excessive condensation of insulated shed roof

Discussion in 'Roofing and Guttering' started by Gerald0766, 12 May 2009.

  1. Gerald0766

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    I have a garden shed that has been insulated and semi soundproofed for use as a music room. The ceiling is mdf, with a 2" layer of celotex insulation sandwiched between the mdf and the plywood roof, which has shed felt on top. On hot days in the summer condensation appears inside the shed on the roof and drips onto the floor. I have cut plastic vents into the mdf but it hasn't stopped the problem. This only happens in the summer or on very hot days. I need to stop the condensation as the water gets into the light fittings and trips them out, and the mdf has discoloured with mould and is starting to sag
     
  2. big-all

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    do you have gas or oil heating in the shed !!!
    if not i would suspect you have a leak or trapped one hell of a lot of moisture!!!!
     
  3. Gerald0766

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    Reply...no gas or oil heating, only electric and fan heaters. No leaks either, this condensation is only in hot weather, no problem in Winter at all
     
  4. big-all

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    you can only get condensation with moisture/humidity finding a cold surface cooling the air and reducing its ability to hold water causing the excess to be left behind
    what do you use the shed for and what temperature do you get up to !!!
    what age is the building and what is the floor made from!!!
     
  5. masona

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    Ideally a solar attic fan but only available from USA :cry:

    Maybe fit a Humidity Controlled Fans kicked in when too much moisture is in the room, really need more ventilation
     
  6. Gerald0766

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    The shed is around 6 years old has a wooden floor and the whole structure is suspended above the earth on struts of 4 x 2" . The condensation only appears in Summer when the heating is off but the outside temperature is hot. I think the condensation appears because there is no ventilation between the shed felt and the plywood roof, and the celotex between the roof ply and the mdf inner ceiling is acting as a conductor in hot weather. When it is very hot it is dripping very badly but on a cloudy and wet but warm Summers day there is no condensation! Several roofing contractors have inspected it, scratched their heads and been unable to explain it. I really need to know how to ventilate the roof or what to do. I have fitted interior plastic vents into the ceiling which have made no difference, the condensation just congregates around them, presumably because heat rises and these vents are fitted at the highest point of the slanting ceiling

    Help!!
     
  7. Gerald0766

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    Another question regarding my shed condensation problem; Would a dehumidifier solve the problem? Manufacturers Web sites suggest that they will suck up 6-10 litres of water a day which is promising but probably less than drips off my ceiling on a hot day! They also suggest they work better in cold weather, which is not the problem I have. The only time condensation appears is in sunny, hot weather.
     
  8. big-all

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    do not spend any money untill you find out where the damp/moisture is comming from!!!

    what are your walls made from and is there any soil/bedris against the walls
     
  9. Gerald0766

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    The walls are made of exterior timber slats with an interior of 12mm mdf, with celotex insulation sandwiched in between. No condensation appears on the walls probably because there will be a slight air gap between the slats. My neighbours lawn runs up to one side of the shed at a slightly higher level and is against the wood but there is a plastic sheet between the soil and the wall, this could be the reason for the excess damp.

    Big all - you seem to know a lot about this (far more than me!) and I notice you are in Surrey, if you want to have a look please do, I am in South West Surrey, my mobile is ****************
     
  10. big-all

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    what is confusing me is i have a 10x12ft shed with 18mmply floor and roof coverd with 3 layer felt system /txg shiplap walls pressure treated and 3 coats of sadolin the walls are and roof are insulated with loft insulation with 12mm ply on the walls and 6mm on the roof no insulation on the 18mm floor

    the temperature during the winter is anywhere between +3 to+12 regulated by a fan heater at +3 on cold night or 12 when the workshop is in use

    in summer the double doors tend to be wide open unless the neighbours are in the garden

    now i only ever get condensation on the glass mainly the door i never have any trouble with any moisture of any sort winter or summer

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  11. masona

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    Yes and no because they blow warm air back into the room and producing more moisture.

    If you put a plastic bag over your shed the moisture can't get out therefore more condensation problem, the heat maybe also coming from the ground. Really need more ventilation, any photo of your shed?
     
  12. Deluks

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    The very nature of soundproofing requires the room to be airtight. This is bad for any room as ventilation and air change are a must.
    What kind of music do you make in there? Banging on drums will produce a lot of sweat, and singing will produce a lot of 'breath' (both containing water)

    The foil on the celotex and roof felt will prevent any moisture from escaping, rockwool would have been a better product for soundproofing and is also breathable.

    Your vents alone won't help if there is nothing to motivate the air to leave (heating or fans for example)

    I would suggest fitting at least one extractor fan, with another passive vent at the opposite end of the room. Ideally you'd fit two fans, one in/one out, so the air is constantly getting changed.
    Fitting these will create 'holes' in your soundproofing and also annoy you when trying to play music so they'll either need to be installed in expensive soundproof ducting, or you can use standard fans encased in an mdf box lined with rockwool. A couple of S&P TD160's would do the job. (very popular with those who like to 'grow their own' ;) )



    If the mdf is sagging and discoloured, ripping it out and starting again would be the proper way to proceed, and replacing all that celotex while you're at it.
     

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