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Skylight condensation problem

Discussion in 'Roofing and Guttering' started by thedigger, 18 Dec 2011.

  1. thedigger

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    Hi, we moved into our new house this year in the summer and one of the first jobs I did was to reglaze a broken skylight. The skylight is a fairly conventional wooden box with a metal frame on top. It doesn't open or have any vents.

    It originally had one pane of georgian wire glass (and flashband covering the crack). I think it was 8mm thick, but this was replaced with toughened laminated glass of the same thickness. The frame was resealed, but I'm now getting a lot of condensation on the inside of the glass. It's been damp as soon as winter started and is starting to make the plaster crack.

    I guess it's a fairly bad place for condensation; it's right at the top of the stairs, at the highest point of the house, and just along from the bathroom door. The house was extended in the 1970s and this is in the "new" part of the hallway. It has a flat roof immediately above it.

    Does anyone know a way to prevent this from happening? I know I could use a moisture trap in the short term but I wouldn't want to spend every winter with pots of silica gel on the carpet.
     
  2. joe-90

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    As long as you have warm moist air reaching a cold surface you'll have condensation. Can you double glaze it so that the inner pane is too warm for condensation to form?
     
  3. thedigger

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    Cheers for the advice mate. I'm not sure how easy it will be to get double glazing in there though... the frame only really suits 6mm glass (or 8mm at a push maybe) and the glass would need to be laminated and toughened (it's dead flat so will potentially have snow sitting on it in the winter). I reckon a sealed unit would need to be at least 15mm thick or so.

    What about if I got some secondary glazing (the sort of stuff you get on sash windows) on the inside of the skylight, say about 10cm below the outer glass. Would that be likely to do me any favours?
     
  4. joe-90

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    Secondary glazing will work but ONLY if it is airtight. As soon as warm moist air gets past it you'll have the same problem.
     

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