We have a 1988 home constructed of structural insulated panels with a very open floor plan and vaulted ceilings. At some point the main slope of the roof was torn off and replaced with a ceiling/roof of typical construction, with rafters, fiberglass insulation, and a tongue and groove cedar ceiling. Due to roof leaks and carpenter ant issues discovered after moving in, we replaced (overlaid) the asphalt shingle roof with an aluminum shingle metal roofing system last year. This solved the actual leaks, and carpenter ants, but revealed/created winter water problems from frozen condensation on the back side of the roof decking, melting and dripping brown water through the beautiful cedar ceiling. How do we solve this? Seal up from the inside with vapor barrier? Tear out insulation from the bottom and spray on urethane foam? Do we want to seal up the roof system as it was designed with the SIP, or leave with open soffit venting etc? Please help, everyone we have talked to is at a loss to decide on the best solution. Starting to wonder if maybe a heat recovery ventilation system would be a big part of the solution. Live in northwest Ohio and really need to find someone who understands SIP and the complex issues we are facing. In a short time googling I have realized we have a severely compromised SIP system going on and need to figure out how to proceed.

It sounds like you understand your leakage is from condensation on the back side of your new metal roof causing leakage through a standard (non-SIP) roof. If that is the case you don't need an expert at SIPs but someone to detail your roof correctly. There should be a drain path under the roof (underlayment, building paper etc. Once the condensation is trapped trying to plug the hole from the inside will likely be a very frustrating unsuccessful experience.

I agree in that it doesn't sound like your issue has anything to do with SIPs. I'm guessing that your ceiling assembly has no functioning air or vapor barrier on the interior side. I know ceder T&G ceilings and fiberglass insulation both leak air excessively. Hence, your moisture laden air leaks into the cavities filled with insulation, the moisture in the air is condensing on the underside of the roof deck. This condensate is dripping back down through your ceiling.

The problem is a function of air leaks, relative humidity, and an inferior insulation material. The situation is exacerbated by large temperature differentials, (ie: the dew point) depressurization of the interior space, wind, and the "Stack Effect" (In addition, outside venting of the rafter cavities, if installed, is insufficient to maintain drying)

An HRV would not be the solution to your problem! It may reduce the problem slightly if the unit installed is capable of pressure balancing.

The solution depends on a number of things.

Would you rather tear off your shingles and make corrections from above or tear off your cedar T&G and make corrections from inside? If the assembly has been exposed to a significant amount of water, your fiberglass insulation is even more useless than it was when first installed. If you attack from the interior, you can replace the fiberglass with any number of superior types of insulation. Then you can install a proper vapor barrier along with all your reclaimed T&G. If you attack from above, tear-off to the roof deck and add a nail-base panel on top with a new roof. Using at lease 4 inches of closed cell foam will allow the foam layer to act as a vapor barrier. You must ensure proper air sealing of the panel joints. Leave the fiberglass alone and it may help with overall thermal performance by a small percentage.

Thanks for providing your location. I wish all people would provide that information before launching into their question. It makes a difference.


Al Cobb
Director; SIPschool dot org

Training and consulting for the SIP Industry

I fully agree with Al. The cause of this problem is water vapor making its way to a building assembly condensation layer that is at or below the dew point temp. There are three solutions to prevent this from occurring: 1) change the permeance of the assembly layers such that water vapor can’t take this journey, 2) change R-values of the assembly layers such that the condensation assembly layer is either eliminated or moved to a new location where condensation is acceptable, or 3) some combination of 1) and 2). We have building assembly moisture analysis software that you may find useful in understanding and resolving this problem:

Borst Building Assembly Moisture Analysis Software