I have a question regarding a roof leak in a 4 year-old house. We have a post & beam home with a cathedral ceiling in the living room. It’s constructed as follows: I have 2×6 t&g (2″ thick) boards laid over the rafters, it appears that there’s a piece of sheathing over them -although it wasn’t specified in the plans, then “sleeper” rafters and probably another 2x ridge. In between the sleepers is solid foam insulation. On top of that there’s another piece of sheathing, roofing felt and then the roof shingles.
On a hot afternoon a week or so ago, we began to smell a moldy, mildewy odor and my wife noticed asomething drip from the ceiling. When we checked, there was a line of water drops at the joint between the fist and second boards. I got a ladder and went up to check it out. The boards were hot to the touch. It only affects two sections of the ceiling; everything was cool and dry further along the ceiling.
I theorize that rain has blown under the cap or first row of shingles and soaked into the the sheathing. We live in a high wind area on the Oregon coast and get lots of rain and high wind. From the ground, none of the shingles appear missing, loose or damaged. I’m going to have the roofer come back to look at it, but I want to have my ducks in a row first.
i can imagine him telling me that it’s nothing major: just paste the shingles down and things will dry out over summer. (We’re going into a period of at about 4 months of no rain.) My question is: If the roof no longer leaks will the sheathing, sleepers, or whatever dry out with time and months of hot sun on the shingles or will (should) everything be opened up from the top.
My first thought was to remove a small section of the ceiling to get in there and see for myself what’s going on. I haven’t been successful in doing that and all work, it appears, will have to be done from the outside.
Replies
I don't see why you need your ducks in a row. He's the roofer, it's his roof that leaks, he needs to fix it. Ask him to figure it out and take care of it.
My general feeling is that something that gets wet once or twice will dry out and will not rot. The moisture will either leave where it came in or will 'osmote' within the building assembly and dissipate. I wouldn't rip the whole thing open. Others may not agree.
It sounds like a classic case of condensation to me. You have not reported anything to make me think the roof is leaking when it rains, only that it is heating up and sweating in locations where condensation can be expected.
There are several things that lead me to expect condensation,
You have nowhere mentioned an good vapour barrier.
The "sleeper" space is located to the inside of the insulation package. I belongs to the outside of it or not at all.
Foam was placed between the rafters. That lends itself to allowing air to vent into the roof, bringing moisture with it. The rafters themselves become a thermal bridge to attract condensation.
Cathedral ceilings and condensation go together like Sh!t and stink. You can have one without the other, but it's not too convenient to explain or do.
Unfortunately, the problem is easier diagnosed than fixed.
A year ago, JLV ran an article on several houses similar to yours with extreme condensation and mold issues from faulty installations
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I think he's describing shingles over felt over plywood over insulation/sleepers over 2x6 decking over rafters. Your description is 'foam between the rafters' and 'sleeper space', neither of which I get from that description. Can you elaborate?
Sure.
" I have 2x6 t&g (2" thick) boards laid over the rafters, it appears that there's a piece of sheathing over them -although it wasn't specified in the plans, then "sleeper" rafters and probably another 2x ridge. In between the sleepers is solid foam insulation. On top of that there's another piece of sheathing, roofing felt and then the roof shingles. "
from this I understandf him to be describing the situation from bottom up through as it was apparently installed.
So there are rafters of some sort, then the exposed decorative ceiling of 2x6T&G.
IOmmediately above this is where there should be a vapour barrier. He does not mention it but does seem to think there is a sheet of sheathing, perhaps ply or osb. that sheathing would help to reduce infiltration a bit, but probably not totally, especially for a ceiling.
Then, after the sheathing is on, there are sleeper rafters. Now maybe there is a misapplicatioin or misunderstanding of terms at this point. I took sleeper top miean that the secondary rafters here meant that they were laid flat but maybe he means that they are simply not structural and still stand vertical as typical for rafters. I've seen both so I'm not sure without his return to clarify.
But the important point is that the foam is installed BETWEEN the rafters instead of being continopus and that there is no apparant VB.
That means that warm moist air can carry moisture up through the assembly especially at the point where the foam meets the sleeper. That moist warm air will hit the upper surface backside where things are cooler and the moisture will condense and leave the moisture in the wood. Nasty things happen then.
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I've seen that problem in lids like that, but spread out, not just at one elevation. The one I looked at last summer (beautiful house it was, too) had drips coming in thru the joints in the t&g at various levels from high to low along the slope of the ceiling, which was maybe about 1:12 pitch. That house had 4x8 rafters 4' OC, 2x6 t&g decking, continuous insulation (I think it was the OSB-faced foam), and then built-up roofing. I take your point about the foam being continuous. Since he said the water is just at one level (sounds like near the eave) it seems to me that a leak is likely. With condensation wouldn't you expect it to be more spread out, high to low?
Hmmmm....
I had to go back and read again. between first and second boards. Interesting isn't it how you understand theis to mean first from bottom and I took it to mean first from top???
Anyway, you may be right on that, but it can still be that thew condensation happens in a large area but only shows a concentration of water in one place, due to drainage as it runs down. That would depend on the slope of the roof - how fast it runs with surface tension in the assembly or drips through.
I have indeed seen more condensation issues locallized. Several reasons for that.---
-air flow is not equal in the living spaces below due to temperature gradients.
- some parts of a house will produce more moisture than others
- the noth side of a house normally gathers far more condensation due to colder mean temperatures.
When I was in Colorado, I regularly got calls to fix leaking roofs in deeep cold winters. Probably seven times out of ten, it was a modular or mobile and the "leak" was over a bathroom on the north side of the home, downstream from the vent stack. Most of the rest of them were in cathedral ceilings, north side, not far frome either klitchen or bathroom.
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To clarify a little:
The "sleepers" are nonstructyral rafters of 2x material standing straight up just as if they were regular rafters. The drip that we noticed is on the firts and second board from the top...ie: adjacent to the interior ridge.
The tails of these sleeper rafters extend beyong the wall plate of the room giving the impression of conventional construction from the outside. The framer left the space between sleeper rafters partially open and screened it - similiar to what was done over the conventional flat ceiling. When I shine a flashlight up into this opening, it appears to be completely filled with the foam. It seems like it would have been more effective if a small air space were left above the foam to increase circulation.
The question remains; what can we do about this now??
Additonal clarification after rereading your messages.
The room has five "bays" between interior rafters set 4' oc- it's 20 feet long. Only 2 bays show any moisture, and they're in the middle of the room. The ridge runs north to south so the slope of the roof is in the east & west side. The wind here comes in off the ocean which is to the west and it's the west side of the ceiling that's dripping.
The room isn't near either bathroom. We have an open floorplan and the kitchen is adjacent to the living room. We have a gas (propane) stove, but always use the rangehood fan whenever we cook.
We also have a inline fan that vents the entire house. Anytime it's turned on, there's air replaced in both bathrooms, a lavatory, a walk-in closet and the laundry room. I would think that this air movement would pull mositure out of the ceiling if there was any.
By the way, my helpful spouse pointed out that we've had a week or so of warm, dry weather and the odor is no longer noticeable.
Thanks for continued input.
Dry weather and the problem goes away.
West wind creates water problem on west side.
Whole house ventilation to deal with interior moisture.
OK, maybe, just maybe, your first instincts are right and water is being driven on the wind. Now I want to know if there is underlayment beneathe the shingles.
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... and if there's a ridge vent? Did they intend for air to flow thru the space between the sleepers? How thick is the foam?
I don't remember a ridge vent mentioned, but it will do no good without a channel for air passage from the soffit vents
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I did some measuring and maybe this makes sense. There's a piece of the foam that apparently blew away when they were installing it that's laid out in the woods for 5 years. I hiked out in the rain and measured it. It is 2 1/2 inches thick. It has a "paper" covering on both sides. The exterior is sort of a silverish and the inside looks like what I call tar paper. The faux rafters, or sleepers as I call them, are 2x6's, the screened vent area is 1/2 inch high.
I'm thinking that if I stacked two sheets of foam next to a 2x6, I'd have 1/2 left over. This would be the ventilation channel mentioned in a previous post of mine that I suggested should have been put in and wasn't. Apparently i was mistaken when I shined a light through the screening.
There aren't roof vents on this portion of the house. The part with flat ceilings has the traditional square boxes that are installed before the shingles go on. I'm guessing that they assumed that air would just move in and out on its own through that vent channel above the foam.
By the way, that piece of foam that's laid in the woods for almost 5 years looks fine. The paper is still adhered to both sides and there's no mold on it even though it's been in contact with the ground.
I'm thinking that if the problem is condensation, we could install small vents near the ridge.
I'm thinking that if the problem is condensation, we could install small vents near the ridge.
That is still a crap shoot because if there is no vapour barrier on the inne5r sheathing, the suction created by the draft can such even more moisture laden air from the interior into the rafter spaces.
With only 1/2" vent space, if they did not do anything postive to maintain that space at that dimension and in the right location, it is concievable that some insulation panels f;laoted around and there is a blockage to air flow.
Without vents at both ridge and soffit, there is effectively no ventilation at all, IMO.
The type of insulation you describe sounds like an open cell instead of closed cell. That means that it can absorb moisture, hold moisture, or let moisture pass through it. A closed cell is preferable for roofs and foundations where moisture is expected. The advantage of the open celled ones is that they generally offer a higher R-rating.
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I'm confident that there is underlayment even though I wasn't on site when the shingles were installed. I'm going tobe talking to the roofing company the first of the week and verify that. I can't imagine them not installing it.
First from top is consistant with condensation problems since hotter wet air hangs out up there.
What can be done?
I ain't a pretty answer I have. And I am sorry for that.
IMHO, the whole roof design is questionable. It is the designer and the builder who need to answer first and foremost. There might be compromise solutions but you know how well compromises work.
Did you say what your climate is?
I don't know what the open screening at bottom is supposed to be doing if there is no air channel and no out-venting at the ridge. I don't imagine the builder knew either.
I could answer better if I could talk top him and know what is really in that space. I don't doubt you, but you are only reporting what little you can see peeking into a hidden space.
It might be that providing a ridge vent in this roof would facilitate some venting of the moisture to alleviate the problem, but it is equally true that the suction created would increase your heating bill and by increasing the airflow within this assembly, you could increase the total amt of moisture coming into contact with the cooler condensing surface beneathe the roof.
The only way to gaurantee the fiox is to remove it all down to the "sheathing" and do it right, but that is based oin my limited knowledge of the site. An in-house genius might find a better solution when viewing the whole job as it exists.
If this is truly in one place only, it hints that the foam between rafters might be poorly installed in only that one location, with some gaps between joints or between foam and rafter. If the shingles and upper sheathing were removed there in a localized "surgery" you could use a canned spray foam to eliminate the air flow that is bringing the moisture to the cool condensing surface. That exploratory surgery would also let you study the problem, see if mold is rampant, and see if the problem is more or less likely to spread to the rest of the building.
If you have the ability to do digital photos, you coule demo the progress here and we could be more accurate in our responces.
BTW, is the location of the worst of this problem near a bathroom or kitchen? How thick is the foam? or in other words, how deep are these faux rafters?
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What is the roof pitch?
The roof is 8/12