Intake only problems - cathedral ceiling

I have here a six year old SBS roof, nailed base w/ cold adhered cap sheet. 2/12 - The shingles were torn off, decking repaired as necessary, and mod bit put down. Chimney was sealed w/ roofing cement, other than this it's a solid installation.

Now the decking is rotting out from under the membrane. It VERY bad between three rafters for about 15-20', starting about 4' up from the eave. Then another similar issue near the upper corner of the roof, but not near as big.

Thing is, it's not leaking. No stains on the ceiling, no signs of leaks, roofing looks good. It does however have circular soffit vent's along the bottom. Could those have caused this plywood to complete disintegrate in six years? Any thoughts appreciated.

Good idea about the frost. We had just recently started getting frost again, hadn't thought of that yet!

We're covered up now though!

There is normally a reason that has been "added" to the mix. for every action, there is an equal and opposite reaction

I was doing maintenance on a house I have done numerous cleanings and addition/remodel work over the years. A couple of years ago, I noticed that around the air vents in one area, there was heavy efflorescence under the head lap of the tile. This is an indication of a large amount of moist vapor condensing on the bottom of the tile. I initially suspected a lap pool in the exercise room. Even though it was not directly below the area, the problem spot was the highest ridgeline on that wing of the house. I added additional venting.

Then, earlier this week on a brisk cold morning, I noticed a large vapor cloud directly below that area when the two heat pumps there kicked on, much of it following the wall and curling around the soffit (and soffit vents). I felt dumb for not picking up on that as being the source earlier.

Go up on the roof on a cold frosty morning and see if there are melted areas. That will be more conclusive than the infrared shots from below.

I couldn't find a source inside. Had a energy auditor come out w/ his infrared gun to see if we could pinpoint anything, but it was inconclusive.

Chimney is mudded, but no leaks on the inside around it and the plywood touching it is still solid.

probably not much. I am thinking that there are spots below where it is rotted that for some reason or other there is more moisture getting into the system. Water will follow the path of least resistance down, and the water vapor will follow the path of least resistance period. The vents on the bottom are not much good as they can't let anything in because there is no where for it to go. It is not leaking from above, it is condensating from below. You will find mold on the bottom side of the decking too.

OS, what do you think would be the result of blocking the intake and installing an epdm or similar roof? Creating the dreaded hotroof.

Thanks for the input OS. I've built several 2x roofs, they do work great :) But I've never seen this kind of damage in such short time. And it was usually distributed throughout the roof. I just want to make sure that COULD be the problem before I make plans to fix it.

YES!! Can't you install a ridge vent? I have done that on the lower pitched roofs before by making a one foot high "steep" ridge at the very top to get it above the rest of the roof. One other option since they have had the problem is to install a cold roof over the existing one. Just make a soffit that you can fully ventilate and then lay some 2 x lumber over the existing rafters so that you have at least 2 inches between the old roof and bottom of the new decking. vent the top with a ridge vent and it will make a "bunch" of 2" high attics that will vent independently of each other but it will draw out all of the excess moisture and heat from the building. You can even insulate between the existing rafters if they want it too. It works like a charm, and will solve other problems they don't even know they have. Email me if you need more information.