Advise about damp in rental period property

[Clarert]

Hi
I'm Clare. I have two period homes, I live in a Georgian farmhouse in Norfolk with no problems excepts its bloody freezing in winter and a much older (1700s) semi detached cottage in Cambs which I bought when I was 25 in something of a state, I spent a few good years renovating it before moving abroad and running as a holiday cottage for the next 10years with no major problems.
Since I returned to the UK I have let the property residentially. When the first set of tenants moved out after 2yrs there was a blob of damp behind where they had the sofa, and where they had a TV unit. Condensation I thought, so thought it would dry out. however the next lot have now moved out and despite me saying not to have the sofa up against that wall, they have and now there is a huge damp patch behind there. It also seems as if no windows have been opened over the last 2yrs as the windows were a bit stuck when I opened them. The extractor fan in the kitchen which adjoins the lounge has also packed up which I wasn't told about.......arrrggghhhh!
My question really is
1) How long does it take for these damp patches to dry out? the property was closed up for two weeks (I was away when the tenants left) since then I have placed a dehumidifier in the room, switched the heating to come on low during the night, and cracked a few windows open. Over 4 days the damp patches don't seem to have changed.
2) any practical ideas I can install in the house to aid ventilation and combat condensation?
The walls on the other side in the kitchen and bathroom show no signs of damp just in the lounge where furniture has been, there is no mould and no salt deposits, although the paint is a bit flakey. The house is lathe and plaster, beams exposed on the kitchen side are solid. The floor is cement I think. Two windows upstairs have vents built in to the frames which I have opened, and I am getting the kitchen extractor fixed, the bathroom has an extractor which is operated manually.
Any suggestions would be great.

 

[andrew gayton]

hello.

do the internal damp patches correspond with an external problem (failed pointing/render/rain water disposal/etc)?

If all is ok externally, is the internal damp patch made visually worse by mold growth?

provided the fabric of the building is permeable, ventilated, sensibly heated and not being continually saturated, it should dry relatively quickly.

I can imagine the scenario of keeping the windows shut and cranking the heating on for 2 hrs a day would result in condensation and associated mold growth.

 

[Roger H]

Hi Clare.

I wonder if you should be thinking about a single room MHRV (Mechanical Heat Recovery Ventilation unit). They work as an extractor fan but pass incoming fresh air over a baffle which sucks out damp warm air, exchanging some of the heat. Vent Axia and so on do them. See http://www.earth.org.uk/MHRV-Vent-Axia-Lo-Carbon-Tempra-P-REVIEW.html.

As they re-capture heat, tenants may also be less inclined to turn them off as they'll grasp they are not sucking out heat/money as with a conventional extractor fan. They are a couple of hundred quid.

 

[tobydog]

Hi Clare and welcome to the forum.

This is intriguing. Unless I'm reading this wrong, I see you said that "The walls on the other side in the kitchen and bathroon show no signs of damp". This would suggest the problem wall is, in fact, internal. Is that correct?. You also say the house is lathe and plaster which suggests the problem wall might not be brick. Is that correct? If it's an old stud wall with lathe and plaster then I have no idea what's going on other than a leak in the kitchen or bathroom. If it's brick, then the concrete floor might be causing trapped moisture to migrate to this particular area, hence the damp.

What's also odd is that, if it is condensation, it's occurring and you're noticing the damp patch at this time of year. As Andrew suggested, is it actually very damp now or are you looking at a wall that's still showing signs of damp from last winter?

Although I've never had tenants, I would guess they have a tendancy to hang washing all over the radiators and cook with the extractor off because it's too noisy when watching TV :roll: . Whilst the resulting condensation would move all round the house, it would particularly show itself on cold surfaces (walls and single glazed windows). Behind your sofa there may have been a succession of wet wall days with no air circulation to dry it off and I guess your sofa probably isn't great around the back either but this is assuing the wall is brick.

Normally, with the sofa moved, and you continuing what you are doing I think the wall could dry out nicely but not totally if it's floor related (4 days isn't actually very long in terms of house drying). Might take little longer than you hoped and as we are heading into autumn, we have some days of high Relative Humidity coming up. Once winter proper gets here, and those easterly winds whip across the Fens, the air will start drying out and hopefully so will your house.

One suggestion would be to have a new bathroom fan connected to the light switch with an overrun. That way, in the winter at least, the fan will always be on when people have showers or baths.