Green Building Forum - Help for a very damp house, where to start?

Help for a very damp house, where to start?

RobinB — Thu, 01 Nov 2012 14:16:25 +0000

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.

Help for a very damp house, where to start?

tony — Thu, 01 Nov 2012 14:21:28 +0000

It 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.

Help for a very damp house, where to start?

HalcyonRichard — Thu, 01 Nov 2012 15:15:37 +0000

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

Help for a very damp house, where to start?

djh — Thu, 01 Nov 2012 15:28:38 +0000

Posted By: RobinBMould 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.

Is that by the vents? What is the humidity in "the house" as opposed to near the floor? How about the temp and humidity near the ceiling?

Help for a very damp house, where to start?

SteamyTea — Thu, 01 Nov 2012 18:17:48 +0000

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.

Help for a very damp house, where to start?

rhamdu — Thu, 01 Nov 2012 21:53:08 +0000

Sounds like the cavity wall insulation was badly done, or has settled.

All those vents are simply making the place cold. Find out if the wood stove can be fed with external air through a pipe.

Help for a very damp house, where to start?

Gotanewlife — Thu, 01 Nov 2012 23:59:02 +0000

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

Help for a very damp house, where to start?

Gavin_A — Fri, 02 Nov 2012 01:18:21 +0000

has it got worse since the cavity wall insulation?

check all the vents aren't blocked into the underfloor areas, and check the loft is well vented - IMO a well vented loft will help wick moisture out of the hose below as long as nobody's put a vapor barrier in the way.

They also need to look at moisture sources, and ways of reducing them, so lids on saucepans, drying washing outside if possible, and definitely installing a fan (or preferably MHRV unit) in all shower rooms if there isn't one.

Then it's down to ventilation either natural, forced, MHRV with a particular focus on kitchen, bathroom, and rooms where mould is a problem.. and / or the use of the wood burner to draw air through the house. I'd think that room sealing the wood burner would make the damp issues worse not better btw.

Help for a very damp house, where to start?

Triassic — Fri, 02 Nov 2012 07:59:51 +0000

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

Help for a very damp house, where to start?

SteamyTea — Fri, 02 Nov 2012 08:18:42 +0000

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'.

Help for a very damp house, where to start?

Jonti — Fri, 02 Nov 2012 08:48:32 +0000

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

Help for a very damp house, where to start?

SteamyTea — Fri, 02 Nov 2012 08:56:52 +0000

Even today I could dry my clothes outside if it was not raining

Help for a very damp house, where to start?

Gotanewlife — Fri, 02 Nov 2012 09:01:49 +0000

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.

Help for a very damp house, where to start?

Gavin_A — Fri, 02 Nov 2012 20:00:03 +0000

Posted By: GotanewlifeGavin 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.https:///forum114/extensions/Vanillacons/smilies/standard/sad.gif" alt="" title="" >

I didn't see it, I think I started mine before you posted yours or something.

I tend to post on here between doing other actual work, so will often start a post, then come back to it a bit later and finish it. This is one of the hazards of that method of posting.

Help for a very damp house, where to start?

Gotanewlife — Fri, 02 Nov 2012 21:31:09 +0000

At least we agree!

Help for a very damp house, where to start?

RobinB — Fri, 02 Nov 2012 22:00:56 +0000

Our router broke as soon as I posted and I've just arrived down south and got online to find all these replies!

I've been reading my new Passivhaus Handbook (good because it's UK-centric but quite pricy) on the train down which has those RH tables and graph showing what bad things happen either end of the RH spectrum which I'm going to share with her. Not sure I can show her the post which describes her home as a "dog" - though I can see why you said it!

Thanks everyone for you help and suggestions.

RobinB

Help for a very damp house, where to start?

Ed Davies — Fri, 02 Nov 2012 22:07:34 +0000

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.

Help for a very damp house, where to start?

RobinB — Fri, 02 Nov 2012 22:13:14 +0000

Posted By: HalcyonRichardI used a B&Q "leak detector" which is really an infrared thermometer.

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

Help for a very damp house, where to start?

Beau — Sat, 03 Nov 2012 07:22:38 +0000

Posted By: RobinB
Posted By: HalcyonRichardI used a B&Q "leak detector" which is really an infrared thermometer.

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

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

Help for a very damp house, where to start?

HalcyonRichard — Sat, 03 Nov 2012 08:49:23 +0000

Hi Beau,
That's the one. I must be border line lexdisic. I bought mine from QVC The QVC part no. is 564482.It was about Â£20 but my better half has an account number

Robin It's the best thing I have ever bought and if it broke I would buy another. I also have a "weather station" that also measures Relative Humidity this has also been invaluable.

Good video here :-http://www.yougen.co.uk/blog-entry/1581/Eliminating+the+draughts+that+push+up+your+heating+bills/?utm_medium=email&utm_campaign=Consumer+newsletter+October+2011&utm_content=Consumer+newsletter+October+2011+CID_5cf7b04033256972d066da837419aeb2&utm_source=Envirosend&utm_term=read+my+review+here

From Stannn on this thread :-http://www.navitron.org.uk/forum/index.php/topic,15707.120.html

I believe knowledge is power. Knowing what is going on allows you to get the best solution for your particular situation.

Richard

Help for a very damp house, where to start?

jamesingram — Sat, 03 Nov 2012 08:52:44 +0000

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

Help for a very damp house, where to start?

SteveZ — Sat, 03 Nov 2012 16:37:23 +0000

I bought one of these B&D TL100 a while ago and it does what it is supposed to do. You set a temperature by pointing it at an object then watch the colour changes as you move the beam across the area investigated. I saw a suggestion to take colour photographs from a fixed point at stages in the process, then combine the shots to show the room with the different colours in on one picture - poor man's FLIR. I haven't tried this!

Help for a very damp house, where to start?

rhamdu — Sat, 03 Nov 2012 20:02:44 +0000

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.

Help for a very damp house, where to start?

CWatters — Tue, 06 Nov 2012 08:47:57 +0000

Humm. Is it cheaper to use a tumble drier (with condenser) or a rack and a dehumidifier ?

I think OP needs to look at the sources of water in the air, showers, drying clothes cooking etc. Fit and use extractor fans etc.

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

Help for a very damp house, where to start?

Gotanewlife — Tue, 06 Nov 2012 16:30:58 +0000

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?

Help for a very damp house, where to start?

RobinB — Tue, 06 Nov 2012 18:04:04 +0000

In this case I don't think so - the air outside is generally so damp. An extract-only set up will pull it in from under the floor, and through the wall vents and all those nooks and crannies. When it's cold out and warm indoors a MVHR will pull out a fair amount of water fromt the incoming air I think.

I'm tempted to try a single room MVHR unit in the dampest bedroom and ideally also one with a humidistat in the main bathroom which is generally open to the hallway.

Help for a very damp house, where to start?

Ed Davies — Tue, 06 Nov 2012 18:43:25 +0000

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).

Help for a very damp house, where to start?

RobinB — Tue, 06 Nov 2012 18:56:54 +0000

I was wondering if someone would come along and disappoint me! It's got to be better than having the cold air coming in directly hasn't it?

Help for a very damp house, where to start?

Ed Davies — Tue, 06 Nov 2012 19:46:03 +0000

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.

Help for a very damp house, where to start?

RobL — Tue, 06 Nov 2012 21:55:51 +0000

RobinB - The two single room MVHR units I've heard are too noisy (in my opinion) to use in a bedroom. They were the HR25 and the Retrovent.
Suggest you fit one to your bathroom first, or listen to one someone else has fitted. Invariably they state "whisper quiet" or some such - though even if they stated the sound level in dBA it would still be very hard to determine whether you'd hear it in your house. Air heat exchangers persuade you to shut windows so making houses quieter, and so highlight their own noise.