102W: RICS able to make assumptions

The buyer was concern about damp identified by RICS below the roof.

RICS surveyor reported: “The walls were tested with a damp meter and high readings were recorded that gave cause for concern”, “There is evidence of penetrating damp in landing 1 to the external and party wall. This is the assumed to be the result of seals between the roof and the neighbouring roof to the parapet wall. Allow for a roofer to overhaul.”

The RICS surveyor in this case did not try to diagnose the source of damp, but made assumptions that caused the buyer concerns about the need for a new roof.

Root causes

The root cause vapour, caused by bathroom extractor fan venting into the loft, without ducting out.

Surveyor Tips

  • Always check extractor fans are working, using an anemometer.
  • Check inflow (bathroom/kitchen side) and outflows externally where-ever possible.
  • Some kitchen are hard to check both ends, I will use A4 paper to check the up draught.
  • When the ducting is straight (therefore unlikely to be perforated), I won’t necessarily check the outflow if I can’t reach it.
  • I sometimes mount the anemometer on a 5M long extension poll to check external outflow.
  • I always feel with my hands for perforated ducting.
  • If the extractor fan is ceiling mounted and or going through a loft, I will always check ducted through to the outside.
  • I used an extended 2X3M mono-pole with smart phone to look for external defects at height.


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There is a damp patch to the front bedroom in the corner on the party wall side.

There is a small amount of discolouration, but the bulk of dampness is colourless which it would not be if that was penetrating damp, as penetrating damp brings colour from timber and brick. I suspect that the small discoloration is caused by condensation on timber above.

There was a high damp meter reading on the wall in the centre of the damp patch.

I tested the surface on the inside 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. See surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.

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The surface was dry further up the wall.

This pattern of dampness is not consistent with penetrating damp, but is with condensation.

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The ceiling was damp as measured with a damp meter in radio-frequency mode.

I also tested walls in radio frequency mode. Water reflects radio waves at a set frequency similar to mobile phone shields. 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.

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The bedroom trickle vents were closed at the time of the survey.

There is no ventilation to the top floor.

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The damp patch was cold relative to other parts of the building.

Heat loss increases the relative humidity to the point where condensation can form, like a cold bottle of water on a hot summer’s day.

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The front bathroom has no 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. 

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There are signs of condensation on the bathroom ceiling.
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The bathroom had damp deep inside the wall, in the corner.

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There is also dampness to the rear bedroom wall.
The rear bathroom extractor fan ducting is the wrong size for the fan outlet.

No attempt has been made to connect the ducting to the extractor fan. 

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Above the rear bathroom, the ducting is lying idly in the loft above the ceiling.

Clearly there has been no attempt at ducting out the bathroom extractor fan. I recommend ducting out the fan through the rear flue with the missing cowl about it, if that flue is not being used for another purpose, such as the kitchen extractor fan or the downstairs neighbours own use.

The flues have cowls above them except for the final flue, which is hard to see in this picture.

The purpose of cowls is to reduce the risk of rainwater falling down the chimney breast when a chimney is no longer being used for ventilation. The downside is that cowls can impede airflow.

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Looking at the roof above the damp patch, it appears to be in order.

This is not a roofing report. I see a lot of roofs, many of which have significant damp issues, but this roof does not strike me as being one of those.

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The guttering at the corner appears to be working correctly, but it was not raining at the time of the survey.

The flashing appears to be in good order. The tiles appear to be in good order, although slightly raised in the corner above the damp patch. However, I don’t believe that this is the root cause of damp.

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I understand from the vendor, that they had sections of this flank wall repointed where pointing was missing.

It is rare that poor pointing ever causes internal dampness. My suspicions are that the vendor was misdirected to solving penetrating damp when the issue was from internal humidity due to poor ventilation, causing condensation.

The loft has an uneven distribution of insolation.

You should have the loft insulation evenly spread out particularly into the eaves.

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The front section of the loft above the damp patch appears to be in good order.

There were no signs of rot. 

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The timber rafter was dry, which it wouldn’t be if rainwater was penetrating through the roof.
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The timber was not sufficiently damp for rot to germinate, but there is a risk until the ventilation is ducted out.

The wall next to the rafter was damp.

This section of wall is going to be colder relative to other sections of wall, because it’s close to the outside.

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There is a small section of brick missing immediately above the damp wall.

This section of missing brick could cause heat loss to the wall below, increasing the risk of condensation.

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Unusually there is no insolation around the pipework going to and from the boiler.

Apart from the economic and environmental loss, the missing pipe insulation will cause an imbalance between the temperature of this loft and its neighbour, increasing the risk of condensation.


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The kitchen extractor fan is running at 8 l/s, which is less than it should be.

I don’t think this is causing a significant impact and probably not worth changing.

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.

Other matters

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Your lease may require you to share costs associated with your neighbour’s property.

Looking down at the neighbour’s bitumen felt roof below, it appears to be ponding, which I suspect, will eventually find a leak. You should check the lease for such financial obligations and asked the vendor for information about likely costs associated with the neighbouring property.


I should add that there are some render cracks to the front, mainly outside the reception.

They don’t appear to be causing internal dampness, are a shared cost (typically within the lease), and should form part of your regular refresh and repaint, normally about every 7 years.

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