Here is a vacant terraced Victorian house, almost certainly a probate. It needs little more than a “lick of paint”, a couple of vents and TLC, to bring it up to modern standards.
“A reading above 20% WME (wood moisture equivalent) is a cause for concern and is caused by rising damp. This will require a chemical damp proof course injection. Note: there may be further defects including wet rot under the floor as a result of the damp and further investigation is recommended.” Additional details given at end.
This is written by a RICS surveyor unable to differentiate between Rising Damp and Condensation or any other form of dampness. Incorrect diagnosis can lead to a down valuation, resulting in a lender offering less money for the purchase, or worse still, a mortgage provider refusing to write a loan. These words are those repeatedly used in the report of a London based RICS surveyor. Around 10 – 15% of our homebuyer enquiries come from one surveyor. He doesn’t appear to recognise the signs or significance of prior damp proofing treatment.
If a property has been damp proofed with chemicals, and is still damp, does that not suggest 1) it doesn’t cure the problem, 2) that there must be another root cause.
Here is an example of a French drain (invention of Mr French, not especially well known in France). It may have some benefits if properly draining. However, not, like this property, where it does not drain away from the building. The shingles reduce evaporation, keeping water at the base of the wall for longer, thereby increasing the risk of condensation through heat loss and sub-floor humidity. See; Dr Robyn Pender of Historic England https://youtu.be/Jo8oF9ubvtI.
Surveyor Tips:
- Mould is inhibited by nitrates found in groundwater.
- Groundwater is the source of dampness in rising damp,
- It follows that if there is mould at the base of a wall, that there is no rising damp.
- Condensation and mould is patchy, although most common at the base of a wall.
- Condensation tends to rise into corners and cold wall in front of the door.
- Beware damage caused by chemical damp proofing.
- If you need a perimeter drain, use an Aco drain and make sure that it drains away from the property.
- Roofs failed when nails break, look for signs of corrosion in nails.
- If you plan to have a loft extension, wait until then before replacing the roof.
- Make sure to have adequate ventilation.
- Insulation imbalance can cause mould.
ILLUSTRATIONS
Even if there were a risk of rising damp, it could not possibly reach to ceiling level. This section of wall is now dry, presumably the house has been empty for some time.
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 vapour.
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. Walls measured were largely dry on the surface except where mentioned in this report.
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.
It is likely that moisture, such as from condensation, has been absorbed deep into the building material.
There were no nitrates found on the surface which again eliminates rising damp as the root cause of dampness.
There were no high damp meter readings in conductance mode to the front of the property.
Looking in the room above we can see mould growing on the bay ceiling.
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. The secondary cause of high relative humidity is low temperature relative to the source of humidity, see surveyor.tips/humidity.
There is mould growing on the front bedroom wall and condensation dribble marks down it.
The only high damp meter reading in conductance mode on a wall, is to the rear of the property.
Here we see a section of plaster is missing from the wall. Less plaster means less insolation, heat loss, increasing the risk of condensation.
Again less render means less insolation. Damp bricks have half the insulting capacity of dry bricks. There is also an increased possibility of penetrating damp. The render should be repaired. Note also that you can see the thin black line of the original damp proof course (“DPC”) roughly halfway up this image.
Again we can see what appears to be condensation dribble marks by the back door.
Note there is no externally ducted extractor fan in the kitchen.
From the evidence around the property, I suspect the bathroom extractor fan is not running at building regulations speed. 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.
Unfortunately the trickle vents were closed, effectively sealing up the property.
Note this is not a roofing survey, but a damp survey focused on actual damp found within the property.
That said I believe this roof will last for at least 5 years. The cost of replacement it’s not a lot less than the cost of a loft conversion such as on either side of this building.
Slate tiles are durable, capable of lasting for hundreds of years. The lifetime of a roof is primarily determined by the corrosion of the nails holding up the tiles. Nails tend to corrode at the same rate; therefore a roof tends to fail at a point in time.
The tile nails appear to be quality, galvanised nails. There is no sign of corrosion. Therefore the tile aspect of this roof should survive for many years.
Looking closely at the valley we can see a crack appearing. You could paint this with valley sealant to provide short-term protection. However, longer term it would be wise to replace the valleys.
I did not see any cracks in the left-hand valley, but I suspect there must be one because the timber below is damp.
There are signs of mould, which tells me that there is high humidity in the loft (and insufficient ventilation for the amount of water coming in).
Timber of more than 28WME is at risk of rot. There is no sign of significant rot, but there is a risk of rot if the valley is not repaired within the next few months.
At the top of the right-hand party wall, one of the coping stones is missing.
Replacing the missing coping stone should also be of interest to the right-hand neighbour.
The neighbours currently have scaffolding so it would be in their interest as well as yours to replace the coping stone now.
It is probably only a few months before rot is likely to set in, you should look to replace the shared coping stone now.
This inconsistency of installation is the reason why you have mould growing on top of the bay. You would be wise to insulate above the bay.
Other matters
It would only take a few minutes for somebody to rearrange the flashing to minimise the risk of water splashing in under the loft.
You would be wise to have a roofer look at the roof.
Rainwater is clearly bouncing onto the windowsill and wall below.
There are no signs of this is causing internal dampness. However, have somebody check the gutter and adjust it so that all water from the gutter is drained away.
There are no signs that this is causing internal dampness. However, it would be wise to fill the crack and repair any missing sealant around windows.
The old coal shoot to the front of the building, accessible from the cellar, is very damp.
The coal shoot was closed off by section of plastic. The dampness is caused by vapour condensing on the cold metal coal shoot lid. It would be better to keep this area open to the rest of the seller. Consider insulating the old coal shoo lid.
The were no signs of structurally significant rot in the subfloor void.