Safe upper range wintertime humidity level – GreenBuildingAdvisor

Climate zone 6. 

I’m having skim coat plaster applied on my second floor walls and it’s driving the humidity level up pretty high. I’m wondering what’s the upper limit to try to stay below to avoid any issues with excess moisture in the house. 

Second floor is 1160 sq. ft.

House temp is kept at 58 degrees with 51% humidity, heating with a woodstove. 

Walls from outside in: 1” wood siding, 1” airspace, 2 1/2” xps sheathing, 2×6 studs/r23 rockwool, membrain, 5/8” blue board. Ceiling insulation is sprayfoamed. 

The plasterers skimmed over seams and completed one 12’ x 90” wall the other day and humidity hit 76% @ 58 degrees.

Thanks, Daniel