Thursday (Sept 2)
I installed the solid floor blocking today.
Solid blocking isn’t really necessary since the joists are plenty strong (I went with 16oc joist spacing instead of my originally planned 24oc, since I decided to use 1" spruce boards instead of 3/4" Douglas Fir ply), and the floor boards themselves would have limited the lateral deflection of the joists.
However, because most of the walls of the screen house are open, and so don’t provide any bracing against lateral forces, finding other ways of protecting the structure from wracking is an ongoing concern. In this case, my (admittedly ad hoc) theory is that by adding tightly fitted, mid-span floor blocking, which has made it virtually impossible for the joists to deflect laterally with respect to each other, the whole floor will now function more like a moment frame (i.e., like a very wide box beam) and so provide some increased stability to the rest of the structure.
I also started installing the floor boards - a very exciting moment, the screen house will finally start looking like a usable structure!
I’ve actually been preparing the floor boards since last week, and the details of how I went about this might be useful to others who are contemplating such a project. Although the boards were technically kiln dried, they’d been rained on before I got them so the first thing I did was let them bake in the sun for four days to dry up (I could tell how dry they were by how much they’d twisted up - gotta love 2nd growth flat sawn spruce lol). Once dry, each board was soaked in a trough of clear wood preservative for 5 minutes. After this treatment they were baked in the sun for another 4 days.
Since I’m using cheap 1x6 T&G spruce boards, a good deal of surface prep was also required to deal with knot holes. Once the preservative was thoroughly dry I glued all the loose knots in place (using an exterior wood glue). In retrospect I obviously should have done this
prior to treating the boards with preservative, since being impregnated with paraffin wax is unlikely to improve glue-adhesion. So, as an added safeguard, I nailed a scrap of wood across the back of each loose knot so they won’t fall out even if the glue fails. There were also a couple of open knot holes which I filled with PC Woody epoxy (again, nailing on a backer strip).
Since the boards were notched to fit around the posts/balusters/studs, all these fresh cuts were soaked in more wood preservative before the boards were nailed down. I also put a bead of silicone caulk down each groove before driving the tongue home, so that water can’t get into this joint and rot the tongue out.
Due to their warped personalities, many of the boards had to be forced into place using temp braces, levers and/or feet, and then held down, kicking and screaming, until secured. As a result I’m quite proud of how tight the joints turned out.
Another picture showing the superfluous roofing felt I added to the blocking and joists: