Replies

1. 
   Deleted | Jan 07, 2025 11:52am | #1

   Deleted

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   pmny | Jan 07, 2025 12:11pm | #2

   Thanks for the response.
   I think the 2x4 sleepers have the ext plywood sheating on top.
   I take your point on the vapor barrier and taping, which I will follow up with the architect.

1. 
   freyr_design | Jan 07, 2025 12:30pm | #3

   Hey I accidentally deleted my post trying to edit… anyways maybe he is trying to say they are faced mineral wool batts that you are taping? But then it says insulation boards which implies rigid, and staggered and taped seams also seems to imply this. . And the 2x4 sleepers appear twice. It’s a confusing description and would not be helpful for a contractor. Perhaps ask him to be more precise in his defining layers.

   Also tell him to be diligent in the use of vapor retarder and vapor barrier as they have much different meanings.

   And lastly you have no good air control layer.

2. 
   Malcolm_Taylor | Jan 07, 2025 01:05pm | #4

   Paul,

   Like Freyr-design, I’m confused by a few things.

   - How do you get R-49 in a 12” rafter bay and still leave space for the required venting above?

   - Mineral wool isn't a vapour-barrier, and vapour-barriers of any material don’t benefit from being taped.

   - The roof assembly lacks an air-barrier, which is essential for it to work.

   - Most meal roof manufacturers do not allow #15 felt as an underlayment as it gets too hot and deteriorates.

   Edit: I got called out by a neighbour to dig up their septic tank before I could post this so freyr-design may have already covered these points.

3. 
   | Jan 07, 2025 08:07pm | #

   Was a layer or two of foam board on the underside of the rafters omitted? The lines about staggering joints and taping seams suggests that, with the words vapor barrier hinting that they should have foil or plastic facings.

4. 
   user-5946022 | Jan 07, 2025 10:28pm | #5

   Before you check with the architect, can you also please post a cross section detail of the cathedral ceiling? If you do that, we can identify any other issues so you can address all of them with the architect at once, and advise if/how the section detail does not match the spec...