This is a a Edwardian house on a hill. It was dry lined many years ago, presumably because of dampness. The neighbours gulley and underground drain appears to be leaking.
- Be prepared to recommend further action, such as drain CCTV.
- Make sure buyer is aware of the potential risk of rot to sub-floor joists.
- Here there was an overlaid floor, and no under-stair cupboard access.
- It would have caused almost as much damage to investigate, as replacing the rotten timber.
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.
Chimneys tend to absorb more moisture than walls because more bricks are in contact with moist air or moist soil.
The front wall has been dry lined, where plasterboard is separated from the wall with batons. This affectively hides the damp and suggests that there has been a history of dampness to the front wall. I spoke to the vendor about it, but she seemed unaware of what changes her husband had made.
Normally when there is active rot the relative humidity exceeds 95%RH. However, any reading above 85%RH is considered high, and a sign of water entering the subfloor void and insufficient sub-floor ventilation.
Dry rot, produces a lot of moisture and therefore is associated with high relative humidity over 95% – see later in this report. The risk of Dry rot is remote.
There is a risk of cellar rot affecting joists in the subfloor void. I have considered the risks. In my opinion, significant decay of structural timber is unlikely. The cost and disruption caused to checking for timber decay, would be high (a few hundred pounds) compared to the cost of replacing damaged timber (maybe five hundred pounds), so not worth doing. So long as the cause of dampness is confirmed and stopped, the risk of rot will disappear.
I spoke to the tenant of the left-hand property, who told me that they had no dampness in the front room. However their property is approximately 1 m above your property, and therefore any dampness and bricks will be more evident on your side of the party wall.
I suspect but don’t know that there is damage to the neighbour’s drain running under their property. The crack may or may not be linked to this drain.
Rising damp is caused by bricks being in contact with the groundwater. The property is built on a hill, at the back of the building there is a roughly 2M drop. Groundwater is highly unlikely to be present on a hill and even it if were, it could not possibly rise by 2M.
Mains water pressure held for 30 minutes. Therefore I conclude there is no significant mains water leak.
There are signs of ponding, this could result in water flowing back in under the house. But I doubt that this is the root cause of internal dampness.
A high damp meter reading was found in the rear reception chimney breast.
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.
Seal up around the window frames to reduce the chance of penetrating damp.
The roof looks “tired” although there are no signs of internal dampness. I would expect you to have to replace the roof within about 10 years. I would recommend replacing it with EPDM, a seamless rubber covering. Make sure that the EPDM is not in direct contact with the bitumen felt. The cost should be around £1,000 for replacement with EPDM.
Consider installing cowls over chimney pots, to reduce the risk of rainwater penetrating through to the rooms below. The cost would be around £200, but could increase demanding on access requirements.