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Single Storey Extension Cost & Prices 2023

Moving to a bigger home comes with a large cost and lots of upheaval. During uncertain times, it is no wonder that more people are choosing to stay in their current home and extend.

Single storey extensions allow families to add more space to their current home and save time and money in the process, usually in the form of a side or rear extension.

But it can be difficult to know exactly how much you can expect to pay for an extension.

This article will cover what you can expect to pay for a single-storey extension, factors that affect the cost and ways you can reduce the cost of your extension.

Cost Per m²

The starting point in putting a price to your extension would be deciding on the size of the extension. 

The cost of a standard masonry extension in the South-East would be approximately £1450 per m² on average to a finished liveable standard.

The best way to deal with bespoke features which are going to increase this cost is to add these as an additional cost on top of your per m² calculation.

The figures below show the total cost for a variety of extension sizes.

Extension SizeCost
3m x 5m (15m²)£30,000
4m x 5m (20m²)£40,000
5m x 5m (25m²)£50,000
4.5m x 7m (31.5m²)£62,000
6m x 6m (36m²)£72,000
5m x 8m (40m²)£80,000
6m x 8m (48m²)£96,000

The £1450 per m² figure can be broken down as follows:

ElementCost Per m²
Demolitions & Alterations£90
Substructures & Ground Floor Slab£140
Structural Steel£70
External Walls£150
Windows & External Doors£120
Internal Walls£70
Internal Doors£80
Wall Finishes£35
Floor Finishes£55
Ceiling Finishes£35
External Works (Drainage, mains connect etc)£55
Design Team Fees£160
Prelims - including scaffolding, welfare, warranties and site attendances£160

There are some optional items that need to be included on top of the baseline figure if you decide to include them within your extension. Some of these include:

Small Velux Rooflight+£770
Large Velux Rooflight+£970
Aluminium Double Patio Door (2.4m x 2.1m)+£1800
uPVC Double Patio (2.4m x 2.1m)+£110
Aluminium Double Sliding Door (2.4m x 2.1m)+£2100
uPVC Double Sliding Door (2.4m x 2.1m+£1000
Aluminium Bi-Fold Door (2.4m x 2.1m)+£2900
uPVC Bi-Fold Door (2.4m x 2.1m+£2200
Kitchen+£5000 - £12,000 (depending on specification)

Factors That Affect the Cost

A complex project like an extension has multiple reasons why the cost can vary from the baseline price. However, the factors below are among the most important.

  1. The size of extension – The bigger the extension the greater the cost overall, but a lower cost per m²
  2. The materials used in the extension – A standard masonry construction with small window and single door will cost a lot less than a high end extension with sizeable rooflights and large patio sliding doors.
  3. The function of the extension – An extended living / dining room will have a much lower cost per m2 than a kitchen extension where you will be paying extra for built in kitchen units and appliances.
  4. The location of the extension – An extension in the South and London will cost more elsewhere in the UK. The prices given above are for prices for the South-East. The following table can be used to adjust prices.
Region% Adjustment
South East (Southampton, Oxford, Kent, Outer London)0
Inner London+4%
South West (Bristol, Exeter)-4%
West Midlands (Birmingham)-10%
East Midlands (Northampton, Nottingham, Leicester)-10%
East Anglia (Cambridge, Norwich, Ipswich)-5%
North West (Liverpool, Manchester)-12%
Yorkshire and Humberside (Leeds, Sheffield)-11%
North East (Newcastle, Sunderland)-10%
Scotland (Edinburgh, Glasgow)-6%
Wales (Cardiff, Swansea)-9%
Northern Ireland (Belfast)-12%

Get Prices on Single Storey Extensions Near You

We’ve done our best to give you a good idea of what you can expect to pay for a single-storey extension.

However, our guides are not a substitute for a quote for your specific extension.

We work with all the best extension builders ready to price your job. Get free, no-obligation quotes in your local area and compare prices using the form below.

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About the Author

Alex Johnson is a qualified quantity surveyor and writer with a passion for conducting original research and uncovering the true cost of jobs. His cost data has been referenced by EDF Energy and the Scottish Government.