This Edwardian semi-detached house on a hill has had damp proofing, yet damp persists. The key concern was dampness to the rear of the property, which appeared worse on the party wall side. There were many, complex overlapping issues.
Surveyor Tips:
- They key findings was damp coming form the neighbour’s side, which would not have been picked up without assistance and access from the neighbour, with whom the client had good relations.
- It is very important for neighbours to avoid disputes, as it makes it so much harder to identify issues, costs escalate when often the problem is easy to fix.
Root cause
Leak on the neighbours side, almost certainly coming from obsolete heating system pipes buried in the floor of a rear extension. The issues were made worse by insufficient ventilation and heat distribution. There were hygroscopic salts on the first floor, around two separate chimneys.
Illustration
There are a lot of the separate damp issues. It’s easiest to explain from the top of the house working down.
Hygroscopic salts originate mainly from burning the timber. Calcium nitrate is the most common of these salts. It causes condensation at ~50% RH. See later for more details.
Mould grows where relative humidity exceeds 85%RH for 6+ hours. Excess humidity results from insufficient ventilation, poor air circulation and cold surfaces. See surveyor.tips/mould.
It looks like condensation has formed on the single glaze window and is causing slight window rot to the timber below it.
I understand that you had the leak repaired. Note the discolouration like a tea bag stain. This is a sign that water has passed through brick or over timber, bring the colour with it.
I tested internal walls with a Protimeter damp meter in conductance mode. These meters measure electrical conductance of salts in water, a proxy for damp.
Wood weevil occurs with Coniophora puteana, or cellar rot, a brown wet fungus, see surveyor.tips/rot. Rot requires water to grow. Remove the water and both will stop destroying timber. I recommend that the skirting board is removed and replaced.
The step is loose and damp inside.
I understand that the floor is a solid floor and that therefore and there is no such structural implications to the rot. See later in the report.
A blocked drain could cause water to flow into the sub-floor resulting in high humidity, which in turn can cause moisture to condense on the damp proof course and for rot to grow on timber. I measured the sub-floor humidity, it was 75%RH, which is normal, suggesting no condensation or rot in the sub-floor void.
The drain should be unblocked or bypassed as soon as possible.
Humidity will inevitably form in the poorly heated rear of the building.
Blue is roughly 5° colder than yellow. I suspect there is poor insulation and that the heating is switched off at night.
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, 999 REL is the limit. These meters are for scanning, mapping and profiling, see surveyor.tips/profile.
The rear section of the ground floor is an extension into what would have been an outbuilding, built without insolation in mind. Note the dribble marks a sign of condensation. The colour is odd, although it does not look like a leak or penetrating damp.
Calcium sulphate is a key ingredient in cement and other building materials. If diluted in water salts tend to move to surfaces. These can be removed with sandpaper and decorated.
The wall is stained which suggests that water it’s coming through brick, such as from a leak. They have more salts in a smaller area, suggesting that the leak is from their side. I understand there used to be a boiler here. It is possible that the pipe to the boiler is leaking or there could be residual moisture. They should test for a mains leak.
See https://surveyor.tips/leak-tracing/
At first I wondered whether water was leaking across the solid floor.
For this reason I think the root cause of damp on the neighbour’s external wall is hygroscopic salt and the damp on the party wall is probably from the old boiler pipe. I think condensation taking place in the rear of your ground floor, accentuating damp on your side.
Datalogger
Thank you for sending a csv file from the datalogger.
There is nothing remarkable. Humidity appears consistently below 65%RH and temperature consistently around 15°C.
That said, the profile, extend and dribble marks in the utility room, looks like condensation is a component. It is possible that condensation is taking place during a cold snap, or is historic.