Basement & Cellar
Conversions and
Waterproofing.
Turn the space beneath your home into rooms you'll actually use. Structural waterproofing designed to BS 8102 across Oxford and Oxfordshire.
Basement & Waterproofing
Structural waterproofing specialists in Oxfordshire.
Turn the space beneath your home
into rooms you'll actually use.
A basement or cellar conversion adds valuable living space without extending outwards or upwards — ideal for Oxfordshire homes on tight or protected plots where a conventional extension isn't possible. Whether you're converting a damp Victorian coal cellar into a home cinema, or excavating a brand-new basement beneath a period property, the project lives or dies on one thing: waterproofing.
At Crawford Construction we do both, properly. We design and build basement and cellar conversions across Oxford and Oxfordshire, and we install structural waterproofing systems to the British Standard so the finished space stays permanently dry. Free survey, itemised fixed-price quote, and a guarantee behind the work.
Our expertise
- Full cellar & basement conversions
- BS 8102-compliant waterproofing
- Cavity drainage & sump systems
- Underpinning & structural works
- Standalone damp proofing
- Planning & Building Control
Basement and cellar conversions
We transform below-ground space into valuable, usable rooms.
Home cinemas & media rooms
Naturally insulated from light and sound — the perfect subterranean entertainment space.
Gyms, studios & games rooms
Dedicated workout and recreation spaces below ground, away from the living areas.
Bedrooms & guest suites
Additional bedrooms with en-suites, adding real value to your home.
Home offices
A quiet, focused workspace away from the bustle of the house.
Utility, storage & wine cellars
Practical below-ground storage, utility rooms, and temperature-stable wine cellars.
Self-contained annexes
Where access and head height allow, fully self-contained living spaces.
Conversion work typically involves lowering the floor level to gain head height, underpinning the existing foundations, installing a proper staircase, and creating natural light through light wells or sunken courtyards where possible — all on top of a complete waterproofing system.
Structural waterproofing — done to the standard
Below-ground waterproofing in the UK is governed by BS 8102:2022. A proper design assesses the water table, soil conditions and hydrostatic pressure, then specifies one — usually a combination — of three approaches:
Barrier protection / tanking
A continuous waterproof barrier applied to the structure, such as cementitious tanking slurry or a membrane.
Structurally integral protection
The structure itself, typically water-resistant reinforced concrete, is engineered to hold back water.
Drained protection / cavity drainage
A cavity drainage membrane manages any water that penetrates, channelling it to a sump and pump system that discharges it safely away.
Our recommended approach
For most Oxfordshire cellar conversions we design a robust system — frequently Type C cavity drainage, or a belt-and-braces combination — because it manages water rather than simply trying to block it, and remains maintainable for the long term. Every design should be signed off by a CSSW-qualified waterproofing surveyor and backed by an insurance-backed guarantee.
Standalone damp proofing
We also carry out standalone damp proofing and cellar waterproofing where you don't need a full conversion — tackling damp walls, salts and water ingress in existing cellars.
Why waterproofing matters especially in Oxford
Oxford sits between the Thames and the Cherwell, and parts of the city and surrounding villages have a high water table and a history of flooding. Many older homes have brick or stone cellars built long before modern waterproofing existed. That combination makes a correctly designed, properly installed system non-negotiable here — a cheap "tank and hope" job will fail. We survey the specific conditions of your property before we specify anything.
Planning, building regulations and party walls
Planning permission: Converting an existing cellar that doesn't change the external appearance often falls under permitted development, but excavating a new basement, adding a light well, or altering the façade usually needs full planning permission.
Building Regulations: All habitable basement work requires Building Regulations approval, covering structure, waterproofing, ventilation, fire escape and natural light. We manage Building Control in-house.
Structural engineering & party walls: Lowering floors and underpinning are significant structural operations requiring a structural engineer's calculations. Where the Party Wall etc. Act 1996 applies, we guide you through serving notice early.
How we work
From first survey to final handover — a thorough, transparent process.
Survey & feasibility
We assess head height, structure, water table and access, and tell you honestly what's achievable.
Design & waterproofing specification
Engineering, drainage strategy and a BS 8102-compliant waterproofing design.
Approvals
Planning, Building Regulations and Party Wall handled for you.
Construction
Underpinning, excavation, waterproofing and fit-out by skilled trades, fixed price, regular updates.
Handover
Full walkthrough, completion certificate, guarantees and aftercare.
Why choose Crawford Construction
Conversion and waterproofing under one roof — no gap between builder and waterproofing specialist
Designed to BS 8102 — the proper structural-waterproofing standard, not a quick tank job
Local knowledge of Oxford's water table, rivers and period cellars
Everything handled — structural design, planning, Party Wall, Building Control and build
Fixed-price, itemised quotes — you pay as work is completed
Insurance-backed guarantee on the waterproofing system
Areas we serve
Oxfordshire
Basement and cellar conversions and waterproofing across Oxford City Centre, Headington, Summertown, Jericho, North Oxford, Cowley and Iffley, and throughout Oxfordshire — Witney, Bicester, Abingdon, Didcot, Kidlington, Woodstock, Thame, Banbury and the Cotswolds.
Start your basement project
Tell us about your project and we'll reply within 24 hours with the next steps. Free survey, no-obligation, and 100% confidential.
Frequently asked questions
Everything you need to know about basement conversions, waterproofing and cellar work.
In Oxford, where space is at a premium and many plots are protected or built-up, a basement can be one of the few ways to add significant living space — and it can add real value, particularly when it creates an extra bedroom or a dedicated cinema or gym. It's a higher cost per square metre than a loft, so we'll give you a frank cost-versus-benefit picture at survey stage.
Not if it's designed and built correctly. A properly specified system to BS 8102 — usually cavity drainage with a sump and pump — manages groundwater and keeps the space permanently dry. The failures you hear about almost always come from cheap, single-layer "tanking" with no drainage and no guarantee. We don't work that way.
Converting an existing cellar without changing the outside of the house often doesn't need planning permission, but digging a new basement, adding a light well or altering the façade usually does — and conservation areas and listed buildings add further requirements. Building Regulations approval is always needed for habitable space.
It varies widely with whether you're converting an existing cellar or excavating new space, the amount of underpinning, the waterproofing system and the finish. Excavating a new basement is a major structural project and priced accordingly. We provide a free, itemised, fixed-price quote after surveying your property rather than a guess.
Converting an existing cellar is quicker than excavating a new basement, which is a substantial structural undertaking. We give you a clear programme before starting; survey, design and approvals also add time at the front end.
Tanking (Type A) tries to block water with a barrier. Cavity drainage (Type C) accepts that water may find a way in and manages it — channelling it via a membrane to a sump and pump. Cavity drainage is generally the more reliable, maintainable choice for habitable basements, which is why we favour it.
Yes — a properly installed structural waterproofing system should come with an insurance-backed guarantee, so you're protected even in the unlikely event of an issue down the line.
Yes. We carry out standalone cellar waterproofing and damp proofing to make an existing cellar dry and usable for storage or utility, without a full habitable-room fit-out.
Let's build
somethingremarkable.
From first sketch to final handover — Oxfordshire's trusted team for homes built with precision, craftsmanship and care.
