102N: Rising damp? Not even close!

The buyer was concern about this 1920 / 30s semi-detached house where the RICS survey wrote the following:

Condition rating 3a – Further Investigation: The rising dampness identified should be investigated now. As this is potentially serious, urgent, and likely to be costly, you should instruct a Property Care Association (www.propertycare.org) registered company surveyor to inspect all areas for damp and report to you, before exchange of contracts.

The RICS surveyor’s rising damp diagnosis, with no evidence other than a small semi-circular patch of dampness by the entrance door.

Root causes

The root cause was vapour from insufficient ventilation, made worse by damaged render by internet service provide or telecoms company, to outside of the wall and a recently enclosed porch.

Surveyor Tips:

  1. Look for and test for dampness a wall with the same plaster, or even better, an unplastered brick wall, lying level or below the damp patch. If it’s dry you know there can’t be rising damp, as damp rises evenly up a wall.
  2. Then look for reasons why there could be any other form of dampness.
  3. Externally look for signs of damage to wall, render or paintwork.
  4. Internally test the kitchen and bathroom extractor fans and ask occupants how they dry clothes.
  5. Test the mains water for leak, here using the mains water meter, with the camera set on time-lapse over 5M. Check with the mains to make sure it connected. If there is movement check all the service, shower head and toilets for any water movement.


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I checked every wall for dampness. The only area of dampness is a semi-circle zone by the front door.

There is a small amount of disruption to the plaster next to the door frame, otherwise there are no visible signs of dampness.

There is a high damp meter reading by the front door in conductance mode.

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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I also tested the wall with the damp meter in radio-frequency mode, able to detect moisture deep within a wall.

Water reflects radio waves at a set frequency similar to mobile phone shields. Radio frequency meters can’t differentiate moisture from other dense matter such as metal and concrete. They help trace damp in a normal, homogeneous wall.

Readings below 300 REL indicate that a wall is dry below the surface, 999 REL is the limit. These meters are for scanning, mapping and profiling, see surveyor.tips/profile.

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The damp meter quickly dropped down to low levels of moisture, further along the same wall.

This profile of dampness is not consistent with rising damp which is horizontal, where groundwater acts like flood water, rising evenly up a wall.

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Some of the highest meter readings were by electrical wires next to the sockets.

Electrical wires are made of metal and lose heat rapidly increasing the risk of condensation.

There is a high damp meter reading on the render in the porch outside.

Condensation is visible on the external glass. 

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There is also a high damp meter reading in the corner of the reception.

The rest of the rest reception wall was dry which would not be if there was rising damp.

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The cupboard on the other side of the front door has exposed bricks. Those bricks were dry.

Again this wall would not be dry if that was rising damp.

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Looking immediately outside of the wall we can see there that a section of external render has fallen off.

I understand that this area has had a lot of wires installed over the years from telephone companies and internet service providers.

Other potential sources of water

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I tested for a mains water leak using the analogue wheel at the centre of the water meter.

The analogue wheel is very sensitive to water loss. There was no significant movement in the wheel over about 10 minutes, I therefore concluded that there was a no significant mains water leak.


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The kitchen does not have an externally ducted extractor fan.

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.
  2. Kitchen 30 l/s adjacent to hob; or 60 l/s elsewhere in kitchen.
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The bathroom does not have an extractor fan.

Modern bathing habits result in increased vapour production and increased risk of condensation.

Other matters

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The upstairs bedrooms have eaves at ceiling level.

These eaves are normally poorly insulated and therefore at greater risk of mould and condensation. There was no sign of mould and condensation, suggesting that the family is good at keeping an even temperature and ventilate the bathroom with the window open and door closed.

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The external render sounds hollow when tapped.

Temperature fluctuation can crack external render. There is no immediate concern, but  check the property twice a year for render cracks and cracks around windows, as well as gutters, downpipes, drains and gullies. Make sure to fill cracks as soon as they appear.

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Although the outbuilding don’t form part of our damp survey, I was shown and looked at the outbuilding.

I noted what appears to be rot to the timber roof. Creosote or a similar antifungal timber protector should solve this problem. Consider installing ventilation and heat into the outbuilding.

Rising damp risk assessment

Elevation is: 43M above sea level.                 The flood risk is: no risk.

Sub-soil rocks are: Near low productivity aquifers in which flow is virtually all through fractures and other discontinuities. Bedrock geology: Lewes Nodular Chalk Formation, Seaford Chalk Formation and Newhaven Chalk Formation – Chalk..
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

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