A picture containing wall, tub, bathtub, bath Description automatically generated

104O: Tenants suspect rising damp

Finding the source of water from penetrating damp can be a changes when you don’t have direct access at roof level.

Surveyor Tips:

  • Get tenants to send data back from dataloggers.
  • Use a mon-pole extension to get as close as possible to roofs and chimneys without use of drones.

Root cause

Root causes will be updated soon.


A close-up of some stairs
Description automatically generated with low confidence

The walls have been damp proofed against rising damp by injecting chemicals. Typically damp proofers replace ground floor internal plaster with an impermeable plaster, known as slurry. This increases condensation risk.

A room with blue curtains
Description automatically generated with low confidence

The tenants main concern was damp and mould to the front wall, which they say they have to wipe away.

There were signs of ingrained mould in the painted wallpaper. 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 https://surveyor.tips/mould.

The secondary cause of high relative humidity is low temperature relative to the source of humidity, see https://survey.tips/humidity.

A person holding a cell phone
Description automatically generated with medium confidence

I measured the wall surface for dampness and found that it was dry.

I tested the surface on the inside at the base of all external walls every 1 metre, chimney breasts and a sample of internal walls with a Protimeter damp meter in conductance mode. These meters measures electrical conductance of salts in water, a proxy for dampness.

Readings below 20WME are considered dry. The range is 8WME to 99WME. See https://surveyor.tips/dampmeter.

A picture containing background pattern
Description automatically generated

Looking through a lens, where blue is a about 5°C colder than orange you can see heat loss to the front wall.

The radiator is not sighted by the front wall, reducing heat, increasing the risk of condensation.

A person holding a cell phone
Description automatically generated with medium confidence

I left a datalogger to log humidity and temperature over time, see later.

Note the temperature of the front wall is 15.2°C, about 1.3°C colder than the datalogger.

A picture containing indoor, basket, container, plastic
Description automatically generated

There is dampness high on a wall separating a kitchen from the cold toilet and bathroom.

The bathroom, toilet and kitchen are cold and appear to be poorly heated and insulated increasing the risk of condensation and mould.

A picture containing text, indoor, person, hand
Description automatically generated

There is metal above the lintel causing a thermal bridge, or heat loss.

A toilet in a bathroom
Description automatically generated with medium confidence

Condensation has been forming on the toilet walls

A picture containing indoor, toilet, dirty
Description automatically generated

The mains water pipe comes in at about 8°C in winter increasing the risk of condensation.

A picture containing device
Description automatically generated

The primary cause of excess humidity is insufficient ventilation. The bathroom has a manual extractor fan.

About 90% of humidity remains in a bathroom after the shower has stopped being used. It would be better to have a faster fan, either set to continuously flow or at least remain on for 30 minutes.

A picture containing device, hand, gauge
Description automatically generated

A humidistat is running by the rear door. This is insufficient for a kitchen where the door is open to the house.

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 P39 and P19 in https://surveyor.tips/vent_regs specifically:

  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.

A picture containing indoor, curtain, wall, bathroom
Description automatically generated

The tenants complained about damp and mould between the master bedroom window. The wall looked mouldy.

There were no damp issues on this wall at the time of the survey.

A picture containing indoor, ceiling
Description automatically generated

There are no trickle vents to many of the windows including the master bedroom.

You should consider retro-fitting trickle vents and instructing tenants to always keep them open.

A chair in a room
Description automatically generated with low confidence

In the upstairs rear bedroom there is a damp mark on the inside wall.

A picture containing wall, tub, bathtub, bath
Description automatically generated

The mark is discoloured, this is a sign of water passing through a wall or ceiling.

A person holding a watch
Description automatically generated with low confidence

There was a high damp meter reading in this section of wall.

There was a wasp next above. I understand from the tenant that this may have been fumigated.

A picture containing person, holding, hand, device
Description automatically generated

The chimney breast above was damp.

A close-up of a brick wall
Description automatically generated with low confidence

Looking outside there are a few issues that should be dealt with. However, a closer inspection will be required.

The flaunching, that is cement on top of the chimney breast needs repair. There appears to be a small crack around the brick flashing. The pointing could be improved. The lead flashing may need adjusting, repair and improvement. Ideally there should be some ventilation, such as using a cowl.

Monitoring relative humidity

I encourage homeowners with property showing signs of damp or mould to monitor the relative humidity. The data can be used to identify ventilation, heat or airflow issues.

Chart, line chart
Description automatically generatedThe tenants sent back data from a datalogger located on the front wall.

Looking at your data, there is constant heat and reasonably constant humidity suggesting that the tenants have changed their habits. Such conditions would not result in mould and condensation to the front wall. However, given the reported experience I would a) install a continuous fan in the bathroom and b) monitor humidity, with a Govee WIFI datalogger.

Leave a Comment

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.