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Community and Q&A

SIP roof details

LynnAnne Vesper | Posted in Energy Efficiency and Durability on

I have read a lot of what is already on GBA forums, but I could not find answers to a few questions.

I live in northern Minnesota (Zone 3 = can be very cold!) and am building my first home, SIPs over timber frame. I am preparing for a standing seam metal roof and I have three questions about roof detailing.

First, a little bit of background. The company that installed the SIPs did a lousy job of sealing the panel joints. They were to install Ice and Water barrier full coverage from eave to ridge, but they ran out of it so the roof was not covered about 10′ down from the ridge. They made no effort to cover the rest of the roof with a tarp even though a huge black cloud was looming on the horizon at the time that they “finished” the job and left. So a heavy rain poured down and ran under the I&W. When I came the next day, I had standing water on my subfloor. This indicated to me that the panel joints were not well sealed. They insisted they used caulk in the joints, but at any rate, the seams have gotten water in them. The seams got wetted a few more times before I figured out that the tarps I put up were not entirely waterproof for some of our heavy MN downpours. I had the SIP installers come back and look at the problems they caused (as well as fix another detail on the eave). We tore back the I&W and could see that it was trapping water, causing the OSB to remain wet. We then tore the I&W off the whole roof so it could dry. I can see why roofs grow mold under I&W! I think the stuff is evil.

So, question #1: Can I leave off the Ice & Water? Code requires I&W at the eaves. I understand its intended purpose under a shingle roof. However, I think it would be detrimental to roof drying in my case. I am planning on putting down a grid of vertical 1×3’s and then 2×2’s horizontally for the metal roofing to attach to. So I will have a breathing plane. I think that Ice & Water would be detrimental to allowing the roof to breathe and I would like to leave it off. Am I missing something?

Question #2: Should I seal the seams? We have had warm, breezy weather for about a week and I have been letting the roof dry without a tarp on. The seams appear reasonably dry at this point, but I suspect some residual moisture remains in the seams. Should I seal the seams before putting down underlayment? When I had the SIP installers come back, they foamed the roof panel joints (which they had not bothered to do before), but I understand that foam is not a good long-term seam sealer. Should I seal the seams both outside and in with something like a Siga tape (Wigluv)? Since I am making a breathable roof assembly, I think that failing to seal the seams on the outside could cause stack effect, or air being pulled through the seams. I am wondering if sealing on both sides is a good idea.

Question #3: Underlayment. The metal roofing company cannot get here for about 8-10 weeks. In the meantime, to save money I am planning to put on the underlayment myself and the wood grid. There are several fans on this forum of roofing felt for its waterproof / breathable characteristics. However, I understand it is not very durable and I am concerned about leaving it exposed for 2 months, with the high probability that the roofers will be shoveling snow before they get started. (However I do plan to put a tarp on top of the grid in the meantime.) So my current thought is to install #30 felt and then put on a more durable underlayment like GAF Deck Armor. Does anyone see a problem with this belt and suspenders approach?

Thank you for your excellent forum. I have been reading for about a year and finally decided to join.

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  1. GBA Editor
    Martin Holladay | | #1

    Your SIP installers sound incompetent. You can pursue remedies by negotiating, or you can take them to court, or you can chalk up the entire experience to one element of your construction education, and write off the losses as part of your tuition.

    SIP seams need to be taped. The usual location for this tape is on the interior of the house.

    In your case, I strongly recommend that you install a vapor-permeable European tape on the exterior side of the SIP seams. You can call up Small Planet Workshop or 475 in Brooklyn and ask which tape they recommend. Whatever tape you by, make sure that it is vapor-permeable.

    Your roofing underlayment should also be vapor-permeable. You can use asphalt felt, or a vapor-permeable underlayment from Small Planet Workshop or 475. Some U.S. roofing underlayments, like the GAF Deck Armor that you are considering, are also vapor-permeable, and would work in this case.

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