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TOPIC: Ventilation

Attic ventilation and vapor barriers

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I've probably asked 20 people in residential construction if a vapor barrier should go on top of the ceiling (or below the attic insulation), and half say yes and the other half say no. For an insulated vaulted deck like R-Control Panels (SIPs), a few years ago the manufacturer said no need. Now when I ask them, they say use a vapor barrier under the sheetrock. Now this brings me to attic venting. Seems to me it's more important to have venting in a warm climate for removing heat from the attic, but in a cold climate it's more important for prevention of ice dams, or to keep vapor from turning to ice in the attic. So, in a climate with hot summers and cold winters, attic ventilation helps for both seasons. I read where some builders say to super insulate the attic (R50 or higher), which reduces heat transfer and therefore vapor transfer, then ventilation is not as important. My metal roof panels are too short at the ridge, and the ProfileVent material does not have enough metal panel under it in places, to prevent wind driven rain out. Seems like one solution is to not vent the ridge, but seal it tight. Since the metal ridge piece screws to the tops of the standing seams, what material is normally used to fill in between the standing seams? My standing seams are 1 inch tall, and 16 inches on center. I need a durable air and water tight material for the gaps. I could use caulk, but once the ridge piece is caulked, it would be difficult to remove. Thanks, Mark
Guest User

10/11/2002
Hi Mark, My opinion (and you're correct in that there are different opinions on this), a general rule of thumb is that, if the attic is well-vented, the placement of a vapor barrier does not make a difference. If, however, it is an unvented situation (such as with SIPs), the vapor barrier needs to be as close to the living space as possible. Regarding the ridge closure -- there are foam closure strips available to match most metal panel profiles. The manufacturer of your roofing should be able to help you locate them. Aside from that, another way to close off at the ridge is to use a color matched Z Channel cut into sections to fit between the ribs. It then gets screwed into the roof deck through the panels. Seal the joint well with a quality sealant. Todd Miller
Todd Miller
Isaiah Industries, Inc.

10/12/2002
Many thanks Todd!
Guest User

10/12/2002
I have an existing metal roof approx 11 years old. We have a problem with what I believe must be condensation. We have one main large roof beam and along its sides there's evidence of moisture discoloration. It's never enough to feel anything but we're now seeing signs of mildew in a few places. We know others with the same problem and they think they solved it with drilling holes at the roof peak under the roof cap. Is this a viable solutions? Thanks! Nancy
Guest User

10/12/2002
It does sound possible that this is from condensation. If it is, there are a couple of things you should do: 1) Eliminate any soruces of excessive moisture in the home. Make sure that all plumbing vents, dryer exhausts, etc. are vented to the outside. If you have a ventless gas stove, make sure you're abiding by its manufacturers instructions as far as how much it is operated. 2) Look for achieving positive airflow ventilation in the attic. This requires intake and outlet vents. As far as vents which must go through the roof, I really advise that you contact an experienced and qualified metal roofing contractor to do the work. Without seeing your roof and knowing more about it, I do not know whether drilling holes would help. Right off hand, though, I'd be very concerned that doing that could jeopardize the integrity of the roof system. It is probably not the right thing to do and it could bring on more troubles. Sorry. Todd Miller
Todd Miller
Isaiah Industries, Inc.

10/12/2002