damp and mould

I have had a call from the letting agents for my sons house that the tenants are complaining of damp and mould appearing on bedroom wall and ceiling. I am going over to investigate on Saturday, what should I look out for?
It did not happen when my son lived there so its either a new fault or something the tenants are doing.
Its a terraced 1960s ex council house, brick and render walls, with concrete tiled roof which was replaced about 6 years ago. My son had UPVC double glazed doors and windows fitted, and the old gas boiler replaced with a new condensing combi.
I already intend asking if they are drying laundry on the radiators.
Mike
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Occupation/lifestyle difference? Lots of showers, cooking without extract etc. Window vents plugged to save on heating.
Lots of ventilation is likely to be the answer.
We fitted a heat recovery extractor in my wife's '60's flat which had similar mould problems when occupied by a family with a young child. Fortunately the flat lent itself to convenient routes for the ducting although I still need to vent the cooker extract externally. A better solution might have been cavity wall insulation but this has ownership issues in blocks of flats.
regards
--
Tim Lamb

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On 08/12/2011 09:55, MuddyMike wrote:

Probably due to high humidity and cold walls. We had the same problems with the house here. One solution is to have better wall insulation but obviously that isn't an option for everyone. The next option is to reduce the condensation that is causing the mould, so more ventilation, more heating or run a dehumidifier. My guess is the tennants lifestyle is causing the problem e.g. not enough heating or ventilation. If they are unwilling to do anything to redress that then I don't know where you go next.
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On Thu, 8 Dec 2011 08:55:52 -0000, "MuddyMike"

As you say, it's probably a lifestyle issue. I know a landlord who presents his new tenants with an 'operating manual' detailing how to use the appliances, where the stopcock is, care of the special blinds etc. Seems to be the perfect place to add stuff like ; this house is designed to run at 20deg C with x litres per hour air exchange. If air-drying clothes, increase x to y. Etc, etc etc.
Nick
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Lack of heat + lack of ventilation. Drying washing on radiators. Guttering leak. Roof insufficiently ventilated re rubbish semi-permeable membrane.

Why was the roof replaced, 45yrs is very little (ok council quality "varies")?
Check the loft for damp insulation. Traditional felt is waterproof, semi-permeable membrane relies on capillary action & vapour pressure - but not all of them work despite as BBA certification was handed out like attendance certificate. The one that does work is Proctor Roofshield (about 6x the price of the worst). Those that do not work can be made to work by adding ridge vents and more soffit vents and extra vents lower down the roof and extra double brick vents in the gable end.
Absolutely almost certainly they are insufficiently ventilating and drying washing on radiators. A cooker extractor must extract to the outside, a shower extractor likewise.
As mentioned in another thread you can get 4" fans which run on a timer, 6-12-23min every 4-8-12-24hrs, which will enforce ventilation silently. Window trickle vents need to be open, they are not optional.
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wrote:

Thanks for all the feedback guys. Just back from investigating the problem and apart from a gutter joint that has pulled apart above the bathroom I can find nothing wrong. No wet patches in the loft, damp isolated to wall/ceiling far corners of two bedrooms and along outside bathroom wall/ceiling and (apart from a patch on the ceiling above the bathroom towel rail) extending about 4 inches down the wall and across the ceiling. I used a damp meter and got quite a high reading in the actual damp areas, reducing to nothing 6 inches away.
Spoke to tenant about ventilation and it turns out they have never used the bathroom extractor fan! The third bedroom has no damp and coincidentally is the only one with a wall vent! The other rooms has masses of condensation running down the windows (double glazed UPVC) and pooling on the sills.
I advised them to use the fan and that I will fix the gutter next weekend.
What else should I be doing?
Mike
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Whatever you do, keep an eye on the situation. I tend to favour a dehumidifier in situations like this, its a great insurance against 4 figures of damage, and costs not much.
NT
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On 10 Dec,

The problem would be getting the tenant to use it. They would get the electricity bill which may not be insignificant. Ours gives a noticable significant increase in the bill.
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On Dec 11, 11:31pm, "Dave Liquorice"

Dehumidifier varies from 35p to 70p a day to run.
Compressor type - 35p. Air exhaust feels cold in winter. Dessicant type - 70p. Air exhaust feels warm in winter.
They are noisy at night, the high velocity airflow can disturb the boundary layer on walls & ceilings so if poorly insulated can make the place feel cooler. The dessicant ones I have used seem to cause nasal irritation and do cause a dry throat, the Mitsubishi one caused instant sneezes from the exhaust - like a HVAC unit you need to use a spray cleaner every so often so stop stuff growing. No idea if anything can grow on dessicant type, but I suspect "something can somewhere". Some use a silver filter, but I am not convinced it can handle the airflow - a 9W UV bulb would be more effective.
Best is a fan extractor, you can pick up fans which run x-minutes every y-hours. They can be fitted in a ceiling of a hall so basically just enforce a house-level Air Change Per Day - about 25dB(A) to 15dB(A) fitted so very inobtrusive. Beware anyone stuffing up an AC fan, such fans can catch fire. Soffit exhausting fans avoid the "flap- clatter" of conventional wall mounted fan outlets (even baffled, they really need a weak magnet & steel strip to hold shut until the fan turns on).
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Why, you get the added heat from the compressor as well as the heat from condensing the water. Are you confusing air conditioning with dehumidifiers?

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wrote:

The heat input per volume of air is tiny, so the temp rise is trivial.
NT
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Its not trivial if its cost 35p a day, its about 150 watts continuous just for the electricity.
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.
You'd have to have rain pouring in the roof to warrant running a dehumidifier 75-100% of the time. Its not reality.
NT
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200w domestic model running 10% of time = mean 20w. 24hrs makes that 0.5kWh, cost 6p.
To get costs of 35p and 70p you'd need to run it 60% and 120% of the time respectively. The latter is a challenge left for the reader :)

models vary from totally silent to noisy. In practice even oisyish ones are unlikely to be heard at nigh if theyre not in the bedroom.

But running an extractor fan costs much more, all that heat chucked away. It also adds dust to the air, as air has to come in soemwhere to replace the exhausted air. It also makes the bathroom etc cold. A dehumidifier does neither.
NT
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