Over the past couple of years, we have seen a significant increase in the amount of UK homeowners planning to add a single storey extension to their house. It is hardly surprising given what we have all endured since the pandemic hit in March 2020. The lockdown in England forced many people to experience their homes in ways they previous had not. Working from home became the norm, and spending a lot more time with family in close proximity made many of us value space more than ever.

Of course, once faced with the reality that you need more space to live, you have a few options. You can:

1. Do nothing
2. Shuffle some furniture around and hope for the best
3. Sell up and move to a larger abode
4. Create extra room by building a single-storey home extension

Skipping to the third option, moving house has been chosen by many during the post-pandemic house buying boom. In fact, the number of first time buyers dropped by 12% in the second half of 2020, when compared to the same period in 2019. On the flip side, the surge of house market activity was led by second, third, and fourth time buyers who had higher levels of equity, and were able to take full advantage of the stamp duty holiday.

We found it is generally more cost effective in the long term, and less disruptive to not move and improve your house with an extension, or loft conversion. There are several hidden cost related to moving home that buyers often forget to consider. The average distance buyers move is 10 miles, which may not sound like much, but can cause noticeable disruptions around support networks, schools for children, and more.

How much does a single storey extension cost in 2025?

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So, how much does a single storey extension cost in 2026?

To build a single storey extension in 2025, it will cost £35,000 on the smaller and lower end, and around £105,000 on the larger and higher end. Although cost can vary significantly based on where you are located in the UK, and from builder to builder, so make sure you at least three quotes, if not five.

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If you like your street, neighbours, or local area it can often be too expensive to upgrade to a bigger property locally, especially if you live in a sought after location. After accessing your unique financial and emotional circumstances, you may decide that staying in your current home and extending it is the best option for you.

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On average, a good-sized affordable single-storey extension of 20m2 in 2025 would come up to around  £40,000- £45,000. This includes the cost of installing a kitchen as it is the most in-demand function for  single-storey extensions.  

The cost per square metre for a low-cost extension in 2025 generally starts from £1,500 - £1,900, £1,900 - £2,200 for an averagely-priced extension and £2,200 - £4,000 and more for a luxury level project.  

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What are the primary costs involved in a home extension  

The numbers can vary and increase based on several factors such as the type of extension, location and  existing conditions, approvals, architect’s fee, drawings, materials and labour. Here are some tips to reduce the cost of building an extension.

See also: 15 renovation tips to reduce stress

Council application costs in 2025

There are certain rules and regulations set by the government that need to be considered right at the  initial stages. Based on your extension, you may have to submit applications for several reasons and get  them approved prior to construction.  

The two main types of applications are Planning Application and Building Control (building regulations)  application. Depending on your extension, sometimes you may require both, sometimes one, and in a  few cases, none at all. 

Planning application costs in 2025

Not all extensions require a planning permission. Permitted  development rights enable you to carry out the construction for your extension without the need for a planning permission. These rights are mainly centred around dimensions of the proposal, position relative to existing structures and proximity to boundaries. 

All the guidelines set forth by the authorities that need to be considered before making a decision on  whether you need a planning permission can be found on the planning portal. 

A general rule is that a single-storey rear extension - extend only up to 8m from the original rear wall  (detached house) and up to 6m for all other house types. If the extension is less than 8m(detached  house) or 6m (other house), then the project falls under permitted development rights and hence, do  not need a planning permission. 

Another case where a permission may be required is when the proposed extension covers more than  50% of the land around the existing property. 

In a case where your extension is larger or exceed the limits, then you are required to submit a planning  application prior construction.  

For a basic home extension, the planning application is currently £238 including a £20  processing fee if you’d like to submit documents via the Planning Portal. You also always have the option  to drop the hard-copy of your application at the council 

A planning permission is only one of the many consents that may be required for your project. Some  properties have clauses that require written consent of the owner/original developer. In the case of  such consents not being put in writing, you could be in breach of covenant and you may even be asked  to entirely take your extension down.  

All extensions, regardless of planning permission, Will require a building control application to be  submitted 

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See also: Do I need planning permission for a fence?

Building control (building regulations) application costs 

Building regulations are a series of documents that have to do with all buildings and they deal with the  technical aspects of the design. Almost every alteration to a property requires a Building control  application, be it new development, extensions or even alterations. They ensure that the building is safe  and fit for use, both for the people living in and around the property.

Building control application costs vary depending on the size of your property and type of extension. It  generally falls between £500 to £1,000 for a small extension or conversion. 

You might want to look up the most recent updates put out by your local authority to ensure a fool proof execution of your project. 

If you’ve got architect and consultants on-board, your project is in safe hands as they would be well versed with such regulations right from the start. 

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What about extension drawing costs? 

First, a measured survey of the existing house needs to be done which would be around £500 to £1,500.  In addition to the property survey, you require a topographical site survey which can cost around £400  to £800.  

Following planning drawings of the house (plans, elevations, sections, construction drawings etc. and a  similar cost for building regulations drawings usually fall within the range of 10-15% for each and are  done by architectural team. 

Subsequent costs such as contractor’s fee would be 15-20%.  

If you’re well-versed with the processes you can cut costs here by managing your own project. Listed  below is a rough breakdown for drawing costs - 

Extension plans for permitted development

An architect’s fee would come up to roughly 10-15% of the total build cost and this generally includes  design + drawings + supervision. Additionally, there are firms that charge a fixed amount, i.e. the fee is  generally structured based on factors such as floor area, number of floors, level of complexity, etc.

On average, you would be charged around £800 for a single-storey extension and £1,600 for double storey extensions for planning permission drawings and the same for building regulation drawings. You can get a free quote from us here.

In addition, you would need to consider the fee for other consultants for surveying, structural  engineering, project management, etc. Sometimes, you would need to hire a site surveyor separately,  but a lot of the time, the design team would take care of it. 

Structural drawings and calculations 

Structural calculations and drawings done by a structural architect/team fall within the range of £50 – £90 per hour, depending on their experience, location and whether they work independently or as part  of a firm. 

Ground soil investigation 

Prior to commencement, there is a requirement for a ground soil investigation. A desktop study would  be around £600 and a complete site soil investigation is charged from £1,000 +VAT based on your  property and project complexity. Water mains survey / CCTV drain survey.

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What are the construction costs involved?

Materials and finishes take up a significantly large percentage of the extension cost. You can easily save  costs here with the type of finish and fittings you choose from.  

If you’re looking for minimal wall paints and simple wood floors, you can save a lot here, however, more  high-end and in-trend designs that include bespoke flooring, fitted joinery, etc, would clearly lead to  increased costs.  

For example, a 2.5m wide opening with bi-folding doors which is largely popular right now, can be  expected to come around £5,000 and flooring can vary from £25 to £100 per square metre based on the  type and style of material

Listed below is an average cost breakdown for building materials -

Cost for different extension types

The first step you are most likely to think about when beginning the process for extension would be the  type and overall look of the extension. Costs for different extension types are widely ranged  

Timber extension - Timber extensions are one of the most popular types due to its reliable and  lightweight nature which makes it extremely cost-effective in the long run. It usually comes within the  range of £1,400-£2,400 per m2.

High-end glass extension - Glass extensions have a more contemporary, modern look and are priced at  around £3000 for glazing per m2.

Pre-fabricated extensions - These are built off side and fixed in place using cranes and average to around  £2,000 per m2.

Conservatory - A traditional conservatory is a relatively cheaper option for an extension. It is a  combination of glass and brickwork and totals to around £15,000.

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Recommended reading: Conservatory or extension?

Cost for different roof types make illustrations

The type and build of roof you opt for can also increase or decrease your costs. When you think about  the type of roof for your extension – its usually a pitched roof or flat roof.  

Pitched roof

The initial cost for pitched roof is more essentially because of the longer work and time required to build  it. Pitched roofs, however, have a longer lifespan as the materials used are more durable, weather  resistant and they do not come with the risk of water pooling which reduces chance of leaks. Pitched  roofs also contribute to more space beneath which can later be used for other home renovations such  as a new loft. A pitched roof also helps keep energy bills lower as it allows for more insulation to keep  the house warm.  

Flat roof

A flat roof, on the other hand, is cheaper as it involves a much quicker and straightforward installation  process. It saves a lot of material, labour and time. Flat roofs require more maintenance in the long run to  protect the home from water ingress. A home with a flat roof is also more likely to release heat and  have higher energy bills as a result.  

In short, both pitched and flat roofs essentially their own set of pros and cons, so, you’ll need to choose  the one that best suits your needs.

Aside from pitched and simple flat roofs, there are other options such as glazed roofs and green roofs. Glazed roof

Glazed roofs are priced at around 1,000 per panel and are more commonly found in use for side  extensions. This type of roof is on the expensive side but they let in a lot of natural light and gives a  stunning modern look to the house.  

Green roof

Green roofs are a good environmentally conscious option as they provide high insulation. The roof is  used to grow plants and shrubs. Green roofs being quite expensive, costs around 100-140 per m2.

Cost for installing kitchen, bathroom and utility rooms

More utilities and fittings lead to larger costs. If your extension includes a new kitchen to be installed,  expect anywhere around £5,000 to £20,000. A new bathroom would fall between £4,500 to £11,000. A  new utility room falls anywhere between £1,500 to £11,000, based on the level of complexity and luxury  you’re looking for.‍

Cost for Doors and windows  

When it comes to doors and windows, the cost varies based on a number of factors such as size of  opening, material, opening-type, etc.  

Internal doors fall within the range of £50- £200, external doors within £300- £500 and patio doors - £300- £1000.  

Windows based on size and type vary from £100 to £400.

Roof lights

A largely popular feature among homeowners right now are bi-folding doors. Installation of these can be  expected to come around £5,000.

Cost for Flooring and finishes

Flooring and finish costs vary based on material quality, location where available, laying-out cost, etc

Flooring - Cost per square metre for wooden flooring falls between £17-£70, vinyl flooring between £7- £20, carpets fall between £4-£40 and tiles fall within the range of £10-£6.

Cladding - Wall cladding usually falls between £25 to £100

Render – Wall rendering would come between £25 to £100

Internal plaster - Wall and ceiling finishes are expected to be around £85 per square metre for plaster or  dry-lining plus paint.

Lighting - Lighting can fall anywhere between the range of £3 to £80, and up.

Labor costs

Labour costs are usually calculated by the hour. Builders would be charged at around £20- £40, a  plumber’s fee would be £30- £45, electricians fee would be £50- £120 and so on.  

Value Added Tax (VAT) is an additional fee based on current rate that is added to services (and goods)  supplied by VAT registered suppliers, contractors and sub-contractors that are involved in your project,  it generally stands at 20%.  

Most online quote calculators that you may come across do not consider VAT upon calculation, so, it’s  something you need to factor in while determining your project costs.

Hidden costs you need to consider

Location

Location matters from factors like material purchase, transport as well as the terrain to be built on. If  you’re looking to build upon an area of uneven terrain, you can expect prices greater than if you were  building onto something existing and flat.  

Another important factor to consider is the ease of access which can add to costs of transportation of  materials, tools and equipment in and out of your property.

The soil type on your property, too, can determine the construction technique and material which can  impact the cost.

In addition to site conditions, costs also vary across the country. For example, the average cost would be  around £1,200 to £1,500 in most areas, while it could go up to £1,500 to £2,000+ per sq. metre towards  London and the South-East.  

Party Wall Fees

A party wall is one that is shared by 2 or more owners and either form a part of a building (1), is not part  of building like a garden wall (2) or it stands on one owner’s land but used by other neighbours as  separation (3).  

You are legally required to inform your neighbours if you plan to carry out any building work on or near  your shared property boundary, or ‘party wall’

In the case of an extension, the party wall fee would be £700 to £900 with each neighbour.  

However, if you can get your neighbour to complete a party wall agreement waiver or put in writing that  they do not object, you can save here by getting your surveyor to arrange a party wall settlement

Trees –Tree Preservation Orders (TPO)

A Tree Preservation Order is an order set by the local authorities to protect specific trees, groups of  trees or woodlands across the country. If you’ve got trees in and around your property, it is definitely  something to consider as it gets tricky in these cases

Community Infrastructure Levy  

The Community Infrastructure Levy is a fee set by local authorities on new developments within the  locality that is put in use to deliver sufficient infrastructure required to support development in their  area.

If the extension increases the floor area by more than a 100m2, you might need to pay a fee under the  Community Infrastructure Levy which is currently £95 per square metre. This fee only applies to certain  localities and not all.