This early twentieth century house on a hill is suffering from damp in an internalised outbuilding.
Surveyor Tips:
- Internalised outbuildings are at risk of mould and condensation through poor insulation and heat loss.
- Where there’s mould there is insufficient ventilation.
Root cause
Excess vapour causing mould and condensation.
Illustrations
The primary concern is damp and mould on the back wall.
Mould is inhibited by nitrates found in groundwater. The presence of mould at the bottom of a wall eliminates rising damp as the root cause and points toward condensation from unvented or excess vapour.
Using a damp meter I was able to determine that the surface was dry.
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.
There is a salt patch part of the way up the wall. The meter reading was 17.3WME i.e. “at risk”.
There are calcium sulphate salts on the surface. Calcium sulphate is a key ingredient in cement and other building materials. If diluted in water salts tend to move to the surface. They tend to result from daily alternating condensation and evaporation. These salts can be removed with sandpaper and decorated.
Usin a metal detector I found metal in line with the salt patch.
The thermal image also highlights a cold bridge, where blue is about 5°C colder than yellow
I understand that the rear wall was part of an outbuilding now incorporated into the property, and that that was a door which is been replaced with a window. It would appear metal remains left in the wall from the old door frame.
Looking on the outside there is a crack in the render probably caused by variation in building materials.
The crack has been filled. I don’t suspect penetrating damp as there would be a brown stain.
A small crack has appeared around the window. This should be filled.
These cracks can cause the external skin of a building to become damp, increasing heat loss and therefore the risk of internal condensation.
I tested the wall with the radio-frequency meter these measure damp deep within the wall.
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.
There is mould growing up on the rear wall.
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.
There is a metal around the external doors.
The secondary cause of high relative humidity is low temperature relative to the source of humidity, see surveyor.tips/humidity. Metal loses heat rapidly when it is cold outside.
Again there is no high damp meter reading on the surface in the front reecption.
This image illustrates the thermal challenge, made worse by warm air currents blocked behind furniture.
Upstairs there is damp staining to wallpaper on the flank wall.
Although the staining looks like penetrating damp, mould can also stain in a similar fashion. The top of the stairs is next to a bathroom. Although the vent is strong, I understand the data bathroom door is left open and the vent is not kept running sufficiently long after taking a bath or shower.
A wrought iron soil pipe has become imbedded into the rendered wall, causing a substantial thermal bridge.
Heat is drawn out by metal when relatively cold. Condensation forming within the wall will redistribute itself through the force of absorption (often called capillary action) and gravity.
The effect of the soil pipe can’t be seen running up the side of the first-floor window.
We can see from the rust stains that there is metal incorporated into the render.
Rainwater may also be bouncing off the roof to the side. Again this is likely to cause heat loss, increasing the surface relative humidity, rather than causing penetrating damp. T is advisable to solve the internal humidity issue first, then see if any dampness remains.
There are high that meter readings deep within the wall (in radio-frequency mode).
All the high damp meter readings coincided with embedded metal.
In the front bedroom there is mould growing in the corner in the poorly insulated eaves.
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.
The double-glazed windows don’t have trickle. Windows were locked suggesting they are rarely opened.
Is it is important to ventilate all rooms in which vapour is generated. Since respiration is a primary source of vapour, bedrooms should be ventilated or purged of vapour.
There is a vent into the bedroom chimney breast. It was closed so I opened it during the survey.
Chimneys constantly draw air out whichever way the wind is blowing. They are a good form of natural ventilation.
There were signs of condensation and mould by the front door.
There is only about 100mm, separating internal walls and external walls around openings, compared to around 250mm on a normal two skin wall. This causes a thermal bridge. Each drop of 1°RH increases relative humidity by about 5%RH, increasing the risk of mould and condensation.
Furniture and unstuck wallpaper can trap humid air increasing the risk of mould and condensation.
Other matters
I noted a few render cracks that need regular check and to be raked out and filling.
The render surrounding the pillar has broken off.
It would be best to remove the render and applying a similar cement-based mortar.