Warning this was my first hardwood floor install so it’s possible I made multiple mistakes. That said, I’ve done my best to search for answers but can’t quite find anything conclusive.

About a year ago I installed unfinished 8” white oak hardwoods in the living room of my house. As a part of that install I replaced the crappy mdf subfloor with plywood. Flooring was drilled and screwed in place with trim head screws. I used a flooring jack to eliminate gaps in the floor. Finished the install and it looked great.

I’m doing some extensive renovation/remodel so after install the floor was never sanded. I am finally at a point where it’s time to sand and finish. On inspecting the floor I noticed an area that has some cupping/peaking less than 1/16th which led to me looking closer at the whole floor and finding similar peaking on about 30-40% of the floor. Very little and generally has to put a straight edge to see the variation with a few spots being visually obvious.

There are no active leaks and the floor isn’t near any plumbing etc. I do live in NC and summers are humid, and AC was set to minimum. So my first thought was moisture. So I got on Amazon and bought their a pin moisture reader that had decent reviews. The area with the worst cupping gave a reading of 7-9% with the most cupped area reading closer to the 9 range.

I know you the most obvious answer is moisture but I have one other doubt I’d like to have some experts confirm or deny. I was pretty aggressive with the flooring jack when removing gaps between the boards. I read everywhere that installs shouldn’t have gaps. Is a possible source of the cupping/peaking an overly tight install? Should I unscrew the floor and allow some relief between the boards?

Or is moisture the answer? Ambient humidity high due to the summer? Or potentially high humidity in the plywood subfloor?

Thanks for the help

8" wide boards are tough to install. You probably got them too tight when fastening them down. Minor cupping is not unusual and more prevalent with plain-sawn flooring. Once the flooring is sanded you ought to be careful to keep the humidity about the same as during sanding. The plywood sub-floor has a low permeability rating so it is very stable. AC can be a great help during humid Summer months. Check your weatherstripping around outside doors.

Thanks for the response Pete.
Once we get back into the house the temp will stay more constant and I’ll monitor humidity and use a dehumidifier if necessary during the summer months.