I think I'm looking at original floorboards, rotting underlayment on top of those, a delightful assortment of other boards on top of that, then Pergo flooring.

I'm unsure of the best way to proceed. My gut says to pull up the top layer of boards to remove that underlayment, but then I worry that that turns into ripping up the whole floor.

(Left Side cabinet)

(Right side wall)

Pull up everything rotting and replace. Not fun but might as well do it right.

I'm not an expert, but I think this is fairly typical. Unless any of that wood is actively rotting (which would indicate a larger moisture issue that needs to be addressed), using old ugly boards to stabilize and level cabinets and countertops would seem to me like the appropriate approach during installation.

It looks like this was a remodel? If so, they definitely wouldn't have bothered to make anything look pretty if it's going to be hidden behind cabinets.

In other words - it's probably not as bad as it looks. If it ain't broke, don't fix it.

The photo does not show any signs of obvious rot. Maybe add a moisture barrier underlayment before completing the floating flooring, the install your new cabinets.

If there is moisture, identifying it's source is critical prior to applying a moisture barrier!

But yes, a barrier may be appropriate here.

This is some minor water staining in an unseen area that's been around for a long time. Ain't nobody used that color green in 50 years.

_maybe _ there is a bit of.rotnon the bottom right wall but can't tell from this.

Are you just planning on putting a dishwasher back in the hole ? What's your goal? Because this is fine and honestly I wouldn't do any of what you are thinking unless part of a much bigger project

There is nothing obviously rotted in this. Some stains. But that's it

Yep. Basically I was planning to ensure a level surface with more of that flooring in top so I can slide the dishwasher in. After running the new outlet to the breaker.

Run your hand under the boards on the right and push into the surface to check for any rot. It doesn't look like rot but good to check since you are in here.

Then for the leveling.. I'd get some furing strips and some shims and a panel of plywood get get a level set. Your going to need to redo the trim in the front regardless and you want the washer to fit well so you'll need at least some furing strips and shims regardless.

Anything like a washer or a dishwasher that has pumps and shit that spins and a basin of water, you really want them level. But depending on the size of the washer and the hole, you might only be able to use shims.

How tight is the washer to the hole vertically?

My house looks like this. I laid flooring not new cabinets. The builders laid flooring under the cabinets. I used some off cuts to fill the gap to let the dishwasher be level.

Mine basically looks like that behind the dishwasher as well ,70s house ! I love finding stuff like that.

Not the rot but the old paint and flooring

Yeah, the hardwood flooring is kind of neat, but it would be a nightmare to try to maintain.