Copper porch roof with exposed rafters - condensation issue

[Jay]

Hello team,

Have a situation where we renovated an open porch here at the NJ shore. Assembly is .032 copper over 2 layers blueskin over 3/4" cdx over pvc bead board over wood rafters. The "builder" designed this assembly. He said he was going to use Spanish cedar for the exposed rafters and rafter tails but instead he used Doug Fir and says he will paint it. He made some azek rafter tails to wrap the ends. A few days after rain, if it is hot and sunny, we get water coming through the porch ceiling at various spots no rhyme or reason (yet). Much comes through the azek rafter tails which I believe might be trapping water. Roofer thinks the issue is condensation getting trapped between the plywood and pvc bead board, says "give it time to dry out". No underlayment was installed between these two components. On a hot day, the plywood is dry and warm and the pvc is much cooler. We are about to do some more exploratory surgery. FYI roofer used stainless steel screw to secure the copper cleats to the roof framing. Builder only flashed 6" up the wall and his work is less quality than I am used to seeing. Curious if anyone has heard of this condensation phenomenon on an open roof system like this. Any thoughts on this assembly would be appreciated. Thanks!

 

[Beniah Naylor]

I have not heard of this before.

Is the PVC bead board installed in a way that would allow vapor to go upward through the seams?

How hot does it get there? What is the relative humidity level? Is this area able to get any wind under that cover? Are there a lot of plants beneath this cover that might add to the humidity in that area? Or a pool?

 

[Jay]

Hello and thanks for the reply., PVC board has seams which I suppose could allow vapor to pass through. Lately it is around 70 degrees and we can get into the 90's in the middle of summer. Midday relative humidity is around 65% this time of year. It is an open porch near the beach so yes, plenty of wind and air moving around beneath the porch roof. No plants or pool. We have a few independent contractors coming by to assess. I have photos of poor workmanship and way too much silicone at the critical flashing areas along with some WRB seams that are lapped the wrong way. Original builder claims this is normal drying of the plywood and since the moisture has no where to go, it is coming through the pvc. He wants homeowners to leave it for the summer and then see what happens come fall. This is the guy that did not use Spanish cedar for the open rafters, he used doug fir with the intention to paint it - to save owners money!!

 

[Beniah Naylor]

Original builder claims this is normal drying of the plywood and since the moisture has no where to go, it is coming through the pvc. He wants homeowners to leave it for the summer and then see what happens come fall.

He may be right, especially if he let the plywood get rained on during construction. Not saying that he knows what he's doing, but he may have gotten lucky with that answer... Also possible that the roof leaks.

In the conditions you describe, I really can't see vapor driving up through the assembly and stopping at the blueskin - to have vapor drive you have to have wet on one side and dry on the other, and I can't really see that you would have much difference under the conditions you describe in such a well-ventilated area.

If you figure out what is going on, I would be interested to know!

 

[Inspector Gadget]

My guts say you've got a leak.