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General: Help for a very damp house, where to start?

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    • CommentAuthorGotanewlife
    • CommentTimeNov 6th 2012 edited
     
    Posted By: RobLThe two single room MVHR units I've heard are too noisy (in my opinion)
    absolutely concur! No matter what the marketing blurp, silent this, whisper that - the minimum is 20dB @ 3m across dozens that I looked at and that dear friends is not acceptable in a bedroom - indeed my wife took some time accepting it in the bathroom - didn't want it (Venta Axia Solo Humistat 23dB@3m) on full-time trickle. I won that battle but put the kitchen one in a stack of full height units (containing 2 ovens) opened the service void and boxed in the fan etc - this works really well but wouldn't for a HR version obviously!:wink:

    In my view ducted ventilation is the only option in a bedroom, think of that ticking watch or clock that kept you awake once, my wife's phone charger used to make a tiny, tiny whine once the phone was fully charged - annoying.
    • CommentAuthorRobinB
    • CommentTimeNov 7th 2012
     
    Thanks everyone for you helpful advice and caveats!

    One fundamental I'm not yet clear on is if most of the damp is from the inhabitants and their activities or from the outside.

    Short term plan is to use tumble dryer and the outdoors, not the kitchen, for drying clothes, get MVHR unit for bathroom (instead of opening window as now. I need to check if their loft insulation is blocking any vents at the eaves and look for ways the damp is getting in.

    Longer term to replace most or all windows with DG or TG and perhaps full house MVHR.

    thanks again

    Robinb
  3.  
    Assuming there are no plumbing leaks, broken gutters, etc & its warmer inside than outside then any damp can only be coming from inside the house. Heating & ventilation will fix all (non-leak related) damp problems, but this may not be economic (or environmentally sound) depending upon the level of insulation. Better to reduce the humidity at source, increase insulation & then increase heating & ventilation.

    David
  4.  
    Certainly ventilation is needed but HR ventilation can cost one hell of a lot more than extract only ventilation - and unless the house reaches a certain level of air tightness it is commonly accepted that HR ventilation is not indicated.
    • CommentAuthorseascape
    • CommentTimeNov 7th 2012
     
    Not sure if this is correct but If it's covered in moss, surrounded by trees with watercourse/moat close by, wouldn't that indicate the outside humidity is high too - maybe a bit of judicial pruning (for their health of course) would create more sunlight/draughts around the house. I thought of this as there is another thread recently about a MVHR pulling in moisture into the house with bad results. It made me rethink the position of my intended MVHR inlet.
    • CommentAuthortony
    • CommentTimeNov 7th 2012
     
    In general there is far less moisture in cold air from outside than there is in warm air in the the house, problems happen when warm air from inside is cooled.
  7.  
    Hi,
    Outdoor humidity is usually reasonable low and if cold are comes into a warm house it's unlikely to cauase condensation. From the graph on this thread even if the outdoor air is 100% relative humidity and it comes into a warmer house and heats up by 10 C it's realatve humidity will drop to 50%(which is what I aim for). I have a weather station indoors and try to keep it at about 50%. It can go up to 70% when we are cooking on gas/have boiling water in pans.

    From my experience it's likely that it's internally generated water and the big thing is that if the house has different temperatures then this will locally increase humidity and cause mould and if cool enough then condensation.

    Could you measure the temperature with a "leak detector" or infra red thermometer and use a hygrometer to measure humidity. This will hopefully give an idea of variations. Then you could deduce the cause.

    Richard
    • CommentAuthorcrusoe
    • CommentTimeNov 8th 2012
     
    Loft-mounted pressurisation unit - Drimaster or Pozidry - solved our black mould problems at a fraction of the cost - ergo energy consumption - of a dehumidifier. Better than sliced bread IMO.
    • CommentAuthorRobinB
    • CommentTimeNov 8th 2012
     
    Posted By: crusoeLoft-mounted pressurisation unit - Drimaster or Pozidry - solved our black mould problems at a fraction of the cost -

    Interesting, thanks, and I have ordered the IR thermometer as suggested further above. (another toy for my toy box)
  10.  
    Posted By: crusoeLoft-mounted pressurisation unit - Drimaster or Pozidry - solved our black mould problems at a fraction of the cost - ergo energy consumption - of a dehumidifier.

    A quick look at the products shows that the Drimaster relies on heat from the loft to heat the air in the winter i.e. heat loss from the house and the Pozidry has a 500w heater to lift the air temperature to 10 deg. Perhaps both could be expensive to run in a house with, say 30 cm insulation in the loft, with the Drimaster pushing cold air in and the Pozidrive running a 500w heater to get the temperature up. I can see it could work in some cases but good loft insulation IMO would be detrimental (from the view of comfort or cost) to the running of the units.
    • CommentAuthorRobinB
    • CommentTimeNov 8th 2012
     
    Posted By: Peter_in_HungaryI can see it could work in some cases but good loft insulation IMO would be detrimental (from the view of comfort or cost) to the running of the units.


    I've been looking at it too. It's a relatively inexpensive thing to try and I'm tempted. I think it's got to be one step up from pulling in outdoor air (I'm not considering the heating element as too expensive to run). Perhaps on a timer from an hour or so after sun up to just after sun down or longer would be best? Agree decent loft insulation will make less good.
    • CommentAuthorrhamdu
    • CommentTimeNov 10th 2012
     
    Positive pressure units may improve comfort in the house by reducing 'draughts'. Cold air is still coming into the house but it enters the living space at high level and by the time it reaches your skin it is moving slowly and has mixed with the warm air that naturally accumulates under ceilings. Stratification is reduced. If the ceiling temperature is reduced from say, 21C to 19C, heat loss into the loft will also be somewhat reduced. This might, to some extent, counteract the increased heating demand that would normally be the consequence of pumping cold air into the house and pushing warm air out.

    So in terms of comfort per kWh of heating, positive pressure units might be the most efficient pure-ventilation solution to a condensation problem. Compared, that is, with extractor fans or open windows. Heat recovery is going to be way more efficient if you have a sufficiently airtight house to take advantage of it.
    • CommentAuthorjules
    • CommentTimeNov 12th 2012
     
    Just to confirm the other comments about where dampness comes from. As I write this humidity outside is 100% - but the temp is only 3C, which means that the outside air contains approx 6g/m3 of water. Inside air, assuming 20C and 60% humidity, will contain about 10.5g/m3. So if you replaced all your inside air with outside air warmed up to 20C your internal humidity would drop to about 35%.

    I have a couple of HR25H fans. If installed in a solid brick wall I find them quiet enough to be drowned out by the sound of the freezer in the utility room, and the fluorescent light in the bathroom. But in a dead quiet bedroom it might be different.
    • CommentAuthorseascape
    • CommentTimeNov 12th 2012
     
    So if the inside of a house didn't have anyone in it and no appliances running etc it, the inside humidity should be exactly the same as the outdoor humidity? Do walls act like blotting paper, taking a little bit of moisture each air change?
  15.  
    Hi,
    There are a number of things to consider. Mortar/plaster can act as a humidity stabiliser as plaster in particular will absorb moisture in high humidity and dry out in low humidity and temperature is also important. The other problem is a house will hardly ever have the same temperature as outdoors. The mass of the house will take a long time to heat up/cool down. So even with 0 C outside for days on end the water in the house will not freeze. Outdoor temperatures can change by 10's of C in an hour - inside a house this could take days. In the very rare event (if ever) will steady state be reached then the indoor and outdoor humidity will be the same for any length of time.

    Richard
    • CommentAuthorSteveZ
    • CommentTimeNov 12th 2012 edited
     
    As we live in Cornwall, the real one, not that county of endless sunny days on the telly, keeping our place dry and healthy is taken seriously. We do not dry washing inside the house - either it goes outside on the line or in the vented tumbler. I wipe down the walls of the shower room each day. (I have measured the daily quantity removed in the past out of curiosity - around 0.5 litre)

    The attached photo, if it appears, is of a couple of cheap temp/humidity monitors bought for a few quid on eBay. I bought two, to check the correlation, as I wouldn't trust a single cheapie, but if two agree reasonably well, they are probably OK.

    The 17.3°C and 58% RH readings shown in the photo were taken on a mild day with water on the ground and a light drizzle falling. During a really wet spell, I have seen RH readings of 80%, but we do tend to keep our place around 18°C

    If you are going to buy a tumble dryer, the latest models have an A+ rating. I think the jump from B to A represents around a 50% energy saving, so what the A+ indicates is anyone's guess.
      DSCF0349 (Small).JPG
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 12th 2012 edited
     
    Those meters seem to be pretty good on the °C and RH, you would miss a train or busif you used the one on the left.

    The A+ is based on the previous generations mean rating I am told. Somewhere on here there is something about it.

    I have pictures of the real Cornwall :wink:
    • CommentAuthorRobinB
    • CommentTimeNov 12th 2012
     
    I have two of the same monitors - they're at my sister's house right now. I never could work out how to change the time but at less then £5 each they're pretty useful.

    Interesting that you scrape about 0.5l off the shower!
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 12th 2012
     
    Posted By: RobinBInteresting that you scrape about 0.5l off the shower!
    Does not surprise me as it is not unusual to have 50 kg of water at 40°C being sprayed around and it is cooling rapidly.
    • CommentAuthorSteveZ
    • CommentTimeNov 12th 2012
     
    Hi Robin - I have just corrected the time on those monitors to show GMT. I'd forgotten that it is a clock, an alarm clock and calendar as well as thermometer and humidity monitor, and it keeps a max and min temp and RH reading - all for a fiver, not bad! Search for HTC-1, if anyone wants one.

    PS Steamy - those things you mentioned earlier - bus, train? We hear talk of them around population centres such as Penzance, but they are rarely found out here in the sticks :sad:
    •  
      CommentAuthorSteamyTea
    • CommentTimeNov 12th 2012
     
    Every Wednesday, but it does not stop at Camborne :cool:
    • CommentAuthorRobinB
    • CommentTimeNov 26th 2012
     
    meanwhile back at the house ...
    The roof looks like this - should we do something? They said they got the moss off when the first moved in 12 years ago. Should that undercloaking (is that the right word) be ventilated?
    • CommentAuthornikhoward
    • CommentTimeNov 28th 2012
     
    Spray it with bleach 1:1 with water, buy a few cheap bottles of it, buckets under down pipe then you can reuse it on rest of roof, wait till summer when it's not growing so much. Get it off, look at thread on clean roof from a few weeks ago

    With that much moss you must be very shady, get a tree surgeon in, more light and air will help with the damp too.

    Undercloak is the bit that the mortar of a verge sits on under the tiles, is that what you mean, not normally vented, normally vented at eaves/soffit and ridge, but depends on age of house (60's), roof membrane, insulation, etc
    • CommentAuthornikhoward
    • CommentTimeNov 28th 2012
     
    Are you following the condensation control thread
  25.  
    ''Should that undercloaking (is that the right word) be ventilated?

    I think you mean the soffit - the horizontal bit which turns back from the gutter to the wall - and yes, it should. There should be cross-ventilation from side to side of the roof, equal to about a 15mm slot across the full width of the eaves at each side.
    • CommentAuthorrhamdu
    • CommentTimeNov 28th 2012
     
    What harm is the moss doing? It's pretty normal for moss to grow on shaded roofs. Unless the roof itself is faulty, I don't see how moss on the roof can affect conditions inside the house.

    Once you start loosening it, however, it may block your gutters and rainwater pipes.

    My reaction to the picture is - lucky you, you must have nice clean air there.
    • CommentAuthorRobinB
    • CommentTimeNov 29th 2012 edited
     
    Two opposing views on the mossy roof! Any more? I am down there tomorrow. Surrounding trees all have TPOs.
    thanks!
    • CommentAuthornikhoward
    • CommentTimeNov 29th 2012
     
    Posted By: RobinBTwo opposing views on the mossy roof! Any more? I am down there tomorrow. Surrounding trees all have TPOs.
    thanks!


    Trees with TPOs can all still be pruned, I was not suggesting cutting them all down, I like trees.
    • CommentAuthornikhoward
    • CommentTimeNov 29th 2012
     
    Posted By: rhamduWhat harm is the moss doing? It's pretty normal for moss to grow on shaded roofs. Unless the roof itself is faulty, I don't see how moss on the roof can affect conditions inside the house.

    Once you start loosening it, however, it may block your gutters and rainwater pipes.

    My reaction to the picture is - lucky you, you must have nice clean air there.


    It will block gutters, can lift tiles, can wick moisture into the roof, etc

    I know most roofs are well over engineered to include snow loadings, etc but 40mm thick soaking wet moss on 150m2 of roof = another 6 tons on the roof
    • CommentAuthornikhoward
    • CommentTimeNov 29th 2012
     
    oh, also HTC-1 on the way from Hong Kong, £3.36 inc P&P

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