The buyer was concern about a small patch of damp found by his RICS surveyor. The RICS surveyor did not specifically recommend a damp survey.
RICS surveyor reports: ‘It is thought the property has a slate damp proof course and these can deteriorate over time, there is a risk in a property of this age of rising damp occurring within the future.
In a property of this age, the foundations to the main superstructure are likely to be positioned at a shallower depth than would be required by present day standards. Reduced foundational depths increase the susceptibility to super structure disturbance due to seasonal sub soil moisture fluctuations.
There was an area of high moisture to the left of the rear door which should be monitored, given the age of the property there is a risk that damp may occur within other areas of the property. No other areas of high moisture were found when inspected with a damp proof meter.”
With respect to RICS and its surveyors, 1) slate does not deteriorate, at least no one ever proves deterioration of slate DCP, it’s just a commonly held supposition to justify damp at the base of a walls despite a DPC, 2) even if slate were to deteriorate, the gaps would be significantly bigger than the micro pores that cause rising damp – try it for yourself.
Root causes
The root causes; penetrating damp from the neighbour’s blocked gulley and vapour causing condensation, through broken bathroom vent and no kitchen vent, made worse by Covid.
Surveyor Tips
- Always check gullies, including the neighbours gulley. Here is poured water I found that had been collecting in a dustbin, into the gulley to check.
- Measure the sub-floor humidity, over 85%RH needs further investigation to find out why.
- If you are uncertain, return to check, especially if there is a concern about rot, or extend the time on site.
- High sub-floor humidity normally means that there is a blocked gulley or broken drain.
- If you spot any evidence of damp proofing treatment, especially dry-lining, assume the worse and look for an alternative root cause than the rising damp probably used to justify the damp proofing treatment.
Illustrations
Even before entering the property I could see there was a condensation problem.
Single glaze window creates a sacrificial surface for colonisation the form on. They work as a form of dehumidifier. The situation would be even worse if there was double glazing, especially without additional ventilation. Covid in significantly increasing the level of condensation and mould in properties. Some of the saving from not working from offices should be spent on improved ventilation, insulation and balanced heating.
The carbon dioxide levels were high, this suggests that windows are not being opened enough.
High carbon dioxide levels are not dangerous, but makes a place feel “stuffy”. It is a sign that there is insufficient fresh air entering a property. The meter reading of 1012ppm is high is double the normal levels of 500ppm.
I asked the owners to move their sofa from the front wall so that I can see behind.
The corner it’s full of mould on the carpet, skirting board and wall. Mould grows in the same conditions as dust mites, which can result in allergic reactions.
I measured the wall with a damp meter, the wall was dry. This is unsurprising given the wall has been dry lined.
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 d Readings below 20WME are considered dry. The range is 8WME to 99WME. See surveyor.tips/dampmeter. Walls measured were largely dry on the surface except where mentioned in this report.
There was a high damp meter reading in the corner by the kitchen rear door.
It is common for there to be condensation at the base by a kitchen door.
Using the meter in radio-frequency mode I mapped damp profile – which was quarter circular.
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.
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.
The quarter circular profile is consistent with condensation and not rising damp.
The dampness on the wall soon drops to normal levels, a short distance from cold rear door.
This person of darkness is inconsistent with rising damp but consistent with condensation which forms around cold spots.
There is a high damp meter reading in the timber by the kitchen sink.
It is possible that some water is splashing from the sink. However, I suspect the primary cause of here is condensation forming on the window. Condensation was visible on the window and window sill at the time of the survey.
There is no externally ducted kitchen extractor fan.
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 tested the bathroom extractor fan over the course of a few minutes, I could not get any air movement.
The vendor assures me that the extractor fan is working, but the evidence suggest otherwise.
There is a high damp meter reading in the bathroom, there was also a lot of mould.
The height of the high meter reading is inconsistent with rising damp, which has only been shown to rise up a few courses of bricks. It is, however, consistent with condensation such as typical in a bathroom.
There was a lot of mould around the flat including in the bathroom.
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. 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 excess vapour.
There are some damp stains in the utility room, but these were dry, suggesting they are old.
Surprisingly the utility room has a radiator. In my humble opinion it would be more cost-effective and energy-efficient to insulate the utility room rather than heat it.
I found a leak at the top of the cold-water inlet behind the washing machine.
When I returned the leak had been fixed. I looked for rot, but didn’t find any signs. I measured the subfloor relative humidity underneath the floorboards. The humidity level was normal which it wouldn’t be if rot was growing.
I left a hygrometer probe about 1M into the sub-floor void during the first visit.
The hygrometer probe measured 99%RH (it is only accurate to 95%RH). This tells me that there is a risk of rot and condensation forming on the damp proof course.
I returned a few days later when it was warmer.
The relative humidity is still high, but not critical. Suggesting that there is no rot growing.
On my return visit, the vender provided access to the subfloor from the under stairs cupboard.
I left datalogger in this centre of the subfloor and boarded up the access panel. The datalogger measured 56%RH. This tells me a) the likelihood of active rot especially Dry rot under the kitchen floor (very expensive to replace) is very low, a) there is no rising damp, as the humidity would high , and c) there is probably no need to increase subfloor ventilation, so long as you monitor (weekly) the sub-floor humidity. It will fluctuate with external cnditions, but should be below 75%RH most of the time.
I searched for signs of rot using an endoscope, accessed from both the front air brick and under stair.
There were no signs of significant rot in the subfloor void.
If there is no risk of rising damp, yet there is localised high subfloor humidity, it begs the question why?
I looked into the neighbours down-pipe, which drains into a gulley sitting under a party wall (so presumably shared) and found the gulley to be blocked with the detritus.
I tested the blockage by pouring water into the gulley.
The image above is after about 10 – 20 minutes. Clearly very little water is pouring away. It appears some of the water it’s moistening the subfloor. It would account for the high humility and would have been the root cause of dampness when property was first misdiagnosed and mistreated for rising damp.
The neighbours kindly allowed me to check the wall on their side.
The neighbours told me that they had had a lot of damp issues flag up on the RICS survey report when they purchased. The front wall immediately to the left of the subject property had a very high damp meter reading.
About 10 cm to the right, further away from the party wall, the damp meter reading is normal.
These damp meter readings are consistent with water flowing from the gulley or drain into the sub-floor void of the subject property.
Other matters
There is rot forming on the inside and outside of windows.
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.
The door has suffered from window rot.
You can probably save the door, but I understand you’re considering double glazing. If so make, sure to include trickle vents.
There are various cracks in the render around the property.
These cracks should be raked out and filled with either acrylic external caulk for small cracks, or a cement base render similar to the current render. These may be a shared responsibility and cost through the freehold.
There was an icicle growing under the front left hand gutter at the time of the first visit.
I looked up at the gutter when I returned. Water is sitting in the gutter, so the gutter leak is not substantial. There are signs that water is damaging the flat above but not the subject flat.
Ideally reposition the gutter so that water flows of the downpipe and consider installing an additional downpipe from the left side of the gutter to the neighbour’s downpipe, subject to permission.
Rising damp risk assessment
Elevation is: 17M above sea level. The flood risk is: no risk.
Sub-soil rocks are: Rocks with essentially no groundwater.
Signs of groundwater: there are no signs of groundwater.
Therefore the risk of rising damp is a remote possibility, see a good explanation by Dr Robyn Pender of Historic England https://youtu.be/Jo8oF9ubvtI
The building has been damp proofed against rising damp, the horizontal covered drill holes across the centre of this image, is a sign of chemical damp proofing, hear what Dr Robyn Pender of Historic England says about it.Despite the low risk of rising damp, there has been an attempt at chemical treatment against rising damp. Rising damp treatment is normally a sign of insufficient ventilation. The walls have been drilled into by about 200mm and injected with damp proofing chemicals. In theory the chemicals are absorbed into the brick pores reducing the bricks ability to absorb moisture. Normal absorbent plaster was dry lined (plasterboard and battens). This can cause condensation and mould to form between the plasterboard and wall. There was evidence of condensation elsewhere and mould on the surface of the dry lined plasterboard suggesting that there may be trapped mould behind plasterboard, this increases the risk of