*
First, thanks for a great message board. I’ve been reading for several weeks now and have learned a lot.
I’m renovating a house with 5/4×4 T&G heart pine flooring nailed directly to the joists on 24 inch centers. Most of the floor is in splendid shape, but there are several soft spots and a couple of cracked boards, and large folks (like me 🙂 can easily feel the floor give a little at every step. There is a crawl space under the house, but most of it ranges from 3-6 feet high so it won’t be too hard to access.
I need to strengthen the floor and of course I want to insulate and seal it at the same time. I’d like to get some feedback about the best way to apply bracing from underneath.
My current plan is to:
1. Keep the floor only one board thick, but add another joist in between each existing pair.
2. Fill the spaces between joists with unfaced insulation.
3. Face the bottom of the joists with plywood and seal the edges.
One other possibility I’ve considered is to fasten 3/4 plywood against the floor before adding the new joists. This would give full support to every square inch of the floor, but (it seems to me) it would be a lot more effort for not much more support than I would get from just adding the joists.
Finally, I can support the new joists at each end with joist hangers and/or use cross bracing to tie the new joists to the existing joists (The spans I need range from 11 to 14 feet). I’m thinking that I will need to use 2x10s if I’m not cross bracing, but 2×8 (or even 2×6?) would be enough if I added the bracing.
Any help or advice you guys can give on this topic would be very welcome.
Replies
*
Jim,
I think the most effective way to reduce the deflection would be to reduce the span of the joists. That would entail running another joist/support perpendicular to the existing joists. This would run underneath the existing ones, but it sounds like you have room to do it. You might even put two, effectivily turning it into 3 spans.
Rick M.
*You have two spans to be concerned about. The first is the span of the joists. As Rick suggests, the easiest and most effective way to remedy this is with a girder running perpendicular to the joists. This will cut the span in half and make the joists very rigid.The second span is the distance between the joists (24"). Do the floor boards themselves flex when you walk on them? You may have to have someone look up from underneath while you walk on the floor. If the floor boards are flexing significantly you will need to add framing to reduce the spacing to 12".
*I should mention that the existing joists are extremely stable and flat (except for one end of the house where there is a sill problem). The joists are 2.5x10 (fully dimensioned) and the stringers supporting the joists are 5x12. Still, I plan to add some additional bracing center-span when I tackle the foundation work I need to do.My big concern right now is the floor boards themselves. There is no subfloor, just the 5/4 decking nailed directly to the joists. This decking flexes when I walk on it and I want to stabilize it before I damage it. I guess my question is really whether I will get a better result by (just) adding framing or if I need to add some sort of pieced-out subfloor between the joists and then add framing.I want to make this house last another 120 years but I don't want to cut and piece out some lame attempt at a subfloor unless I really need to.
*like Rick say's, split the span of the joist's with a girder. then add your joist's in the centre of your joist bay's, forget the subfloor, but add a little glue to the top of the new joist's, for the 'belt's + braces' approach. then insulate to your hearts content. the plywood sealed is a good approach, as the structure will now just be a horizontal wall.good luck