Why is there condensation behind my vapor barrier?
Hello I'm turning the loft over my work shop into an apartment and insulating the walls and roof with Rockwool insulation with a plastic vapor barrier and then drywall today while putting up drywall noticed that the vapor barrier is covered with condensation how do I stop the condensation. Have put a halt to this project until I can solve this problem
Condensation behind vapor barriers with newly built walls is not good, but it is also not uncommon. For moisture to form on your vapor barrier there needs to be a source. That can be a few things, so I’ll throw a bunch of thoughts and questions at you and we can go from there. It could be from water coming off the roof, any chance there is a leak? Was it new lumber you framed the walls with and was it wet? Any chance the Rockwool batts got wet? What is the inside-to-out wall assembly, can the wall dry to the outside? And where are you located?
Here is our Building Science Made Easy video that explains moisture movement through walls, that will help you understand where the problems can be and help you troubleshoot it. If it were me - I would cut some pretty good slits in the poly barrier and let it dry out first, then tape it up and see if more moisture returns. All lumber freshly purchased will have high moisture content so there is always some moisture that will need to escape, which can usually happen through exterior walls. If you get the same result then you may have a more consistent source of moisture. The first step is definitely determining where the moisture came from, then give us some more info and we can help you sort it out.