I have a log cabin 24 x 28, the floor joists are rough cut 2x8 on 24 inch centers spanning 12 feet, there is 3/4 inch compressed wood and 1/2 inch plywood on top. If I put 1/4 inch plywood on top of this, it will give 1-1/2 inches of wood. I want to do ceramic tile but it seems the joists do not give enough support across the 12 foot span, there is some flex if you jump up and down. How do I best reinforce the structure? Could I nail 2x8 or 2x10 along the side of the existing joists, or nail pieces perpendicular from one joist to the adjacent one say 24 inches apart like a sort of blocking. Any suggestions short of running new beams under the middle of the span.
Answer:
The sister joists won't do you much good because its the span between joists that's giving you most of the bounce. I think even with the beam along the middle of the span, you're going to need half-inch plywood on top of what's there. Some you win, and others turn out like this.
