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Posted by on December 11, 2006, 5:20 pm
nicksanspam@ece.villanova.edu wrote:
>
> >Here in the southern US, not leaving a place for ventilation will cost
> >you a roof job about 10 years before it should.
>
> Why would you say that? Seems unlikely to me, if there's no chance of
> condensation from moist house air leaking up under the roof.
>
> Nick
Because that's how cathedral ceilings are built base on years of
construction experience. You provide a space between the insulation
and the sheathing so that air can move from soffit to peak, where it
exists via a ridge vent or other venting mechanism. I doubt you;d get
a building inspector to pass off on an unventilated cathederal ceiling.
Besides moisture, what do you think having no air flow under the
sheathing is going to do to the life of the roof when it gets to 150 in
the summer?
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Posted by on December 11, 2006, 5:27 pm
>> >Here in the southern US, not leaving a place for ventilation will cost
>> >you a roof job about 10 years before it should.
>>
>> Why would you say that? Seems unlikely to me, if there's no chance of
>> condensation from moist house air leaking up under the roof.
>Because that's how cathedral ceilings are built base on years of
>construction experience...
You might say the same about shark repellent in Kansas :-)
Nick
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Posted by marson on December 11, 2006, 5:49 pm
where I'm from, Duluth, MN, the airspace is required by code. I think
it is important to use a chute the entire length, not only because it
ensures airflow, but it also reduces "windwash" which strips heat away
from your insulation. I like to use cardboard vent chutes (available
at good lumberyards). I also think adding a layer of foam to the
underside is a good idea. even a layer of 1/2" polyisocyanurate
(thermax is a good brand) would reduce thermal bridging and provide an
air/moisture barrier.
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Posted by Nick Pine on December 11, 2006, 7:16 pm
>where I'm from, Duluth, MN, the airspace is required by code.
IIRC, ERVs are also code, and a big waste of money.
>I think it is important to use a chute the entire length, not only because
>it ensures airflow, but it also reduces "windwash" which strips heat away
>from your insulation.
"Chutes" encourage "windwash," no? I suggest that you
ignore the code and take control of your own life.
Nick
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Posted by marson on December 11, 2006, 10:16 pm
Nick Pine wrote:
>
> >where I'm from, Duluth, MN, the airspace is required by code.
>
> IIRC, ERVs are also code, and a big waste of money.
>
> >I think it is important to use a chute the entire length, not only because
> >it ensures airflow, but it also reduces "windwash" which strips heat away
> >from your insulation.
>
> "Chutes" encourage "windwash," no? I suggest that you
> ignore the code and take control of your own life.
>
> Nick
no, chutes don't encourage windwash because the chutes keep the cold
air from the insulation. it's easy to say "take control of your own
life" but when a building inspector is standing there telling you you
must have vent space period, what are you going to do? we have had
trouble getting hot roofs with 12" of icynene by our building
department, let alone fiberglass.
ironically, i basically agree with you. if i was building my own house
and i didn't have to deal with inspectors, i wouldn't vent the roof
either...but i would also be very anal retentive about my vapor
barrier. in practice, cathedral ceilings do fail (condensation raining
in the house), and unless someone is there who really knows what they
are doing, the safe bet is to ventilate.
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