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Internal condensation - double glazed windows

  • 29-09-2021 11:47am
    Registered Users Posts: 23 Sublime79

    Hi all,

    House is a dormer bungalow - built 2003, windows from same time. Not sure on U value for them - we did not have the house built ourselves. The windows upstairs have a major condensation problem in cold weather (starting already now). Hardly any issue downstairs, yet having bought a small basic hygrometer the RH value seems to be relatively the same in both areas. For example this morning, it was about 62/63% upstairs, about 57% downstairs.

    I've been looking into how to resolve this and if we need to install some sort of ventilation system. We've been told about a PIV or DCV system which I am reluctant on since it will be bringing in the air at outside temperature. Other option is HRV system which is more invasive to install and more expensive (about €7k) - however if the issue is ventilation it would resolve the problem. And I guess this is the crux of the matter - I don't know if it's windows or ventilation (or maybe both i guess!) - hence I don't want to fork out €7k on a vent system if the issue is with the windows.

    Would it be a fair assumption that with an RH value of 62% that the issue is with the windows and not ventilation? As I said, the RH value is the same upstairs and down at times and we have no issue with the windows downstairs. Temp would be similar in both also - maybe a degree or two colder downstairs.

    Any advice appreciated.



  • Registered Users Posts: 23 Sublime79

    Hi Mick,

    Thanks for the reply.

    • is the house heated adequately throughout the heating season? Is there excessive heat loss? - Yes, heated well throughout. Doubt there is much in heat loss, we've just had the knee walls upstairs and attic area above done with spray foam which has made it noticeable warmer.
    • is the moisture load excessive (drying clothes indoors, loads of potted plants etc). - No clothes drying, some potted plants in the house but none in the bedrooms/areas where the condensation problem is worst.
    • how is the house ventilated currently? - Rudimentary - some trickle vents, open/close windows - that's about it!
    • is the condensation issue persistent throughout the heating season or does it die away? - Yes, pretty much, as soon as the nights start to get colder.

  • Registered Users Posts: 278 ✭✭ coffeyt

    Sublime79 I'm not an expert, but said I'd throw my opinion in as no one else has responded yet. Going off your answers above I would assume that lack of ventilation is the issue, I'm assuming you keep windows closed at night? From research I've done the trickle vents don't really cut it especially at night when people are in bedrooms breathing out moist air and if the windows are closed them it would explain why you are only seeing the problem in upstairs rooms (again I'm assuming here that it's the bedrooms)

    With regards the piv system, I actually installed one myself last year to remedy a similar problem and while the air is cold from outside its only really noticeable if you stand directly underneath the vent. I installed one with a built in heater, it doesn't heat the air but rather takes the chill out of it. Also something to consider is that the air coming in is drier which is easier to heat.

  • Registered Users Posts: 2,544 ✭✭✭ MicktheMan

    Research cMEV (central mechanical extract ventilation) and DCV (demand control ventilation). CMEV would be cheaper to install and might well be adequate in conjunction with your current window trickle vents.

  • Registered Users Posts: 3,108 ✭✭✭ 10-10-20

    I'd caution that while the RH will have a lot to do with the level of humidity on the windows after a cold morning, I have a mix of old (2003) double-glazed units and brand new double and triple glazing units in the master bedroom (upgrading at the moment) and it's by far the old double-glazing which is developing condensation far more so than the newer units.

    If they are the same manufacturer as mine, I'd suggest that the quality of the glazing is a significant factor.

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  • Registered Users Posts: 23 Sublime79

    Thanks lads - some interesting responses and all food for thought!

    @coffeyt - "I'm assuming you keep windows closed at night?" - yep, and it is the bedrooms. Interesting on the PIV system - is there only one point of entry for the air into the house or is their vents in every room? Also you didn't say the most important piece 😀 - did it resolve the problem?

    @MicktheMan - Will take a look at cMEV, thanks! Is it very invasive to install in an existing house I wonder?

    @10-10-20 - yep, despite comments here, my suspicion is still with the windows/glazing. Would you be able to PM me the manufacturer of your windows? Also, have you tried anything to remedy it on the older windows? Or I guess you'll just be replacing them in the end so no need!

  • Registered Users Posts: 278 ✭✭ coffeyt

    Piv has one point of entry, usually central in the upstairs landing as it is fed from the attic. It works on the premise that the fresh air will push the stale moist air out through any existing vents or gaps in the structure.

    And yes it completely solved the condensation issue we had within about 48 hrs of being installed. 😀

  • Registered Users Posts: 3,108 ✭✭✭ 10-10-20

    I self-installed new double and triple glazing windows and frames on the worst affected windows last month. Got them from DL Windows in Meath, if you're feeling adventurous in the DIY department!

  • Registered Users Posts: 1,478 ✭✭✭ Bawnmore

    Do you mind me asking which PIV unit you installed? I'm looking at this guy. An did you self install or have someone fit it?

  • Registered Users Posts: 7,238 ✭✭✭ the_pen_turner

    Are there showers near by and how are they ventilated.

    You windows could well be your problem if the seals are gone or the glazing is old broken or crap.

    Could you run a dehumidifier on a timer

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  • Registered Users Posts: 278 ✭✭ coffeyt

    That is the unit I bought but purchased from a ventilation company in the north. We self installed the unit itself but got an electrician in to hook it up. Very straight forward to install.

  • Registered Users Posts: 1,478 ✭✭✭ Bawnmore

    Appreciate it - we'll likely do the same. Found it at a better price here - will do a little more research and pull the trigger.

  • Registered Users Posts: 278 ✭✭ coffeyt

    Best of luck with it, we have been extremely happy with its performance since we installed it last year.

  • Registered Users Posts: 23 Sublime79

    Showers yep but there is skylight window which we open every morning after showers.

    What specific part are the seals? Is that the sort of narrow rubber like line of material that runs between the frame and the actual glass?

  • Registered Users Posts: 7,238 ✭✭✭ the_pen_turner

    yes the rubber seal between the frame and glass