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SIPS, roof seams & mystery brown drips — any guesses?

tim_in_nc | Posted in General Questions on

This is sort of a two-part question, I thought about breaking it up into two posts but have read enough rambly forum questions that I figured y’all could handle it :D. But moderators, feel free..

I live in a 2-years-old custom-built & designed SIPs house in NC (zone 3 or 4?). The house has a unvented standing seam shed roof supported by LVLs at 48″ OC which span the full length of the roof. Panel seams sometimes fall over the beams, sometimes not. There’s a portion of the ceiling that is inside an attic space (about 1/3) and the remainder is a cathedral ceiling with beadboard glued to the OSB face of the SIPs between the joists, framed by flat trim pieces, and then the whole thing caulked and painted with semigloss paint.

Despite me forwarding some of the GBA articles on the topic at the time, the builder decided it wasn’t necessary to tape roof seams (his logic was those failures were coming in regions with much bigger temperature differentials than ours). At the time, I didn’t have the energy or knowledge to fight that battle any further. Now we’re here in the house, learning more, and hoping to do what we can to mitigate future risks, without going overboard or getting too stressed out about it, since we do love living in the house, and if in 20 years we have to put a new roof on it again, c’est la vie.

Question 1
We recently came back from a 2-week trip and found some weird brown drips coming from one place in the cathedral ceiling (see pictures). This seems to be localized to one particular spot, and the drips are dried up, as if it was a one-time event. When I’ve looked up-close, I can’t seem to see any “up-stream” traces leading to where the drips start (like, when I scraped away the caulk along the joist beam with drips, I didn’t see anything underneath there that looked like water had been there, and the other set of drips that are coming off a drywall corner, the back side of that piece of drywall also looked clear).

I’m curious if anyone has thoughts about what might have caused these, and how I can investigate further and/or mitigate? I have 3 working theories:

1. Pinhole leak in the standing seam roof — we had some tree branches hit the roof in a storm in the past month, and then there was heavy rain while we were out. I can’t visually see any damage from a distance, but the roof is too high off the ground to investigate up close, so it’s possible.

2. The classic SIPs failure folks have described around water condensing on the roof surface and dripping back down definitely comes to mind. But these happened on a very hot summer day; are super-localized, and the A/C has been keeping our indoor & dewpoint consistently low. So something about that doesn’t quite make sense to me. Plus, in the attic space where many of the seams are fully exposed I didn’t notice any similar drips.

3. Some sort of heat-induced construction glue, caulk, or spray foam failure? The drips are coming from a part of the ceiling which would get really hot, and we had turned up the thermostat before we left town, so there would have been some periods of higher heat up there potentially. This would explain not being able to see damage anywhere else, but it would still be strange.

Question 2
Regardless of the immediate issue of these drips, what’s the best approach to retroactively trying to air seal some of the seams within a limited budget?

My current plan is to:

1. Go up in the attic and use Siga Rissan tape on all the exposed panel seams there, plus tape panel edges to the joist edges (as should have been done in the first place)
2. Spot caulk places along the cathedral ceiling where we can see visible gaps in the existing caulk
3. Hire someone to come out and do a blower door test and ID any remaining air leaks in the sealing to caulk.

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  1. tim_in_nc | | #1

    Noticing that there's some good advice to question #2 in this related thread (! Wondering if anyone has a gut instinct of what these brown drips might be, though?

    1. DC_Contrarian_ | | #3

      In my experience brown drips are water seeping through the wall very slowly. It's either rusting fasteners and the brown is from rust, or it's leaching something out of the wood. If water is flowing more quickly it tends to flow clear.

  2. plumb_bob | | #2

    A forensic investigation of this type of situation is extremely difficult in person, let alone from some pictures and a written description.

    My GUESS would be the brown drips are from water logged OSB, and the cause is failed air sealing somewhere in the system. Or a simple leak.

    Check out Building Science Corp., he has some great articles on SIPS and common problems. He recommends a moisture diffusion port near the roof ridge, not sure if this would be relevant in your situation.

    1. tim_in_nc | | #4

      Thanks, that makes sense -- and a good kick in the pants on my end to try to get someone out here in person to diagnose.

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