Condensation Problems

Roof has been in place two years. When frost forms on roof and melts, I get leaks at all (seven) skylights. Roffer did my barn but I find out has never done roof on new construction. Roof is 12/12 pitch, 2x12 with 1/2" OSB, 2x4 horizontal grid over OSB, metal over that. Metal is screwed to 2x4's with what look like sheet metal screws (exposed) with rubber washers. Insulation between rafters inside. Underside of 2x12 rafters are open to living area, I cannot drywall of finish because or exteme moisture from condensation. HELP!!!! Pllease!!!! Carl D.

Leaks occure at the skylights because the water tracks down the plywood until it hits the header for the skylight. Styrofoam shields create an air spaces between the insulation and the plywood. They are in each space between the rafters running from soffit to peak. The soffit and peak are vented. I will call the roofer to get the manufacturer, he bought materials at Menards. My StarBand internet connection has taken a hit and I will post pictures after it is restored, I am using a temp dial-up and only getting 16K throughput, how do I post pictures? Thank You for trying to help!!!!!!

Also, Carl, I am curious, is there any underlayment on top of the plywood? There also may be a problem with the way the ridge is finished. In most cases, manufacturers of roofing similar to what you have will wnat it installed direct on top of the decking (and underlayment) rather than on top of strapping boards.

Ihave read your posts about condensation ;however I think you folks have danced around the complaint. I am currently working on plans for a mountain home and all of your competition that I have talked to advise me not to use metal roofing as the problem perpetuates to dry rot and serious mold conditions ,be specific what is your rebutal to these statements, FRANK

Craig, I do appreciate your questions. Thank you. First of all, with a roof that is just 2.5:12 pitch, you must find a roof system intended for that pitch. Next, you must make sure that the roof system you find is approved by its manufacturer for residential application. Following the above, I have a hunch you will find a product which must be installed over solid decking and underlayment rather than over purlins, especially for a residential job. In your case, you will likely end up with drywall, vapor (air) barrier, insulation meeting the requirements of your cold climate, vented attic (soffit and ridge vents), solid decking, quality underlayment, metal roof system. By the way, increasing your roof pitch to 3:12 or 4:12 will open you up to a much wider variety of product choices.

Hi Carl, Sometimes, it is so hard to really explain things in these postings. There is certainly every chance that there is something going on with your general construction which is a contributing factor here. The fact that some leaks were fixed by working on the ridge, though, really makes me wonder if there are not additional ridge problems. I would encourage you, if you wish, to call me at my office so we can talk this through a bit. You can also email photos to me. My office number is 1-800-543-8938 ext 201 and my email is tmiller@classicroof.com Following is a good summary of a roof system that will work. Yes, there are other possibilities but this listing of roof assembly components, from the living space to the outside will work: 1. Drywall or other ceiling finish; 2. Vapor (air) barrier; 3. Insulation; 4. Properly vented attic space; 5. Solid decking; 6. Quality underlayment; 7. Metal roof covering designed for the pitch of the roof.

Building codes call for a 1" vented airspace beneath all roof decks. Ignoring this is asking for trouble, regardless of the roofing material. Additionally, I would suggest an air barrier behind the drywall. There is no "quick cheap" fix to the mistakes made on this roof. I am sorry.

I think i got a bit zealous with sending the first message. I want to say that i think this a wonderful site and i hope to resolve my problems with your help. some of the particularities i left out are the fact that most of the leaks or dripping points are from the cathedral ceiling proximate to the wood stove. Around the skylights and in the adjacent room where there is an area that warm air pools. I've stopped some momentum with fans toward the particular area.

Hi There Just recently found this forum - it's exactly what i was looking for. I am in the process of winterizing an existing porch on the front of my house which has a metal roof. I have installed windows and enclosed both open walls. I have noticed on the last few mornings after a cold night that significant condensation is forming on the inside of the roof. How can I eliminate this? Do I insulate from the inside? outside? I have not insulated the walls or put in the floor yet, but have put in foam insulation to close the openings at the ends of the metal roof, which I know believe is the wrong thing to do. Thank You Art P.S. I am just north of Toronto, Ontario, Canada

As an Architect, I worked on two single family home projects years ago here in Minnesota. We used two different contractors and two different roofers, all very highly respected in this area. Both houses had flat roofs as the Architect I was working for at the time, Ralph Rapson, always wanted flat roofs. One roof was filled with 12" of fiber glass insulation in the 2x12 ceiling joist spaces, then stripped in both directions with wood nailers, then covered with a plywood deck and a BUR. The finished ceiling was sheet rock over a standard 6 mil poly vapor barrier. Metal wind-powered vents were installed in the roof deck to allow the entire roof area to be vented to the exterior. The second house had the same 2x12" ceiling joists stuffed full of fiberglass insulation, with the 3/4" t&g plywood decking installed directly on top of the joists so there was absolutely no air space above the insulation. A BUR was installed as well. The interior of the exterior walls and ceiling was wrapped with two layers of 6 mil poly which was carefully taped everywhere. The second roof system was not vented, intentionally, in any way whatsoever. The first roofer said that, of course, a roof has to be vented, especially a flat one here in Minnesota. The second roofer said that with his roof system (and the extra 6 mil poly vapor barrier very carefully installed by professionals), the dew point would be in the plys of the exterior grade plywood roof decking (because there was no dead air space above the insulation and open to the outside ambient temperatures) and, because moisture could not penetrate that decking, there was never any condensation. Does anyone want to guess which roof failed, partially collapsed and had to be completed replaced? Of course, it was the first roof, the one that had been vented. There was so much condensation held in the insulation, and above the vapor barrier, that it rotted out the joists; first the sheet rock dropped and then the joists gave way. The solution was to remove the entire roof and framing, re-frame, and foam the entire roof cavity full with no venting anywhere. Since then I have been vary wary of vented roofs here in Minnesota where the outside air can get down to -30 and drive the dew point into the insulation if there is a vented air space open to the exterior. The logic of the second roofer seems to make lots of sense and his roof is fine after 30 years. I mention these examples as I contemplate installing a steel roof system (my first)on my unheated (except for a few days in the winter when we will use a wood burning firebox) cabin in Northern Minnesota. I have 3/4" 1"x12" roof boards/decking as the exposed ceilings at an 7/12 pitch over 2x4 rafters with a king-post truss design. I am planning on installing 30 lb felt, then 2x4's running with the rake, eave to ridge, spaced every 4' with 4x8 sheets of rigid foam in between. Then I was going to lay down another set of 2x4's running parallel to the eave, spaced 4' oc, with 4x8 sheets of rigid foam in between. Then I was going to nail down the exposed-fastener steel roofing, using my horizontal 2x4's as nailers for the roofing. Does that sound like a good plan? I don't know how often the steel needs to be nailed in each direction and have seen no directions on other web sites yet. Thanks for ideas and sugestions and comments.

I would consider a poly iso spray insulation for the bottom side of the roofing.

You probably have no interior air barrier like Todd noted and warm moist air is moving up through the assembly. Additionally you probably do not have enough insulation which further contributes to heat loss and condensation from ambient air. With no vented air space there is no place for the condensation to migrate out except into the assembly which indicates that a proper moisture barrier may not have been installed. Forcing the hot air down will help reduce the stack pressure however sooner or later you will need to address the deficiencies.

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