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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthormarsaday
    • CommentTimeAug 2nd 2020
    I have a bay window which is double glazed in a property i rent out. The new tenants are talking about condensation forming on the inside even in the summer time. So i imagine it will be quite bad in the winter. They are a family of 2 adults and 3 young boys. So quite a big family and they will be in the lounge quite a bit.

    Any ideas on how i can solve this issue? The windows are in good condition so i do not want to replace for pvc.

    They dont have any trickle vents so i thought maybe i could fit some. If so would you fit one or 3 (one for each section)?

    Any other solution ?
    Is the condensation forming even when the windows are open? What proportion of the total area opens?

    If the answer to Q1 is 'no', encourage opening wins when it is not too cold or when security is not compromised, and provide (yes, I'd say 3x) trickle vents for when you can't open windows.

    Have you seen it? (It sounds like not). Is it condensation on the inside of the inner pane? Could it be a failed seal and condensation between panes?
    • CommentAuthormarsaday
    • CommentTimeAug 2nd 2020
    I think it is on the inner pane, not a failed pane. The amount of glass which can be opened is small. Just 2 top square ones.

    I dont think it is forming when open as they are not open that much from what i can see.

    I will get the trickle vents in before winter.
    What sort of DGUs do you have? In particular how do you think the walls fare compared with the windows.? Say the wins were post-2010, and 1.6 U value, sitting in a solid brick wall with U = 1.7-2.1, depending on which version of SAP you look at - you might be getting condensation and mould on the walls too, particularly in hidden places with little air-flow. Apologies if I am teaching you to suck eggs.
    • CommentAuthormarsaday
    • CommentTimeAug 2nd 2020
    Thants ok, i am not fully up on the technicals with regards to heat differences etc.

    The house does have the blown fibre in the walls, and i think the base of the bay.

    Windows were in when i bought it and i am thinking they are now 15 years old min.

    Yes i think there has been a tiny bit of black mold on this external wall, but the previous tenants never mentioned it. Only when they moved out could you see this issue. The new tenants have fully repainted the room so it is all new. They are more fussy than the previous tenants, so i will certainly here about any issues this winter.

    The DG glass was smashed in 2015 when i was renovating the house. So i had new ones made up. I think 12mm depth and in C rated glass.
    • CommentTimeAug 2nd 2020
    Ventilation is the main issue. If you fit trickle vents then the tenants will need to leave them open. That will cost them money for heating, just as opening the windows would, so it's important they realize that that's their choice. Spend a little bit more on heating or suffer condensation and possibly mould.
    • CommentAuthormarsaday
    • CommentTimeAug 2nd 2020
    Thanks for that. I will explain it to them. They are reasonable.
    • CommentAuthortony
    • CommentTimeAug 2nd 2020
    Can you get a photo please
    I can confirm that three kids breathe out an awful lot of moisture vapour, which (if not ventilated) will condense on the coldest surface of the room. If that is the window, then that's kind of good news: a) that the wall insulation is working and b) it doesn't do much damage if wiped and it's dehumidifying the rest of the room...

    I found having a few cheap humidity display meters lying around the house helps to prompt us to ventilate the right amount, usually before condensation appears.

    Edit to clarify: I'm not saying condensation should be tolerated. Just that the moisture vapour has to go somewhere, and if you improve the glazing then it will condense somewhere else less visible, unless you address the root cause and improve the ventilation, with consequent heat losses.
    • CommentAuthormarsaday
    • CommentTimeAug 6th 2020
    I cant upload photos on this site anymore as i have a new computer and cannot seem to shrink the photos down. Its a windows one as opposed to the apple i had before (which sadly died)
    • CommentAuthormarsaday
    • CommentTimeAug 6th 2020 edited
    Double post sorry
    • CommentAuthortony
    • CommentTimeAug 6th 2020
    Try a link to Dropbox or flikr etc ?
    Try... Picture Manager; Edit Picture; Compress; Documents
    Try opening the photo on your screen and then taking a’snip’ with snipping tool. Save this as a jpeg.
    Because this is a screen grab it is lower quality than the photo. But when posted/viewed on this forum it’s plenty good enough.
    • CommentAuthorphiledge
    • CommentTimeAug 8th 2020
    If theres already condensation in the warmth of summer, trickle vents would be a minimum. If the condensation is limited to the glass, Id be looking to fit hi spec DG units. Over time, if theres water sat on the inside of the frame theyll start rotting.

    Weve got a couple of DG units that were bought separately from the rest of the K glass units and theres a massive difference in the condensation that gathers on them compared to the K glass units.
    If you took the photo with your phone, use 'Photo and Picture Resize' app to shrink the file before uploading. (Android)

    Just to clarify my last post: I'm not saying condensation should be tolerated on glazing. Just that the moisture vapour has to go somewhere, and if you improve the glazing then it will go and condense somewhere else less visible, unless you address the root cause and improve the ventilation, with consequent heat losses.
    • CommentAuthorJeff B
    • CommentTimeAug 8th 2020
    Marsaday - I am not a landlord but I know a few and a constant complaint is that tenants are drying their washing indoors on radiators/clothes horses during wet weather. Do you know if this might be the case here?
    • CommentAuthorEd Davies
    • CommentTimeAug 8th 2020
    I'm a tenant and I dry washing indoors on radiators/clothes horses a lot, during wet weather because it's the only option and during dry weather because I'm likely to be out but not trust the weather not to become wet before I'm home.

    But, I use a dehumidifier to keep the water vapour under at least a bit of control (and to speed up the drying). Makes a big difference though it's not entirely cheap though I do try to do laundry in windy weather when the local grid is fairly organic.

    Remember that a dehumidifier is no less efficient than any other form of direct electric heating and probably a little more efficient as there's a certain amount of latent heat extracted which would otherwise be lost if the humidity is controlled by ventilation.
    FWIW, best numbers I could find suggested that our family of 5 emit about 6kg/d of moisture vapour in our house by breathing, and about 1kg/d by each of: showering; cooking; drying washing indoors; and watering houseplants. About a bucketful in total each day, and pretty much the same irrespective of time of year or of drying washing indoors or outdoors.

    At most, a few hundred ml (1-2%) of this are disposed by condensing on windows and being mopped. The rest condense unseen elsewhere in the fabric, or permeate or ventilate out.

    When were tenants we got on with the landlord and tried to avoid condensation mould, but could never understand why he fixated on drying washing and yet wouldn't fit a kitchen extractor.
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