water drip in foam insulation
I have a shingle roof that’s less than 2 years old and just had closed cell foam sprayed between the rafters. Today I noticed that there is a very slow drip, a drop accumulates over maybe half an hour, out of a 1/4″ opening in the foam by the chimney under the ridge. I’ve not seen any leaks there before the foam was blown in. The ridge is vented and was blocked off with tar paper before the foam was sprayed.
Three things I can think of that could be causing this:
1) It’s cold outside now, teens overnight, mid-twenties during the day. There’s a void in the foam that warm moist air gets into and condensation forms. Or that hole just leads to outside space and the same thing happens.
2) Water or snow got blown into the ridge vent and it’s slowly melting.
3) The roof or chimney flashing is leaking. Water made its way under flashing and is slowly draining out.
I really hope it’s the first one because that’s a five minute fix with a can of foam but is there some way to figure out which of these it is without going up on the roof and taking things apart? It seems like it shouldn’t be 3 because that water should be frozen in this weather but the gas furnace does exhaust through that chimney and could have melted it.
Edit: a few more details The rafters are flashed over so mostly covered but there are some spots with sistered rafters where the space between the sisters is open. I see no condensation there and I found no drips anywhere else on the insulation. The gable walls have no wallboard or insulation right now, just studs and sheathing, and I see no condensation there but I do see condensation on the storm windows that cover the double-pane windows in those gable walls.
Replies
“[Deleted]”
That other thread is a different person with a similar problem.
The drip seems to have stopped last night. Since it's as cold or colder now, that makes me think the problem isn't condensation.
“[Deleted]”
Could you tell us a bit more about this roof assembly? Do you have baffles behind the foam all the way from the soffit to the ridge? If not, it's not a vented roof. Is the plan to insulate and finish the walls and turn this area into a conditioned space? A few pictures of the situation would be very helpful.
It's an unvented roof assembly but there is a ridge vent that should have been blocked off before the foam was sprayed. The original plan was for a vented roof but that had to be abandoned. There is foam sprayed directly on the sheathing from soffit to ridge. Between the foam and a vapor barrier on the gable walls, everything will be conditioned space.
The drip seems to have dried up last night and it was about the same weather as the day before. Right now there is a foot of snow on the roof and I don't see any water getting through. The last crazy storm was over a week ago and all we've had was some fog and weak rain between then and now.
Picture of the leaking spot attached. The red arrow shows the opening where the drip is coming from. It's next to the chimney but on the other side of the double rafter that is adjacent to it. You can make out the brown trail where the water seeps and accumulates.
Is there just not enough to go on here or do people think this is the same as that other thread that sounds similar?
The roof has had close to a foot of snow on it for a few days now and there's been no more drip still. The snow seems to be melting faster directly over the spot above where the leak was (on the left side of the chimney in the attached pic.) Also attached a picture of the spot where the drip was from a different angle.
We spray foamed the chimney in the attic on a house we did last year. The brick is an effective thermal conductor as shown by the lack of snow around it on your roof. Spray foaming the top 2 feet of the brick within the attic space helps to at least reduce direct thermal bridging from warm attic air to the sheathing, etc it is in direct contact with at the roof line.
It's possible you have a chimney flashing problem. It's also possible that melt water is simply backing up through your ridge vent. You may only see evidence of that where the foam isn't continuous. If that hole goes through to the ridge vent and you have humid air entering the attic from the rest of the living space, it's conceivable (though I'd think unlikely) that moisture in the air is hitting a condensing surface, accumulating, and then dripping back down. It's really hard to say without inspecting it, and harder when everything's encapsulated in spray foam. When you close up that ceiling, two important things: 1. make sure you have a good air barrier to prevent bulk indoor air from getting into the roof assembly (airtight drywall is an option, but a high-perm membrane is probably a better idea), and 2. make sure you have good ventilation at the ridge. This article from Building Science Corp. has the details of what I'd recommend for that to make sure those rafters and sheathing near the ridge can dry out: https://www.buildingscience.com/documents/insights/bsi-088-venting-vapor
Matt, I'm unclear what you are suggesting. The article looks like it's mostly providing a solution for warmer climate zones and attics that don't have a ridge sealed up with foam. How do I have good ventilation at the ridge? Do I just want the top of the ridge to air out through the ridge vent that I already have? The house is a cape with a finished attic so there are rooms up there. The drywall should keep most of the air inside the living space but it's a pretty old house and there's not a good way to keep air from downstairs from getting into that ridge area or the triangular "side-attics" by the eves which is why we decided to bring them into the envelope.
I don't think it's melt-water backing up because there's a lot of snow now and it's dry on the inside. I don't thing it's condensation because it stopped dripping while the outside conditions were about the same as when it did drip, maybe even colder. It could've been the bad noreaster we got blowing slush inside the ridge vent but that would mean it took 10 days for that to dry or run out. I think I need to just leave it as is and keep watching it as the weather changes.
Please finish reading the article. It includes examples of the same technique being used in cold climates, including Alaska. The key is getting enough venting at the ridge to take away the moisture that you seem to have. If you can't locate its source and stop it, the next best thing is providing a way for that water to dry.
Matt, I read and re-read the article. I might just not understand it but it doesn't sound applicable. The idea is to have a ridge vent that blocks air flow but permits vapor flow then you condition the attic and let the extra vapor escape through the vent. Sounds great but all the pictures, including the ones from AK, show a ridge with empty space below it so inside air can actually get to the vapor diffusion vent. I've got closed cell spray foam from eve to ridge. We'd have to cut the foam off the ridge board for this to work as described. Is this what you're suggesting? Please clarify.
Or do you mean I should just have this setup over the top of the ridge with impermeable foam below it so any water that seeps in however gets a chance to evaporate?
Matt's article seems geared toward venting of fiberglass or cellulose (I love Joe Lstiburek its a well written piece) However, I think you have a classic unvented assembly and I'm not sure the article is applicable to your situation. The article mentions many times that its only good to Zone 3
I guess I misunderstood when you wrote: " The ridge is vented and was blocked off with tar paper before the foam was sprayed." If the ridge is indeed covered with spray foam, that's typically a safe assembly from a vapor standpoint. But it is not vented. The way you described it, I was under the impression you had a vented ridge, which would require that you not use SPF at the ridge. I haven't heard of anyone doing that and can't wrap my head around why anyone would, but my suggestion of a diffusion vent and doing everything you can to keep water vapor from that space was based on the impression that that's what you had.
I don't think you'd hurt anything by including a diffusion vent, but if the foam installation was done well, I don't think you need it. The fact that you have water somehow making it through voids in the foam suggest that it wasn't done particularly well. Before I did anything, I'd figure out where the water is coming from. If it's a leak from above, that's a relatively easy fix. If you have lots of holes/voids in the foam that are letting moisture-laden air through it, that's trickier to track down. If there's rafter depth left, I'd consider going over the existing foam with another thin and continuous lift of foam to ensure any pathways to the sheathing are covered.
It was a tricky description to word for me. "There's a ridge vent on the ridge but it doesn't vent because it's blocked off." I wanted a vented roof assembly but ran out of time to build it before winter set in so I had a contractor come in and spray over everything.
The insulation is mostly iffy in that one spot because mineral wool they stuffed in the gap around the chimney got in the way but I'll look over the rest of it in case there are more problems. Another trouble spot is that they didn't thoroughly spray over the doubled-up rafters on either side of the chimney so air seems to be circulating in those cracks and I can see the snow melting faster over them on the roof.
The roof had a foot of snow sitting on it for a week slowly melting during the day, no drip. We had a rain-storm that dumped over an inch of rain and washed away all the snow, no drip. It's been 4 days of nice weather since that rain, ~40 deg days, upper 20s during the night, clear or partly cloudy. Now the drip is back.
I cut away some of the foam and see a small slit between the foam and the rafter that looks like it leads to the top of the rafter bay next to the chimney. I'm thinking it's a leaky chimney flashing or ridge vent, the water gets trapped and takes a long time to get in. Or the wind is driving water into the baffled ridge vents. We haven't had plain rain with no strong wind since I noticed this happening.
What's strange is I hadn't seen any water getting in before the foam was sprayed in and that it takes this long to show up. I had been looking for leaks too because we've had problems before but I guess the old insulation might have hidden it. How does it take 4 days for water to show up after rain?
I had a similar problem with an unvented assembly before. It was a bit of a head scratcher at first, but sorted it out quickly after arriving to work early one morning on an extremely cold day. I noticed the brick on first course tight to the roof had formed frost (on interior of roof in climate controlled space). I realized the thermal envelope has a break within the brick itself. The foam was tight to the brick and air sealing was good and a new roof with excellent flashing. What was happening was the cold from the brick was dropping into the heated space by convection within the brick itself and condensing on the surface of the brick within the heated space. To solve the problem we wrapped the brick chimney in the attic space with mineral wool. This acted as a thermal break, no more problems after that. I don’t know if this applies to you, but it could be that the brick has some condensation and when drying off falls down the foam in a channel of foam. If you are absolutely certain no leak from roof, flashing or crack in brick, there’s a good chance it’s condensation.
Thank you all for the comments.
The drip was active, then it rained overnight and the drip stopped. I'm living in the Amitiville house.
The chimney and roof were done in 2019 so less than 2 years ago but I'm not 100% confident in them. The foam guys stuffed mineral wool into the 3/4" space between framing and chimney but it wasn't actually filled. There's only about an inch of mineral wool loosely stuck in the gaps and there are openings even in that so it's not really blocking air. Think it's just there to keep the spray foam from getting in gap. Moist air could be traveling up and condensing on the underside of the flashing.
Would mineral wool actually stop air from migrating if packed tightly or does this require fireblock foam to really seal up?
Are there conditions I can look out for when condensation is most likely to happen or is it a crapshoot because you never know when enough will accumulate to start dripping? The drip doesn't seem to follow any real pattern. I pulled some of the mineral wool out so now I can see if it gets worse and stick a snake cam up there.
If it is condensation I would handle it in one of two ways. If your chimney has a liner it essentially means the chimney is just a chase to house the liner, you do not have to concern yourself with combustibles touching the brick as they’ll never get hot and chimney isn’t really functioning as a true masonry chimney. If unsure about the type of liner (if one) best to assume the brick will get hot and treat it as a masonry chimney. If the liner is good and clearances jive with liner specs you can air seal the gap between chimney and frame with spray foam. If you have a true functioning masonry chimney it needs to be handled differently. First, pack mineral wool into the gap from roof deck all the way to bottom of the rafter. Second, nail pieces of tin to the underside of the rafters with tin tight to the brick to cover the gap. Third, apply fire caulk around the tin where it meets the brick, on all tin seams and seams where tin is nailed to frame (essentially encapsulating the tin and making it air tight).
In my case the chimney had a liner and spray foam was filled in the gap. It was airtight. The issue I had was the cold of the brick itself was sinking into the warm airspace of the attic and condensing on the face of the brick. It was only the first course of brick that I noticed the frost, so the dew point temp was occurring below the rafter. To resolve this I applied mineral wool around the entire exposed chimney in the attic. I wrapped chicken wire around the wool to keep it tight and in place. I could have also used rigid foam glued to the brick as well as combustibles were of no concern, but I had the wool and wire on hand.
Your chances of seeing condensation increase during winter months as the warm air of home is meeting the cold air of outside.
Thanks for the info. The chimney is just bricks around flue tiles but it's only a furnace and a hot water heater venting through it. Both are powered by natural gas and I've never felt the chimney get hot. I have a structural inspection coming up, I'll ask the inspector.
The foam is already touching the chimney in places and there's plenty of overspray on it.
If the gap around the chimney is only 3/4 to 1 in wide, can I just fill it with caulk and tool it flat without the tin strips?
If combustion is of no concern I would fill the entire gap with foam (closed cell type). The tin option was if combustion is a concern. I would consider wrapping the brick chimney as well in insulation. If any brick is cold to the touch during cold days moisture can condense on the surface.
I have a similar problem and originally thought it was a chimney flashing leak but was not able to locate the leak. My 125 year old house and 2005 addition have cathedral ceilings. The addition was finished with 4" of pinkboard caulked in the rafter bays with 3" of foam sprayed to fill the bays. One winter I found a leak in an interior wall and traced it to a pin hole in the insulation. I determined that condensation made its way through the insulation. A squirt of canned foam seemed to correct the problem but I also cut back the ice shield at the ridge and installed a ridge vent so any moisture could dry to the outside.
At the same time I had water running down the vapor barrier in the old part of the house. Long story short, I have replaced the raters from the inside because many were totally rotten. I think the moisture problem is due to moisture migrating in poorly installed foam board insulation and condensing at the ridge. During the winter the condensation would freeze then melt due to warmer weather. There was no correlation between the drips and rain/snow fall. I replaced the foam board and took great pains to seal each panel into the rafter bays. Its too late now but in the summer I will open up the ridge to vent any future moisture.
Based on your description, and what I experienced, I suggest that condensation is your problem and if the ridge is not vented, I would open the vent along the ridge even with the rafter bays completely foamed. I think moisture is moving into the space by the chimney, freezing and thawing as the outdoor temps and sun change.
Filling the hole and gap by the chimney should solve your problem. Best of luck in resolving this problem.
Thanks for the tip. That absolutely stinks about the rotten rafters. Was there ANY pattern you could detect for when the condensation drip happened or did it seem completely random?
Using expanding polyurethane foam is one of the best ways to stop water leaks because the foam will expand into the cracks and help prevent future leaks. You don't need chisels or drills as the polyurethane will enter into any existing cracks and seal them.
Had a roofer come out to take a look once the weather improved. The flashing lead wasn't caulked down and not much ice and water up the side of the chimney if any. Looks like water was getting driven behind the lead by the wind. Only saw it in the winter because we don't get storms with strong winds in the summers here. Water must've taken a long time to show up because it took a while to work through and needed just the right wind to drive it into the interior once it was behind the flashing.
Seems like the most likely diagnosis and the simplest explanation.