Top floor of a large Victorian house, now rented out. Landlord feared expensive penetrating damp treatment. Fortunately the root cause was insufficient ventilation and heat imbalance.
- Look above and outside damp patch using a monopole extension and crawling across loft.
Condensation and heat imbalance.
The primary concern is damp in the rear bedroom wall close to the ceiling.
Drible marks are a sign of condensation. If there were a problem were penetrating damp from rain, then there would normally be a distinctive brown discoloration like a tea bag stain. Also there normally be one or two entry points, typically close to the entry point.
At the time of the survey the damp meter reading was low. Above 300REL being damp.
Looking at the thermal image you can see heat loss.
Blue is a bout 5°C colder than orange. The reason for the heat loss at the top is the party wall above the roof, drawing heat out, made worse by the missing insulation in the corner.
The laser thermometer shows a heat loss of about 2°C compared to background temperature.
The heat loss is likely to be around 5°C when the property is inhabited.
The thermal image at the rear highlights the effect of a thermal fin, that is a protrusion with large surface area.
Here the party wall can be seen drawing heat out against a cold sky.
There are no nearby downpipes or signs of damage to the rear gutter.
Expansion cracks are forming around the lead. However, these are too small to result in significant damp.
The gutter looks clear and flashing in reasonable order. I recommend looking every 6 months or so. However, in my opinion there is no need for remedial action at this point.
I measured dampness in the walls and timber in the loft immediately above the damp wall.
There were no high damp meter readings, which there would be if water was coming in from above the rear bedroom.
I noted missing insulation in the loft immediately above the damp wall.
Poor insulation will increase the heat loss and risk of condensation and or mould.
The flank wall is harder to explain, and probably has been subject to clothes drying or similar.
The flank wall was dry at the time of the survey. However, I understand it has been damp, including one time in winter when unoccupied.
There is considerable heat loss in the corner.
External corners have increased surface to loss heat through, they also have reduced airflow from radiators.
The wall is dry at the time of the survey, here using a radio frequency damp meter.
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 200 REL indicate that a wall is dry below the surface. These meters are for rapid scanning, mapping and profiling, see https://surveyor.tips/profiling.
A metal detector identified metal within the wall. Metal loses heat rapidly when it is cold outside.
The image you supplied, again shows a colourless damp patch, a sign of condensation not penetrating damp.
There is something sticking out of the wall externally losing heat. It may be obsolete, if so consider removing it.
It is difficult to be sure, but there appears to be a crack in the render causing penetrating damp to the external skin of wall. I don’t believe this is causing penetrating damp to the inside wall as if it were there would be brown discolouration, but a damp external skin is likely to cause heat loss to the internal wall, resulting in an increased risk of condensation.
There are signs that the masonry paint is blistering, suggesting that water is getting in behind the paint.
If it were me, I would deal with in the internal humidity issue and easy to reach flacking paint patches now. Then programme a roughly 7-10 year cycle using scaffolding for render crack filling, tile, gutter and window repair, external painting etc.