Here in CA most natural stones get installed over plywood to allow for a built up edge treatment. The 20 year old kitchen we ripped out had plywood under the granite and the kitchen we installed last year has plywood under the quartzite.

I also think most of the slabs sold in CA are 2 cm, with very few 3 cm ones offered. Other geographic areas seem to offer more of the 3 cm slabs.

Just installed granite on new Ikea cabinets 6 months ago, no plywood. It'll be fine.

I’ve installed a dozen ikea kitchens, my personal homes, my three last offices including two at my current office, clients houses. NEVER installed plywood on top of the cabinets. NOT ONCE.

Find out the weight of your granite per square inch and have ikea verify that they will hold up. Twice, I know if homes with solid custom oak built cabinets, which had granite counters installed after the cabinets were 10 years old, replacing formica. Twice, within 48 hours, ....these are solid oak cabinets with drawers and doors configuration...no particle board....the drawers would not open atop and the stove top(not range) fell low in the front. Quickly called were carpenters who installed metal brace posts on the vertical lines of the cabinet FRAMES, BETWEEN the doors and drawers to add support. Figure twice, do it once ...but Good Luck~

No need for plywood. The IKEA boxes will hold your standard thickness counters. Ours are 3cm on top of IKEA cabs. No problem.

"Twice, I know if homes with solid custom oak built cabinets, which had granite counters installed after the cabinets were 10 years old, replacing formica. Twice, within 48 hours, ....these are solid oak cabinets with drawers and doors configuration...no particle board....the drawers would not open atop and the stove top(not range) fell low in the front."

Correlation is not causation. Rising ice cream sales and an increase in drownings in summertime are positively correlated. Eating ice cream does not cause drowning. Same thing here. I'm not doubting that there may have been a cabinet failure, however, it was not caused by the weight of a granite countertop. On properly built and installed cabinets it just doesn't happen.

I am reassured by these responses. Thank you.

So... soapstone is pretty heavy, and that’s what I’m going with over Ikea Akurum (bought them before they switched to Sektion) cabinets.. I’m sure my installer will know, but am I going to need plywood?

I have Quartz, Quartzite, Dolomite and Granite in my new build. All counter-tops were placed over Ikea cabinets with plywood underneath. Never questioned the fabricator. Just thought this was standard.

@lindacottonwood: I am hoping they do use plywood, but they won't know until templating, but the majority on this thread don't have it. We're just going to add a half to the originally planned distance between the countertop and the rail for the upper cabinets, so we'll end up with either 18 1/2 inches (no plywood) or 17 3/4" from countertop to bottom of cabs (assuming they'd use 3/4" plywood).

what it comes down to is how thick is your granite? 2 mm typically needs plywood and 3 cm does not............................

This has nothing to do with the weight. It's about the edge profile. If it's just 3/4" edge profile then there can't be plywood under it or you see the 3/4" edge of the plywood. If it's a built up edge 1-1/2" then there has to be plywood to raise it up level with the top of the cabinets because only the front edge is 1/2" in that case. Cabinet legs and hanging rail would be adjusted to each situation depending on finished height you want. IKEA fixa brackets can be added to even the top of cabinets to the metal rails which distributes the weight and adds more contact points. This is 3/4" quartz stone on Ike boxes.

We always install a plywood sub-counter (as we always do drop-edge counters), but the main advantage in my view is it allows the client's kitchen to be "in service" for the entire duration of the counter fabrication period, rather than having to wait for the counter to be fabricated and installed (which typically takes two weeks or longer). With plywood, you can install and connect the sink and faucet right away.

Millworkman You are right in my case. I checked and the only counter-top that doesn't have plywood is the 3cm one.