchen and the more traditional living space of the original house, while the previous extension was reconfigured to create a utility room. Triangular glazing above the black aluminium bi-fold doors, together with rooflights, maximises light. White-painted render ties it in to the rest of the house.

The cost: The project cost £60,000, including the kitchen and utility room.

Dittrich Hudson Vasetti kitchen extension

7. An £85,000 orangery extension

The design brief: David Salisbury was tasked with creating an orangery-style extension in Stone, Staffordshire. The owners wanted to open up the house, creating a larger kitchen, dining space and relaxed seating area for entertaining; introducing natural light was also key, to take advantage of the fabulous views. Bricks were matched to the existing house, windows finished in a Shaker cream shade, and the interior mirrors the existing kitchen.

The cost: The project cost £85,000 for materials, construction and electrical work.

David Sailsbury orangery extension

8. A £30,000 glazed side return extension

The design brief: The owners of this west London house asked IQ Glass to open out their narrow kitchen. A rear extension wasn’t an option due to their small back garden and proximity to neighbours, so the side alley was used to gain extra space, with a glass roof included to compensate for the loss of a window and to make the space brighter.

A fixed design using grey aluminium casement doors has created sufficient ventilation and saved on cost, and brick slips are featured to match the house.

The cost: The project cost around £30,000 including a glass roof, party wall connection, supporting metal works, rear aluminium doors and pressing covers to external drainage.

IQ Glass kitchen extension

9. A £100,000 timber clad extension

The design brief: The owners of this East Sussex house asked architect Alan Cronshaw of Acronym to create more living space. The side and rear extension is constructed from a timber frame clad in locally sourced sweet chestnut, in contrast to the symmetrical 19th Century red-brick property. Two rooms were knocked through into the extension, and rooflights incorporated with bi-fold doors to connect house and garden

The cost: The project cost just under £100,000 for materials and construction.

Find more ideas for cladding your home's exterior in our feature.

Chiddingly Private House by Acronym. Architecture and Interiors photography by Jim Stephenson / clickclickjim

10. A £70,000 period-style extension

The design brief: English Heritage Buildings’ managing director Darren Hook wanted to extend the kitchen of his own home in East Sussex to create a larger, light-filled space for year-round use. Materials had to match the existing house as a planning requirement, and oak is used internally, including beams in the roof space. Pitched and flat sections create a lower roofline underneath first-floor windows, and a glazed roof lantern maximises natural light.

The cost: The project cost £70,000 with materials and construction.

English heritage kitchen extension

11. Design a modern, family-focused space

The design brief: Creating space for the family and plenty of storage were essential for the owners of this house in Wimbledon, London, when they asked Architect Your Home to reconfigure their small dining room and design a rear extension.

The resulting space is a open plan kitchen, dining and living room area, together with a utility room and a separate WC. Their architect also made sure that the new extension incorporated sufficient storage for the children’s toys. Bi-fold doors were part of the brief – they connect the extension to the garden and achieve the contemporary feel the owners wanted.

The cost: The project cost £90,000 for materials and construction.

Find out how to design an open plan kitchen diner in our guide.

architect your home rear extension

12. A £54,000 conservatory extension

The design brief: Apropos was tasked with designing an extension to provide a second living room with great garden views for this Berkshire house. The owners requested a traditional aesthetic, with the look of an orangery, so a full glass roof ensures the new room is filled with light, with automatic ventilation to ensure that the space doesn’t overheat.

The Pilkington Activ Blue glass used is self-cleaning, and bi-fold doors open out at one end of the new extension to link it with the decking and garden beyond.

The cost: A similar design would cost around £54,000, including design, optional planning, materials, delivery, construction and installation.

Apropos extension

13. A modern £87,318 extension with streamlined cladding 

The design brief: The desire to rework this 1930s house in Bristol led its owners to call on Moon Design + Build. An extension of the ground floor was required to create an open-plan space with a living room, kitchen and dining area, together with a separate home office, providing a generous space for the family to spend time in. Clad in cedar with extensive glazing, the timber-framed extension also has a lift-and-slide door that links the living spaces to the garden.

The cost: The project cost £87,318 for construction and materials.

14. A £54,000 glazed kitchen diner extension

The design brief: With extensive renovations already underway, the owner of this Manchester property called on Apropos to design a glass extension for an open-plan kitchen and living area. A lean-to conservatory takes advantage of the generous rear width, and bi-fold doors open out to a new purpose-built deck, which more than compensates for the loss of outdoor space.

The cost: A similar structure would cost around £54,000 including design, optional planning, materials, delivery, construction and installation.

open plan kitchen extension apropos

15. An £84,000 glass box extension

The design brief: The owner of this Grade II-listed London home wanted to create a large open-plan kitchen and dining area on the lower ground floor of the property. As a preferred brick extension wasn’t allowed under planning regulations, which called for a glass extension, APD Interiors negotiated with the council and reached a compromise agreement, designing a structural glass box extension for the lower ground floor.

This means that the new kitchen can be used in natural light, and a new shower room has also been created on the floor above. As there was no access to the rear of the property, all the building materials had to be brought in through the house, including the glass and five-metre steels – a challenge that also had to be factored in to the design of the project.

The cost: The project cost £84,000 for construction and materials, including the glass box.

grade II listed house extension by APD interiors

Want to get started on your dream extension? Our handy guides are here to help: