The most important tool to include in every damp survey of a property with a ground floor is a desktop rising damp assessment.Every buyer, landlord and homeowner of a property with a ground floor should expect a competent damp surveyor to undertake a rising damp risk assessment.Contents hide3 1. Groundwater
What is a rising damp assessment?
- Rising damp is the upward absorption of groundwater.
- Groundwater is the water under the water-table.
- If there is no risk of groundwater, then there is no risk of rising damp – end of.
Desktop rising damp risk assessment
In and around most of London the sub-soil rock is a type that does not contain groundwater – therefore the risk of rising damp is remote. Furthermore in the areas where rock could contain groundwater, the groundwater is pump out to a level below the underground network otherwise there would be a risk of flooding.
Look up sub-soil rocks; British Geological Survey
2. Flood risk
If there is a risk of aquifers below ground, i.e. there could be groundwater, you then have to assess if the groundwater will flow towards your property by using the surface flood.
3. Look for groundwater
If you have a risk of groundwater and a risk that groundwater will flow towards the property, then look to see if. you can see 1 or meters below the ground level, for example:
- road outside or
- is there a slight slope away from the property.
If you can’t see damp in any of these then you don’t have groundwater within reach of your property.
This is not always easy, but Thames Water show a cross section of the water table through London. In 1967 the water-table was estimated to be about 100M below Nelson’s Column.
5. Drill for groundwater
If you can see water within 1M of the ground level then:
Referring to local searches for drain and mains water pipes and taking great care not to cause a leak or manage wires, slowly drill with a meter long drill bit 1M below the ground level away from drains and electrical wires (we cannot take any responsibility for damage resulting this or any other test or recommendation). Place a tube into the hole and leave to giving water time to rise and leave a “tide” mark on the inside of the tube. Inspect after a day or so.
6. Drill in multiple locations for groundwater.
If you have water, then it is possible that you have a local leak. If there is groundwater, the level will be more or less horizontal over a distance of about 20M or so. You can test for presents of nitrates. However, mains water often contains nitrates as can rainwater percolating through soil. You can drill multiple holes to establish if the water levels are horizontal.