Victorian ground floor flat with insufficient ventilation.
Surveyor Tips:
- The existence of ventilation does not mean that is it working, or sufficient.
- Always check the vent speed, ideally in and out of a building.
Root cause
Excess vapour causing mould and condensation from insufficient ventilation.
Illustrations
I’ve never understand why chemical damp proofers repeat the same procedure expecting a different outcome, here we see two sets of damp proofer’s drill marks after injecting chemicals. The solution is through ventilation.
There is mould growing in the front room by the bay window.
There is increased heat loss in bays because of more external surface area. Heat imbalance compounds this. The radiator is located on an internal wall and the curtain blocks airflow.
There is a similar issue in the corner.
Corners have reduced airflow and increased heat loss. There is a green streak between the buildings suggest water is flowing down the wall which causes heat loss and increased risk of mould/condensation. However, rain is not penetrating through as there is no damp stain.
Looking at the thermal image where yellow is ~5°C warmer than blue, we see heat loss in the corner.
Note the bay is warmer in this image, that is because it warms up during the day but looses heat at night.
I measure the temperature at 12°C, in the corner of the room.
The mould point is 12.4°C meaning that it is at risk of growing mould, see mouldpoint.co.uk for a mould point calculator and daily mould and condensation risks forecasts.
Note the plants are blocking airflow and respire increasing vapour.
Vapour could be seen condensing on the front window. There is a risk of window rot from condensing water.
I tested walls for damp, walls were dry in the front room.
I tested the surface of 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.
There is mould growing across the bathroom wall despite insulation.
The wall has been damp proofer twice. In addition the bathroom walls have been dry-lined with thermal insulating plasterboard. Although beneficial it is not addressing the root cause.
As can be seen in the thermal image, corners and recesses are hard to insulate, increasing the risk of mould.
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. Once mould grows it starts to spread. Take surface. Mould off with sandpaper, then spray anti-mould spray or concentrated bleach (the active ingredient).
Most of the walls were dry, but there was a high meter reading in the corner caused by condensation.
There is mould growing on the uninsulated section of bathroom door joined to the cold external wall.
The secondary cause of high relative humidity is low temperature relative to the source of humidity, see surveyor.tips/humidity. Relative humidity is a measure of how much vapour is in the air compared to air’s capacity to hold vapour. It is a function of vapour pressure (quality of vapour) and temperature. As temperature rises, air can hold more vapour.
The bathroom extractor fan is running at about half the building regulations required rate of 15 litres/ second.
This fan switches off soon after lights are turned off. I increased the overrun to 30 minutes.
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:
- Bathroom 15 l/s with a 30-minute overrun.
- Kitchen 30 l/s adjacent to hob; or 60 l/s elsewhere in kitchen.
The airflow is being blocks by flexible ducting, which was out of line, dirty and slows the flow rate. I removed it.
You should be able to speed up the flow rate by installing a piece of 100mm ridged ducting. Given the mould I recommend replacing the extractor fan with a continuous flow fan, such as Elta Mori dMEV (available on Amazon).
The kitchen extractor fan is not ducted externally.
Consider installing ducting to the fan or be mindful to cook with tops of pots and pans.
The heating system is an “on-off” thermostat controlled boiler.
It is better to have a modern thermostat, capable of multiple temperature settings such as a Hive or Nest etc. As an alternative is to put the boiler on for 15 minutes in every hour or two at least at the night.
Other matters
There is some damp staining above the kitchen door.
Penetrating damp tends to draw colour from building material through a wall causing stains.
Looking at the image of the outside we see a crack which is likely to be the root cause of this damp.
The cracks should be repointed, ideally with lime as this was probably the original mortar. Lime allows some movement and doesn’t trap moisture, unlike cement. However, most builders use cement. So unless you can find a good builder who uses lime and or wish to repoint extensively, pragmatism might be allowed to outweigh purism.
There is dampness at the base of the kitchen wall. There is an area of heat loss.
The damp appears to come from condensation through heat loss. Relative humidity is a measure of how much vapour is in the air compared to air’s capacity to hold vapour. It is a function of vapour pressure (quality of vapour) and temperature. As temperature rises, air can hold more vapour. Conversely as temperature drops, air holds less vapour until it meets the dew point at 100%RH, when dew or condensation forms.
There are no obvious signs of dampness on the outside.
It is possible that is coming from a different building material use on the inside, or front splashing rainwater causing heat loss on the inside.
You asked me to check dampness in the cellar. Cellar walls appear to have been tanked.
Tanking cellars rarely last more than about 10 years. There is hydrostatic pressure from penetrating damp (rain) below ground level. In my opinion it’s better to allow penetrating damp to evaporate and flow out by subfloor ventilation, then to try to block moisture with impermeable material.
There is dampness deep within the wall as identified by the damp meter in radio-frequency mode.
These damp metres use radio waves to detect dense matter up to 70 mm below the surface.
A small crack runs along between the plinth and ground.
Ideally have the crack filled with ~ 50mm fillet skirting made of a cement-based mortar.
Bricks have become damaged. They should be repointed and ideally the plinth continued horizontally.
Looking under the ground floor, timber does not look rotten. Nor were there signs of mould in the cellar.
Mould is happily drive next to the passive vent. Passive vents only benefit if there is external air flow, i.e. wind.
None of the following issues is causing internal dampness, but could be improved
You are aware that the drain from the bath is blocked
There appears to be cracking in underground pipework nearby.
Some of the walls and render to the front need attention.
You should be aware bamboo is considered by many experts to cause more damage than Japanese Knot Weed.
Datalogger
You left the datalogger in the property which I moved during the survey.