The Cost Of Building An Extension


The cost of building an extension on your house

The Cost Of Building An Extension In The UK

A simple house extension can cost between £1,300 and £1,600 per square metre using basic fittings. If you choose better quality fittings the costs rise to between £1,700 and £2,000 per square metre. Opting for an excellent finish will add to the costs which can be between £1,800 and £2,500 per square metre.

The cost of an extension or any other renovation work to a property in London and the South East is generally more expensive due to labour costs.

In current times there are more people working from home and this has increased the number of homeowners who want to add an extension to their property. In addition to adding more living or working space an extension can add value to your property so what is the actual cost of building an extension?

Image showing a house with an extension on one end
If you use higher quality materials then the cost of building an extension can increase dramatically. Photo © Roger Templeman (cc-by-sa/2.0)

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Planning An Extension To A House


It is an exciting prospect to add an extra room in a home and if you sit down and make some firm plans you can avoid some of the pitfalls that have happened to others. Getting the right advice and an expert to help plan the extension is the first step towards improving your home.

A professional architect will be able to design an extension for your house that suits your needs and ensure that you get the best possible outcome.

Find a designer or an architect who will be able to show you previous work projects and demonstrate that they can keep within a budget. It is important to think carefully about what type of extension you want and make sure that it meets your personal needs.

Photo of a house with a small extension on one end
Costs of building an extension can be quite low if the extension is for a simple utility room. Photo © Roger Templeman (cc-by-sa/2.0)

The design will ultimately depend upon the amount of space available and if you can obtain the necessary planning permission. Take time to think about whether you can cope with a major building project and the disruption it can cause to family life or whether you need to move out whilst the work is completed.

Image showing a small brick extension
House extensions can be cost effective and blend in perfectly with the main building. Photo © Roger Templeman (cc-by-sa/2.0)

Finding A Builder For A House Extension Project

You may have heard horror stories about ‘cowboy builders’ but in truth most builders are professionals who will do their utmost to do a good job. You can ask for recommendations amongst friends and family or search for a reliable builder who is part of a trading association.

There are number of basic questions that you can ask a prospective builder and the answers will allow you to determine whether or not this is the right person for the job. Confirm how long they have been operating and ask for a written quotation instead of an estimate.

Make sure that they are fully insured and have the requisite permits. If possible obtain references and photographs of previous projects. Finally, make sure that the time span of the project is agreed along with terms of payment. Making staged payments for your building project is preferable to paying the whole amount up front.

Make sure to get multiple quotes for costs and references for any builder before they begin building an extension on your property.

Photo of a grade II listed property with an extension.
if you own a listed property, such as this Grade II listed building, make sure you have correct planning permission before beginning any building work. Photo © Alan Murray-Rust (cc-by-sa/2.0)

Home Extension Cost FAQ

Do I Need To Pay VAT On A Home Extension?

When working out the cost of building an extension you will need to factor in VAT. The standard VAT rate is 20% but in some circumstances this can be reduced to 5%. If the property in question has been empty for more than 2 years or a commercial building is being converted to residential the lower rate can apply. Ask your builder about the rate before any work is started.

What Is The Cheapest Type Of House Extension?

Working out an effective design can help reduce the cost of building an extension. A simple design with a rectangle or square shape is cheaper than adding elaborate corners and curves. Basic materials for fixtures with standard fittings for doors and windows can also help to make the extension cheaper. Using a builder who trades below the VAT level will also make your project more cost effective.

Will An Extension Add Value To My Property?

A well built extension can increase the value of your property. Adding an extra bathroom can increase the value of a home by 6%. A extra double bedroom can increase the property value by 12% and one with an en-suite bathroom adds as much as 23% to the value. The cost of building an extension may be easily offset by the extra value added to your home.

Factors Affecting The Cost Of Building An Extension


The cost of building an extension will depend upon several factors. The size of the extension and how many storeys you want building will affect the price. If you opt for standard fittings it will be cheaper and of course higher quality materials can increase the costs of your renovation project.

If you are personally involved in the work it can help to cut costs but only go down this route if you are sure of your capabilities. Employing a building project manager makes the cost of building an extension higher but can ensure the project finishes on time and on budget.

Other factors like the type of soil which can affect foundations may also make costs vary as can the amount of windows you want. Additionally, location is very important as costs in some parts of the country like London may be increased due to higher wages and labour costs of building contractors.

Photo of a house with a high quality extension
When done properly an extension on house can blend in seamlessly. This extension turned the house from three to six bedrooms. Photo © David Hawgood (cc-by-sa/2.0)

Reducing The Cost Of Building An Extension

There are number of ways to reduce the costs of building an extension on your house. A simple design with either a rectangle or square shape will be cheaper than one with curves and corners. Basic fittings for flooring and fixtures like kitchen units can also keep costs down. You can always upgrade these later.

Choosing off the shelf products like doors and windows of a standard size and products that are readily available will also help to cut down on costs. If you can avoid complicated problems by building away from drains and trees your extension costs can also be lowered. One final point to think about is that if you live in a period property the choice of materials may be limited.

Examples Of House Extension Costs


Adding an extra room to your property might seem simple but there are several different types of extension. Single storey extensions are popular and can cost around £40,000 or up to £67,000 in the London and South East area.

A two storey extension to a house costs around 50% more. If you want to extend your bathroom expect to pay around £10,000 for a small extension.

Other possible ways to add space to your home are dormer rooms in a bungalow and attic or basement conversions. If you have room you can think about adding a conservatory, orangery or sun room. Finally, adding a porch can make a difference and this kind of extension does not need planning permission.

Photo of a cottage with a modern conservatory extension
In some cases a conservatory can be a viable alternative to a traditional house extension. Photo © Stanley Howe (cc-by-sa/2.0)

Advice About The Cost Of Building An Extension?

There are many organisations that give good advice about how to go about building an extension and the costs involved. The Homeowners Alliance is one good source of information. A competent local builder will also be able to provide useful information about costs and regulations that may apply specifically to your area.

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If your house is leasehold you will need to check the terms of the lease before starting any property alterations. It is also important to advise your nearest neighbours so that it does not come as a shock when they are notified by the local authority of your plans to extend your house.

Make sure to get more than one quotation (not an estimate) in regards to the cost of building an extension on your property. A good rule of thumb is to get three quotes before engaging a builder.

Additionally, make sure that funding is in place before the work commences and any builder you use sticks to their side of the bargain in regards to your quote for an extension.

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