Hello, does one need a layer of plywood on kitchen cabinets before putting a wood countertop as it is done for stone c/tops? Or, in other words, is plywood underneath stone c/top used for strength or for other purposes? Thanks, h.

It's for strength only, but it will depend of course on what they are made of, how they are made, and how thick they are.
Think in terms of someone standing on the counter in the middle of a 3' wide cabinet. That's how strong you want it to be.
I have maple butcher block countertops with walnut edges. Mine are 1 1/4" but 1" would be fine, or even 7/8. Mine aren't tied down. If you do, allow for a little expansion/contraction. Or if you use 3/4" wood on top of plywood, be aware that the top wood will expand differently from the plywood. For large slabs, butcher block has an advantage because the glue is actually stronger than the wood, plus the grain is on edge for better tensile strength.

One reason is it gives you a level smooth top. If you just put it on cabinets, it will rock around due to uneven height. That's why you see wood shims epoxied under granite slabs.

Appreciate your replies! Does this mean that even for wood countertops a layer of plywood underneath is necessary too, for strength and even surface?

I considered a granite countertop at first, but not sure now. What concerns me is a slight but noticeable flexing of the floor in this small kitchen. As the result, even when one person walks, the extremely heavy fridge and the oven range, both sitting against wall, are rocking to the point that, for example, the pots on the range are rattling and shaking. My worry was that because of this flexing, the granite backsplash, glued to a stable wall, would be detached from the granite countertop itself, which can rattle with the cabinets/floor.

I guess the 10', 2"x6", 16" oc joists are to blame. Someone at a stone shop suggested that with a granite countertop installed, the floor won't be able to move much under such a heavy load. I suspect this might not be the case.

Should I go through the kitchen floor retrofitting project first (which I can hardly do myself) if I want to install granite, or wood c/top is the only option here? Thanks again!

If you want granite, go with granite.
Your 2 x 6 joists aren't going to all come crashing down (unless they aren't attached at the ends). On the other hand, the granite isn't going to stop the floor from moving.
If you want to sister some of the joists and add a post or two, fine. It's not even a big job.
With any top, you shim as needed above each cabinet. Few floors are ever totally level. And almost all dip down from the outer walls over the years.

With either granite or a good solid wood top, you don't put plywood underneath (unless maybe under 3/4" thick wood top).

That floor joist is undersized according to load charts. You can sister 2X4 or 6 and make it a lot stronger. The reason it may be quitter with granite is that the floor is flexed (sagged) and won't go anymore but not a good idea. Average granite weight of 3cm. Is about 33# per lineal foot @ 24" deep.

That floor joist is undersized according to load charts. You can sister 2X4 or 6 and make it a lot stronger. The reason it may be quitter with granite is that the floor is flexed (sagged) and won't go anymore but not a good idea. Average granite weight of 3cm. Is about 33# per lineal foot @ 24" deep.

Yes, the floor sags too much even for ceramic tiles. I hoped that for a stone countertop this wouldn't be a problem, because the stone would sit atop cabinets, which surface was not going to bend. The cabinets could only tilt a bit toward the center of the kitchen, when a person walks around. Although this is no danger to the c/top itself, the seam where it is connected to the backsplash may crack. But the same thing applies to a wood c/top too: waterproof seal to the wall may fail as well.

Backsplashes don't have to be glued or cemented to counters.
Tile is a good alternative to granite for backsplashes, especially in a house with uneven walls.

As Brian stated your floor beams are under sized. Sister a 2x6 to each beam and bolt every 2 feet. This will give you all the support you need.

Chuck

As Brian stated your floor beams are under sized. Sister a 2x6 to each beam and bolt every 2 feet. This will give you all the support you need.

Chuck

Thank you for your feedback. I guess I will try sistering. There is almost no space in the "crawl space" for doing anything though -- one can only squeeze himself through between joists and the ground. Careful planning and maybe some digging should help.

Won't be able to sister along the entire length though because there is no space to move 8' 2x6s in that constricted space.Where should shorter, 6-7', sistering beams go, in the middle or underneath where heavy appliances are?

Sistering isn't much help unless the load transfers to the ends and then to sills and beams and the foundation walls.
You can cut 8' lengths in half with a kerf, and bolt well along each side of the kerf.
Or add a support post, but that requires a footing, which you are not in a position to put in.
You might want to wedge a 4 x 4 post under each kerf anyway, assuming your crawl space has a concrete floor, not dirt.

Or add a support post, but that requires a footing, which you are not in a position to put in.
You might want to wedge a 4 x 4 post under each kerf anyway, assuming your crawl space has a concrete floor, not dirt.

Nope, it's a dirt. Why is adding a support post not hard, but building a footing is?