From: Keith Kaplan <keithka@Exchange.Microsoft.com>
To: shop-talk@autox.team.net <shop-talk@autox.team.net>
Date: Wednesday, November 08, 2000 12:29 PM
Subject: Attic vents
>
>What's the actual purpose of attic vents? What am I trying to vent?
Moisture and heat. Moisture rots stuff. Not good. Here where we have
snow, heat escaping through the roof heats the shingles. Melts the snow.
Water runs down to the eave area where it freezes. Ice dam forms. More
water gets dammed and freezes. Ice backs up under shingles and destroys
roof.
>I've always thought the purpose was to prevent condensation in the
>semi-heated area above the insulation. Is that right?
Yes. Your attic should be cold and dry.
>My new shop is a metal pole building (well, actually the poles are wood)
>which has some kind of (blown-in?) insulation held between the metal
>roof and a layer of heavy white plastic tarp-like material. Looks like
>the white plastic was attached to the roof joists before the metal roof
>panels were attached. So the insulation is pretty much sealed. There
>are two ridge vents, which don't seem to do anything to vent the
>insulation, but it sure seems like they'd let heat out of the shop.
Vents are meant to be above insulation, in the part of the building that
supposed to be cold. The insulation is supposed to keep the shop warm and
the attic cold.
>I'm hoping to install a natural gas shop heater this winter, but I don't
>want the gas bills to be outrageous. What will I harm by closing off
>those vents? I'm near Seattle, where it's not _that_ cold (never cold
>enough to worry about ice dams), but it sure is wet a lot of the time.
What you need is ceiling with a serious vapor barrier and insulation above
it. My shop ceiling is, from the bottom up: White-painted hardboard; 8-mil
plastic; 6-inch fiberglass batts beteween the joists; open-air attic.
Ventilation in my case is that the attic area over the shop is open to the
unheated and unsealed garage. The 8-foot portion of new-construction over
the shop has soffit vents with wide plastic channels separating the ends of
the fiberglass from the roof. The other 20 feet of the parking garage of
course has the soffit vents too. The big garage door gets opened every day
for the Saturn to do it's daily-driver thing, too. The shop door stays
closed. I didn't even notice a jump in the gas bill since I have been
heating the shop to 50 degrees all winter. It gets a LOT colder here than
in Seattle.
If my entire building was heated shop, and the attic was completely cut off,
I'd want vents in the gable ends in addition to the soffit vents. I know
that ridge-pole vents and mid-roof vents are popular, but I just hate to put
anything through the shingles. I don't have anything disturbing the
straight-gable roof, and that's the way I like it.
>keithka
>125 shifter kart
>Elva 300 FJr.
Phil Ethier Saint Paul Minnesota USA
1970 Lotus Europa, 1992 Saturn SL2, 1986 Suburban, 1962 Triumph TR4 CT2846L
LOON, MAC pethier@isd.net http://www.mnautox.com/
"It makes a nice noise when it goes faster"
- 4-year-old Adam, upon seeing a bitmap of Grandma Susie's TR4.
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