Our 850 sq. foot house has three soffit vents on the west underhang, but no
soffit vents on the east underhang (nor roof vents on the east half of the
gable roof. We have two (passive) roof vents on the west half of the gable
1) Is this enough ventilation??
2) Our garage in the back has no roof ventilation (believe it or not).
Should I put in a roof vent and two soffit vents??
Regina, Saskatchewan, Canada
This is the first time I've ever read that one can have too much
ventilation. Are you sure about that? Every manufacturer's vent
instruction and other recommendations I've read always phrase ventilation
requirements as minimums. Never anything mentioned about problems with
exceeding those minimums. They do indicate a 50/50 balance between high
and low vents is best and, if there's an inbalance, the low vent free area
should be greater than the high vent free area.
Sure there is, especially in cold climates. If you have a
50 mile an hour wind outside and enough vents to have a 50
mile an hour wind through your attic, that wouldn't be
good. Now if you had 40 inches of insulation and it was
tied down tight, it might be ok.
What you really need (especially in a cold climate) is
enough venting to get rid of the moisture but not so much
that you have to have an unreasonable amount of insulation.
An attic getting warm from sunshine during a cold day is
much preferable to an attic that stays cold because of
Actually you have a point and maybe after you reach 18 to 24
inches of fiberglass or R 66 excess venting may not have
much effect. Unfortunately, you can expect most people
don't have that much insulation.
On Fri, 22 Aug 2003 04:37:34 GMT, "George E. Cawthon"
Actually, without considering ridiculous amounts of insulation,
you will have heat escaping into the attic in cold climates. This
heat will warm the attic enough to cause ice dams when outside temps
are down low and the snow cover is insulting the lower levels of
snow. Unless you get ridiculous with the venting, you can't have too
much with this in mind.
True, so it all depends on the climate. Some places are
cold but with little snow so ice dams don't form. I've seen
icicles on some of our houses that were essentially
continous along the eave and maybe 10 feet long. Thank god
there were no damaging ice dams. But it was a clear
indication that lots of heat was going into the attic,
especially near the eave. The real solution, however, is
more insulation, not more venting.
On Sat, 23 Aug 2003 02:49:32 GMT, "George E. Cawthon"
How about adequate amounts of both? :-)
But, I'll still hold out for reasonably maximum venting. When it snows
a _lot_ and you get a deep cold snap of a week of two, your heating
system is pumping full time to keep the house warm. The colder it is
outside, the more you pump, and the more you pump, the more heat goes
outside due to the differential. Even houses with thick insulation
start to develop ice dams in these situations.
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