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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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?
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.
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.
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.
Todd,
We are building new with standing seam roofing on a multi-gable one story roof. We do get winds regularly so is not soffit & ridge venting combined the best option?
For most types of construction, the most effective ventilation is a combination of soffit and ridge vent. It sounds like your home is no different.
We have a one-story summer-use lake cottage in Northern NY, that we have been remodeling. There is no ridge vent in our metal roof which we just had installed last summer. I would like to add ridge vent and soffit vents. Soffit vents seem simple enough, but I am not sure how difficult it will be to add ridge vent. The rafters are 2X6 construction on 16” O.C. attached to a 2×6 ridge beam. Roof decking goes all the way to ridge beam where it is connected.
Thanks so much. Is there any way that you can send me a photo of the metal roof? That would help me to know what you’re dealing with a determine how difficult it will be to add ridge vent. Frankly, it probably will not be easy. My email is todd@asktoddmiller.com
Thanks.
Hi! We have a two-story, post-and-beam construction, cathedral ceiling salt-box style house and we’re replacing a failed metal roof with a new one. (The failure was bad, thin gauge metal and too many seams).
We want to do a dark/black one and there is NO attic in the house. There’s never been a noticeable heat issue (or water issue) but I’m curious if that will make things too hot inside. We are in direct southern sun all day (upstate New York), so there’s a high degree of direct sun.
There are black metal roofs that have reflective pigment in the paint and meet Energy Star standards. Looking for one of those would be wise. Even in reflective pigment, though, black is a hot color. Doing something to create a thermal break between the metal and the roof deck is also very helpful. A product like this could be helpful: https://www.roofaquaguard.com/products/dry-tech-entangled-mesh/
We have a one story, 900 sq. ft. home that we are remodeling for an investment Air BnB. It was built in 1935. It has a metal roof that has some rusting, but no leaks. The metal roof has no decking on the underside whatsoever. The house has 7′ ceilings and a gable roof. There are vents in the walls up high on each end of the house under the gable. I am not sure if there are soffit intake vents? We could add them though if not. Should we? What is the best way to insulate this home? Is it worth it to spray foam the underside of the metal ? Open or closed cell? What happens when I have to replace the metal roof? Or is it a good idea to just put spray foam on the top of the roof (on the outside)? Or is it an option to put the spray foam on the top of the ceiling deck (where you walk) inside the attic? Or is fiberglass batting or even blown insulation the best scenario for this project?
Thanks. Sounds like a great project.
Generally speaking having a metal roof exposed to the attic is a recipe for condensation. Right now, moisture generated in the home is likely going out through the walls and windows and doors. But, if you tighten those things up, that moisture will migrate to the attic and condense on the underside of the roofing.
Realizing that the roof will need replaced at some point, I’d probably not spray the underside of the roof. Closed cell foamm on the floor of the attic will keep moisture from migrating out of the living space. That should work well. Then when the roof needs replaced, I’d suggest solid decking on the roof hopefully followed by a new metal roof. Re-roofing then is also the ideal time to ensure you have good attic ventilation. Sounds like adding soffit vents at any point would not be harmful. Make sure that when they spray the foam they do not block any vents or limit the possibility of future venting.
Regarding this:
“Unbalanced ventilation in an attic can contribute to wind damage”.
I have a pitched metal roof. I’m getting new A/C is located in the attic. I am SWFL, 2nd street back from beach.
The metal roof is from 1989, was inspected and told it has 17 more years of life. No rust. Screws intact. Looks good.
A/C person came out, suggested to get roof vents to extend life of new A/C.
I called a roofer, he suggested 2 off ridge roof vents on backside & 1 on each side of house. He said for ascetics none on front. (I have photos of diagram).
My concern is twofold-
1. Will this create an “unbalance” (hurricanes)?
2. Nervous to mess with existing roof with no current issues.
I should mention that I am new to Florida. I am just learning about tropical climate.
I have a small 12×16 foot cabin that will be an office for myself. It has a pitched metal roof. The cabin will be fully insulated. Do you suggest venting the attic space?
Thanks. I’d love to know more about the location of the cabin and also its overall construction. I would err on the side of ventilation but if you’d like to tell me more, that would be great as well. In particular, is there decking beneath the metal roof? Can you provide both intake and exhaust vents? Will there be plumbing or other moisture sources inside? What sort of climate are you in? Will it be heated or have A/C?
Hi Todd I have an enclosed patio with a metal roof. There are two windows and the ceiling and walls have shiny silver insulation that feels like bubble wrap. I also have a door on the patio. The metal roof was not vented. Is there anything I can do to cut down on the heat and humidity ? This is all that has been done.
Is there any chance you can send photos of the patio to me? Want to make sure that I am not missing anything. My email is todd@asktoddmiller.com
hello Todd I am building a new home with a ridge beam and rafter roof. I plan to use fiberglass insulation with 6 ml poly as a vapor barrier on the living space side. Do i need to vent in this situation? i’m nearly at the point where i need to decide if soffit vents and some type of gable vents are needed or not. The roof will be decked with sheathing prior to metal instalation. Thanks
Hi Todd – Great site. In about 2 weeks I’ll be replacing the asphalt shingles on my 1920 home with standing seam metal. I’ve made a number of efficiency improvements to the house including airsealing, new floor/walls/attic insulation, etc. The issue I’m having is that there are no soffit or other intake vents and I’m not sure how to tackle adding them. Roofer will put on a ridge vent, but what would be your recommendation for adding intake vents?
If it helps, I am in northern california so no snow concerns, and my unconditioned attic has not had any mold/moisture issues that I am aware of.
Thanks!
David