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Roofing/metal condensation and frosting

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QUESTION: We installed a metal roof back in the fall and had no problems until it started getting cold and the roof started to sweat. We tore off the original shingles and removed the sheeting on most of the house and installed 2x4 perlins over the rafters, installed the bubble type insulation/vapor barrier on top of the perlins then installed the metal. On one section of the house we just removed the shingles and installed the perlins over the sheeting then the bubble type insulation and metal, this section only had a tiny bit of condensation in the ridge cap while the rest of the house was dripping. We also installed vented ridge vent at the time of installation of roof. We then installed all the soffit ventilation we could get in hopes that this would solve the problem but it has only made matters worse. Now the whole area is condensating and frosting and with this extreme cold in Ohio it is building up ice. We have put extra insulation at the ceiling level but nothing has helped I've contacted the metal guys and nobody has come up with solution besides ventilation. The house is an old log cabin that has been added onto several times this is the part that has a walk-in attic that is used for storage and was where the problem was found first. There was R-13 insulation in-between the rafters at the roofline but when that got soaked we never put it back up and that was before we added the soffit ventilation. Thank you for your time and i look forward to hearing form you soon.

ANSWER: Thanks Glenn. I am sorry to hear about these problems. Being in Ohio myself, I can relate to the cold temperatures.

Well, I hate to say it but first of all I am very much against residential metal roof installations without decking.

Do you have any unusual sources of moisture inside the home? Plumbing, bathroom, or dryer vents not going outside? Ventless gas stove for heating? House plants? Wet crawl space or basemet? No exhaust fans in bathrooms? Humidifier on furnace?

Anything you can do to cut moisture levels in the home should help.

Is there any way to add a vapor barrier behind your ceilings?

Does your ventilation consist strictly of soffit vents as intake and the roof ridge vent as exhaust?

One option is to spray the underside of the roof with closed cell urethane foam.  That will act as a vapor barrier and an insulator?

Where are you in Ohio? I'm north of Dayton. I have to go to Columbus tomorrow for a meeting. I won't be driving by your place, will I?  I'd be happy to stop by and take a look if I am.

All Best,

Todd Miller
tmiller@classicroof.com

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QUESTION: i'm in Chillicothe thanks for offering. I don't think there are any unusual moisture sources. How can I add a vapor barrier behind the ceiling? Part of the roof is to close to the ceiling to get into where it has a low-slope. Even the sheeting is frosting up now. There is a gable vent on the part that has the sheeting under the roofing. We have tried to leave the access open between the 2 spaces and tried it closed and it didn't seem to make any difference either way. We have tried running a fan, putting an exhaust fan in the window up there before we vented the soffit but nothing has worked. We also vented the rake but it seems like it has let in too much air if that is possible.

Answer
Wow. Sorry you're so far away from me. Usually a vapor barrier is polyethylene behind the drywall.  There's not much you can do to change that.  Polyethylene on top of your insulation on top of the ceilings may be an option.

As far as ventilation ... air flows in the shortest route. I like to think of good ventilation as continuously bathing the entire underside of the roof system with fresh air. The only way to do this is to have continuous eave soffit vents as intake and continuous ridge vent as exhaust and no other vents.  Close off any other vents or openings into the attic. The only air flow should be from the eaves to the ridge. You want roughly the same amount of net free air flow as intake (adding the two eaves together) as you do ridge vent.

Make sure that any access panels to the attic are well sealed. keep the attic as closed as possible.

I would look for some way to get a vapor barrier above the ceilings as well.

And, again, the other option is closed cell urethane foam.

I wish I had some other ideas.

I will keep thinking.

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Todd E. Miller

Expertise

I am available to answer any questions pertaining to residential (or other sloped) metal roofing. I have knowledge of most available products but I like to approach projects from a "needs" basis and analyze them individually. Additionally, I can answer most questions about building ventilation.

Experience

I have worked for a manufacturer of residential metal roofing since 1980. I currently serve as President and have been involved with a wide variety of projects of all types across the world.

Organizations
I am a board member for Metal Construction Association, Metal Roofing Alliance, the local United Way, our church, and our son's school.

Publications
Over the years, I have had articles appear in several trade journals including RSI, Remodeling, and Qualified Remodeler.

Education/Credentials
I have a B.A. in Communications and have also completed three years of training with the E-Myth Academy.

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