102X: RICS rising damp claim

The buyer of the Victorian terraced house in North London, was concerned about the accuracy of his RICS homebuyers report:

“E4: Damp Arrange for a PCA registered contractor to inspect the whole property and make recommendations for dealing with rising damp in the property.”.. “Evidence of significant rising damp was also recorded on the ground floor living room, extension, and basement level.”

There was no attempt to provide evidence of groundwater. He made no attempt to talk to the owner about the background, if he had, he would have found out that the roof was new and rainwater goods were replaced. Damp was not profiled. Bathroom ventilation was not checked..

Root causes

The root cause penetrating damp and vapour from a cold section of boxing caused by the bathroom ducting.

Surveyor Tips

  • Always talk to an occupier about the background, history and anything you are uncertain about. Be respectful, but sceptical – without showing it.
  • In the case of a sales transaction always look for persuasive, corroborating evidence for any information provided by an owner, whether you are acting for the buyer, or indeed seller and provide the evidence in the report.
  • Check risk of rising damp against know risks. In London, where groundwater is pumped out, it is highly unlikely that there will be rising damp. In chalk or limescale areas such as the Clearwater Chalk groundwater flooding around Oxfordshire, rising damp is rare, but more likely – see an interesting report.

Illustration

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There is a high damp meter reading to the right of the front bay (as seen from the street).

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.

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The damp meter drops to normal levels, away from the bay, here by the front door.

If there was rising damp, which there isn’t, then then the base of the wall would be consistently damp in an approximate horizontal band like the rise of damp above a flood.

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The cause of the damp is evident on the outside where a crack in the windowsill is causing penetrating damp.

These cracks should be filled with either a cement-based render or external acrylic caulk. Some timbers are showing early signs of Phellinus contiguus or window rot. Window rot is very common in old properties, it is a slow growing white rot. None of the timbers are structurally significant. The rot can be cut out, sanded, filled and painted for protection.

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There is a similar crack on the left-hand side.

The crack in this windowsill and render at the base of the wall is almost certainly the root cause of penetrating damp to the top of the internal plaster in the basement.

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Note the downpipe in the front left-hand corner is missing the elbow and extension.

You should re-attach the downpipe extension so as to drain rainwater from above the bay, away from the property.

We can see the brown teabag like stain, immediately below the bay, in the basement.

This is penetrating damp and likely to be caused by the crack to the windowsill and/or the downpipe.

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There is also a stain to the rear section of the basement by the French windows.

The wall by the French windows was dry on both sides as seen in this image (above) of the damp meter reading. Note the lack of digits is because the wall is too dry to be read by the meter

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The owner told me that this damp stain is old and results from a defective hopper which he had replaced.

The hopper looked to be in good working order There were no signs of ongoing penetrating damp from the rear rainwater goods. 

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There is a patch of surface salts under the ceiling void, near to where the bathroom ducting exits the property.

The meter reading was marginal high. There is an ongoing risk of condensation moisture caused by heat loss near the external vent.

The roof looks new and in good order.

Note London (or butterfly) roofs have a valley in the centre of the property. They are often poorly installation under the valley, resulting a risk of condensation and mould. There were no signs of damp under the valley, but it is common for owners (and builders advising them) to replace their roofs believing that the damp problem is external, rather than internal.

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There are signs of penetrating damp by the skylight.

There are signs of condensation forming on the cold window and dribbling down the timber, causing discolouration.

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Condensation was forming on this metal bedroom window frame.

Modern timber or UPVC double glazed windows have better insulating properties.

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There is no ventilation in the upstairs bathroom.

Ventilation is most effective when air is extracted close to the vapour source; bathroom, kitchen, drying clothes and occupied rooms. The internal ventilation does not meet Building Regulation 2010 Part F requirements. This is best achieved with mechanical extractor fans. 

See surveyor.tips/vent_regs specifically P39 and P19:

  1. Bathroom 15 l/s with a 30-minute overrun (downstairs bathroom is fine, not upstairs)
  2. Kitchen 30 l/s adjacent to hob; or 60 l/s elsewhere in kitchen (kitchen extractor is good).

Rising damp risk assessment

Elevation is: 20M above sea level.                 The flood risk is: No flood risk. Slight risk of  surface water to rear of building (i.e. penetrating damp from rainwater, not rising damp from groundwater).

Sub-soil rocks are: Rocks with essentially no groundwater.
Signs of groundwater: I can see 1M+ below ground level, 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 property has been damp proofed using a cavity membrane system.

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