Closed cell attic insulation with condensation at chimney flashing
What I first thought was leaky flashing now appears to be something else entirely. After a recent windy rain, we discovered a small amount of water in the attic at the chimney. I thought it must be wind-driven rain. But today I had a roofer come take a look and his hypothesis follows.
As background, the attic roof deck has been sprayed with closed-cell to bring the attic into the building envelope. Within the attic, there is a gap between the chimney and the roof framing members. I believe that per code that should be 2″, the gap at our framing is more like 1/2″ – but I digress. There isn’t any insulation in this gap.
The roofer thinks that the water is condensation – forming from attic air meeting the cold air at the chimney penetration. I suppose this could be happening both inside and outside – eg there does not have to be a leak in the roof for us to experience water in the attic.
The said, is the answer simply to break out my foam gun and hit this gap to seal it up? or should I stuff it with mineral wool first and then some foam, or caulk, or?? Could any of this be coming from warm flu air hitting the cold and then dripping back down the chimney?
Here are some photos of the flashing. You can see some water/ice on the flashing – dripping down from condensation between the brick chimney and the copper flashing? I also included some photos from inside the attic looking up at the gap and some thermal imaging of the same https://www.icloud.com/sharedalbum/#B0yGtec4XGtYmux
We’re in the NYC suburbs – it’s 18 degrees out tonight.
Thanks again for any guidance or insights.
Replies
That's a nice looking job, assuming that's the counterflashing we see. But, it shouldn't leak and if it does you should not caulk it at all. Caulk traps water inside and can make the problem worse. You need to find the leak and have it fixed. Whatever you do please don't use silicone!
@florida, thanks and yes, I'm staying away from caulk until we're more sure of the issue here.
Most things I flash and/or counter flash starts at the bottom (lower), gets covered by the sides as it goes up and which gets covered by the top (upper) or head flashing. In the pictures it appears the lower counter flash is bent over the top of the side counter flash, which is then bent over the top of the head flashing.
What’s underneath all that is not visible.
@calvin, thank you. going to respond to your follow up below.
calvin,
Maybe what we see is the head flashing? I've never seen one that big but it could be. I wouldn't object to running a bead of poly between the underside of the shingle and the hem of the bottom flashing in the last 2 flashing photos. Hard to tell but the bottom flashing does look like it doesn't extend over far enough on each side.
thanks! I should have check this post earlier. I just reposted what might be the culprit. What do you guys think?
Here’s my reply to your other thread. And note, if you keep the same topic in one thread it makes it easier to follow.
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You saw my post in your other (( this )) thread about chimney counter flashing sequence?
In addition, wind driven rain can go places that a moderate straight down rain doesn’t. If I remember correctly, your chimney is up towards the ridge. You won’t get much volume coming down there.
Also, slow melt snow can wick up slow and easier.
If you seal up from below and it stops a leak from the flashing above, slow punky rot could be the result you don’t find for a while.
I’m also a believer in looking up from the ground and NOT seeing roof goop on a chimney. Seems to be the first line of attack on some repairs. And your job is brand new, be a pity to put a 5 yr fix on a 30 yr job.
Other than that, I could surely be wrong and it wouldn’t be the first time.
@calvin, thank you. We think the entire exterior portion of the chimney, the flashing, and roof assembly were all done at the same time - about 5-7 years ago. I'm trying to get progress photos of the job that might inform more about the flashing or the other unknowns. Some clues of that fix is evident in the water stains and major cupping of the attic floorboards where the chimney enters the attic from below. I added a few photos here and you can see the water stains and some rot (was bone dry at the time) - I had assumed that the new work on the chimney had addressed whatever water issues had caused this but now I'm not so sure. https://www.icloud.com/sharedalbum/#B0yGtec4XGtYmux
We've owned the house for 1.5 years. This spring we sistered the 2x6 rafters with LVLs to install solar. Then we had the roof deck and gables ends sprayed with closed-cell. Given the bulk water coming through the framing into the attic recently I'm starting to think that I should remove the closed-cell from the immediate area of the chimney to investigate this from the inside...
Anyway, perhaps there are two issues - 1) the flashing is not adequate for the wind-driven rain, and 2) there is a condensation issue. The water that forms the ice on the flashing in the photos seems like it must be from condensation, while the damage to the roof deck and the recent bulk water is from the wind-driven rain/lack of adequate flashing.
thanks for your thoughts on this, and agree on the roof goop, too.
Calvin, that other thread is about a different house by a different person. Now it looks like it's not getting much attention because it's got your reply attached saying it's a repost.
Ok, I deleted my post in the other thread.
All of it including any info I gave.
Best of luck.
Calvin: thank you for the info. I don't mean to be ungrateful.
“[Deleted]”
@florida, thanks. Seems like the only way to know is to pull up the shingles surrounding the flashing and investigate how far the lower flashing extends from the chimney? Or maybe bore a 1/8" hole that is stepped away from the chimney an inch at a time until I don't see a layer of copper under the shingle?
Thanks again for all the pointers above. Mystery solved. Our cap flashing wasn't done properly and water was entering thru the groove in the mortar joint. It was pricey but we had them rip out the flashing and replace it with a soldered setup. No more water in the attic. Thankfully the roof deck hadn't started to rot.
Great news!