Builders
Carpenters
Electricians
Flooring Specialists
Gardeners
Handymen
Heating Engineers
Painters & Decorators
Plasterers & Renderers
Plumbers
Roofers
Tilers
myBasement Conversion Cost
At a Glance
- The average cost of basement conversion is around £100,000 in the UK.
- This job will usually take between 2 to 3 weeks to complete.
- A complete pricing breakdown which includes what you need to consider, along with what such a task usually involves.
- How long the job should approximately take and a general overview of what types of services can be performed.
- How to find and hire a local basement conversion specialist.
Trying to find out how much a basement conversion costs? Got basement conversion ideas?
In this guide, we breakdown what the cost of basement conversions is for different-sized areas and types of basements — so that any homeowner can calculate how much they need to budget for a cellar conversion in 2025.
But to give you a quick idea, you're looking at a spend of around £100,000 for a basement conversion in the UK.
We do this by providing an average cost per square metre, so whether it's a basement conversion or cellar conversion, finding out how much it will cost has never been easier!
Looking to get a quote now?
MyJobQuote has a Trustpilot score of 4.8 (25,000+ reviews) and is used by more than 1 million homeowners across the UK every year.
Tell us what you need and we'll connect you with basement conversion companies near you who can provide quotes for this job. It's free and there's no obligation.
Want to find out more before you start comparing prices?
Check out our full guide below!
£100,000
Table of Contents
How Much Does a Basement Conversion Cost?
Converting a cellar or basement can provide valuable extra living space without drastically altering the exterior of your home.
This type of conversion is expensive, but once you have made good use of all the useful interior space including the loft, if you do not have space around the house to extend further, it's really the only option, other than moving to a larger house!
The one thing that almost everyone wants is more space, and converting the cellar into a basement storey beneath the existing property can be a good option. However, it is so expensive that you may not get a full return on your investment unless you live in London or other areas where property prices and space are extremely high.
Basements are also created as part of newly built properties, but this article is primarily concerned with renovating an existing basement or cellar to create additional living space or even creating a new basement in an existing home and potentially extending outside the existing property boundary, into the garden.
How much would a basement extension cost (in a home where none exists)?
"It depends on the size of the basement, but prices start from around £30,000 to £50,000."
Obviously, converting an existing basement into a useful living space is much easier and less expensive than creating a new basement from scratch. This is a simpler conversion that can also be tackled by the average DIY enthusiast. However, excavating a new basement is a job that is definitely best left to the professionals!
You can use this website to easily gather quotes by simply describing your job and leaving contact details with one simple online form. Then, you can sit back and receive quotes from reputable tradesmen in your area - all for free!
Get started by filling in the easy form then let us get to work finding the perfect tradesman for your basement conversion project. You will receive up to three quotes from our local tradespeople. You can then choose the tradesperson for the job — with help from our members' previous feedback and comments.
Basement Conversion Prices
| Job Description | Duration | Material Cost | Labour Cost |
|---|---|---|---|
| Retrofit properties without existing basements price per square metre | NA | £1,000 | £2,000 |
| Basement conversion of an existing cellar but extended in both height and area per square metre | NA | £1,000 | £1,500 |
| Basement refurbishment of an existing cellar with additional waterproofing per square metre | NA | £400 | £1,000 |
| Creating a lightwell/external access | 2 weeks | £3,000 | £4,000 |
Want a custom price?
Post your job
Things To Consider When Planning a Basement Conversion
In some parts of the UK, especially in London and parts of the South East where property values are at a premium and stamp duty is expensive, many are considering basement conversions as a cost-effective option.
A basement conversion allows you to create a whole new floor for a variety of uses and the living space is more usable than for example a loft conversion, which can only really be used for additional bedrooms or an extra upstairs bathroom. That being said, extending into the loft will be much cheaper!
I have a basement that I don’t really use. Would it be a good idea to convert it into a bedroom and rent it out? Or would people be put off because it's a basement?
"If you have proof that it's been damp-proofed and can provide the building regs, then you could rent it out."
Extending underground also brings some additional headaches, namely due to the fact that the new living space will often be under the water table level.
So when building a basement, it's important to understand that every building is different and, as a result, there are a number of options when it comes to waterproofing.
But there are two primary methods that are most often used: membranes and structural waterproofing or tanking. Membranes are the most common and are created using high-density polyethene, which is fixed physically to the wall and on which the internal plasterboards can be fixed.
What are the best damp-proofing options for a basement that's going to be converted into a utility room?
"Membrane fixed to walls, boarded with moisture proof boards, and skimmed to take decoration."
The type of waterproofing membrane that is most suitable for your basement conversion will be determined by the anticipated water flow rate.
British Standard 8102 from 1990 requires the use of damp-proofing membranes in the UK, and there is a wide range of specialist membrane products on the market designed to address a variety of issues.
Whichever membrane product is fitted, there is little to no preparation required and they are very quick to install.
Can You Convert a Basement Yourself?
If there is an existing basement which is dry and well waterproofed, converting storage space to living space is fairly easy and well within the scope of the average DIY enthusiast.
Would I be able to turn my basement into an indoor squash court?
"Yes, you will be fine as long as it’s tanked, damp proof, and ventilation is good."
However, if it is damp, or the basement needs excavating to provide more headroom or needs to be extended – then this is a job best left to the experts! Excavating around the foundations of a property is not a job for an amateur, and there will likely need to be some underpinning required for structural safety.
Getting this wrong could cause the basement to collapse and even damage the structure of the property!
Ask a Trade
Got a question that only a tradesperson can answer? We have thousands of trades ready to answer any question you may have.
Ask your question
Basement Conversion Checklist
- A basement conversion is a very specialist job, so always employ an experienced architect or a dedicated conversion company.
- The main problem with any subterranean space is the lack of natural light - consider skylights, sun pipes and tunnels.
- Many Victorian and Edwardian houses already have basements, and sturdy foundations can be ideal for conversion.
- The proposed new basement may well be below the water table, so check with your architect or builder to find out which waterproofing method is the most appropriate.
FAQs
What can I use my new basement area for?
A basement offers additional family living space, which can be used as a playroom, home gym, swimming pool, sauna, home entertainment room, home office, or utility room.
You can even use the basement to create a self-contained unit as an annexe. However, if you want the basement to become an independent separate dwelling, you will need express consent for this purpose.
You can even use the basement to create a self-contained unit as an annexe. However, if you want the basement to become an independent separate dwelling, you will need express consent for this purpose.
Is a basement conversion a good investment?
Whether the basement cellar conversion is financially viable or not depends on the cost of the conversion relative to the local property values. In high-value areas, it almost always makes sound financial sense to add a lower ground floor, so in central London and other expensive urban centres, the answer is definitely yes!
Elsewhere the financial return needs more careful thinking about, a local estate agent should be able to give you a good indication of how much the extra space will be worth.
Elsewhere the financial return needs more careful thinking about, a local estate agent should be able to give you a good indication of how much the extra space will be worth.
Do I need planning permission to convert my basement?
Converting an existing cellar or basement beneath a dwelling from a storage area to a living space does not generally require planning permission.
This will normally be covered under Permitted Development unless in a Conservation Area or Listed building. However, excavating the floor of a cellar to increase ceiling height is treated as an extension and so may well need planning permission.
This will normally be covered under Permitted Development unless in a Conservation Area or Listed building. However, excavating the floor of a cellar to increase ceiling height is treated as an extension and so may well need planning permission.
Will I need to move out while the work is in progress?
If there is access directly onto the garden for the removal of soil and your existing ground floor is standard suspended timber, then you can continue living in your home whilst work is in progress.
But if the ground floor is concrete and has to be removed and rebuilt with much of the spoil being carried through the house, you will almost certainly have to move out.
But if the ground floor is concrete and has to be removed and rebuilt with much of the spoil being carried through the house, you will almost certainly have to move out.
How much will it cost to convert my existing basement or cellar?
This is difficult to answer because there are many factors affecting the probable costs, such as the type of property, the approximate size of the basement, what you want to use the space for and what the existing walls and floors are made of.
Other factors to consider are the proposed plumbing and electrical work required, current floor-to-ceiling height, access in and out of the property, and any existing dampness.
Other factors to consider are the proposed plumbing and electrical work required, current floor-to-ceiling height, access in and out of the property, and any existing dampness.
Sources
https://www.planningportal.co.uk/permission/common-projects/basements/planning-permission
https://www.trimblearchitect.uk/top-5-conversion-ideas-for-small-basements
https://www.granit.co.uk/is-adding-a-basement-worthwhile/
