My sister's family home in Sussex is very damp. It always has been. Built in the 1930's as a little weekend home for rich Londoners it has thin walls cavity filled a couple of years ago and a suspendended timber floor which they recently covered with an expensive wool carpet. The vents to the outside at the top and bottom of the walls have been left in place.

The roof is tiled but can't be seen much as it's covered with moss. The house is surrounded by trees with TPOs. There is a moat about 200m away (not theirs) and a suspicion of an underground river or old watercourse nearby, although the ground is pretty flat. It is mostly single glazed with pretty little leaded diamond paned windows mostly with secondary glazing and a couple of new DG ones.

There is gas central heating to radiators and a woodstove in the sitting room with an enormous nonclosable vent as per regs about a metre from the stove. The loft has been insulated but there's not much on the sloping ceilings.

Mould grows on external walls up near the ceiling and down near the floor as well as around the old windows. Last weekend it was 16.9 degrees near the floor and 88% humidity. The house was more or less at 19 degrees.

What else do I need to find out to start an improvement plan? Where should we start? I don't think the cavity fill has made anything any worse, but not much better. My initial feeling is the moss on the roof is not really an issue, as in not worth trying to get rid of it, but the damp ground is. I have a mad idea of trying to lay a sheet of DPM over the ground under the house. To see under there I will have to dig out an airbrick and put my camera in.

Hi,
I have a bungalow and did have problems similar to those described. 88% humidity is very high - conventional wisdom is to aim for 50%. If the house is insulated to different standards then this may cause problems even if well ventilated. I used a B&Q "leak detector" which is really an infrared thermometer. Using this I found a few areas that were not insulated as well as the rest. also I increased ventilation and have heating in all rooms or make sure they are properly isolated and ventilated. Is the mould/condensation in particular areas that are unheated or unisnsulated ? I found that even a few degrees difference on walls/ceilings can cause localised high humidity and mould. Mould will grow if humidity is above 60 %. Attached is a graph that would suggest at 88% humidity a drop of a couple of degrees C could lead to condensation. In total agreement with Tony.

Richard

Posted By: tonyIt sounds to me like all the problems are to do with condensation.
Need to get the humidity down a dehumidifier in the short term, then
as always my plan would be to air seal and insulate, install a small MHRV and live happily ever after.

Nothing to add to that.

Robin,

Of course Tony is right, as ever, however, this house sounds like a 'dog' (in livibility/renovation terms) and the costs in making it airtight and insulating and installing MVHR quite likely both prohibitive and, in terms of payback/added house value, nonsensical . There is another way maybe but as a rather non-technical person it is just my version of KISS.

Given that the outside humidity is lower than indoors (and, really, 88% is hugely unhealthy) it seems to me you need to swap the air more often and reduce the amount of humidity being added by those living there. If you do this, perhaps with a little temporary help from the dehumidifier then after a while, like 4-6 months, you will be able to tell if there is an underlying problem (pun intended). But it will have to be done seriously, religiously, call it an experiment with rules. Room by room extraction - little single room things with continuous trickle and boost on timers and switches and humidity sensors - bedroom ones only operate during the day as too noisy, it might be a different strategy for every room - perhaps in some rooms as radical as opening the window. Furniture away from external walls. Is the bathroom one in the best place, does it come on religiously whenever the bathroom is used. Yes it will cost more to heat - talking of which the house temp need to be increased to 20 deg - less condensation (raised dew point) and much more effective dehumidifer. Then work on reducing the added humidity. Buy one of those blue lighted kettles that you can set at 90 deg to boil (not), that everyone on here hates, no boiling of a pan without a lid, does the hob extractor do a good job, is it used every time - also put it on when the oven is on, tumble dryer must exhaust outside, clothes must only be dried outside or in tumble dryer etc etc. And monitor the humidity in lots of rooms whilst noting the external humidity. The outlay for all this will be less than installing a good MVHR unit.

If it works, your sister might be motivated to spend the money to upgrade the house, or look elsewhere, or perhaps continue with her new way of living, or if it doesn't work then perhaps there is some other issue but either way I doubt a house ground sheet will help.

Good luck Duncan

Drying laundry in the home poses a health risk to those prone to asthma, hay fever and other allergies, according to new research.

A study carried out by the Mackintosh School of Architecture found that many homes had too much moisture indoors.

Up to a third of this moisture was attributed to drying laundry.

The researchers have called on housebuilders to build dedicated drying areas into new housing to address the health concerns.

A study of 100 homes by the Mackintosh Environmental Architecture Research Unit in Glasgow found 87% dried their washing indoors in colder weather.

http://www.bbc.co.uk/news/uk-scotland-20176376

Posted By: SteamyTea

Posted By: TriassicThe researchers have called on housebuilders to build dedicated drying areas into new housing to address the health concerns.

Good idea, will it be called 'Outside on the washing line'.

I lived in a Finnland a few years back and my flat there had a wet room bathroom which had a couple of large windows and was large enough to put up a clothes horse. It got nice and warm even in the winter with no daylight so clothes dried in a few hours.

As ST says though through if you have a good back yard then washing line.

Jonti

Gavin A - It looks like you didn't read my Post, is that because it was too long, it would help to know because I'll need to reduce them, which of course needs more time.

At least we agree!

Just like to add my support to the dehumidifier idea.

Last winter I was talking to my neighbours in an old croft house who were having problems with condensation upstairs (which is basically unheated apart from heat from the downstairs wood burners radiating from the chimneys and wafting up the stairs). I suggested a dehumidifier. Spoke to them a few weeks ago - they were raving about how the upstairs now feels much nicer and is much drier as a result. It'll be interesting to see how they get on over this winter.

<blockquote><cite>Posted By: RobinB</cite><blockquote><cite>Posted By: HalcyonRichard</cite>I used a B&Q "leak detector" which is really an infrared thermometer.</blockquote>
diy.com (B & Q) really has the worst search engine ever! It never ceases to wind me up!
any link to the infrared thermometer or similar elsewhere?
thanks!
RobinB</blockquote>

I suspect HacyonRichard ment a B@D thermal leak detector. Quite agree B@Q site search is truly dreadful.

Other retailer may also supply :)
http://www.amazon.co.uk/Black-Decker-TLD100-Thermal-Detector/sim/B0044R87BE/2

If no one has mentioned it already - you gotta choose between a ventilation strategy and a dehumidification strategy. This is particularly true in warmer weather when the 'fresh' outside air may carry a lot of moisture.

If you want to go on drying clothes indoors, put a dehumidifier in the room with the damp clothes. The dehumidifier will not only dry the air but warm the room, because it reclaims the latent heat of evaporation.

Alternatively get one of the fancy tumble driers which recycle their own heat (not one of those 'condensing' ones which use cold water to flush the waste heat down the drain.)

We were having trouble drying clothes in an Irish holiday cottage (in the cool damp summer weather so typical of Cork and Kerry). We found the combination of a dehumidifier, a wood-burning stove, and closed windows worked wonders.

Posted By: CWattersMHRV seems to work well. No condensation on windows in our house with MHRV. All previous houses would have condensation on bedroom windows overnight.

But do you think central extraction only (ie no HR) would have had the same effect?

Posted By: RobinBWhen it's cold out and warm indoors a MVHR will pull out a fair amount of water fromt the incoming air I think.

Not really. The MVHR will increase the temperature of the incoming air and thereby reduce its relative humidity. However, it won't affect the absolute humidity (actual amount of water in the air measured in, say, grams of water per kilogram of air).

Yes, it is better but that's only because the incoming air doesn't tend to cool the house down so much. Nothing directly to do with humidity.