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TOPIC: Ventilation

Roof-mounted attic fan ("dome" fan) w/ metal roofing?

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Hi Experts, I'm in the planning phase of building a home. One of the options I'm considering is metal roofing, specifically 26-gauge galvalume-coated-steel "5V-crimp"-style metal roofing, which is both inexpensive and historically-accurate around here. Because I live in the hot & humid southeast, and because I don't want to be doomed to a lifetime of high air conditioning bills, I want a power ventilator (attic fan). In an ordinary gable-end house, this would be easy -- just have a gable-end fan. But this house is a complete square (four equal triangular roof sections - refer to the attached image file for an idea of the type of roof I'm talking about), so there aren't any gable ends, so my only option is a roof-mounted attic fan (the "dome" a/k/a "mushroom cap" style). This is very easy to do with asphalt shingles, but I have no idea whether or not it's compatible with metal roofing. Is it? And if so, how would it be done? 5V metal roofing is "crimped" ever 12 inches, but the fan and its flat (non-crimped) flange are wider than that, so I'm worried about water leaking in around the fan. Thanks for any answers you can provide, -Pierce
Guest User

8/22/2008
WELL, AS YOUR ROOFR I WOULD CUT 2 PANELS EVEN ABOUT 3/4 OF THE WAY DOWN THE VENT (BELOW THE OPENING OF THE VENT HOLE). I LIKE TO REMOVE THE TOP OF MY VENT 1ST FOR A BETTER, EASIER FIT. NOTCH MY METAL OUT FOR THE HOLE, APPLY A SEALANT TO THE BACK AND SIDES OF THE VENT. SIDE THE VENT UNDER THE PANELS. INSTALL 5V CLOSURE AT THE TOP. INSTALL 2 NEW CUT OUT PANELS UNDER MY VENT (APPLY SEALANT ON THE UNDERSIDE OF MY VENT FIRST). INSTALL MY CLOSURE, TAPE, SEALANT UNDER THE THE BOTTOM EDGE OF THE VENT. SEAL AROUND THE METAL AND SCREW DOWN THE PUPPY. YOU'LL ALSO NEED TO PUT THE TOP BACK ON.
Guest User

8/23/2008
This has served to convince me that metal roofing is the wrong way to go. Back to Owens-Corning asphalt shingles. Thanks! -Pierce
Guest User

8/23/2008
Venting a pyramid shaped roof is tough for any roofing material. And with metal we want to depend upon flashing nethods, not a bunch of sealants. One option, rather than a power vent, which actually would provide a more complete air exchange in the attic, is a hip vent. I would suggest working with your metal roofing manufacturer to see if they have such a thing. I have provided hip vents before to customers for my company's metal roofing. Also, especially for a profile like 5V, there are flexible flashings available that accommodate the crimps in the profiled roofing. Todd Miller
Todd Miller
Isaiah Industries, Inc.

8/26/2008