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Trouble on the Roof

Who is responsible for fixing a problem with ceiling condensation under a SIP roof?

Posted on Aug 3 2015 by Scott Gibson

Jeremy Ballard is living in a relatively new home built with structural insulated panels (SIPs), and he's already spotted something that's keeping him up at night. The weather in Kentucky is turning hot and humid, and with the humidity has come condensation on corrugated metal panels installed on the interior of the roof.

"Our center ceiling beams are dripping wet throughout the day, causing small puddles on the floor," Ballard writes in a post in the Q&A forum at GreenBuildingAdvisor. "The ceiling is hot to the touch at the very peak on either side of the center beam. I believe hot outside air is leaking in."

As he starts a round of calls to his builder, the SIP manufacturer, and the manufacturer that provided the frame, Ballard looks for recommendations on how the problem can be corrected. Seams between SIPs are not taped, either on the inside or the outside, and they're now inaccessible. Other possible clues: the unvented metal roofing is installed over furring strips and a layer of "double bubble," a foil-faced product sold as insulation.

Another question faced by Ballard: Who's responsible for making it right? Among the candidates are the general contractor for the house, the manufacturer of the SIPs, and possibly himself.

"I couldn't sleep last night thinking how this cost our family over $32,000 for the SIPs and the first summer [they] are failing," Ballard says.

That's the topic for this Q&A Spotlight.

Yes, air leaks are the culprit

David Meiland has no doubt the problem is a leaky roof assembly. "As you allude to, the issue is probably air leakage and the solution is to seal the joints where air is leaking in," he writes.

If the builder responds to Ballard's requests for help, Meiland adds, he will probably want to correct the problem from inside the house by caulking the seam on either side of the ridge beam. But the real solution is elsewhere: on the outside of the house, where the seams between adjoining SIPs should be sealed with tape.

The builder might be able to expose enough of the roof to correct the leaks by removing the ridge cap, but that prospect seems unlikely because in an unvented roof the metal roofing would extend very close to the ridge. "But perhaps," he adds, "the ridge cap is large enough to allow some wiggle room up there."

He also suggests that a home performance contractor equipped with a blower door and an infrared camera might be able to identify other air leaks in the house. A good home performance contractor might also help determine whether the HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system is depressurizing the house and contributing to the problem.

Exposing the ridge might also reveal the "other side of this coin," writes Andy Chappell-Dick: "warm, moist air leaking out in the winter."

Everyone in the SIP business, from manufacturer to installer, knows the importance of a "belt-and-suspenders" approach to air sealing, he adds. "Due to the high pressures of winter stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season., the most critical interior joint to seal is the peak, that one that is now inaccessible," Chappell-Dick says.

Suspect seals at the ridge

Ballard can add some visual evidence that air leaks at the ridge are behind the problem. He provides a photo taken during construction showing a gap of at least an inch between SIPs at the ridge, with a bit of gasket material showing (see Image #2, below).

"I was ignorant during construction, but realized this was not right," he says. "I sent the picture to the manufacturer a year ago when it occurred and the response was that my concerns were not valid. I poorly chose to rely on the professional opinion. However, the evidence now is that my concerns are valid."

Ballard doesn't quibble with any of the comments that have been posted, but the real question is how to fix it. He thinks a possible solution is to seal the entire ridge from the inside and "basically build the ceiling down below some sort of added seal and barrier."

Following that, he adds, the ridge should come off and the seam sealed from that side as well.

"I have no idea what could seal it, but I wouldn't be opposed to a solution of adding up to a couple of inches to the inside if it assured a bullet-proof seal," he says.

Start at the ridge, says GBA senior editor Martin Holladay, by removing the ridge flashing. "If the removal of the ridge flashing exposes enough of the SIPs on both sides of the ridge to install SIP tape," Hollladay says, "then the fix would involve spraying the gap between the SIPs with spray foam; trimming the foam after it cures; and then installing SIP tape that is wide enough to stretch from the SIP on one side of the roof, over the ridge, and onto the SIP on the other side of the roof."

If removing the ridge flashing does not expose enough of the SIPs to do this work, the builder will have to remove enough of the roofing screws to lift or remove the roofing panels, "as needed to gain access to the ridge area."

And while this work is underway, Ballard might think about hiring a home performance contractor to find out why the house is depressurized in relation to the outside, a condition which is encouraging the influx of warm, moist air.

And who's responsible for this mess?

There seems to be some consensus on how to fix the problem (tackle it from the outside, not the inside), but now it gets a little sticky. Who is legally responsible for the repairs?

Ballard had a general contractor/builder for the house, but he hired a SIP installation crew under a separate contract. To be precise, he says, he paid the SIP manufacturer, paid their installation crew, and then paid his GC to come in and finish the roof with flashing and trim. "In my mind," he says, "the SIP install contractor is the person I need to be talking to."

That makes you the GC for the SIPs, says Holladay, adding, "It's up to you to pursue the problem with the crew that you paid."

Stephen Sheehy, who practiced construction law, suggests that Ballard invite both the general contractor and the SIP contractor to the house for a chat.

"Otherwise, it is highly likely that the SIP contractor will blame the GC and the GC will blame the SIP contractor," he writes. "You need to emphasize that they have a problem and you need it fixed by either or both of them. I'd copy my lawyer on any correspondence.

"One lesson you've learned the hard way is that there is significant risk in carving out a part of the construction of the building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. and hiring a sub yourself," Sheehy continues. "While the SIP installer may very well have screwed up, maybe the GC made matters worse. Maybe the GC should have noticed the problem before the roofing went on. But does the GC have an obligation to inspect work by subs hired directly by you? Probably not."

Our expert's point of view

Here's how GBA technical director Peter Yost looks at it:

Having investigated a number of SIP roof moisture problems, rule number one is to back up every panel joint that is foam-sealed with a pressure-sensitive adhesive (PSA) tape. Over time, even the best of foam sealants can develop hairline cracks with repeated contraction and expansion. The flexible PSA tape maintains the air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. should the joint sealant fail. And because of wintertime stack effectAlso referred to as the chimney effect, this is one of three primary forces that drives air leakage in buildings. When warm air is in a column (such as a building), its buoyancy pulls colder air in low in buildings as the buoyant air exerts pressure to escape out the top. The pressure of stack effect is proportional to the height of the column of air and the temperature difference between the air in the column and ambient air. Stack effect is much stronger in cold climates during the heating season than in hot climates during the cooling season., even the smallest of cracks at the roof line lead to warm moist air leaking into the panel joint and condensing. So, all SIP joints need to be sealed and taped to be part of a longterm continuous air barrier system. The need for this is greatest in the roof system, typically, because it goes through the most dramatic temperature and expansion-contraction cycles.

In this case, I am afraid that the roofing panels need to be removed so that all of the SIP joints can be taped. Leakage may be most pronounced at the ridge, but sooner or later, you will almost certainly be needing that flexible backup PSA tape at all panel joints. And yes, the SIP installer is liable here, to the extent that best practice is belt-and-suspenders at panel joints.

Rule number two: check the building pressure balance with the HVAC running. You need to know whether the HVAC system is making matters worse.

Rule number three: check to see if your HVAC system is both properly sized and has the climate-appropriate Sensible Heat Ratio (SHR). An oversized AC unit could be short-cycling and not accomplishing enough latent heat (moisture) removal, aiding and abetting condensation at your interior roof finish. And a unit with the proper SHR means the AC unit is designed to “favor” latent heat or moisture removal in hot-humid climates. An SHR no greater than 0.70 makes sense in Kentucky.


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  1. Jeremy Ballard

1.
Aug 6, 2015 6:06 PM ET

Tropuble on the Roof
by Rick Blumenthal

I agree with Peter on this one, specifically, his post suggests there is likely more than one contributor to the condensation issue. Having seen this condition many times, (especially on metal roof systems)and without the use of SIP's, I have diagnosed multiple conditions that have influenced condensing:
Air leaks are generally a prominent contributor, temperature differential between the cool metal surface on the conditioned side and the warmer surface on the bottom of the SIP panels, (is there enough insulation above the roof to prevent this in extreme conditions), as mentioned the HVAC system may not be sized or installed correctly, (or both) and cannot handle the RH, let's not forget occupant behavior as well.

If it were my building, I would conduct a complete diagnosis before attempting any trial and error tactics; this may provide a more focused approach. A ventilation system was not mentioned in any of the posts. A balanced ventilation system like an ERV may be appropriate although after the fact installation may be difficult.

I would also be concerned about the condition, especially at the seams, of the SIP's. Remember the Juneau AK SIP roof failures? These were do to improper joint sealing and taping. Sealing and taping from the top side of the SIP may be problematic. I'm just thinking about pressures on the conditioned side (possibly) being greater than that of the roof side except in high wind conditions. My concern is that if the SIP's are sealed and taped from the top and moisture is transferred from in to out, what is the drying potential at the seam. At least if the panel seams were sealed from the under side, (not possible in this application) I'm guessing the seam would have a greater potential to dry.

Let us not forget the "house as a system" concept: many systems are involved all having to work in compliment with each other to manage the conditioned space. I'd appreciate any comments on my thinking. It's all educated guesswork.


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