New roof, new skylights, new condensation… and not a lot of answers. Any help?
Hey everyone. I don’t normally post to anything but I’m at the end of my rope and not sure which experts I can trust so looking for some extra opinions before I go and do nothing or start making tons of holes in my roof.
It’s Winter time and I noticed some discoloration on my ceiling near my skylights. Took a trip up to the attic and tried to take a look down one of those small gable rafter bays that you can barely see/peer into on a vaulted ceiling. At first I thought I was looking at an ice dam, but then realized I’d have much more water coming in and the pattern of the moisture is towards the joists and less in the center. I believe this condensation.
So, my issue is that I have a new roof and new skylights. Did I have this problem before? No idea, I’ve only been in the house for 5 years, but I do know I painted my ceiling last year and we were in the house for three years before that with the old skylights and not a single discoloration came through.
If I assume I have condensation in my two rafter bays for each skylight (my skylights are the width of two bays, 3 rafters) that are above the skylight going to the ridge vent, then I am not sure how to get it out naturally. The skylight blocks any upwards venting from the bottom of the rafters. Which is my next issue. I have slight discoloration at the bottom of my skylight now. Is that from the top traveling down the rafter or do I have condensation forming at the bottom now as well with no real soffit vent to push it out.
Every other rafter and rafter bay is dry as a bone, even the nails. So, I think I can assume that if those bays are dry, then soffit or not, it’s my skylights that are causing this.
I included some pics here: https://onedrive.live.com/redir?resid=A87CD5E7C4551226%21173
Any help, opinions, advice, would be greatly greatly appreciated!!!
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Replies
If the roof is new and the skylights are new, the first thing to look at is the flashing.
If it was the flashing around the Skylights, I would expect to see some water inside the house, maybe the the sides or some other location instead of the top or bottom of the skylight wouldn't I? Maybe condensation on the inside of the windows as well?
S.B.,
The moisture in the photo is condensation. Here's the mechanism: there is a path by which warm, humid indoor air is gaining access to the cold roof sheathing.
There are three ways to solve this problem. You can either:
1. Track down the air leakage path and seal it. (Air might be entering the rafter bay through an electrical box, a recessed light fixture, a plumbing vent penetration, or a convoluted path via an interior partition. If your ceiling drywall was installed over 1x4 strapping, you can multiply the possible air leakage paths by a factor of 10.) Solving the problem this way is easier said than done, because these air leakage paths can be quite tricky, especially if your drywall was not installed according to the Airtight Drywall Approach, using gaskets at the top plates.
2. Raise the temperature of the roof sheathing. The best way to do this is to install one or more layers of rigid foam above the roof sheathing. Of course, this solution requires you to re-roof your house. It's worth pointing out to GBA readers that this is always the best solution, and every GBA reader should keep this fact in mind when re-roofing.
3. Install an air-impermeable barrier of spray polyurethane foam against the cold roof sheathing. This solution requires you to pull down at least some of your ceiling drywall.
Thanks @Martin,
Curious if you have an opinion about condensation showing at the bottom of the skylights as well or if you think it's the top condensation dripping down.
I was thinking of spray foaming (closed cell) the north and south side of the skylight from the inside with a ceiling penetration. My guess is that a few inches against the wood structure of the skylight should stop anything coming out of them and insulate it. I think it will also help because I just noticed today that the skylights are about 1 to 2 inches larger than the last ones. The roofers couldn't find a Velux compatible so they had to go with a self-sealed Wasco that was slightly bigger. So, I am wondering if those extra few inches on the exposed deck is also contributing. Thinking spray foam should do the trick. Anyone have thoughts on this?
I am not opposed to re-roofing if it was free, but the cost was incredible with the last one. Mostly because I had a massive leak that caused me to re-frame the corner of my house and tear a living room to pieces with a 9-month very pregnant wife. So the pallet for anything like that again is extremely low.
S.B.,
Q. "Curious if you have an opinion about condensation showing at the bottom of the skylights as well or if you think it's the top condensation dripping down."
A. It's hard to say. If this were my house, I would demolish the drywall all around the skylight. Get on a step ladder with a powerful flashlight and inspect the perimeter of the skylight and the nearby roof sheathing. Your eyes should tell you what's going on.
Today was an interesting day. It was mid 40's today and I got called home to a leaking skylight. I uploaded some more pics here w/the thermal images as well (borrowed from work). Almost 2 cups full of water came out of a bulge that developed in the lower right of the skylight. Once it was drained, the water stopped.
Here is what I am not understanding:
- In my new picture of the rafters, some of the sides are wet, but not all. I find this odd as I would expect it to be wet up and down a rafter to the skylight. That only happens in one of the rafter bays for the skylight, the other bay is spotty. My other skylight today showed absolutely no signs of anything. Same vault.
- Almost 2 cups of water is a lot of water coming from a little hole in a ceiling. Could I really have that much moisture up there? The roofers say I have Ice and Water Shield up to 4' above the skylight and that if it was a leak, it would be constant as the snow is still melting. In principle I agree.
- I have thermals of the bad and good skylight. What's interesting is that the good skylight has some nice heat dispersion on the north and south sides. The other skylight does not, but I am not sure if that's because it's wet now.
To complicate it more. One of the roofers says he thinks the flashing (with my Wasco is rubber, not metal) may not have been sticking well so he threw some GSL up there. The insulation guy thinks it's caused by the warm air in the house making it's way in the cavity. If it's a seal issue, why doesn't it show when it rains? Why not last year either? Also, I have wetness for 3' above the skylight. Water can wick, but I am not sure it can wick that much if the leak is all the way down by the skylight. On the other hand, 2 cups of water seems like a lot to come down.
The only thing everyone can agree on is that it needs to be fixed.
Any other opinions?
All Pics: https://onedrive.live.com/redir?resid=A87CD5E7C4551226%21181
The good skylight in the pictures doesn't look nearly as dispersed in heat.
S.B.,
Here's the thing: if you are collecting two cups of water from this problem, it won't take long for your drywall to be ruined.
Face it: you are going to have to remove the drywall at some point (if only for cosmetic repairs). If the drywall will need to be repaired anyway, then now is the time to open up the drywall -- because opening up the drywall helps you diagnose and fix the problem.
So open it up and see what's going on.
Quick update. Called an insulation company and they recommended two things. All of which require the ceiling to come down (which I'm fine with in light of the issues).
1.) Spray foam the north and south side of the skylights. I am in agreement with this based on what everyone said as well.
2.) Dense pack the rafter bays south of the skylights. This approach, I am not too keen on. Even though I don't have soffits south of the skylights (goes into a fake gable), everything I have read says this is a big no no.
Insulating the exterior deck is not an option right now, so I am curious if spray foaming the underside of the deck is a good idea. If so, how much? The whole cavity? An inch? Note, that there is Ice and Water shield on the top side of the deck.
S.B.,
Unless I'm not paying attention, we still don't know your location or climate zone. That makes it hard to answer your questions.
We also don't know which way "south" and "north" is with respect to your skylight. It would be helpful to say something like "below the skylight" or "above the skylight" -- or perhaps "on the right side of the skylight" or "on the left side of the skylight" (although those terms are ambiguous too).
It sounds like you live in a snowy climate.
If a contractor is installing closed-cell spray foam on the underside of the roof sheathing, code requirements (and building science advice) dictate the minimum R-value of this spray foam layer. Here is a link to an article that explains these code requirements: How to Build an Insulated Cathedral Ceiling.
Here's the short version: the minimum R-value of the spray foam layer needs to be R-20 for Climate Zone 5, R-25 for Climate Zone 6, R-30 for Climate Zone 7, or R-35 for Climate Zone 8. So, one inch of spray foam won't work.
Once these minimum R-values for the spray foam layer are met, the rest of the required R-value (usually R-49) can be provided by adding air-permeable insulation (fiberglass, cellulose, or mineral wool) under the cured spray foam. This method is called the "flash-and-batt" method.
If your spray foam contractor starts spraying in the rafter bays below the skylight and above the skylight, the entire rafter bays need to be addressed, from the soffit to the vented attic. These will become unvented rafter bays (unvented insulated roof assemblies).
Thanks Martin! I am in climate zone 5, with a county next door at 6. North and South should be better said as Above and Below, with above being the ridge and south being the soffits, that don't actually exist.
This was really helpful and greatly appreciate the advice!
Have you absolutely ruled out a roofing or flashing issue? If not, I would do that before installing spray foam. If you simply turn this over to an insulator to remove drywall and spray foam as they see fit, you could be causing a larger problem down the road. Take the drywall off now and figure out if there's a leak.
I haven't ruled out the skylights yet either. I am now just waiting for a drywaller to get in here to tear it down. Until that happens, I am going to assume it's moisture. Also, my wife and I realized that our fireplace was ran REALLY hot this year and even though it's in another space w/out a vault, it's only about 8-10 ft away from the vault and the skylight.
I appreciate all the advice and opinions. I have some more options for spray foam that I'd like to run by everyone.
1. Tear down the vault and spray foam it. All of it. Preferred closed cell in my climate. This is a big job, and what makes me think this isn't quite necessary, is that my other rafter bays on the sides of the skylights are completely dry (perhaps there is venting of sorts?) Also, I am not sure what this would mean for replacing the drywall, as right now it has foil-backed ridgid underneath the drywall as a moisture barrier for the vault. I should also mention my walls have plastic behind the drywall as well. The vault joins the rest of the attic that has a ridge vent. So, in addition to it being a big job (which I'm committed to) I'm not sure how closed cell on the roof sheething in my rafter bays that seem to have airflow up to the ridge would work well. Shouldn't the vault be completely sealed from the attic then (flash and batt @Martin)? Not sure why they didn't suggest this. What about the foil-backed ridgid board?
2. Spray foam all around skylight cavity with closed cell. This would encapsulate the skylight with spray foam, but knowing that I don't have a soffit at the bottom, I am thinking I might as well just spray foam the whole rafter bay... and then backfill with dense pack blown in cellulose. which leads to option 3
3. Spray foam the rafter bays with the skylights with closed cell. Encapsulate the skylights and take it all the way to the ridge vent. backfill with dense pack cellulose. The part I am unsure about is my drywall/ridgid foam board again. Can I/should I still use foil-backed ridged foam board under the drywall in the rafter bays that now have some closed cell spray foam applied to it?