I recently purchased around 600 sq feet of 3 1/4 inch solid hickory from Bruce, which I'm installing over a crawl space. I put down a 6 mil vapor barrier in the crawl space.
I'm measuring the moisture level of my plywood subfloor as the wood has been acclimating about a week. Most readings are right around ~13% with the overall range being 10-13% with some spots measuring as high as 14%. This is during the humid August summer in Kentucky.
The wood still has some time to acclimate. Readings for it at the moment are around 9-10%.
I'm wondering whether I'm in a safe position to install solid hardwood here. I'll be installing this with a #15 felt underlayment. If it matters the bedrooms have 2 1/4" red oak installed (might be original to the house) and those floors are in great condition.