Hello fellow woodworkers. I have a situation I could use a second opinion on. I have a new construction home that we made T&G 1/8 nickle gap white ash ceiling material for. Its a mixture of flat sawn and quarter sawn material, all select and better, very few little knots. dried to 7% MC. The longest run width wise is 20'. We installed in January 23, also we are building in central WI. Everything was stable until April 23 when the weather changed (85 plus degrees) and we got 2 spots where the ceiling material buckled. This was due to my lack of research initially, and we only left 1/4" expansion joint on the end walls. The wood expanded tight to the walls and had no where to go. We have since remedied the issue and straightened the ceiling back out. We left a 3/4" gap on the end walls and made new trim to cover. Recently the temp has risen back to 85 degrees plus and we are seeing more boards starting to buckle. The 3/4" gap on the end walls hasn't changed. But in the process of "fixing" the problem initially, we used some finish head screws randomly through the face of some boards to draw the ceiling back tight. I'm guessing those screws aren't allowing the expansion that is needed and is causing my problem now.
I have dehumidifiers and A/C running to maintain climate. I tested the MC of the floor and ceiling recently and it was still between 6-10% depending on the grain and type of cut on the board.
Any insight to hardwood tongue and groove ceiling expansion would be very much appreciated.
The interesting part of the story is that I also made flooring with the very same material in the same house and I hasn't moved at all. all the margins arounf the floor perimeter have been stable.