I've been battling with this problem in different ways for about four years, but I'll fast forward to the most recent. I did read many of the posts regarding Lofts and condensation.
About four weeks ago I removed the four year old roof from my 12'x10' shed dormer - 4:1 pitch, nearly flat. Once the Lifetime Architectural shingles and plywood were removed, I removed all the insulation and began reinstallation. First the insulation - 2" x 10" joists - then proper vents (to move air from the sofit to the ridge vent ) then plywood then and EPDM rubber membrane.
Last weekend the bathroom cieling fell in...the sheet rock was soaking wet. When I removed the sheetrock I was shocked by the amount of water/condensation on the inside and outside of the polystyrine? proper vents. The water completely soaked the insulation, the sheet rock and Hardy Board over the shower.
There were two joist channels that were too small for proper vents and i was again shocked but by how dry these two areas were.
Observations:
The temps outside have been colder for longer than they have been in four years. I am guessing that the big temperature differential is at least part of the cause...if not most of it. But I believe that the small pitch in this roof does not allow air to flow to the ridge vent. when I checked behind the knee walls front and rear - this is a Cape - everything is bone dry.
The EPDM roof does not have any leaks as we have not had any significant snow this year - 2". And with the insulation gone, and heat turned off in the bathroom, the underside of the plywood is dry. As an experiment I turned the heat on and it basically rained in the bathroom.
Questions:
could the lack of adequate air flow cause condensation? My guess is an uncertified yes. Second, I was thinking of spraying 1" - 2" of closed cell polyurethane insulation under the plywood then adding the appropriate amount of fiberglass insulation.
I am somewaht concerned about moisture building up between the poly and the underside of the plywood...but if the R value is between 7 and 14 for the first 1" - 2" then the temp gradient should not be nearly as bad as it was.
Any thoughts are welcome. I like the idea of sofit vents and moving air from bottom top, but when codes dictate the need for these tpyes of vents in a roof that is nearly flat, the codes illustrate some lack of understanding for different building types.
Thanks all
About four weeks ago I removed the four year old roof from my 12'x10' shed dormer - 4:1 pitch, nearly flat. Once the Lifetime Architectural shingles and plywood were removed, I removed all the insulation and began reinstallation. First the insulation - 2" x 10" joists - then proper vents (to move air from the sofit to the ridge vent ) then plywood then and EPDM rubber membrane.
Last weekend the bathroom cieling fell in...the sheet rock was soaking wet. When I removed the sheetrock I was shocked by the amount of water/condensation on the inside and outside of the polystyrine? proper vents. The water completely soaked the insulation, the sheet rock and Hardy Board over the shower.
There were two joist channels that were too small for proper vents and i was again shocked but by how dry these two areas were.
Observations:
The temps outside have been colder for longer than they have been in four years. I am guessing that the big temperature differential is at least part of the cause...if not most of it. But I believe that the small pitch in this roof does not allow air to flow to the ridge vent. when I checked behind the knee walls front and rear - this is a Cape - everything is bone dry.
The EPDM roof does not have any leaks as we have not had any significant snow this year - 2". And with the insulation gone, and heat turned off in the bathroom, the underside of the plywood is dry. As an experiment I turned the heat on and it basically rained in the bathroom.
Questions:
could the lack of adequate air flow cause condensation? My guess is an uncertified yes. Second, I was thinking of spraying 1" - 2" of closed cell polyurethane insulation under the plywood then adding the appropriate amount of fiberglass insulation.
I am somewaht concerned about moisture building up between the poly and the underside of the plywood...but if the R value is between 7 and 14 for the first 1" - 2" then the temp gradient should not be nearly as bad as it was.
Any thoughts are welcome. I like the idea of sofit vents and moving air from bottom top, but when codes dictate the need for these tpyes of vents in a roof that is nearly flat, the codes illustrate some lack of understanding for different building types.
Thanks all
