Cellar damp and tanking in Doncaster: groundwater, options

Parts of Doncaster borough sit on low, flat ground near the River Don and its tributaries. That can mean a high water table, slow-draining ground and below-ground rooms that struggle to stay dry. This guide explains why cellars and semi-basements in Doncaster get damp, the main tanking options and what to ask before work starts. It also covers under-floor voids, which are far more common. It is general information, not a diagnosis.

Why cellars and low floors get damp in Doncaster

Low-lying ground and a high water table. Groundwater can sit close to cellar floor level, particularly after prolonged rain (see the groundwater section below).
Poor surface drainage. Blocked gullies, broken drains and gutters discharging at the wall let water collect against below-ground walls.
Porous brick below ground. Older cellars were built to be cool and slightly damp, not waterproof.
Ground movement. In former mining areas, ground movement can crack walls and floors and open new routes for water.
Condensation. Cool cellar walls and poor ventilation produce musty air and mould even when there is no leak. See condensation or rising damp? and black mould removal and causes.

Damp, wet or flooded?

A damp cellar has patches, salts, a musty smell or condensation. A wet cellar has standing water or visible flow after rain. They need different solutions. If water has come from a river, surface water or a sewer, that is a flood issue, not a damp one. You can check your area’s risk at GOV.UK: check your long term flood risk.

Groundwater: when water comes up through the floor

The Environment Agency describes groundwater flooding as water under the ground rising to the surface, and says underground rooms such as cellars and basements are particularly at risk. It can happen in river valleys with sand and gravel. The signs are different from a flood off the street: water comes up through the ground or floor rather than through doors, it usually arrives days, weeks or months after a lot of rain, and it can last for weeks or months (GOV.UK: groundwater flooding). The Environment Agency also warns that many traditional flood protection methods may not work against groundwater (Environment Agency blog).

Parts of Doncaster are on exactly this kind of ground. The council’s Section 19 flood report describes the soils around Bentley as “loamy and clayey floodplain soils with naturally high groundwater”; see damp proofing in Bentley. If your cellar gets wet weeks after heavy rain rather than during it, mention that to anyone you ask for advice.

Cellar tanking options

Cement-based tanking slurry. A waterproof coating applied to prepared walls and floor. It needs a sound, clean surface and holds water back rather than draining it.
Membrane (cavity drain) systems. A dimpled membrane that lets water run behind it to a drain and then to a sump and pump. Often considered where water pressure is a factor.
Sump and pump. Collects water and moves it out of the cellar. It needs power and maintenance, and back-up power is often discussed.
External drainage. Clearing or repairing drains, gullies and ground drainage can reduce the water reaching the wall.

Building regulations guidance points to a specific standard for this work. Approved Document C says BS 8102 includes recommendations for walls subject to groundwater pressure, including basement walls, and for floors subject to water pressure (Approved Document C (PDF)). It is reasonable to ask whoever designs the work whether it follows BS 8102 and how they assessed the water pressure.

Under-floor voids and air bricks

Most Doncaster houses have no cellar but do have a ventilated void under timber floors. Blocked air bricks, raised paths and ground built up above the air bricks cut airflow and can lead to damp joists and a musty smell. Keep air bricks clear and ask for a void inspection if you notice soft boards or a smell under the floor.

Using a cellar as living space

Using a cellar as a utility room, office or bedroom needs a much higher standard than storage. Expect proper waterproofing, ventilation and building regulations approval. Check with City of Doncaster Council building control and ask any contractor how their design meets the requirements.

What to ask before work starts

Where is the water coming from, and how was that established?
Have drains, gutters and ground levels outside been checked?
Why is this method right for these walls and this level of water?
What happens if the pump fails or the power goes off?
What is guaranteed, for how long and who stands behind it?
Is the quote itemised and in writing?

Next step

If you rent and the landlord has not dealt with a damp cellar, see damp and mould in rented homes. If your cellar or floor void is getting wetter, tell us what you can see through the enquiry form. With your consent, we will pass it to a local damp and mould professional who can talk it through and, if needed, arrange a survey and written quote. See what a damp survey costs and should include first if you want to know what to expect.

Sources and further reading

GOV.UK: groundwater flooding; Environment Agency: what is groundwater flooding?; Approved Document C: site preparation and resistance to contaminants and moisture (PDF); Doncaster Council: Section 19 flood investigation report, September 2020 (PDF); City of Doncaster Council: building control; GOV.UK: check your long term flood risk; GOV.UK guidance on damp and mould.

Related guides

Frequently asked questions

Are cellars common in Doncaster homes?

They tend to be less common than in hillside towns, but older houses, some villas and many buildings in the town centre have cellars or semi-basements. Many other homes have sub-floor voids that can also get damp.

Why does my Doncaster cellar flood or stay damp?

Low-lying ground, a high water table near the River Don and its tributaries, blocked drains and poor ground drainage can all push water towards below-ground walls and floors. Heavy rain makes it worse.

What is cellar tanking?

Tanking means making the walls and floor of a cellar waterproof so the space can stay dry. It can be a cement-based coating or a membrane system that drains water to a sump and pump. The right choice depends on the walls, the water pressure and how you will use the space.

Do I need building regulations approval to convert a cellar?

Turning a cellar into habitable space normally involves building regulations, for example for damp-proofing, ventilation and escape. Check with City of Doncaster Council building control before work starts.

Can groundwater come up through a cellar floor?

Yes. The Environment Agency says cellars and basements are particularly at risk from groundwater flooding, where water rises through the ground or floor, usually days, weeks or months after a lot of rain, and can last for weeks or months. Traditional flood protection may not stop it, so the tanking or drainage design needs to allow for it.