Your Roof: To Vent or Not to Vent a Metal Roof

To Vent or Not to Vent a Metal Roof

October 2, 2017 | Filed under: Home Ventilation, Metal Roofing

Venting can sometimes be a good way to get things off of our chest but, when it comes to home construction, venting can be a great way to get hot air and moisture out of our attic. I had a homeowner recently send me this question about how to vent a metal roof:

Q: “I need a roof and would like standing-seam aluminum since I live on the water, on the coast.

The contractors seem divided as to whether we should install a ridge vent or some type of venting, or should the attic be enclosed and insulated? At present, I do not have soffit vents because a prior insurance company told us that would make us more vulnerable to high winds. A local engineer (PE) swears we need to fully enclose it and spray insulation. Two contractors say that’s dumb because it needs to breathe.”

A: There is indeed a real trend toward “conditioned” attic spaces which utilize closed cell foam sprayed throughout the cavity including floors, gables ends, and the bottom of the roof deck. When this is done, ventilation is removed. Metal roofing works well with this because the metal is unaffected by heat not being able to pass through it and enter the attic.

The other option, of course, is a vented attic which requires an equal balance of intake and exhaust vents. In many cases, for existing homes, this is the easier way to go.

Should You Vent a Metal Roof?

Both ways can work well. The question is whether, for your application, one is better than the other. Due to your potential for hurricane winds, I’d actually tend to gravitate toward the conditioned, non-vented attic. Unbalanced ventilation in an attic can contribute to wind damage.

Unfortunately, though, I am unaware of any actual research or study into this question and would love to hear about it if anyone is aware of any!

todd Miller

has spent his entire career in the metal building products manufacturing industry. He is president of Isaiah Industries, an organization recognized as one of the world’s leading metal roofing manufacturers. Todd is currently Vice President of the MRA (Metal Roofing Association) and a Past Chair of MCA (Metal Construction Association). Through his website, he strives to raise the bar on standards and practices to provide property owners with the best possible products for successful roofing projects.

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8 responses to “To Vent or Not to Vent a Metal Roof”

  1. Teresa Siebel says:

    We had a metal roof installed at our home. It doesn’t have a ridge vent. Since it was installed we have moisture in our home in the summer months, we live in humid conditions, and have to run a dehumidifier. We recently had the siding replaced on our gables and the contractor installed a smaller, octagonal shaped vent on each end of the gables. A few months later we have noticed that we now have mold in our attic. I believe that though the gable vents are smaller, if we had known to have the roof contractors to install a ridge vent, this wouldn’t have happened. Now we are out a lot of money to have the vent problems corrected and mold remediation costs.

    • Proper attic ventilation requires both intake and exhaust vents. Using eave soffit vents as intake and a roof ridge vent as exhaust takes advantage of natural convective airflow. Gable vents are much less effective. Do you have any intake vents in the attic at all, or just the gable vents now?

  2. Courtney Armstrong says:

    We just built a red iron building with metal siding and roof. My builder told us not to use vents in the roof. Our ac guy and a roofer who came out to fix a problem the plumber caused in the roof wanted to know why we have no vents. Both of them think we should vent the attic space. Our builder told us to use regular insulation in the house not spray. He said spray would make the house too air tight and not let it breath. I have been trying to research and found that spray foam in the attic would not require vents, but r13 would? We are fixing to insulate the house next week and we have no idea what we need to do?

    • If this is a house, from the inside to the out, I’d suggest: drywall, vapor barrier, insulation, vented airspace, solid decking, underlayment, roofing. However, I think your construction may be a bit unique. Give me a call at 1-800-543-8938 ext 201 if you would like to discuss.

  3. David Michener says:

    I am building a workshop 20’x 34′ insulated, heated and cooled. Metal standing seam metal roof. Zip system for roof sheathing and foam insulation. I am planning no soffit vents, roof vents or gable-end vents.
    Will this work? I want to build the best structure possible.

    • By foam insulation, are you referring to closed cell urethane foam sprayed to the underside of the roof deck? In that case, yes, I think that would work. I’d suggest considering a vapor barrier behind the drywall as well.

  4. Han Winogrond says:

    I’m remodeling a small home. It has a new metal roof installed on furring strips over an old asphalt roof. There was no ridge vent in the asphalt or now. The old roof was vented via a whirlybird.

    Moving forward I am vaulting the ceiling so there is no attic space on about 50% of the roof. I was planning to just use closed-cell spray foam between the exposed rafters but I can’t get the required r value in the 5 1/2″ rafter cavities out of foam. I can get the R 30 required by using poly – iso foam board. I am concerned the poly iso (unlike spray foam) will leave small cavities between the decking and the iso boards so it needs to be vented?

    So I’m scratching my head on how to handle this. I’ll either need to remove the ridge cap and manually cut back the old asphalt to create a functioning ridge vent (I have vented soffits) and put spacers in to hold the foam board off the decking or fur out the rafters so they’re deep enough to use spray foam if it’s even possible to get that r-value out of foam.

    What if I use an adhesive to glue the foam boards tight to the decking and spray foam every joint, then could I get by without venting? I can’t be the first person to try to insulate between rafters in a living space and need it to meet the code for R value?

    Thanks for any insight!

    • Thanks for your post. It sounds like you have a full understanding of the dynamics involved here and have thought this through well. While I personally have never heard of anyone doing your final idea with sealing in the polyiso boards, I see no reason why it wouldn’t work. I believe that the polyiso boards need to be foil faced (with the foil facing the living space) in order to be vapor barriers themseoves. Please contact me anytime.

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