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I have an ICF house on Vancouver Island with a Open Joist/ T&G Fir roof

Spiderwebb | Posted in Energy Efficiency and Durability on

The T&G Fir is attached to the open joist through the T&G Fir, above the T&G is a layer of Glued Blue Skin followed by 3 layers of High density foam boards (8*4) 3.25×2 with 1×1..25 cross layered there is 5/8 Ply screwdown with long screws to the joists, The tar paper and duroid roofing is attached in the normal manner.
When we moved in (3 years ago) no issues materialised but where the T&G extends over the wall (outside) we are now seeing evidence of condensation when the temperature drops arond 0c. I suspect the T&G has dryed out and shrunk over time
I have caulked the V gallery that exits with the chamfers on the lower side to the drywall using a pressure gun and a stretch caulking (as used on log buildings) but there are still indications of condsensation on some joints.
I suspect the air is leaking in the upper T& G gallery under the blue skin and leaking out, an idea that I am now toying with:- is to drill a hole 5/16″ dia in the v groove up on a slight angle next to the Dry wall interface, terminating close to the blue skin and inject a strech caulking (or simular) in so it provides an end barrier to stop the air escape.
I have considered Great stuff but its so uncontrollable with an interior face, Apart from from redoing the roof do you have any suggestions products to inject or methodology.
I have a sketch of the proposed procedue for clarity if required.
Many Thanks

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  1. GBA Editor
    Martin Holladay | | #1

    Your house has a problematic detail that is not recommended. When tongue-and-groove ceiling boards cantilever through the exterior walls, extending outdoors, you have thermal bridge as well as a thousand small air leaks.

    The best long-term solution is to cut the boards back flush with the exterior siding and cover the stumps with a strip of rigid foam, trimmed with some suitable trim material.

    If you don't want to do that, you could leave the exterior boards in place, and cover the exterior boards (the soffit) entirely with a layer of rigid foam, followed by a new soffit.

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