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Low pitch standing seam metal roof with condensation issues

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Dena Platis
2/8/2012
Hi, This is our first winter in a new home. We have a split shed metal roof with a standing seam. One roof is about 42'W x 40'L (1.5:12 pitch) and the other is 32'W x 25'L (2:12 pitch). The joists below are running perpendicular to the slope of the roof, not allowing for a stack effect air flow, from bottom to top. There are 11-7/8" TJI's every 24" OC which have notched bracing around the perimeter, allowing for potential side-to-side ventilation since the insulation has been held down 2" in each TJI bay. There is a continuous soffit vent on the low and high soffits but again that vents just the one TJI bay that it is in, since the sheathing is sitting on the TJI's. They have recently added six randomly placed 6" dia vents, along each sloped side. From the inside out we have cathedral ceilings: drywall, vapor barrier, R-38 fiberglass batting (10"), approx 2" air space, plywood sheathing, roof paper, metal roof with field crimped seam. We are getting condensation and water is dripping through the sheetrock in various places. We opened a soffit vent and found ice build-up under the sheathing, mold on the wood, and damp insulation. The weather has been very cold and humid. We have been trying to minimize interior relative humidity (keeping it at 35-40%) by raising the inside air temp, not taking showers upstairs (even though we have high cfm fans - they are exhausted under the eave and may be contributing?), and opening windows periodically. We have no can lights except in the master bath which has a dropped ceiling in the steam shower. How do we get better roof ventilation? The architect is proposing we turn it into a npon-vented roof by blowing expandable foam into the ceiling from below. The builder is proposing we add fascia vents (like a honeycomb cor-a-vent) along the sides of the roof, hoping for enough draft to ventilate under the roof expanse. We are also considering raising the roof in the spring and framing in a two inch air flow space under the sheathing, but would that even be effective on such a low pitch roof? What is the best solution, for short term and long term? How can I test the solution is working?
Todd Miller
Isaiah Industries, Inc.
2/8/2012
It sounds like you understand the basics of what is going on and what is required for ventilation. Based upon what you are saying, I would say that your architect's advice is probably the most achievable.
Guest User
2/8/2012
Thanks so much for your advice. We are concerned that making the roof non-vented after-the-fact will be difficult to achieve, especially since we won't be able to see if there are any voids anywhere, if we inject through the ceiling. I thought the effectiveness of a non-vented roof is due to no air being trapped anywhere in-between where the warm interior air can meet the cold exterior air. Is there a way to prove that the expanded foam is 100%, do I need to worry about that? Also, just to clarify, is it due to the low pitch that it is questionable whether I would achieve stack ventilation if we framed in a two inch space? Thank you, Dena
Todd Miller
Isaiah Industries, Inc.
2/8/2012
I think that building in the 2" airspace would work and would provide adequate ventilation. I was just concerned it would be more costly and more trouble than spraying in the foam. It sounds, though, like doing a good foaming job will be tough and, yes, a poor foaming job can lead to more problems.
Eric Novotny
An informed customer is the Best Customer!
2/10/2012
This is a real can of worms here and you have the potential to worsen the problem is your spray foamer isn't really on top of their game. I hate to say it but the best and probably most surefire of doing this correctly is probably removing the roof. This really stinks for you and I am sorry you are dealing with this. Who designed the roof and was this a custom home?

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