Guest User
11/17/2005
I am having a house built it Texas. It is very hot in the summer and mild in the winter. Usually with a south breeze. The builder is putting on a U panel metal roof with exposed screw fasteners over c-purlins. He is putting reinforced vinyl insulation between the c-purlins and metal roof. This is a gabel roof running north and south with a 5/12 pitch with a large triangle shaped gabel vent at each end. We will put 18 inches of insulation in the floor of the attic. Any concerns?
Todd Miller
Isaiah Industries, Inc.
11/18/2005
John, I really would remove the gable vents and add eave soffit vents and a ridge vent for more consistent overall air movement. I would also add a vapor barrier behind the ceilings, beneath the attic floor insulation. The insulation directly beneath the roofing can be risky. If it is not sealed off completely so that moisture cannot get through it, you run a risk of moisture getting against the cool back side of the metal roofing where it will condense. I am not sure that I would run that risk. Instead, you may wish to not use that insulation.
Guest User
11/18/2005
Thanks, Todd. It seems that everyone in this area that builds metal open span buildings is using this 3 inch reinforced vinyl backed insulation directly below the roof panels. The difference with my building is that it will be framed on the interior like a house with an attic. I can add a ridge vent and remove the insulation betwwen the U-panels and the C-purlins. It seems that the sun's heat coming thru the roof panels would make the attic very hot. I will ask the builder about soffit vents. The C-purlins that the U-panels will be screwed too are running parallel with the roof ridge and not perpendicular like a regular wood framed house with wood rafters. Will this interfer with the air flow up and out of the ridge vent? If I understand you correctly I should lay a vapor barrier like a plastic sheet between the ceiling joists the lay my insulation down. If I use batt insulation with a vapor sheet added to it will that work or should I still lay an additional plastic layer down first? If I leave the gabels vents would they do any good with the addition of soffit vents or should I eliminate the gabel vents completely? I know this is very long, but I want to get this insulation right from the beginning. Thanks for your help. John
Todd Miller
Isaiah Industries, Inc.
11/20/2005
Open metal buildings have far different requirements because of the amount of open airspace and the number of air changes they get. I would close off or remove the gable vents and definitely put in a ridge vent and soffit vents. And, I would also use the vapor barrier and attic floor insulation.
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