Do vapor barrier or moisture transfer concerns apply similarly to ceiling and floor assemblies?
Now that i have grasped the concept of Vapor barriers for Walls specifically, (for my Climate zone 4A)… (that rather air sealing is the crucial component to prevent vapor transfer), that i can just use a breatheable vapor barrier one on ONE side… (ie Certainteeds MemBrain btwn my Rock Wool Comfortbatt and Sheetrock) so the walls can still dry to the inside…
Conceptual Question: Q1 So then, how do i approach, the proper way to assemble Floor and ceiling layers? ( other than of course, air sealing the enclosure?)
Q2. Simply to keep the surface of my double layer of Roxul Rock wool ceiling clean from dust and insects, can i gently place a layer of Lowes house wrap ( highly permeable) atop the Rock wool layers, since i have vented gables in the small attic? If not, what other suggestions do you have, and why?
Q3. For the sections of subfloor i had to tear out, which had roofing paper btwn the plywood and base pine planks, what should i replace, the roofing paper, i imagine, with a breatheable semi permeable covering…either the MEMbrain or the Lowes wrap? (It is a crawlspace that i have to clean some mold from Rim joist area, and all dust/spore filled fiberglass insulation has been removed. The Crawl has sealed vents, new 6mil plastic taped to block, and dwhumidifier running. But not FULLY encapsulated.)
Q4: So essentially, do i want to prevent air from crawl entering Living space from below with an impermeable material? Or is better to have it breathable? ( no radon issues last time i checked)
Thx for your advice,
Giovanni
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Giovanni,
Q. "How do I approach the proper way to assemble floor and ceiling layers (other than of course, air sealing the enclosure)?"
A. Building codes exclude Climate Zone 4 buildings from any requirements for vapor retarders in walls, floors, and ceilings (except for slabs on grade, of course, which need sub-slab poly). Just pay attention to airtightness.
Giovanni,
Q. "Simply to keep the surface of my double layer of Roxul Rock wool ceiling insulation clean from dust and insects, can I gently place a layer of Lowes house wrap ( highly permeable) atop the Rock wool layers, since I have vented gables in the small attic? If not, what other suggestions do you have, and why?"
A. Above attic insulation, housewrap is harmless but unnecessary. Researchers have concluded that it's better to use the money that you might have spent on housewrap and spend the money instead on thicker insulation.
Thx for this info. Just want to use it to keep the top side free from dust and insect fragments. The prior house owners let the roof leak and i spent waaay to much time and effort with debris & mold which collected upon the dust that settled on the insulation. If i dont catch a small leak super fast, easy to just roll the dusth wrap up quickly before mold grows on top of dusty insulation.
Giovanni,
Q. "For the sections of subfloor I had to tear out, which had roofing paper between the plywood and base pine planks, what should I replace? the roofing paper, i imagine, with a breatheable semi-permeable covering…either the MEMbrain or the Lowes wrap?"
A. The plywood is usually an adequate air barrier. You can tape the plywood seams if you are worried about air leakage. MemBrain or housewrap make no sense here. If you are re-installing pine board flooring, rosin paper may make sense to reduce the chance of squeaks.
Giovanni,
Q. "Do I want to prevent air from crawl entering living space from below with an impermeable material? Or is better to have it breathable? ( no radon issues last time i checked)."
A. You want an air barrier. There is no particular vapor drive to worry about.
Thank you for all your advice above Martin, the clarifications are much appreciated.