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Last updated on March 31st, 2022

Cost to build a basement

Although basements aren’t generally a standard feature of British properties, more and more homeowners are looking to add space by extending downwards. In this guide, we look at the average cost to build a basement in the UK.

Although basements aren’t generally a standard feature of British properties, more and more homeowners are looking to add space by extending downwards. In this guide, we look at the average cost to build a basement in the UK.

If you have limited options to expand upwards or outwards, building a basement can be an extremely viable option for gaining space in your home – particularly in urban areas where land is often very limited.

All prices included in this article are meant as a guide. For accurate costs to build a basement, we recommend speaking to your local construction experts for detailed prices in your area.

Wondering what you could do with extra space in your house? Take a look at some of our cost guides for inspiration, you could create a home cinema, a home bar, or even a man cave.

ItemRange - LowRange - HighAverage cost
Conversion of existing cellar (per m2)£750£1,400£1,000
Lowering floor and underpinning existing cellar (per m2)£1,500£2,000£1,750
Creating new basement space and underpinning (per m2)£2,000£3,000£2,500
Creating basement under garden (per m2)£1,500£2,000£1,750
Structural engineer (per hour)£50£90£75
Planning application--£165
Building Regulations application£750--
Party wall agreement--£700

Our costs are ballpark averages – get a local tradesperson to quote now

How much does it cost to build a basement?

There are a number of ways you can build a basement, depending on your existing property – and each with its own costs. You could use the below as a cost to build a basement calculator:

  • Conversion of an existing cellar – £750 to £1,400 per m2
  • Lowering the floor level and underpinning an existing cellar – £1,500 to £2,000 per m2
  • Digging a new basement space and underpinning – £2,000 to £3,000 per m2
  • Digging a new basement space underneath a garden – £1,500 to £2,000 per m2

As you can see, the approach to building your basement will directly impact the total cost. For this reason, it’s important to discuss the details of your project with an expert, so they can offer their professional advice and provide accurate costs.

A local expert will also be able to provide you with specific quotes for things like the basement foundation cost per square foot, the cost to frame a basement, and the cost to dig a basement for a new construction.

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basement construction costAdditional basement construction costs

There are a number of additional costs that you’ll want to consider when planning your budget for the construction of a new basement.

Structural engineer costs

Due to the nature of the project, you’ll need a structural engineer to be involved to help plan the basement. The average cost for engineer fees is in the region of £1,500 to £2,000, plus a percentage of the total cost of the construction contract.

You can see more details of prices in our structural engineer cost guide.

Planning costs

As with any major construction project, you’ll most likely need to apply for planning. If so, the average cost is around £165 per application.

Building Regulations costs

In order to ensure you meet current UK Building Regulations, you’ll need to apply for the project to be approved. For that, you’re looking at a cost starting around £750 per application, depending on the value of the work undertaken.

Party wall agreement costs

If your property is joined to a neighbour’s then any work that affects a party wall will need a party wall agreement before the project can go ahead. If required, you can expect to pay about £700 per neighbour.

To find out more about party wall agreements, check out our guide to party wall surveyor costs.

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Garden basement cost

If you’re planning to build a basement in your home and you have a garden, you could combine the two – with a garden basement. Building a basement under a garden is becoming more and more popular with British homeowners for a number of reasons.

The construction process of a garden basement is noticeably quicker, as excavation is much more straightforward. You also have the benefit of being able to include roof lanterns or skylights in a garden basement – something not possible if the basement is underneath your property.

The average cost for building a garden basement is around £1,500 to £2,000 per square metre. Depending on a number of factors, including the size of the basement (the larger the basement the higher the cost), installing light wells, any external access needed, high water table (which can bump up the cost of excavation) and diverting drainage and sewers (which can be expensive).

Basement construction cost calculator

In order to calculate the cost of building a basement, you first need to plan the size of the space you’ll be creating – all costs will then go from there. You need to factor in excavation and underpinning work the waterproofing process, electrical and plumbing work, and the finishes (plastering, painting, fixtures, fittings, and furniture).

The best way to plan an accurate budget for your basement construction project is to speak to local builders and ask for quotes for the job, including a detailed breakdown of the various costs and options.

Basement construction hourly rates

Here are some of the labour rates that you’ll need to factor in as part of your basement construction project:

Basement construction quote

We recommend obtaining at least three quotes from our trusted tradespeople. Our request a quote feature is perfect for getting quotes – you post details about the job you want doing and we’ll send it out to local tradespeople in your area. Try it out!

Factors affecting the cost of building a basement

The total price you pay for building a basement will depend on a number of different factors, which you’ll need to consider when planning a budget. Some of the most important include:

  • Property type and current condition
  • Size of basement planned
  • Ability to convert existing cellar or below ground space
  • Ground conditions
  • Any external access added to the basement
  • Level of the water table in the area
  • Sewer and drain diversions
  • The extent of preparation work and excavation
  • General access to the site
  • Where you live


What building methods are best for a basement?

The construction method used for building a basement typically depends on the budget, soil type and conditions of the site. The different methods include precast waterproof concrete panels, brick and blockwork, and ICF (insulated concrete formwork) or shuttered concrete.

How do you waterproof a basement?

To find out about waterproofing a basement and the costs involved, check out our guide to basement waterproofing costs.

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