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Community and Q&A

Sealing Seams Between Roof SIPs

mikeymunson | Posted in General Questions on

I promise, I did search to see if this particular solution has been discussed;

We received delivery of our SIPs to envelope our recently raised timber frame.  The manufacturer recommends (our choice of) synthetic underlayment above the T&G planking, SIPs panels, foaming panel joints, 30# felt, shingles.  They recommend a “drill and fill” method of foaming joints which involved drilling into a routed channel every 6-8″ and filling it with foam. If installation is happening in the winter months they recommend a butyl caulk in place of the drill and fill.

Our installation is NOT happening in the winter months, but I have some concern about the efficacy of drill and fill.  It can be hard enough to eyeball a 90deg angle when drilling on firm ground, let alone 30+ft. in the air on a 12/12 roof balancing on a chicken board.  I’m considering using snow and ice guard above the T&G planking to serve as a complete air barrier below the SIPs, then using their butyl caulk method of sealing the SIPs joints.  I believe this would be more effective than stapling an underlayment (therein creating hundreds of breaks in the barrier) and hoping all of our drill holes hit the channel as intended.

I’m by no means trying to cut corners, rather looking for the best way to ensure we have no air loss and/or condensation in our panel seams leading to OSB decay.

Thanks in andvace!

-Mike

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Replies

  1. Expert Member
    MALCOLM TAYLOR | | #1

    Mike,

    I know very little about this but the two things that commenters appear to say are necessary are: A belt and suspenders approach of sealing and taping the joints, and venting the roof above.
    https://www.greenbuildingadvisor.com/article/9-21-spotlight-are-structural-insulated-panels-the-right-choice
    https://www.greenbuildingadvisor.com/article/trouble-on-the-roof

    1. mikeymunson | | #3

      Thanks for the links, Malcolm. I've read a lot on the belt and suspenders approach. It seems the common theme is that by putting the planking down first you're not able to tape the seams from the inside, which is best. I'm wondering what the experts think of using the snow and ice guard to act as the tape would. Venting the roof would be ideal, but with today's cost of sheet materials it doesn't look like it would work with our budget. I'm banking on a solid weather seal at the joints to last for the life of the original shingles, then when we put on a new roof down the road we will plan to fur it out and put a vented roof above.

      1. Expert Member
        Akos | | #4

        I think a full peel and stick is a good alternative. This way there is no way for warm air from the house can make it into the SIP.

        You have to take some care with the peel and stick. You want something with either acrylic or butyl adhesive. The standard ones which are modified bitumen can react with sap in the pine and ooze. They also smell like asphalt which you don't want inside your house. I would do a smell test with any of the peel and stick you use to make sure you can live with it.

        This is more for energy efficiency, but it also will prevent your ceiling from dripping water.

        Sealing T&G ceilings is very hard as there is a lot of 3D airflow. You not only get air flow across the gaps between boards but you also get it along the grooves. It is important to seal this over your top plates as all those small gaps times a couple dozen boards add up to a very big hole.

        The best way is to stop the T&G half way across your exterior wall plate and carry the roof peel and stick down to your wall for air barrier continuity. Continue the T&G for the soffit area from the half way point.

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