Damp basement? Find the cause first
A damp basement has one of four causes: groundwater pushing through, a leaking drain or gutter, condensation, or rising damp. Fixes run from €300 to €1,800 for ventilation to €3,000 to €12,000 for a membrane and sump.
Free, no obligation. One local company prices it, not five.
- €300 to €1,800ventilation for condensation
- €700 to €3,600damp proofing a small area
- €3,000 to €12,000a membrane with a sump
- €200 to €500a good dehumidifier
Cellars and basements
Where the water comes from
- Groundwater. Wet patches low on the walls and where the floor meets the wall, worse after heavy rain or in winter. Sometimes standing water. Fix: a drained membrane and a sump.
- A leak from outside. One wet patch under a gutter, a downpipe, a drain or a path that slopes to the wall. Fix: the leak first, then dry the wall out.
- Condensation. Damp in cold corners, on windows and pipes, black mould, worse when people use the room. Fix: heat, insulation and ventilation.
- Rising damp. A tide mark up to about a metre, salts in the plaster, in walls with no working damp-proof course. Fix: a new damp-proof course and salt-resistant plaster.
A cheap test: tape a square of kitchen foil to the wall for two days. Damp on the room side is condensation. Damp under the foil is coming through the wall.
Damp and radon come in the same way
Radon is a radioactive gas from the ground. It comes in through cracks in floors and gaps around pipes, the same routes as damp. When a basement is opened up to fix damp, it's the time to seal the floor and add a radon sump. See radon and basements.
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Questions we get asked
Why does my basement smell musty?
Damp air and mould. Find whether it's condensation or water coming through the walls before spending money on a fix.
Will a dehumidifier fix a damp basement?
It helps with condensation. It won't stop water coming through the walls or floor.
Is a damp basement dangerous?
Mould can affect breathing, especially for children and anyone with asthma. And the same gaps that let in damp let in radon.
Does house insurance cover a damp basement?
Usually not for gradual damp. A sudden escape of water, like a burst pipe, is a different matter. Check your policy.
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