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104D: Vendor lost sale following damp proofer’s rising-damp misdiagnosis

Another tragic lost sale through poor RICS surveying and damp proofing contractor misdiagnosis. Blame the ill-informed judges, such as in Hart v Large.

Surveyor Tips:

  • If it’s already been damp proofed, on what basis do you think more chemicals will solve the internal damp issues?
  • Look for the root cause, suspect inadequate ventilation or use of ventilation firrst before considering damp proofing treatment.

Root cause


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The house has been damp proofed against rising using Chemical injections and dry lining, separating internal plaster from the external wall. Therefore dampness on the internal wall comes from within the property.

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We see a line of damp and rust marks on a plasterer’s corner beading.

Metal loses heat rapidly increasing the risk of condensation from excess humidity.

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I detected dampness by the beading using a damp meter.

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 d 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.

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Surface salts are crystalising high up on the kitchen wall.

There are calcium sulphate salts on the surface. Calcium sulphate is a key ingredient in cement and other building materials. If diluted in water salts tend to move to the surface. These can be removed with sandpaper and decorated.

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There is dampness above the doorway, which could not possibly come from rising damp.

The wall above the door is effectively external, increasing heat loss and risk of condensation.

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I detected metal above the doorway.

Lintels tend to be strengthened by metal rods which lose heat rapidly at night.

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There is damp zone stretching from about 2M on the boxing in the rear reception wall, down to the ground.

The boxing presumably houses water. I believe that there is heat loss resulting in condensation taking place within or on the surface of the boxing.

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There are some surface salts at the base of the same wall, on the boxing.

The high damp meter reading on a section of the dry line wall, i.e. not connected externally also suggests condensation.

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The vertical line of damp proofing suggests that there was concern about dampness from the wall.

Adjoining walls can cause heat loss increasing the risk of condensation, this often leads to misdiagnosis.


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The bathroom extractor and nearby fan were both turned off, suggesting they weren’t always used by tenants.

The kitchen’s extractor fan is not externally ducted. Ventilation is most effective when air is extracted close to the vapour source; bathroom, kitchen, drying clothes and occupied rooms. The ventilation does not meet Building Regulation 2010 Part F requirements. This is best achieved with mechanical extractor fans. See surveyor.tips/vent_regs:

  1. Bathroom 15 l/s with a 30-minute overrun.
  2. Kitchen 30 l/s adjacent to hob; or 60 l/s elsewhere in kitchen.

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The windows were all locked and there are no trickle vents. Windows should allow some airflow.

These windows should be capable of being locked slightly open to allow background ventilation. At the moment there is no background ventilation.

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There are patches of salts near the water pipe in the under-stair cupboard.

The under-stair wall was dry. However mains water comes into a property at about 8°C in winter it is common for condensation to form cold water pipes. Consider insulating them.

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I tested the sub-floor void with a hygrometer, the humidity reading was normal.

If there had been rising damp, or even rot in the sub-floor, then the sub-floor humidity would be over 85%RH.

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I looked in the sub-floor void under the staircase for signs of rot.

There were no signs of rot. A section of timber is green. This suggests that it is tantalised to prevent rot, typically following an outbreak of rot in the past.

Other matters

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There is a build-up of plant growth on the left-hand party wall (when seen from the street).

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Take care to fill any gaps in timber of render, such as the above, and make sure to paint regularly.

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