Large Victorian terraced house on a hill. RICS surveyor thought that there might be rising damp.
Surveyor Tips:
- Rising damp treatment in a house on a hill, makes no sense.
- Rising damp comes from groundwater, i.e. the water under the water table, highly unlikely anywhere, let alone on a hill.
Root cause
Root cause condensation from insufficient use of ventilation.
Illustrations
The house hasn’t been that proved using chemical injections, an impermeable slurry on ground floor walls.
The property has been damp proofed to the front and rear walls.
From the information provided it appears that impermeable slurry has been applied. This has the effect of reducing the normal absorption of vapour, leaving other walls more vulnerable. It had a 25-year guarantee from 1993, which means that it has lapsed. However, the lack of guarantee is meaningless as that was never any risk of this property coming into contact with ground water, the source of water in rising damp.
Over 80% of damp surveys of the Victorian properties with ground floors have been down proofed. If chemical damp-proofing worked, then I would not have a viable business.
I tested all ground floor walls for damp, most of them were dry on the surface.
I tested the surface on the inside at the base of all external walls every metre, chimney breasts and a sample of internal 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. See surveyor.tips/dampmeter.
Curiously there is damp below the steel shutter bar. The metal was causing heat loss and condensation.
I also 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.
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 damp by the rear door, with a triangular profile, not horizontal as it would be if there was rising damp.
Condensation forms on the coldest section of wall. It is common to have dampness in the corner by and external opening.
Dampness stretches in a triangular profile, some 200-300mm up and along the corridor wall.
The condensation is forming on the door part of the wall and dropping down through gravity.
There was a high damp meter reading in the corner.
However, about 200mm away from the external door was dry.
Most of the wall at ground level was dry.
If there was rising damp, then there would be a horizontal band of dampness at the base of the wall.
There were high radio-frequency meter readings on the rear wall.
The damp proofers slurry is holding back water within the rear wall.
The surface was dry, therefore dampness deep within the wall should not be of concern.
I noted that the rear drain was blocked.
It was quickly unblocked without any further concern.
There were some obvious sources of vapour such as for drying clothes.
The area around the chimney breast had high me to readings in radio-frequency mode.
It is possible that there are hygroscopic salts in the chimney breast behind the plaster. These salts are benign but if you do re-plaster consider using an oil-based blocker such as a primer like Zinsser stain cover.
The were surface salts in the meter room on the lower ground floor under the external staircase.
I tested the salts for nitrates they were negative, so therefore don’t come from groundwater. The salts look like calcium sulphate, 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.
There are cracks in the render under the stairs.
It is common for there to be condensation and some penetrating damp underneath these Victorian raised ground floor staircases. For this reason understair cupboards were used for storage, often coal, rather than as a habitable space.
The render cracks around the building should be raked out and filled.
Most of the ground floor is solid. There is a shallow subfloor void under the corridor timber.
I measured the humidity in the subfloor void and found it to be normal. Therefore the risk of rot and the risk of a leak, penetrating damp or rising damp in the subfloor is very low.
I noted some damaged timber under the staircase.
Some timbers have been affected by Phellinus contiguus or window rot. Window rot is very common in old properties, it is a slow growing white rot. None of the timbers are structurally significant. The rot can be cut out, sanded, filled and painted for protection.
There are signs of calcium sulphate salts to the rear wall.
Salts blistering external paintwork is very common in Victorian buildings. It is not a cause for concern, there were no signs of internal dampness. But sanding down and repainting should form part of your annual property management.
There are signs of cracked windowsills.
There was no associated internal dampness detected under the window sill at the time of the survey, but this should form part of the normal annual property management.
I noticed some of chimney pots don’t have cowls.
Placing cowls on top of chimney pots will be easy and inexpensive given the access from the Velux. Capping unused chimneys with cowls is best practice, but not urgent.
I didn’t see any timber defects in the roof void.
I noted that some of the Veluxs have condensation marks.
There are signs of condensation on the wall. Bathroom vapour won’t contribute much to the lower ground floor.
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.