Victorian double fronted house split in half, with damp and mould on front wall.
Surveyor Tips:
- Looks for the clues;
- mould,
- drying clothes,
- bathroom leak,
- insufficient ventilation.
Root cause
Toilet cistern leak and condensation from drying clothes in unvented room.
Illustrations
The house has been damp proofed against rising damp. It is also had an incomplete “French drain” installed.
The issue of concern is mould to the front corner. There are dribble marks from condensation to the front.
Mould grows where relative humidity exceeds 85%RH for 6+ hours. Excessive humidity results from insufficient ventilation, poor air circulation and a cold surface. See surveyor.tips/mould.
Looking at a thermal image, where blue is about 5˚C colder than yellow, we see the corner of the wall is cold.
The wall surface was dry, but clearly moisture has damaged the plaster, probably following use of slurry.
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 8 to 99WME. See surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.
I also tested walls in radio frequency mode to measure to about 7cm below the surface.
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.
I was able to trace damp deep inside the wall from about 1.3M to the base of the wall.
Dampness falls through gravity down to the damp proof course “DPC”. Wet bricks are poor insulators therefore the base of a wall is likely to be colder and a greater risk of condensation.
There is dampness around sockets.
Sockets are prone to dampness as a section of wall is cut out, a metal box installed and covered in absorbent plaster, all of which exacerbate the effects of condensation and absorption, see surveyor.tips/sockets. The wires are probably cooled by the sub-floor void.
I suspect that the primary cause of dampness in the reception is from drying clothes.
The. bathroom extractor fan runs at 10.7 l/s against building regs requirement of 15 l/s. It has a short overrun.
I reduced the humidity that triggers the fan to about 65%RH and increased the overrun time to about 30 mins. By so doing the fan will effectively become a continuous flow fan. There is a thermal cost to running a continuous extractor fan in the order of about £50 a year, see https://surveyor.tips/cost-of-running-extractor-fans/
The kitchen extractor fan is not externally ducted. There is a manual fan providing 40 l/s, which should be used.
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.
Ensuring sufficient heat is challenging. There is a 7° difference between the thermostat and the front wall.
Use daily mould risk forecasts on mouldpoint.co.uk. Heat sufficiently when the risk is high, make sure to have sufficient night-time heat, perhaps on-off every hour.
A leak behind to your toilet doesn’t appear to be affecting any other room, but will add to the overall humidity.
There is white rot growing on the timber surrounding the cistern. It is isolated and not structurally significant.
Water is condensing on the base of the cistern; from measurements I believe that the root cause is a leak.
I recommend monitoring the subfloor void with a hygrometer probe, looking under every 6 months.
Dataloggers
You have been running dataloggers in the lounge and kitchen.
The above graph is relatively complex. The adjusted lounge relative humidity is based on a wall temperature at 9:19am of 12.1°C, when the datalogger recorded 14.9°C. Each 1C° drop increases surface relative humidity by about 5%RH, the adjusted %RH show wall is happening on the wall surface.
Here are my initial thoughts, without seeing up-to-date data.
- The surface relatively humidity in the lounge is consistently between 85% and 95%RH.
- There seem to be some improvement since my survey, it would be useful to see more data after.
- Hopefully the improvement made should be sufficient to solve your damp problem.
- The dew point difference, the grey line, which compares two data loggers, helps identify where vapour is being generated or conversely removed. With a few exceptions, there is more vapour is being generated in the lounge than in the kitchen, or the kitchen is better ventilated. This suggest that drying clothes is the greatest source of vapour – but I could be wrong.
Conclusions from data loggers
- The ventilation improvements should have worked and are probably sufficient to stop condensation and mould growth on walls. However, consider a continous flow extractor fan from the bathroom, such as the Elta Mori £110 Amazon, https://surveyor.tips/extractor, see recommendations.
- Remove obstacles from wall to increase air movement and consider anti-condensation paint. Alternatively try insulation, such as Sempatap thermal lining paper, see recommendations.
I would try a continous flow from the bathroom, remove obstacles and paint anti-condensation paint before considering insulation, which can have unintended consequences.
Other matters
I had a good look and filmed under the floorboards and found no sign of rot.
The subfloor ventilation is blocked by paint, we unblocked it with a screwdriver during the survey.
Subfloor ventilation is a safety mechanism for reducing the risk that leaks don’t cause rot in the subfloor void.
Timber in the corridor is being warped by condensation forming in the unheated corridor.
This corridor is subject to humidity from by houses causing condensation. The cold solid floor exacerbates the risk of condensation.
There is slight damage to your neighbours gutter. I don’t think it’s having an impact on your property.
Gaps around windows should be sealed with an external mastic sealant, similarly, render cracks.
This cracked render should be repaired with a cement based mortar.
Your neighbours has a rainwater downpipe. Rain flows from the roofs of 5 houses without any drainage.
There are no signs that this is causing internal dampness in your property. However, it is very quick and simple to attach a horizontal pipe away from the buildings.