Approved member of the Federation of Damp
Below-ground waterproofing specialists · Dulwich, SE21, SE22
Basement Waterproofing in Dulwich
Dulwich and Herne Hill have large Victorian and Edwardian houses on London Clay, many with cellars that owners now want to use as living space. Advanced Damp designs and installs basement waterproofing across SE21, SE22 and SE24, from cellar conversions to new basements.
Newton Approved
Below-ground waterproofing across London and the South East.
CSSW and CSRT Trained Surveyors
Systems designed and specified to BS 8102:2022.
Long-Term Guarantee
Written guarantee on all new waterproofing installations.
CHAS Accredited
Fully insured, fixed-price quotations after survey.
Dulwich Sits on Clay and a Lost River
Dulwich sits on London Clay, which covers almost the whole area between Denmark Hill, Sydenham Hill and Herne Hill. Clay drains slowly, so after rain the water held in the ground stays against cellar walls for weeks rather than draining away. In winter, many Dulwich cellars are effectively sitting in wet clay.
The area also has one of south London's best known lost rivers. The Effra rose on the slopes around Norwood and flowed north through Dulwich and Herne Hill towards Brixton and the Thames. It was put into culverts in the 19th century, but the shallow valley it followed is still there, and streets along its old course collect surface water and groundwater after heavy rain. Sydenham Hill and Dulwich Wood to the south also feed spring water down the slopes.
Much of Dulwich was built later than inner London, from the 1870s to the 1930s, with large detached and semi detached family houses. Many have a cellar under part of the ground floor, usually brick walled with a brick or earth floor and no waterproofing. Herne Hill and East Dulwich have rows of Victorian terraces with similar shallow cellars.
Dulwich Village and the surrounding estate are also unusual in planning terms. Much of the land is owned by the Dulwich Estate, which manages a Scheme of Management requiring its consent for many external alterations, on top of normal planning permission from Southwark Council. Converting an existing cellar internally is usually simpler, but new basements and lightwells need careful planning.
Because the clay holds water for so long, we usually recommend a Type C cavity drain system for any cellar being turned into a living space. We design to BS 8102 and give you a written specification you can share with your architect, builder or the Dulwich Estate.
Why Dulwich Basements Need It
Dulwich cellars take on water from wet London Clay, from the old Effra valley and from spring water coming off Sydenham Hill. Common local risk factors include:
Left untreated, this sustained moisture pressure leads to efflorescence and salt staining, plaster breakdown, mould growth, timber decay in ground-floor joists and, over time, structural deterioration of the masonry itself.
Our Waterproofing Systems
Dulwich's London Clay keeps cellar walls wet for much of the year. We specify systems that collect and remove that water rather than simply coating over it. A survey decides which system is right for your property.
Type A · Cementitious Tanking
A rigid bonded coating applied directly to sound masonry. Suited to Dulwich cellars with stable brickwork and lower moisture risk storage spaces, plant rooms and vaults where full habitable conversion is not required.
Basement tanking →Type C · Cavity Drain Membrane
Our most specified system for SE21. A studded membrane channels groundwater safely to a sump rather than resisting it. the reliable choice where sustained hydrostatic pressure makes blocking water impractical.
Cavity drain membrane →For new basement excavations or projects requiring Camden planning submissions, see our work on structural waterproofing and cellar tanking.
How We Work
Groundwater & Assessment
A CSSW surveyor visits your Dulwich property, identifies the water source, and reviews any previous failed treatments before recommending a system.
System Design & Fixed Price
We specify the right system for SE21's groundwater conditions to BS 8102:2022 and provide a clear, fixed-price proposal agreed before any work begins.
Installation & Guarantee
Our own teams install the system, no subcontracting. On completion, we issue a written long-term guarantee and advise on long-term sump maintenance.
Why Choose Advanced Damp in Dulwich?
What Our Customers Say
"This is my 4th time hiring Advanced Damp. As a property investor I can't stress how important it is to find contractors you can rely on, and Advanced Damp always deliver. Professional, efficient and trustworthy."
Baylee Greenberg, Google Reviews"The surveyor was very thorough, explaining the cause of the problem and what needed to be done. The team that came to carry out the work were professional and efficient. Very happy with the results."
Tom Rimmer, Google ReviewsPlanning work on a basement in Dulwich?
The right system depends on how water reaches your walls and floor. A survey finds that first, so the design fits your property and the price is fixed before anything starts.
Book a Basement SurveyCall 0300 373 7251- 1. Book online or callPick a time that suits you.
- 2. Surveyor visitsMoisture readings, water source and the condition of the walls and floor.
- 3. Written specificationThe right system for your basement, with a fixed price and no obligation.
A Real London Type C Project
Basement Waterproofing Project in Fulham
See how our team successfully designed and installed a complete basement waterproofing system for a residential property in Fulham. This project highlights our risk-led approach, high-quality workmanship, and long-term waterproofing solutions for London homes.
Basement Waterproofing Across London
We design and install basement waterproofing across London and Surrey. Choose your area for local ground conditions, common problems and FAQs.
Accredited & Trusted
Recent Basement Work Near Dulwich
Our recent basement waterproofing work includes basement flat entrance, SE20; lower ground flat, Wandsworth SW18 and new basement, Fulham SW6. Each case study sets out what the survey found and how the problem was fixed.
Basement flat entrance, SE20
A blistered wall inside the front door was rising damp in one small area, treated with a DPC and tanked render.
Read the case study →
Lower ground flat, Wandsworth SW18
Bedroom mould from condensation and groundwater. Type C waterproofing, smart fans and a mould wash.
Read the case study →
New basement, Fulham SW6
A Type C cavity drain membrane system installed to a newly built lower ground floor, designed to BS 8102:2022 for a Grade 3 dry, habitable space.
Read the case study →Dulwich Basement Waterproofing FAQs
Do I need Dulwich Estate consent to waterproof my cellar?
Internal waterproofing of an existing cellar does not usually involve the Dulwich Estate. If the work changes the outside of the house, such as a new lightwell, window or external drainage, you may need Estate consent as well as planning permission. Check with the Estate before external work is designed.
My Dulwich cellar has an earth floor. Can it still be waterproofed?
Yes. We remove the loose earth or broken brick, lay a new floor slab where needed and then fit the waterproofing system across the floor and walls. An earth floor is common in older Dulwich cellars and does not stop a conversion.
Why does my street flood when other streets nearby do not?
Some Dulwich and Herne Hill streets follow the old valley of the River Effra, which is now in a culvert. Low points along that valley collect surface water and groundwater after heavy rain. We check where your property sits in relation to the old river course during the survey.
What is the best waterproofing for a Dulwich cellar conversion?
For a habitable room, we usually recommend a Type C cavity drain membrane with a perimeter drainage channel and sump. It manages water rather than trying to block it, which suits the wet London Clay that surrounds most Dulwich cellars.
Can you also deal with damp in the rest of my Dulwich house?
Yes. We survey and treat damp above ground too, including rising damp, penetrating damp and condensation. The survey can cover the whole house and the cellar in one visit.
Do you cover Herne Hill, East Dulwich and Sydenham?
Yes. We cover Dulwich Village, West Dulwich, East Dulwich, Herne Hill, Sydenham Hill and the surrounding SE21, SE22, SE24 and SE26 streets.
Related Services
Book a Dulwich Basement Waterproofing Survey
If your Dulwich or Herne Hill property has a cellar or basement showing damp, salts or water, or you are planning a conversion, the first step is a survey by a CSSW and CSRT trained specialist who understands south London clay.
We will assess your specific building, identify the source and type of water ingress, and specify the right system in writing with a fixed price.