Interior barrier, need for
barkingeater
| Posted in Green Building Techniques on
Tim McCarthy here….My wall assembly is as follows from the outside in:
–siding
–dimpled housewrap
–1/2 plywood
–8″ dense pack cellulose in a larsen truss like 2x frame
–taped zip WRB
–2×6 @16″oc filled with dense pack this is the structural and utility wall.
–Gyp board
can I get away with the paint that slows vapor transmission into the wall? Im in nasty part of zone six. I picked/designed this wall to cut down on the need for the extremely expensive fabrics..hoping I can.
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This should help: https://www.greenbuildingadvisor.com/question/poly-and-canadian-building-codes
You want a good air barrier and a vapor retarder before moisture reaches a condensing surface of interest.
The zip WRB seems redundant. With a dense pack Larsen truss setup, your WRB should be outside the trusses. You can save a lot of money by just going with standard OSB.
If your windows are flashed to the ZIP, you should re-do those or go with mineral wool batts for the Larsen trusses.
The ratio of your interior insulation to the exterior insulation is well above the value for zone 6. OSB/ZIP layer in the middle of the wall is a good smart vapour retarder. Provided this layer is well sealed, you should not need anything on the inside other than a coat of paint.
For thick walls, you might want more than dimple map for the rain screen. A proper rain screen gap is not much harder to build and cheaper in materials. Also be careful with dimple mats, some of them are vapour barriers, you DO NOT want one of those.