Did you put a moisture barrier between the wood and plaster? If not maybe moisture is seeping in and is trapped and warping the wood? Did you leave the boards on the room for at least a few days before installing so they could acclimate?

Did they back prime before installing?

Don't know about back priming...believe poplar was purchased pre-primed...and no moisture barrier...wood went onto studs...and house has all new blown in insulation.

Asked if the acclimatized....did not get a clear answer.....what can be done to fix this?

I am really sorry you have had these problems with your paneling! If it is any consolation, our GC would definitely not have known to let the wood acclimatize and it would also NEVER have occurred to him to install it with changing humidity in mind. I knew something like that could happen to wood shiplap, so when we decided to do a feature wall in our basement I specified Hardiplank 8" lap siding, hoping that the combination of the overlap and the material would preclude any seasonal movement. So far....fingers crossed.

Wood will expand and contract at least 1%-2% over the seasons. That means that over 100" of wall, you have 1" - 2" of movement. The narrower the boards are, the smaller the individual movement points become. One wide board (like if they were all edge-glued together) would have a 2" gap, 100 narrow boards would each have 1/50" gap.
This is the reason the raised-panel door was created, it is a way to manage the characteristics of wood, and control where and how the movement takes place, so as not to have the door ill-fitting 10 months of the year.
In your case, no thought was put into understanding or managing the material science.
Casey

Thanks all for your input...We love the builder and the work that's been done on the house...and the floors...I know he is working on fixing the trouble spots...

In addition to the wise words above about a lack of understanding about the material being worked with, the siding should never have been installed directly to the studs. You should have had a layer of drywall first, both to aid as a airstop and as fire prevention. The whole job should really be pulled off and redone properly.

I definitely concur with GreenDesigns. Unless by "blown in insulation" you mean spray foam (which would at least provide an air seal), the gaps in the shiplap are going to allow a LOT of airflow through -- we had the same issue with our family room ceiling, which was planked directly over the joists with only the fiberglass batt insulation between the joists to insulate that room from the attic above. For years, that room was freezing and we couldn't figure out why -- but finally we realized that cold air was coming down from the attic through the gaps in the ceiling boards. We had all the boards removed and drywalled up there, then reinstalled the boards. So much warmer and better!

And I do believe that a layer of drywall is required as part of the fire code in some areas -- I know we first tried to fix our ceiling problem by laying foam insulation boards between the joists from the attic so we wouldn't have to remove all the boards -- that worked to slow the air leakage but then we were told it was a fire hazard to have foam insulation that wasn't separated from the living area by a layer of drywall. And apparently when foam burns, it releases all kinds of toxic chemicals that can poison you before you can escape the fire. So even if you have spray foam in your wall cavities which would insulate you from air intrusion, you may still have a fire hazard without that layer of drywall.

May I ask Diana, was your situation ever resolved.....I am having the same problem....however my planks were primed on both sides, and installed on dry wall, I have dehumidifier and AC in basement ....but just started happening....was there a fix? Thanks

have

Our contractor says you have to take down the Sheetrock and put plywood up and then attach the boards to the plywood instead of the sheet rock and studs otherwise is will always buckle and move. He did this in our summer house and they don’t move at all.