Next Spring I will be replacing the rotting main beam, joists and floor of my 50 year old seasonal cottage. It has a perimeter block foundation on granite, with a shallow crawl space. I can improve the crawl space ventilation but will never entirely eliminate occasional rainwater intrusion into this area, with resulting periods of high humidity. The depth of the crawl space precludes working from below, so all work will be performed by cutting out the existing floor and structure, supporting interior walls, and building a new floor structure from above.
My plan is to use preservative-treated two by tens for beam construction and joists, with a three quarter inch preservative-treated plywood subfloor. I will use ACQ-rated deck screws throughout.
Any comments/advice on what I have described so far will be appreciated, but my main concern at present is this next step: I am contemplating placing a vapour barrier over the subfloor and then installing an underlay of three quarter inch regular (untreated) plywood or OSB prior to installing some type of flooring.
I am a bit uneasy about the vapour barrier but without it I know from previous experience that there will be times that a considerable amount of moisture will migrate up through the floor. (This would really limit the type of flooring I could use.) So essentially what I am trying to do is confine the occasional high humidity to the crawl space and the preservative-treated wood used below the vapour barrier.
Can anyone comment on this?