Insulating floor above vented crawlspace with cellulose
I am building a Passive House outside of Seattle in climate zone 4C. The building site has a high water table with water only 24 inches below grade in the winter after a good rain. I’d like to have at least R-50 for my floor above a vented crawlspace. The sub-floor will be the air barrier. The HRV, all duct work and the water heater will be above the floor in the conditioned space. I would like to use dense packed cellulose between the 18 inch deep TJI. I have concerns regarding the high water table. I plan on covering the dirt floor with 10 mil poly, taping the seams and running the poly up the sides of the foundation walls. Should I be concerned about such a high water table? Is there anything else I can do to keep the crawlspace dry?
Is netting going to be strong enough to support 18 in of cellulose for 100 years? Should I support the netting with furring strips or cover it with OSB? How do I ensure that the cellulose installer is filling the entire cavity when gravity is pulling the cellulose down away from the sub floor and I can’t see above the cellulose?
Which are more economical for an 18 in deep floor, TJI or floor trusses?
Any thoughts or comments would be appreciated.
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