Taping a SIP seam that lands on a rafter
I attended a home show recently and spoke with a SIP manufacturer (a reputable one) and asked them how they handle the internal taping of two SIP seams that land on a rafter. For structural purposes, obviously, one would want the seams of a SIP to land on a rafter.
They said, they typically do only an external spline on these seams and then drill holes every 6″ and shoot foam into the cavity (from the exterior) and then I would tape too.
I wasn’t totally sure about this detail so I thought I would ask what folks here have seen in the field. I do plan to have a proper air gap with furring strips and a 2nd layer of substrate for my installation BTW. If my rafters were 24″ OC, I wonder if it might make sense to not have the seams terminate on the rafters. Or perhaps a bead of an appropriate sealant. The shrinkage of the rafter has me thinking otherwise.
Any thoughts?
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John,
By now, cold-climate builders have lots of experience with SIP roofs that leak air. We have lots of examples of failed SIP roofs. In almost all cases, the roofs fail because of air leakage at roof panel seams. So you need to be careful.
To read about all of the various approaches to dealing with this issue, see How to Protect Structural Insulated Panels from Decay.
The article describes a system used by Chris Koehn: "By draping tape over the tops of timbers, then installing the panels, the seams [can] be sealed on the inside. When a T&G ceiling is going in, Koehn would add spacers on top of roof framing to create a gap between the framing and the panels. T&G boards could be added later."
-- Martin Holladay