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Side Extension Ideas with Project Cost and Build Inspiration

oak frame side extensions to rendered cottage
(Image credit: Nikhilesh Haval)

These side extension ideas offer inspiration for clever ways to add more space to a detached home, and go to prove that where you have multiple options for extending out, a side extension may well be your best bet. 

Whether you want a single or two-storey addition extending out to the side, the available options are incredibly varied. Plus a side extension can be contrasting and bold or sympathetic and subtle — creating great kerb appeal either way. 

Below are stunning examples of building an extension from real projects to inspire your aims to add more space to your home. 

Are Side Extension Ideas Worth It?

"Side extensions are an excellent investment, especially for period properties that tend to suffer from L-shaped rears, caused by defunct alleyways," explains Richard Morgan, Head of Design at Resi (opens in new tab)

"By squaring the property off with a side extension, homeowners are able to create a much more intuitive floorplan, one that’s better suited to modern open plan trends.

"They’re also able to get a lot of new space without having to sacrifice any premium garden space — a common frustration of more common rear extension projects. And, much like rear extension ideas, side additions can fall under your permitted development rights, removing the stress of needing a full planning application."

1. Add a Side Second Storey to a Bungalow

double-storey side extension to bungalow

(Image credit: Richard Kiely)

This 1960s bungalow had been renovated by the homeowners to suit their lifestyle, but after living in the house for a few years, the family acknowledged they needed more space. 

Blessed with a generous garden, a double-storey extension was added to the side in order to make the most of the views across the Cotswolds countryside. 

  • Build cost: £195,000
  • Location: Gloucestershire

2. Add a Small Extension That Makes All the Different

white kitchen with small side extension

(Image credit: Paul Arthur)

Improving the layout of their dated terrace was top of Amy and Gareth Andrews' list so Amy designed a small side return extension and knocked down an internal wall to create an open-plan kitchen, dining and living space. 

The build was completed under Permitted Development and to a tight budget — with Amy, Gareth, family and friends taking on much of the work themselves. 

  • Build cost: £70,000
  • Location: Worcester

3. Create a New Kitchen in a Side Extension

kitchen side extension to barn conversion

(Image credit: Jean-Christophe Godet & SOUP Architects)

While this Grade-II listed barn was being converted, a timber frame extension was added to house a new kitchen and dining area by SOUP Architects (opens in new tab)

Although the homeowners were keen to have an open plan layout, they were also aware that they didn't want the entire house to be a single space, so used a glazed link to provide a porch area between the two structures.

  • Build cost: £425,000 (including barn conversion)
  • Location: Guernsey

4. Open up a Terrace with a Side Return

rear side return extension to terrace house

(Image credit: David Barbour)

Despite originally considering a wrap around extension, an elegant side return extension to this typical terrace has opened up the cramped exteriors into a modern and sociable hub. 

The previous layout didn't connect to the garden at all so inspiration was drawn from glass extension designs to create a sun-filled kitchen and diner. Large bifold doors open the kitchen onto the patio area, while a bank of rooflights along the lean-to extension keep natural light flowing deeper into the floorplan. 

  • Build cost: £180,000 (including dormer loft extension)
  • Location: Hertfordshire

5. Replace Unsympathetic Extension with a Natural Fit

side extension to a listed cottage with matching roof line

(Image credit: Mark Bolton)

Replacing a conservatory with an extension was top of the list when Charlie and Rosie Thomas were faced with various inappropriate additions to their Grade-II listed cottage. 

The new side addition with beautifully balances contemporary and traditional styles. Attention to the tiniest details makes a huge difference in this extension, from the timber-clad 'boxes' which hide the gutters to the combination of reclaimed stone, slate, metal and glass materials. 

  • Build cost: £82,000
  • Location: Wiltshire

6. Extend into a Nearby Garage for an L-shaped Side Extension

bungalow side extension into garage

(Image credit: David Barbour)

Reluctant to knock down and replace their dated bungalow for environmental reasons, Sally and Alistair Campbell commissioned Konishi Gaffney Architects (opens in new tab) to explore bungalow extension ideas. They crafted a radical remodelling scheme which would include a small side extension and garage conversion to create an L-shaped layout. 

Energy-efficiency was also at the heart of this project as an external cladding system of 180mm insulation panels, combined with banks of solar panels and a ground source heat pump, were used. The house is now a net contributor to the grid. 

  • Build cost: £454,336
  • Location: Edinburgh

7. Reorientate a Layout with a Side Porch Extension

zinc roof to glass extension with matching porch

(Image credit: Mark Ashbee)

This old coach house previously had the front door located within the glass box dining room extension (the white door frame is still visible here), but an ingenious decision to re-route incoming traffic into a front porch has completely transformed the layout for the homeowners. 

  • Build cost: £110,000
  • Location: Chipping Campden

8. Contrast Materials in a Side Extension

Granite side extension idea to farmhouse

(Image credit: Nigel Rigden)

When extending this traditional granite farmhouse in Aberdeenshire, a side extension which matches the height and pitch of the existing roof has been used for a cohesive look. 

However, rather than trying to imitate the existing stonework, matching materials for the extension complement the original building, with larch cladding and a stainless roof still reflecting the rustic location of the property. 

  • Build cost: £466,500
  • Location: Aberdeenshire

9. Give a House a Whole-makeover While Adding a Side Extension

Traditional style side extension idea to a bungalow

(Image credit: Simon Maxwell)

This small, but charming 1940s bungalow in Kent has been given a dramatic makeover with a new oak-framed side extension by Border Oak (opens in new tab). By adding a double-storey extension, the property's floor plan increases hugely. 

However, a large design could alter the dynamic of the building if not matching the existing home, but the eye catching but sympathetic oak frame extension is a good fit for the original bungalow. 

  • Build cost: £200,000
  • Location: Kent

10. Contrast Old and New When Extending a Period Home to the Side

Glazed side extension to cottage

(Image credit: Simon Denison)

A modern glass side extension may seem like an unlikely pairing for this old cottage located in Powys. However, it goes to prove that creating a contrast between old and new is an effective way of extending period buildings. 

Rather than trying to recreate the architecture of the original building, this extension highlights the transition between old and new, in a way working better to preserve the cottage's architecture by not trying to pass an extension off as part of it. 

This glazed link connects the existing cottage with two once derelict barns, unifying the structures to create a family home.

  • Build cost: undisclosed
  • Location: Powys

11. Include Amazing Glazing in a Show-stopping Extension

Dramatic oak-frame side extension to bungalow

(Image credit: English Oak Buildings)

This small bungalow has been transformed by a dramatic oak frame side extension. By using floor-to-ceiling glazing, including the glazed gable, the design is stripped back in its use of extra materials, helping the new addition amalgamate with the existing house and offering reflections of the beautiful woodland surroundings. 

  • Build cost: undisclosed
  • Location: Cornwall

12. Play with the Roof Pitch of a Side Extension

side Extension to lochside house

(Image credit: Nigel Rigden)

This unusual side extension idea with a pitched roof intersects the sloping roof of the original house, creating a new, unique profile. Locating the extension on this side of the house helps to add more space, without detracting form the beautiful views of the loch. 

The converted lochside barn was extended to house utilities and the new volume has been clad in larch to compliment and contrast with the original stonework.

  • Build cost: £200,000
  • Location: Highlands

13. Use a Side Extension to Double the Floorplan

Glazed side extension to cottage

(Image credit: Luke Foreman)

Finding a contemporary extension style for a thatched cottage is a challenge indeed, but this project sees a highly glazed extension used effectively to double the size of this 17th-century cottage. 

The use of modern white render and a huge volume of glazing helps to keep the two wings of the property separate, but without an awkward transition between the spaces. 

  • Build cost: £210,000
  • Location: Oxfordshire

14. Connect to the Garden with a Side Extension

Curved side extension idea

(Image credit: Simon Denison)

This single-storey curved addition has been roofed in stainless steel to provide a writing room, utility room and kitchen/dining room for this Art Deco property. The curved extension has prevented the home becoming too linear in its design, instead enveloping the new patio in the garden. 

  • Build cost: £392,000
  • Location: Bath

15. Match a Side Extension with a Farmhouse Style

Side extension to farmhouse

(Image credit: Dave Burton)

The homeowners of this period farmhouse have added space with a sympathetic side extension. It was a challenge to source reclaimed bricks to match the original house, but was an essential step in ensuring that the extension looked the part when complete.

  • Build cost: £60,000
  • Location: North Yorkshire

Can I Build an Extension on the Side of my House? 

“Your extension will need to comply with the Building Regulations," advises homes journalist Rebecca Foster. "In order to do this, it’s best to submit a Full Plans application — commissioning and submitted Building Regs plans that show the building control inspector how to extension conforms prior to the work commencing.

"Building work involving work to boundary wall between your house and your neighbours needs to comply with the Party Wall Act and, as part of the process, you’ll need to serve a party wall notice to adjoining neighbours."

Do I Need Planning Permission for a Side Extension?

"Under the permitted development changes, homeowners can add a single or double-storey side extension under Permitted Development Rights," says Richard Morgan of Resi. 

"However, it’s worth noting that the planning permission rules around two-storey extensions are more complex, so we highly advise working with a designer and securing yourself a lawful development certificate to avoid falling foul of the scheme. 

"You should also check Article 4 isn’t in effect in your area, this is when your local authority suspends permitted development rights and is usually in effect in and around conservation areas." 

Here's what you need to consider:

  • The extension cannot sit forward of the principal elevation
  • It should be built using similar materials
  • If it is within 2m of a boundary, the eaves cannot be higher than 3m and not taller than 4m otherwise
  • The width of the side extension must not be greater than half the width of the original dwelling

If you are looking to extend outside of this criteria, then you will need approval from the local planning department.

If in doubt, always check with your local authority before starting any building work, You can also see the planningportal.gov.uk (opens in new tab) for a full list of caveats.

What is the Average Cost of a Side Extension?

"The cost of a side extension will vary widely depending on your location," says Richard Morgan. "However, on average, a 30m2 side extension will cost between £45,000 - £85,000. 

"This will increase substantially if the project is based in a premium location, such as London, where costs can reach as high as £195,000. Other contributing factors include project size, complexity, the quality of materials and your selected contractor. 

"If someone wants to keep costs to a minimum, I always recommend trying to make savings in terms of fittings, rather than cut corners in terms of the build. Invest in a good builder and good design, as these are costs you’ll most likely recoup from when it comes to selling in the future, whereas things like kitchen fittings will depreciate in value over time."

Katie is an experienced journalist and has renovated two houses including a 200-year-old cottage and a 1950s semi.