Cellar Conversion UK Cost Guide

Quick Cost Breakdown

Costs vary depending on the size of the space, the condition of the cellar, and how much structural work is involved. Here's what most homeowners pay in 2026:

• The average cellar conversion costs £30,000 to £50,000 for a typical 20 m² space.
• Victorian cellars often cost more, from £25,000 for a small space up to £100,000+ where floor lowering is needed.
• Location plays a significant role, with London conversions running 30 to 50% above the national average.

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A Guide to Cellar Conversion Costs

Whether you're trying to work out if a conversion is worth doing or ready to start getting quotes, jump to what's most useful here.

In this guide, we cover:

1. Should I Convert My Cellar?
2. Cellar Conversion Cost by Size
3. Victorian Cellar Conversion Cost
4. Cellar Conversion Costs by City
5. Cellar Waterproofing and Damp Proofing Costs
6. Find Cellar Conversion Specialists on MyBuilder
7. FAQs: Common Questions About Cellar Conversions

Read on for a full breakdown of cellar conversion costs, what drives the price, and how to find the right specialist.

Should I Convert My Cellar?

If you have an unused cellar beneath your home, converting it into functional living space is well worth considering.

A cellar conversion can add significant value to your property, often between 10 and 15%, while giving you extra room without the disruption of a full extension.

Cellar conversions are popular for:

• Home offices: A quiet, separate workspace away from the rest of the house.
• Guest bedrooms: An extra room without sacrificing existing living space.
• Playrooms or entertainment rooms: Ideal for families needing more space.
• Utility or storage rooms: Freeing up space on your main floors.
• Home gyms: A dedicated fitness area without taking over the garage.

Not every cellar is suitable for conversion. Before committing, check your ceiling height (at least 2.4 m is ideal), staircase access, and whether you need planning permission, particularly for listed buildings or conservation areas. If your cellar ticks these boxes, it's likely a sound investment.

Cellar Conversion Cost by Size

Size is one of the most significant factors in your final cellar conversion bill. The table below covers typical prices based on floor area for a basic conversion, which includes waterproofing, insulation, electrics, and plastering on an existing shell with adequate ceiling height.

Average cellar conversion cost:

Cellar size	Basic conversion cost
10 m²	£9,000-£18,000
15 m²	£13,500-£27,000
20 m²	£18,000-£36,000
30 m²	£27,000-£54,000
40 m²	£36,000-£72,000

A full fit-out adding flooring, lighting, plumbing, and finishing will push costs higher. Every cellar is different, so it's worth getting a quote from a conversion specialist near you to get an accurate price for your specific space.

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Victorian Cellar Conversion Cost

Victorian cellars are among the most commonly converted in the UK, but they often come with extra challenges that push costs higher.

Expect to pay anywhere from £25,000 for a small Victorian cellar up to £100,000+ for a larger space, depending on the size and scope of work involved.

The main reasons Victorian conversions cost more:

• Floor lowering or underpinning: Most Victorian cellars don't meet the 2.4 m ceiling height requirement, so the floor needs to be dug out and foundations reinforced. See our guide on lowering a basement floor for a full cost breakdown.
• Damp proofing: Older brickwork is rarely waterproof, so a full tanking or cavity drain system is usually essential.
• Structural repairs: Crumbling mortar, deteriorating lintels, and ageing walls often need attention before conversion work can begin.

Despite the higher upfront cost, Victorian cellar conversions can add considerable value, particularly in period properties where extra square footage commands a premium.

When posting your job on MyBuilder, mention that it's a Victorian property so you can find specialists familiar with the particular challenges of older cellar structures.

Cellar Conversion Costs by City

Where you live has a big impact on what you'll pay. Labour rates, material costs, and demand for conversion specialists all vary across the UK.

Here's how average cellar conversion costs compare for a typical 20 m² space:

• Cellar conversion cost London: £45,000–£75,000
• Cellar conversion cost Leeds: £30,000–£50,000
• Cellar conversion cost Bristol: £32,000–£52,000
• Cellar conversion cost Sheffield: £24,000–£40,000
• Cellar conversion cost Birmingham: £28,000–£48,000

London is consistently the most expensive, with labour rates often 30 to 50% higher than the national average. Northern cities like Sheffield tend to offer the best value, though costs are rising as demand for cellar conversions grows across the country.

Cellar Waterproofing and Damp Proofing Costs

Almost every cellar conversion will need some form of waterproofing. Without it, damp and water ingress can cause serious damage to your new living space, and fixing it retrospectively once a conversion is finished is significantly more expensive than addressing it upfront.

The method you need depends on the severity of the problem and the type of cellar you have:

• Damp proof membrane (DPM): £50-£80 per m². A plastic sheet applied to walls and floors to block moisture from passing through. Suited to cellars with minor damp and no active water ingress.
• Cavity drain system: £80-£150 per m². A membrane with an air gap that channels water to a drainage point. The most common choice for UK cellar conversions, as it manages water rather than trying to block it.
• Tanking (cementitious waterproofing): £60-£120 per m². A waterproof coating applied directly to walls and floors. Best suited to cellars with minor damp and solid masonry walls.
• Exterior waterproofing (excavation required): £100-£200 per m². Waterproof membranes applied to the outside of foundation walls. The most disruptive but most thorough option.
• Sump pump installation: £500-£1,500. A pump fitted below floor level to remove water that collects beneath the cellar, often paired with a cavity drain system.

If your cellar has a history of flooding or visible water ingress, it's worth getting a specialist damp survey before committing to a method. For a full breakdown of treatment options and pricing, see our damp proofing cost guide or damp survey cost guide.

Combining your waterproofing and conversion work into a single project with one contractor is often cheaper than hiring separately. You'll avoid paying for two lots of skip hire, scaffolding, and site setup.

Find Cellar Conversion Specialists on MyBuilder

Getting the right specialist is the most important step in any cellar conversion. Post your job on MyBuilder for free and receive responses from local professionals with availability.

You can review their profiles, read customer feedback, and browse photos of completed projects before deciding who to hire.

All tradespeople on MyBuilder undergo checks at registration, such as ID documents, company details, certifications for regulated jobs and skill assessments, allowing you to hire with confidence.

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FAQs: Common Questions About Cellar Conversions

Do I Need Planning Permission for a Cellar Conversion?

In most cases no. Cellar conversions usually fall under permitted development. However, if your property is listed or in a conservation area, you'll likely need to apply for planning permission. Building regulations approval is always required regardless of permitted development status.

How Long Does a Cellar Conversion Take?

Most conversions take between 4 and 8 weeks for a straightforward project. If underpinning or extensive waterproofing is needed, expect 8 to 12 weeks or more. When posting your job on MyBuilder, include images of your current cellar to help specialists give you a more accurate timeline upfront.

Does a Cellar Conversion Add Value to Your Home?

Yes. A well-executed cellar conversion can add 10 to 15% to your property's value. In areas where space is at a premium, the return can be even higher. You can browse photos of completed cellar conversion projects on MyBuilder to see real examples and get a sense of what different finishes and layouts look like.

What Is the Cheapest Way to Convert a Cellar?

A basic conversion on a cellar that already has adequate ceiling height and minimal damp is the most affordable route. Skipping underpinning and opting for a simple damp proof membrane rather than a full cavity drain system can keep costs under £20,000 for a smaller space.

Is It Worth Converting a Cellar with Damp?

Yes, if the damp can be properly treated. A cavity drain system or tanking will resolve the majority of damp issues. Only in cases of severe structural water ingress might a conversion become unviable, and a specialist damp survey will confirm this before any money is committed.