Surveyor Tips 102D mould, underfloor heating, door curtain, unducted vent

Landlord concerned that there was penetrating damp coming through gaps in render.

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3.3 Damp proofing against rising damp

Root causes

The root cause was vapour through insufficient ventilation, causing condensation and mould.

Surveyor Tips:

No signs of penetrating damp, would see external cracks and internal tea bag stain like discolouration.
Hygroscopic salts in top floor chimney breast.
Fascinating example of old chainsaw retrofitted DPC – the work of Peter McDonald I believe.

Illustrations

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Description automatically generated — *There is dampness in two corners in the rear bedroom.* Colourless semi-circular damp is classic condensation.

There is no tea stain like discolouration, which is the tell-tale sign of penetrating damp, therefore penetrating damp is unlikely. Semi-circular dampness at a wall base is consistent with condensation. Corners lose heat rapidly, as there is greater external surface for heat loss.

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Description automatically generated — *Looking outside of the corner there appears to be metal beading used to form straight render corners.*

A small section of paint has flaked off, I don’t believe the water is penetrating, but it should be repainted, because the paint will retain some dampness resulting additional heat loss. And in theory there could be a render crack behind the flanking paint.

*The relative heat loss at the time of the survey was only about 3°C.*

However, when the property is being lived in, there is likely to be a greater relative heat loss, especially behind furniture.

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Description automatically generated — *A metal detector identified some metal deep in the wall. This could be the remains of electrical wiring or piping.*

Metal courses rapid heat loss and could account for the water damage to the plaster.

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Description automatically generated — *Using a damp meter in radio-frequency mode I was able to identify damp deep in the wall at the base.*

I tested walls with a Protimeter 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. 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.

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Description automatically generated — *By contrast the top of the wall is dry, both on the surface and at depth.*

This tells me that the wall is dry enough to replaster.

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Description automatically generated — *I tested the timber to make sure that there was no rot in the skirting boards.*

Although the timber was slightly humid it was less than the 28 WME necessary for rot to start growing.

Datalogger

The data doesn’t tell us a great deal because the property has been empty with limited heating. I will email an Excel spreadsheet which you can add data to visualise changes over time, once the property is tenanted, see section later on monitoring humidity.

Ventilation

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Description automatically generated — *The bathroom vent is extracting air at 6.2 l/s, with no overrun*.

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.

I recommend to landlords that they install a continuous flow fan see recommendations, as I have done myself.

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Description automatically generated — *There is mould growing in the kitchen, caused by insufficient ventilation and poor airflow into cold corners.*

Consider adding anti-condensation paint or insulation into this difficult to heat corner.

*Flaking paintwork, could line-up with a crack in the render, resulting in ingress. But I doubt it.*

Flaking masonry paint should be removed and repainted. Any cracked render should be raked out and filled. I tend to fill small cracks with external acrylic caulk, and larger cracks with a render similar to your current render, which I believe is cement-based.

*There is a crack to the windowsill and cracks in the render above and below the window.*

These cracks should be filled, but I don’t believe that they are the causing any internal dampness.

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Description automatically generated — *The chimney breast has some dark patches that look like hygroscopic salts.*

Hygroscopic salts come from the historic burning of coal in a fireplace below. They cause condensation at normal levels of humidity, see later in the report.

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Description automatically generated with medium confidence — *There is a high damp meter reading deep in the wall.*

The dark paint obscures the presence of hygroscopic salts. These salts are benign, and not a source of moisture. So there’s no need to do anything. If the patches concern you, a solution is to cover with a solvent-based, primer-sealer such as Zinsser Cover Stain.

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Description automatically generated — *If you’re thinking long-term then you may consider installing a modern Wi-Fi thermostat.*

The benefit is that you can set up multiple temperature settings, without allowing the temperature to drop below the dew point. In addition, as a landlord you can monitor the temperature making sure the temperature never drops to low. Nest (Amazon) allows you to monitor humidity. Other Wi-Fi thermostats include Hive – British Gas and Honeywell. They allow you to site the meter near to the cold wall. However, you need Wi-Fi for it to work.

A kitchen with white cabinets
Description automatically generated with low confidence — *Consider just installing 30 kitchen extractor fan on the wall where there is already an air brick.*

Kitchen extractor fans on adjacent walls should have her 60 l/s speed, and ideally be humidity activated.

Damp proofing against rising damp

One of the most interesting damp proofing techniques, seen in front of the ground floor.

I suspect this retrofitted DPC was installed by cutting out a course of bricks with a chainsaw. Possibly the work of Peter McDonald (now retired, formerly CEO of SafeGuard, PCA trainer – when he worked for or ran South London Damp Proofing – as was, as I recall).

Related Terms:

102Q: suspect penetrating damp – first & second floor flat