Hello to all,
We have a small (16×24) art studio/shed with rafters that are insulated with rockwool. We installed foam spacers between the sheathing and the rockwooll for airflow, and plastic sheeting on the inside as a vapor barrier.
Recently we noticed a drip from inside the the rockwool somewhere dripping down to the plastic sheeting. The drip is reddish colored. At first we thought rodents but there is no smell. Is there something in rockwool that causes trapped moisture to turn red?
Thanks in advance for any help.
Bob
Replies
There should not be any trapped moisture in the rockwool. The top surface should be open to the airflow from soffit to ridge, so any moisture will evaporate. The bottom should be is sealed by the vapor barrier.
Are the soffit and ridge vents open and air moving through all rafter bays?
You may have a leaking roof. Red color is probably rusting nails.
Moisture problems are always compounded in a cathedral ceiling. Check to see if you have an active leak first. If no leak, you could be potentially trapping moisture between the foam and the plastic. In my climate (zone 5) we’ve found plastic sheeting used as a vapor barrier to create more problems than it solves. It performs so badly in my region that drywall contractors will not warranty any drywall on walls surfaces where plastic sheeting is used. Over the past couple years smart fabrics/plastics have been used that perform much better. Plastic sheeting does not allow wall and roof assemblies to dry out. A lot of this is climate specific, but if you are in a climate similar to mine I would suggest you take all the plastic down. If you have two products that are not breathable like the foam above and the plastic below you basically create a moisture sandwich.
You didn't say if the ceiling was drywalled. Is it? Also, what's your climate?
Thank you to all that replied! I am always amazed that professionals who work long days will take the time to answer questions from amateurs. We live in southern Maine (Scarborough, IECC zone 6).The shed was just built by professionals last year so I am hoping it is not a leak. There is no drywall there. I did install a mini-split so I am thinking it is condensation. Plastic is coming down, and we'll check later. In he meantime, we'll research breathable barriers for that application.
Once again, sincere thanks to all that took the time to respond.
Bob