Having the Beams team on hand to manage the project and provide extra reassurance on build decisions was incredibly helpful and made the whole experience stress free."
Kerry
London
They have been extremely efficient and reassuring. It was a complex project but they took it all in their stride. They recommended very good contractors who were all punctual, polite and capable."
Andrew
London
All about trust. I felt comfortable with my money, my project, and my home knowing that the outcome would be to my satisfaction or would be made good."
Chris
London
Streatham's basement conversion experts
We match Streatham homeowners with vetted builders who specialise in basements and cellars, and stay in your corner throughout. Your builder runs everything under one fixed-price contract: waterproofing, structural work, electrics, plumbing, insulation and fit-out, so there are no gaps in responsibility and no juggling trades.
Cellar conversion, basement conversion or new basement?
Cellar conversion: If you already have a sound, reasonably dry cellar, this is the simplest route, waterproofing, ventilation, insulation, lighting and access, often with no planning permission.
Basement lowering and underpinning: Where head height is short, the floor is lowered and walls underpinned, usually needing a structural engineer and often planning.
New basement excavation: Where none exists, a major structural project of underpinning, excavation, retaining walls and waterproofing, almost always needing planning.
How basements are waterproofed
Waterproofing is the most critical element of any basement. UK work follows British Standard BS 8102, with Type A (tanking), Type B (integral) and Type C (cavity drain membrane) systems. For habitable rooms, Grade 3 is specified, and in local clay soils a combined Type A and Type C system is common, designed by a CSSW specialist.
What your Streatham basement could become
The right use depends on your home and what you need most: an extra bedroom or guest suite, a quiet home office, a cinema or media room, a gym or wellness space, a wine cellar, or a self-contained annexe that can house family or earn rental income, subject to planning.
What a basement conversion costs in Streatham
Basement conversions are among the most expensive ways to add space, typically more than a comparable loft, because of the structural work and waterproofing, and the whole-job cost depends most on the size of the space and which route your home needs. We give you an estimate range upfront and your builder confirms a fixed price once the design is set.
As a broad guide to the whole project, excluding VAT and fees:
Basement route | Typical estimate |
|---|---|
Cellar conversion | £25,000 to £75,000 |
Lowering and underpinning | £50,000 to £150,000 |
New basement excavation | £150,000 to £400,000 and up |
These are whole-project London market estimates, not Beams data or fixed quotes. Converting a sound existing cellar sits at the lower end, lowering and underpinning for extra head height in the middle, and excavating a brand-new basement is the major structural job at the top.
How a Beams basement conversion works
1. Get your estimate: Tell us about your property and what you want to create.
2. Design and plan: Visualise the space and agree the specification; your first design call is free.
3. Built by your vetted builder: Survey, waterproofing, structural work and finishing, under a fixed-price contract with a 12-month warranty.
Why a basement conversion is worth it in Streatham
A basement conversion typically adds 10 to 20 percent to a property's value in Streatham, and because it adds floor area without touching your footprint or garden, it is one of the most space-efficient ways to make a Streatham home both more valuable and more liveable.
Converting a basement in Streatham
Streatham's large Victorian and Edwardian terraces sometimes have cellars suited to conversion, with a lowering or dig on the bigger houses.
With the average local home selling for around £580,000 over the past year, the extra floor a basement adds is worth getting right. One thing to plan for early is the local planning picture. Streatham Hill and the Leigham Court Estate are conservation areas, so period streets can carry tighter rules on external work.
Our vetted specialists handle it under one fixed-price contract, from waterproofing and underpinning to the final fit-out. We also help homeowners across South London, including neighbouring Balham, Clapham and Tooting.
Other services in Streatham
We also help Streatham homeowners with:
Builders in Streatham
Kitchen renovation in Streatham
Ready to start your Streatham basement conversion?
Get a free estimate and take the first step. No commitment, no sales pressure.