This vendor has lived in this house for many years, with no mould or condensation concerns, so was shocked when the buyer’s RICS identified rising damp in the front reception. They called in an independent damp surveyor, with no financial gain from the outcome of the investigation.
Root causes
Root cause of damp – condensation
Surveyor Tips
- Measure dampness at the base of the wall. If there was rising damp, then the base of the wall would be damp across a level, with no low damp meter readings at the base of a wall.
- Mould is inhibited by the nitrates fund in groundwater. If there is mould at the base of a wall, then there can’t be rising damp.
- Mould points to excess vapour, poor airflow and heat, or heat loss.
- These types of low level damp and mould are accepted by occupiers without concern, they often only get picked up during the sales process.
- It is not uncommon for damp issues to first start showing themselves soon after the birth of a child, that is because of the increased clothes and bottle washing, more people in doors for longer and perhaps unwarranted, concern about preserving heat, so reducing through windows.
Illustrations
Wires are prone to dampness as metal causes heat loss increasing the risk of condensation. There is mould, which there would not be if there was rising damp as mould is inhibited by the nitrates fund in groundwater, the source of water in rising damp.
I tested the surface on the inside at the base of all external walls every metre, chimney breasts and a sample of internal walls with a Protimeter damp meter in conductance mode. These meters measure electrical conductance of salts in water, a proxy for damp. Readings below 20WME are considered dry. The range is 8WME to 99WME. See surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.
If a property is in contact with groundwater, water will rise up like floodwater or kitchen paper lowered into a basin or water.
If there was a groundwater, the source of water in rising damp, then the subfloor humidity will be high, over 90%RH.
The exposed brick, causes slight dampening of the external skin from rainwater, further increases the risk of condensation.
Condensation forms when the temperature drops below the dew point, which was measured at 8.9° C.
Notice also the slight mould on the skirting board. Mould grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficient ventilation, poor air circulation and a cold surface. See surveyor.tips/mould.
The recorded low point at night was 8.6 °C, almost the dew point of 8.9°C, i.e. if we hadn’t made the improvements, then condensation would have formed during the night.
I opened up the trickle vents during the survey.
I am unblocked the backdraught shutter and cleared the dust.
Ideally dry clothes outdoors, in a vented dryer or in a vented room with the door closed such as a bathroom, perhaps completing the drying process indoors once the majority of water has evaporated.
Datalogger
Rising damp risk assessment
Elevation is: 31M above sea level. The flood risk is: no risk.
Sub-soil rocks are: Rocks with essentially no groundwater.
Signs of groundwater: there are no signs of groundwater.
Therefore the risk of rising damp is a remote possibility, see a good explanation by Dr Robyn Pender of Historic England https://youtu.be/Jo8oF9ubvtI
The line of holes in the bricks shows this wall has already been chemically damp proofed against rising damp, hear what Dr Robyn Pender of Historic England says about rising damp treatment.
Despite the low risk of rising damp, there has been an attempt at chemical treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation. The walls have been drilled into by about 200mm and injected with damp proofing chemicals. In theory the chemicals are absorbed into the brick pores reducing the bricks ability to absorb moisture. Walls are replaced with damp proofers slurry. This can cause problems with absorption imbalance, resulting in increased condensation on other walls or vapour becoming absorbed and trapped behind the slurry. There was evidence of surface condensation in areas probably not treated with replacement plaster but no evidence of trapped vapour. The solution is through ventilation and humidity control.