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Green Building Bible, Fourth Edition
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Fundamentals: Condensation

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  1.  
    • CommentAuthorcha0s
    • CommentTimeJan 7th 2010
     
    Need help with what i would call quite bad condensation on the bathroom wall and front door.

    The house is approx 1850's in parts. and those parts are the problem :-)
    I think the bathroom wall is solid (no cavity) and it gets cold and has lots of condensation. esp around the window.
    Is there anything i can do to minimise this?

    There are vents above the window? will blocking these help?
    We will be looking into external and internal insulation on the solid walls in the house. But need to assess what will happen about having to move windows etc so they are flush with the outside again (is this an issue?)

    (btw the heating has just died in the last couple of days, and guess what, no condensation!)

    The front door also has the same problem, its wood (pine probably), fairly thin. maybe 20mm?

    any thoughts?? thanks.
  2.  
    Condensation forms on surfaces that are below (I think) 13 degrees. So insulating will definately help by keeping the wall surfaces warm. External is best, since you minimise cold bridges where floors and suchlike penetrate through your internal insulation.

    In the short term, you could do what I do and ignore it until you've saved up for your insulation, and bleach it if it gets mouldy. Blocking the vents would probably make it worse, since the moisture in the air from showering etc will be trapped indoors.
    • CommentAuthorcha0s
    • CommentTimeJan 7th 2010
     
    ok, nice to know that when we do the insulation itll probably help.

    yes, were just living with it for now.. its not a great problem, just one more thing on the list to sort out.

    would knocking down the wall and rebuilding with a cavity be too drastic?
    its a bungalow, so supporting the roof would be quite easy (while the was was reconstructed).
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2010
     
    Condensation forms when the temperature falls below the dewpoint. The dewpoint depends a lot on the humidity of the air; it's not a fixed temperature. There's a calculator here - http://www.decatur.de/javascript/dew/index.html - look at the other pages there for more explanation, or google it.

    Reducing the humidity is a good way to reduce condensation. Opening the windows once or twice a day is the simplest way to start doing that. Especially opening the bathroom window after showering/bathing and kitchen window when cooking. Extractor fans are a good alternative.

    What type of heating is it and how is it vented?

    External insulation is likely to be better than a cavity wall when you are able to get around to it. There are various threads about it here.
    • CommentAuthorcha0s
    • CommentTimeJan 8th 2010
     
    great, thanks for the info.

    heating is underfloor (wet).
    The room is vented via an extractor and vents above the windows.
    However due to the cold, and draught coming through the extractor I have temporarily blocked it up with a foam bung.

    As for the insulation, yes, we had come to the conclusion that the whole solid wall (which spans the bathroom, a bedroom and the front door) will need something done, most likley external.
    Its a case of getting someone in to have a look, and advise on what needs to be done about the repositioning of windows etc..
    •  
      CommentAuthordjh
    • CommentTimeJan 8th 2010
     
    Sorry, when I asked about the venting I was thinking of the heating. e.g. an open gas fire will add water vapour to the air. I should have made myself clear.
    • CommentAuthorcha0s
    • CommentTimeJan 8th 2010
     
    oh ok.
    its all electrically heated water.

    i.e. 4 immersions heating a 260L tank.

    We are thinking about going for a wood or pellet burning stove (with back boiler) though.
    • CommentAuthorBrianR
    • CommentTimeJan 11th 2010
     
    Hi chaOs,

    I would recommend buying a dehumidifier. This will reduce the humidity in your house and give extra heating.

    Find out if there was a reason for the condensation i.e. humidity dropping when the heating packed up. For example was someone drying clothes on radiators?

    If your door has large panels in and is around 44mm in thickness at its widest point (and less than 20mm at the thinest points) then you could easily add Aerogel insulation into the panels and then fix thin plywood on top. This is quite cheap and easy to DIY and the effect is dramatic. Also make sure you have good door seals. The foam sticky type is not so good. Better to use the vinyl draught excluder strips that push into rebate slots around the door.

    For your bathroom you could add a through hole heat exchanger. Not sure how good these seal against gales from outside but at least this would reduce condensation and increase the heating all in one unit. This may buy you time while saving for the external insulation.
    •  
      CommentAuthorfostertom
    • CommentTimeJan 12th 2010
     
    Posted By: cha0swould knocking down the wall and rebuilding with a cavity be too drastic?
    its a bungalow, so supporting the roof would be quite easy (while the was was reconstructed).
    Forget cavity walls - now completely obsolete. Your solid walls are ideal for the future - provided your planned insulation is the External Wall Insulation kind, which will make your walls into part of the internal environment, held near-enough at room temp right through - very good for solar and other heat storage, great for internal temp stability. Avoid internal insulation if at all possible - troublesome half-measure not good enough for the future. Don't assume that 'precious' external appearance rules out EWI.

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