Guest User
4/30/2015
I have an older commercial building. The building has metal roofing installed directly over 1x's running perpendicular to the roof joists. There is no barrier beneath the metal at all. You can look right up and see it. There is a small, lofted area on the second floor I need to use as a living space for a time and it will have a metal ceiling installed inside. This area was never heated before. There's no venting of the roof at all. What would be the most effective way to mitigate condensation concerns? I notice other commercial buildings here with un-vented metal roofs appear to have an inch or so of foam sprayed in the ceiling area, and I see no condensation there? Is that overdoing it, and would standard fiberglass & kraft insulation be fine? Thanks.
Todd Miller
Classic Products, Inc.
4/30/2015
You are doing the right thing by thinking about this. A complete, solid vapor barrier with insulation above that and make sure you have no air leaks from the living space into the attic would probably work. Another option would be to the closed cell urethane foam insulation to the back of the roofing.
Guest User
4/30/2015
Thanks for your reply. There is an area with some R19 batting in it now. (It fits nicely, as the rough cut joists are approximately 2x6) Would finishing that out, and following it up with some rigid foam with a foil vapor barrier on it be sufficient? (Maybe even tape the seams with foil tape?) There's a place up the road with 1" rigid foam that has s cu a barrier already installed, and the price is reasonable. Would this prevent condensation from forming in my living space?
Guest User
4/30/2015
Thanks for your reply. There is an area with some R19 batting in it now. (It fits nicely, as the rough cut joists are approximately 2x6) Would finishing that out, and following it up with some rigid foam with a foil vapor barrier on it be sufficient? (Maybe even tape the seams with foil tape?) There's a place up the road with 1" rigid foam that has s cu a barrier already installed, and the price is reasonable. Would this prevent condensation from forming in my living space?
Todd Miller
Classic Products, Inc.
4/30/2015
I feel the vapor barrier needs to be between your ceiling and the insulation. I would suggest a complete layer of polyethylene but if you do something else and you can tape the seams, that should be okay. The point is to make sure the no warm moist air from the living quarters reaches the roof and I'd prefer to keep it out of insulation as well because moisture reduces the R Value of insulation. If the warm moist air reaches the back side of the roof, it will condense and you could find yourself in a rain forest.
Info @windowsonwashington.net
An informed customer is our best customer.
4/30/2015
Vapor barrier does need to be complete and sealed. Some rigid foam across the interior would work but it would need to be covered with an approved thermal barrier if you are using the space. Foam isn't safe if it is left uncovered and without a proper ignition or thermal barrier.
Lee Hedegaard
4/30/2015
I built a small cabin in south Mississippi last year. It has a tin roof, felt, plywood deck, 2x6joist and fiberglass insulation. Vaulted cypress ceiling. Moisture is dripping out of the center ridge. I am keeping AC and fans on to help control amount of moisture. Help what do I need to do? I do have eave vents. We only stay there three or four nights a month.2
Todd Miller
Classic Products, Inc.
5/1/2015
Lee, I take it this is happening even when it hasn't rained, so you're confident it is condensation? I take it there is no ventilation between the joists? Is that area full of insulation?
Guest User
5/1/2015
The area is full of insulation. Tha vapor barrier is turned to the cypress. It heats up in the afternoon and sweats at the ridge. Water drips from the ridge beam unless I keep AC and fans running. I have a loft bedroom with a small window unit.
Todd Miller
Classic Products, Inc.
5/1/2015
Shy of changing the roof system to include ventilation, I think that all you can do is what you're doing -- take steps to reduce moisture levels inside the structure.

If you would like to reply to this thread, please log in. If you do not have an Ask the Experts forum user account, create one here.

Find a Contractor

Get Started Today

Take the first step to increasing the value of your home with a great looking, durable, fire resistant and energy efficient metal roof. Browse our list of qualified MRA Member Roofing Contractors in your area for a free consultation and estimate.