Replies

1. 
   Damage_Control | Feb 17, 1999 07:13am | #1

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   Here we go again. . . . Sorry Marco, I just couldn't resist.

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   Dennis_Loeffler | Feb 17, 1999 08:22am | #2

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   I am not an expert on ice dams and venting attics, so keep that in mind when considering this thought. Water condenses because of dew point. If you look out your window on some mornings, there is frost on the top of the roof as well as the grass. If there is frost on the top of the grass and roof, there is probably frost on the inside of the roof as well. In addition to conductive loss ofheat, a major source of heat loss is radiation. This is of course how the sun heats the earth. As long as your ceiling is warmer than absolute zero, it will radiate heat and any surface between the source of heat and infinity will absorb heat causing the water to melt in some cases. What does this mean in the real world? Well, I have a Wasau home with 2x6 ceiling panels that were insulated between joices with 3 1/2 to 4 inches of bat insulation. There are eve vents and a continuous roof vent. Last winter I had ice dams. This past year I replaced the paper ceiling with dry wall insulating over the rafters with 1" foiled thermax. This not only increases the R value, but it gives a reflective surface to radiate heat back into or out of the room. this year, no ice dams. Does that mean my solution prevented the jams? Nope, maybe I just got lucky with the weather. I do remember reading somewhere that a room could be somewhat colder than normal (70-72 degrees) if the walls were warm, and still be comfortable, while if the reverse were true, cold walls and warm air, a person would lose heat by radiation and feel cold-thus the reason for perimiter heating by radiators be they hot water or forced air.

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   Guest_ | Feb 22, 1999 11:01pm | #3

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   Redear Fred,
   Well, Im a curious soul and as usual my curiosity has
   paid off. I nevertheless feel like I had toilet paper stuck on my shoe: After doing the famous sash test, I conlcuded that I had the stack effect and I closed off the turbine, closed the soffites, and upped very slightly the insulation on the attic trap, and guess what? Duhhhhhh, 95% less condensation on the attic ceiling, indoor humidity went from 15% to 45%, second floor temperature equalized out to ewithin 1 degree instead of the usual 5 (I have heating ducted only to the basement and first floor) and my wife is dancing and cooking me better stuff. And all this at -20 degrees celsius, with a northerly wind of 20 km/hour.
   Needless to say Im a happy man, tho sheepish: after all its painfully obvious that cutting a hole in ones roof will not make a house warmer. Just imagine if I really insulated the attic space which now only has loose white filling between 7 inch joists. Thanks for the balloon drawings on your site. (eureka, I said)
   Just one thought: when I do get around to it, do I allow my insulation to touch the exterior roof sheeting or not? As far as venting goes, good riddance.
   Smuggly yours, Marco

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   Guest_ | Feb 23, 1999 08:18am | #4

   *Hang on, I still have ITS, only the difference is that the upstairs to downstairs difference is now only 1 degree rather than 5. And pardon my ignorance, but Im haunted by the pup tent in the morning syndrome: if I put anything against the tent roof, organic or otherwise, by morning itll be wet. WHy wouldnt it be the same for insul.?Marco

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   Guest_ | Feb 25, 1999 08:30am | #5

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   Howdy, Im new here but ive been following the venting thing with great interest. I have a 200 year-old stone house that never had venting until 10 years ago when a previous owner put in a turbine. My first winter here, it rained in the attic. The previous owner said it was always like that. In january you could go up there and it was like the inside of a old freezer. Crystals everywhere. So I thought, not nough ventilation and I opened the dormers in the attic all winter long and since then Ive opened the soffits. Now its maybe 25% better, and it doesnt precipitate any more, but Im wondering, if I had no vents at all, you are saying I wouldnt have any condensation?, due to higher temps? Also, I plan to recuperate the attic as living space, if I insulate and seal SOTA, should I or shouldnt I vent?
   (Ill then have cathedral ceilngs.)
   Perplexedly yours,
   Marco