This semi-detached 1920s house has mould and condensation on most external walls, there is also penetrating damp, typified by browns stains to the rear bedroom under the chimney breasts.
Surveyor Tips:
- Another case of overlapping damp issues. Be careful to look for the brown stains, a tell tale sign of penetrating damp.
- Make sure to have 3M long selfie sticks (monopole – Amazon etc.) – I use two strapped together. It saves the time and cost of using drones. Put the camera on video mode and review on a big screen screenshooting images for the client.
- Easy bathroom ventilator fixed during the survey – happy client.
Root causes
- Excess vapour causing condensation and mould resulting from insufficient ventilation and cold bridges.
- Penetrating damp from roof and or damaged flaunching on chimney breast.
Illustrations
The brown colour is caused by water soaking through bricks or over timber.
I 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.
The sarking material was full of rubble just below the hip, although not much water lands on the hip. Most roofing issues are low down, where rain is funnelled and accumulated.
The white arrow points to where the rubble from the sarking material appears to originate.
There are no obvious signs of damp there and it’s unlikely that much water could penetrate through the hip.
- By contrast the blue arrow points to damage flaunching – the most likely source of ingress.
- The red arrow points to are damaged tile.
I think the top of the chimney stack is the most likely source of ingress. However, other elements should be checked once there is direct access to the roof.
Ventilation
The extractor fan was running at 9.7 l/s. I cleaned it up so that it now runs at 13.1 l/s, better than most UK extractor fans, but not as fast as building regs requirements of 15 l/s.
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. The secondary cause of high relative humidity is low temperature relative to the source of humidity, see surveyor.tips/humidity.
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.
This is caused by combination of insufficient ventilation, heat loss, and insufficient air circulation.
Blue/green is about 5˚C colder than yellow/orange. The ceiling is also at risk of heat loss, and therefore mould and condensation, consider insulating it.
Again this will be caused by insufficient ventilation and heat loss.
Calcium sulphate is a key ingredient in cement and other building materials. If diluted in water salts tend to move to the surface. These can be removed with sandpaper and decorated.
The presence of mould at the bottom of a wall eliminates rising damp as the root cause and points toward condensation from unvented excess vapour.
Relative humidity 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. Mould forms when there is period of humidity above 85%RH for 6 or more hours.
Given the additional strain on the property, I’m sure the tenants will do what they can to help monitor and minimise humidity.