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How Much Does It Cost To Build A Rear Extension

How much does it cost to build a rear extension?

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Written by

Ellie

Last updated Thursday 11th November 2021

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We know that building a rear extension can seem daunting at first, not knowing where to start or who to talk to. This is especially true for finance, as the last place you want a surprise to pop up is in your budget. If you’ve been trying to crunch the numbers of your dream extension but haven’t been able to nail down the costs, then you’re in luck because we’ve put together this handy guide to help reveal just how much a rear extension can cost in the UK.

How much does a rear extension cost per square metre?

When it comes to building your extension, you’ll find the easiest way to estimate costs is to measure out the potential size of your project. On average, we estimate the cost of a rear or side extension to cost per square metre…

£1500 m2 - £3250 m2 - London and the South East
£1200 m2 - £2650 m2 - Rest of England

For example, an average rear extension tends to be 45 square metres, which would mean your build would cost between £67,500 and £146,250 in the London area.

How much will it cost to build?

Answer a few quick questions about your project to get a free construction estimate.

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What affects the price of a rear extension?

The cost of a rear extension can vary wildly, depending on these factors:

  • Your location in the UK
  • The size of your extension
  • The complexity of the design
  • The quality of materials chosen
  • The size and quality of your building company

On this last point, it’s worth bearing in mind that there are a lot of factors to consider when it comes to picking a builder - not just the price tag! One man bands will offer very cost effective quotes, however, you’ll find this route also puts you more at risk of delays and potential bad practices. Controversy, larger contractor companies will cost more BUT could provide better value for your money in the long run, especially as they’re best equipped to deal with supply hold-ups and labour shortages.

Learn more about contractor types and how they can affect your budget

Material and labour shortages

Since the pandemic in 2020, the industry has been affected by several issues that may affect the cost of your project. Whether it’s VAT, suppliers suffering from delays, or labour shortages, it’s always recommended you have a 10% contingency fund to help you weather these issues.

Learn more: Material and labour shortages push up the cost of construction

What costs do I need to factor into my budget?

While a large part of your budget will go towards construction and the materials involved, there are still some other costs to consider.

A typical budget tends to be split like this…

Architects - 4% (based on Resi’s services)
Administration fees - 1%
Structural Engineers - 3%
Surveyors - 2%
Contractors - 30%
Materials - 20%
Fittings - 5%
Glazing - 15%
VAT – 20%

Structural engineers

Put simply, a structural engineer helps ensure your home stays standing. As their name suggests, they look after the structural calculations required for your project.

A structural engineer will typically start work on your project after planning, during the building regulations stage.

They can cost anywhere between £950 to £2500.

Do you need an architect for a rear extension?

You are not legally required to hire an architect to build a rear extension. However, this doesn’t mean they’re not a worthwhile investment. Architects are masters of their craft and can bring plenty of benefits to the home renovation process. By bringing one on board you will enjoy…

A more beautiful and functional space. Architects can help ensure you maximise your space and customise the layout to the unique way your family lives, rather than just following the trends.

Increased planning success. Architects come with years of experience, not only in design, but planning. Chances are they’ll have dealt with your local authority in the past, and know how to research your area. Meaning you’re far more likely to secure planning success with an architect, than without.

Budget management. At Resi, our architects make sure you have a clear view of not only our charges, but of future professionals you’ll have to contract. We’ll advise on how much you’ll need for what, and when you’ll likely be parting with it. Not only that, our Resi Finance team can also help you explore your funding options and find the right route for your home.

Discover the cost of an architect in minutes with our quick quote tool.

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How much will it cost to build?

Answer a few quick questions about your project to get a free construction estimate.

Loft

Loft

Ground

Ground

First

First

Basement

Basement

Two storey

Two Storey

Phone: +44203 868 9453 | Email: advice@resi.co.uk

Resi Design Ltd. trading as 'Resi' | Company No: 10471125

We are proud to employ architects registered with the Architects Registration Board and were awarded the mark for The Mayor's Good Work Standard for fair pay & conditions, wellbeing, skills, progression, diversity and recruitment.

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