Is it normal for 12-inch wide cherry planks to cup if they aren't glued down in an attic?

Twelve-inch cherry planks are beautiful but they are absolutely going to move, especially in an attic where the temperature swings are that extreme. Since you already have the Advantech down, you should look into a **full spread glue-assist** method rather than just blind nailing. Using a high-quality moisture-cure urethane adhesive along with the nails will give you the best shot at keeping those wide boards from cupping when the summer heat hits that roofline.

Rubio Monocoat is a solid choice for the finish beacuse it’s easy to spot-repair, but it won't do much to slow down moisture exchange compared to a film-forming finish. If the underside of the boards isn't sealed, you're creating a recipe for a potato chip floor. I’d recomend applying a coat of wax or a sealer to the bottom of the planks before installation to help balance the moisture absorption. It won't stop the wood from breathing, but it'll even out the rate so the boards don't stress as much. As for that support column and the built-ins, do not build them on top of the finished cherry. You need to maintain a consistent **expansion gap** around the entire perimeter of the room. If you pin those wide boards down with a heavy column or fixed shelving, the wood will eventually split or buckle because it has nowhere to go when it expands. Install the column and the base frames for your shelving directly to the subfloor first.

You can then run the flooring up to the built-ins, leaving about a half-inch gap that you can cover with a base shoe or custom molding. For the pipe column, you can scribe the boards around it with a small gap and use a two-piece escutcheon plate or a wooden collar to hide the space. It adds a bit more labor on the front end, but it'll save you from watching your two years of hard work pull itself apart during the first humid stretch from the inside out.

Have you ruled out the deflection on those sistered 2x8s? You mentioned making the floor stiff, but 12-inch cherry is alot of mass to add. If there's even a tiny bit of bounce in those joists over the span, those wide planks are going to creak or gap regardless of how much glue you use.

Also, how is the ventilation behind those knee walls? If the attic is getting that hot during the day, you might be creating a humidity trap right under the floorboards. I'd double-check the actual moisture content of your cherry versus the room's current humidity levels before you commit. Attics are notoriously brutal on wide-plank hardwoods.

Twelve inches? Man, you're asking for a headache. Back in my day, we'd never dream of laying anything wider than four inches in an attic without back-planing some relief grooves. If those boards are solid cherry, they’re gonna want to curl like a dry leaf. You ought to flip those planks over and run a couple of 1/8-inch saw kerfs down the length on the underside about three inches apart. It breaks the tension and stops the cupping before it starts. Also, don't just trust that Advantech. Throw down some 15lb felt paper between the subfloor and the cherry. It's an old trick, but it acts as a vapor retarder and stops the squeaks when the wood starts its seasonal dance.

I'm with the others on the glue-assist, but don't forget to check the moisture content of your Advantech subfloor against those cherry planks right before you start. Since it's an attic, that subfloor can hold alot of humidity that the cherry didn't pick up in the shop. If they aren't within 2% of each other, the boards will pull moisture from the bottom and cup no matter how much urethane you spread. Give it a few extra weeks to acclimate right in that room with the HVAC running before you even think about the first nail.

Quick update—checking the moisture levels was a lifesaver. Turns out the Advantech was way wetter than the cherry, so I’m letting everything acclimate longer. I’m still stressed about that support column, though. If I go with the glue-assist you guys suggested, is it safe to bolt the column through the planks, or will that pin them down too much and cause cracking when the heat hits?