Basement conversion cost near you

Basement conversion cost: price guide for 2022

If you’re looking to extend your home but can’t extend up or out, have you considered extending down into your basement? Basement conversions are growing in popularity, especially in London, and they’re a great way to add extra space to your home. But how much will it cost?

When you’re thinking about a basement conversion, there are two things to bear in mind: will you be converting an existing cellar or digging and excavating a new one? To convert an existing basement, expect it to cost around £1,400 per square metre. If you need to excavate and underpin a new cellar, it will set you back approximately £2,280 per square metre.

So what factors do you need to consider when you’re planning the cost of your basement conversion? We’ll break everything down in this guide. 

  1. Benefits of a basement conversion

  2. Will I need planning permission?

  3. Supply costs of a basement conversion

  4. Waterproofing options for your basement

  5. Basement sump pump costs

Benefits of a basement conversion

There are so many benefits of a builder carrying out a basement conversion. Although there’s a large upfront cost, it’s soon offset by the advantages of having your cellar converted. 

Increase your property’s value

Basements are a sought-after feature, especially in London. If you make one or convert yours, your home will become much more attractive to buyers. You can expect a return on investment of up to 1.3%.

Add an extra bedroom

If your family is growing or your children are getting older, they might start wanting some more privacy. A basement conversion works well as an extra bedroom or annexe for teenagers or older family members.

Add an office or gym

Bedrooms aren’t the only options for cellar conversions. If you’re working from home more than before the pandemic, an office might be the best use of the space, but if you’re trying to get fit you could use the room as a home gym. Other popular options include a cinema room or a laundry room.

Alternative to moving

Moving is expensive, and it might be cheaper to stay in your current home but convert the basement. You’ll avoid the hassle and expense of moving but you’ll still get a new space that you love.

Extra storage space

There are lots of ways you can use your cellar conversion to reduce the amount of clutter in your home. Use it as a utility room, a walk-in wardrobe or even a drinks cellar.

Alternative to other extensions

If you don’t have a big enough garden or your home is already extended as far as it can be, a basement conversion is a perfect alternative. They can also be a good option if you’re not able to change the outside of your property since all the work will happen underground.

Will I need planning permission?

It’s unlikely that you’ll need planning permission for your basement conversion as you’re simply converting it into a living space. However, if you plan to add a lightwell or change the usage, then you will need to seek planning permission. You’ll also need planning permission if you’re significantly changing the usage or the basement is a separate unit.

Also, basement excavations are now under permitted development rights, which means you don't need planning permission. However, if you’re having major works or the basement will alter the appearance of your home, it’s worth making sure that you’re covered under permitted development rights. You must also ensure that you’re only digging down one storey and it doesn’t go beyond 3 metres from the back wall of your home. You must also make sure that you leave at least 7 metres between the end of your basement and the boundary of any neighbour opposite.

Listed buildings

It’s worth remembering that listed buildings are dealt with differently. If your property is listed, you’ll require listed building consent if you want to make any internal or external changes.  

Supply costs of a basement conversion

While converting a basement will cost an average of £28,000 for a 20 square metre basement and around £46,000 to excavate one of the same size, there are other costs to think about. For example, if you want to install a new kitchen, this could cost between £4,000 - £8,000. Fitting a staircase could cost £3,000-£5,000, while waterproofing could cost between £1,000-£1,800 per square metre.

Here’s a breakdown of the costs associated with a basement conversion:

Job

Average cost

Installing a new kitchen

£4,000-£8,000

Fitting a staircase

£3,000-£5,000

Installing a bathroom suite

£1,500-£3,500

Floor sealing and tanking

£1,350-£1,650

CDM waterproofing

£1,200-£1,800

Barrier system waterproofing

£1,000-£1,500

Internal wall removal

£750-£1,200

Damp proofing and insulation

£500-£1,000

Painting and decorating

£400-£800

Installing laminate flooring

£400-£700

Laying carpet

£300-£600

Plastering

£300-£600

Installing light fittings and sockets

£100-£500

Waterproofing options for your basement

Waterproofing is vital to any basement conversion. Since a basement is underground, it’s prone to damp and damage due to weather conditions. You must take all the different types of waterproofing into account and see which one will suit your property best. You should also consider a sump pump to remove water should your basement become flooded.

Floor sealing and tanking

You’ll need to seal your floors as well as the walls. With floor sealing and tanking, you can waterproof the walls and floors at the same time. It involves adding a layer of cement, membrane or bitumen slurry coat which waterproofs the walls and floor. This will set you back between £1,350-£1,650.

Cavity drainage membrane (CDM)

A cavity drainage membrane, or CDM, lines the walls and has a pump system with a studded plastic cavity. Water flows down the CDM and directs towards internal drainage channels before being transported away. It costs anywhere between £1,200 and £1,800.

Barrier system

A barrier system, as opposed to a CDM, holds back water rather than directing it into a drainage system. It works in conjunction with a tanking system that is placed on top of the basement’s original walls and floors. This costs an average of £1,000-£1,500.

Basement sump pump costs

If your basement is below the water table, you’ll want to consider getting a sump pump. When it rains or there are high water table levels, your basement’s waterproofing system’s perimeter drains will funnel the water into the sump basin. The pump will then remove the water.

There are a number of sump pumps on the market:

Sump pump name

Approx. cost (excluding VAT)

PermaSEAL Basement Sump Pump System

£488

PermaSEAL Basement Sump & Dual Pump System

£848

Platon Aqua Cellar Sump Pump

£420

Platon Aqua Cellar Sump Twin Pump

£695

Newton Titan Pro White Sump & Single NP400 Pump

£857

Newton Titan Pro White Sump & Dual NP400 Pumps

£1,272

Ebara BEST 4 MA Sump Pump

£930

Get a range of quotes

There’s a lot to think about with a basement conversion, so you want to make sure you’re in good hands. Make sure you get quotes from a number of builders to ensure you get the most competitive price. 

Post a job on HaMuch to get quotes from reliable tradespeople today.


Estimates for common builder jobs;

Job Estimate
Cost to fit windows, doors and conservatories £160
Cost to build a side return extension £61000
Cost to repoint or repair brickwork £405
Cost to remove a chimney breast £800
New fitted kitchen cost £19500
Cost to lay a new driveway £3400
Cost to fit a new bathroom £8000
Cost of a loft conversion £49900
Cost to build a retaining wall £320
Basement conversion cost £43000

Rates for other trades

Basement conversion cost in the UK
Basement conversion cost in the UK (excluding VAT or callout charges)
Location in UKBasement conversion cost
Basement conversion near Aberdeen£37500
Basement conversion near Amber Valley£33360
Basement conversion near Angus£32550
Basement conversion near Arun£34350
Basement conversion near Ashfield£33900
Basement conversion near Aylesbury Vale£34260
Basement conversion near Barnsley£36330
Basement conversion near Basildon£34800
Basement conversion near Basingstoke & Deane£34980
Basement conversion near Bassetlaw£32910
Basement conversion near Bath & North East Somerset£34620
Basement conversion near Bedford£36690
Basement conversion near Belfast£26880
Basement conversion near Birmingham£32460
Basement conversion near Blackburn£32460
Basement conversion near Blackpool£31020
Basement conversion near Bolton£32190
Basement conversion near Bournemouth£34800
Basement conversion near Bracknell Forest£36600
Basement conversion near Bradford£33000
Basement conversion near Braintree£34080
Basement conversion near Breckland£31020
Basement conversion near Bridgend£31290
Basement conversion near Brighton£34170
Basement conversion near Bristol£34530
Basement conversion near Broadland£30390
Basement conversion near Broxtowe£33450
Basement conversion near Bury£32820
Basement conversion near Caerphilly£31020
Basement conversion near Calderdale£31650
Basement conversion near Cambridge£35610
Basement conversion near Canterbury£32010
Basement conversion near Cardiff£30930
Basement conversion near Carmarthenshire£30930
Basement conversion near Charnwood£31290
Basement conversion near Chelmsford£34530
Basement conversion near Cheltenham£34890
Basement conversion near Cherwell£34980
Basement conversion near Chester£31650
Basement conversion near Colchester£33720
Basement conversion near Conway£31290
Basement conversion near Coventry£32010
Basement conversion near Crewe & Nantwich£34440
Basement conversion near Dacorum£35880
Basement conversion near Derby£33450
Basement conversion near Doncaster£32820
Basement conversion near Dover£32010
Basement conversion near Dudley£32370
Basement conversion near Dumfries & Galloway£29400
Basement conversion near Dundee£33360
Basement conversion near East Ayrshire£31920
Basement conversion near East Devon£29580
Basement conversion near East Dunbartonshire£33990
Basement conversion near East Hampshire£34710
Basement conversion near East Hertfordshire£36510
Basement conversion near East Lindsey£32550
Basement conversion near East Riding£32910
Basement conversion near Eastleigh£35070
Basement conversion near Edinburgh£35880
Basement conversion near Elmbridge£36240
Basement conversion near Epping Forest£35700
Basement conversion near Erewash£33360
Basement conversion near Exeter£29580
Basement conversion near Falkirk£32910
Basement conversion near Fife£34530
Basement conversion near Flintshire£32010
Basement conversion near Gateshead£34530
Basement conversion near Gedling£33720
Basement conversion near Glasgow£36510
Basement conversion near Gloucester£33540
Basement conversion near Guildford£37050
Basement conversion near Gwynedd£28770
Basement conversion near Halton£31740
Basement conversion near Harrogate£32370
Basement conversion near Havant & Waterloo£34440
Basement conversion near Highland£32100
Basement conversion near Horsham£34530
Basement conversion near Huntingdonshire£34620
Basement conversion near Ipswich£32370
Basement conversion near Isle of Wight£34620
Basement conversion near Kings Lynn & West Norfolk£31200
Basement conversion near Kingston-upon-Hull£31740
Basement conversion near Kirklees£33000
Basement conversion near Knowsley£30840
Basement conversion near Lancaster£32460
Basement conversion near Leeds£33000
Basement conversion near Leicester£30660
Basement conversion near Lisburn£26970
Basement conversion near Liverpool£31290
Basement conversion near London£35880
Basement conversion near Luton£35340
Basement conversion near Macclesfield£32730
Basement conversion near Maidstone£35700
Basement conversion near Manchester£32550
Basement conversion near Mid Bedfordshire£36330
Basement conversion near Mid Sussex£34260
Basement conversion near Middlesbrough£33270
Basement conversion near Milton Keynes£35790
Basement conversion near Neath Port Talbot£31740
Basement conversion near New Forest£35250
Basement conversion near Newbury£34530
Basement conversion near Newcastle-under-Lyme£32190
Basement conversion near Newcastle-upon-Tyne£34800
Basement conversion near Newport£31830
Basement conversion near North Ayrshire£33450
Basement conversion near North East Lincolnshire£33270
Basement conversion near North Hertfordshire£36330
Basement conversion near North Lanarkshire£33090
Basement conversion near North Lincolnshire£31110
Basement conversion near North Somerset£34440
Basement conversion near North Tyneside£35610
Basement conversion near North Wiltshire£33540
Basement conversion near Northampton£34890
Basement conversion near Norwich£30660
Basement conversion near Nottingham£33720
Basement conversion near Nuneaton & Bedworth£32100
Basement conversion near Oldham£32730
Basement conversion near Oxford£35430
Basement conversion near Pembrokeshire£27600
Basement conversion near Perth & Kinross£34080
Basement conversion near Peterborough£33990
Basement conversion near Plymouth£33360
Basement conversion near Poole£34980
Basement conversion near Portsmouth£34260
Basement conversion near Powys£32100
Basement conversion near Preston£32550
Basement conversion near Reading£36510
Basement conversion near Redcar & Cleveland£33720
Basement conversion near Reigate & Banstead£36330
Basement conversion near Renfrewshire£37410
Basement conversion near Rhondda, Cynon, Taff£30570
Basement conversion near Rochdale£32640
Basement conversion near Rotherham£35970
Basement conversion near Salford£32280
Basement conversion near Salisbury£39570
Basement conversion near Sandwell£32280
Basement conversion near Scarborough£32100
Basement conversion near Scottish Borders£38400
Basement conversion near Sefton£31470
Basement conversion near Sevenoaks£35700
Basement conversion near Sheffield£36600
Basement conversion near Slough£36690
Basement conversion near Solihull£32010
Basement conversion near South Ayrshire£32370
Basement conversion near South Bedfordshire£36690
Basement conversion near South Cambridgeshire£36060
Basement conversion near South Gloucestershire£34350
Basement conversion near South Kesteven£31740
Basement conversion near South Lanarkshire£30930
Basement conversion near South Oxfordshire£35700
Basement conversion near South Somerset£37410
Basement conversion near South Tyneside£35070
Basement conversion near Southampton£34800
Basement conversion near Southend-on-Sea£33810
Basement conversion near St Albans£36060
Basement conversion near St Helens£31020
Basement conversion near Stafford£33540
Basement conversion near Stockport£33000
Basement conversion near Stockton-on-Tees£33540
Basement conversion near Stoke-on-Trent£32370
Basement conversion near Stratford-on-Avon£32460
Basement conversion near Stroud£33360
Basement conversion near Suffolk Coastal£30930
Basement conversion near Sunderland£34440
Basement conversion near Swale£33630
Basement conversion near Swansea£33090
Basement conversion near Tameside£33000
Basement conversion near Teignbridge£31740
Basement conversion near Tendring£33000
Basement conversion near Test Valley£33540
Basement conversion near Thamesdown£33450
Basement conversion near Thanet£30120
Basement conversion near The Wrekin£34890
Basement conversion near Thurrock£34980
Basement conversion near Torbay£33450
Basement conversion near Trafford£32910
Basement conversion near Vale of Glamorgan£31110
Basement conversion near Vale of White Horse£34800
Basement conversion near Vale Royal£32280
Basement conversion near Wakefield£33000
Basement conversion near Walsall£32460
Basement conversion near Warrington£32460
Basement conversion near Warwick£32370
Basement conversion near Waveney£33000
Basement conversion near Waverley£36960
Basement conversion near Wealden£33990
Basement conversion near West Lancashire£31200
Basement conversion near West Lothian£35160
Basement conversion near West Wiltshire£33540
Basement conversion near Wigan£31650
Basement conversion near Windsor & Maidenhead£36780
Basement conversion near Wirral£31380
Basement conversion near Wokingham£36510
Basement conversion near Wolverhampton£32460
Basement conversion near Wrexham Maelor£32910
Basement conversion near Wychavon£32550
Basement conversion near Wycombe£36150
Basement conversion near York£31920