[gslenk]

Background:
I have 2x8 joists 16" OC spanning ~12ft, sistered (glue and screw) with 2x6, some full length, some over 2/3 of the span. Subfloor is 1/2" ply from the 70's. Solid 3/4" hardwood flooring will be weaved in with surrounding areas and be the kitchen floor (replacing the removed laminate floor).

First: (hardwood or advantech under the cabinets?)
I was going to tile, but changed my mind to hardwood, so I have several sheets of 3/4" advantech. I was also going to run hardwood completely under the cabs, but it seems that advantech under would be a stronger and safer installation, and matches the finished floor height. If it really is better to run the hardwood, that is still on the table...

Second (best/sturdy way to level floor?): I will be using IKEA cabinets, and a stone countertop. I want this as sturdy as reasonably possible. The red lines in the diagram represent the joists. I have one just in from the wall, another 10" in, and another at 26" which will miss the cabinet base. The attached diagram shows my floor at the lowest point (zero) and the heights above that lowest point. Spaced every 24 inches apart.

My plan was to rip a bunch of strips of advantech say 4". Then build the ladder (simplified diagram included), scribe it to the floor with construction adhesive, screw it to the back wall. To make scribing easier, I was thinking of scalloping the ladder on parts that wouldn't land over joists, say green cuts for the short (left wall) and red cuts for the long wall. Something about this idea feels off to me, so any tricks for making this easy and still strong? I don't necessarily like the idea of point loads on shims given my 1/2" subfloor, but if it doesn't matter (considering whether it would be on hardwood perpendicular to joists, or advantech if that is ran under the cabinets), it would make life easier.

In general, the right wall's floor is higher at the wall than the front of the cabinets, and the left wall's floor is lower at the wall, if that helps...

Also, is advantech a bad idea instead of normal plywood? It seems pretty sturdy to me, and would help put it to good use since I otherwise may have no purpose for it.

 

[XSleeper]

Putting hardwood over a 1/2 subfloor is a bad idea right there, if I understand you correctly. The nails need more to hold onto than just 1/2" plywood. Can you at least lay down another 1/2" or do you have to meet up with preexisting floor?

Shimming the toekick up with 3/4 plywood so as not waste hardwood flooring makes sense.

Your toe kick bases or boxes (what you call a ladder) sound fine. It's quite typical to shim the toe kick to an out of level floor. Having the 3/4 plywood under the toe kick will stiffen that part of the floor considerably.

 

[Old Thomas]

Hardwood over thin sub flooring is ok if you nail to the joists. Houses built 100 years ago (mine included) had no subfloor, hardwood was installed directly on the joists. In the cellar the bottom of the hardwood shows. No deflection and still going strong after 100+ years.

 

[gslenk]

Yes, I need to match and weave hardwood into the surrounding areas, so no subfloor modifications beyond stiffening joists (which I only really did when I thought I'd do tile...)

I do think the hardwood (perpendicular to joists) over existing 1/2" is gonna be fine. It's everywhere else on that floor, and original construction just nailed it wherever. It doesn't seem like they aimed for joists.

For some reason, I was initially under the impression that plywood instead of hardwood under cabinets was sub-optimal or a cheap way out. Seems like it is actually pretty common, and for my purpose, probably a better idea. Advantech would be more sturdy/stable/uniform than hardwood. Also advantech is pretty water resistant.

If I really have to, I could add blocking to the joists under the cabinets.

 

[gslenk]

Anyone ever use this method to shim the toe kick base?

The plan is to make the base all 4" tall (instead of extra height to be scribed off). Then cut many extra 4" width pieces. Then assemble/level/shim the base. Then attach the extra 4" width pieces in the interior of the frame to secure/stabilize this to the floor. These are green blocks in the figure. Make them as long (horizontally as possible), use more and shorter ones for the extremely contoured areas.

It seems like a good trade off improving strength/rigidity compared to shims alone, and the hassle of scribing the whole frame to the floor. I do lose a tiny bit of floor contact area.

I know its not very efficient on use of plywood, (I have plenty of advantech still...) but does it seem like a good idea?