tiling over 1 X 8 subfloor planks...

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not directly though.

Hi, there's a lot of knowledgeable people here. I just wish the page didn't take so long to load!

Anyway, I've read and re-read that a total plywood thickness of 1 1/4 inch is recommended for tile setting. But my subfloor isn't plywood. I live in a 1947 house with a subfloor consisting of 1 X 8 planks laid diagonally across joists at 16 inch spans. Every other joist is doubled up; I don't know if that's common but that's how ours are. Our kitchen is no more than 9' 5" wide and 11' long.

Should I lay plywood down and then lay Hardiboard over that? I was thinking 1/2" plywood with 1/2" Hardiboard. Or should I skip the plywood and go straight the Hardiboard? Should I strengthen the joists and if so, how? I had my husband walk across the kitchen and, even without any underlayment (our subfloor is exposed because we had asbestos linoleum removed with its underlayment) there wasn't much of a bounce, except, that is, where 2 of our 1 X 8's are broken (from over-zealous asbestos abaters; we plan to fix that).
Please advise on our unique(?) situation. THanks much!!!