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Hi David-<br>
<br>
It seems that the time to ventilate is when you need to evacuate
moisture. You need to evacuate moisture when it builds up or when
it's new equilibrium is above the holding capacity of the materials
- when the settling point supports mold growth.<br>
<br>
Winter air is dry, so ventilation is not needed in winter-as it
warms, it gets even drier, relatively speaking.<br>
But keeping interior vapor out of the attic is critical.<br>
<br>
Summer air is humid, but if the attic matches the temperature of the
exterior, the humidity matches as well. Condensation does not
occur, so accumulation of moisture in the wood should not occur.<br>
But keeping the interior cooling (both via exfiltration and
conduction) out of the attic is critical.<br>
<br>
So, maybe you really <b>never</b> need ventilation but <b>always</b>
need airflow and thermal flow control. <br>
<br>
The one exception: rain penetration will wet the wood. But that
situation is catastrophic and a repair since it means your design
sucks or your roof is leaking.<br>
<br>
Thoughts?<br>
-Brian<br>
<br>
<br>
On 10/3/10 11:09 PM, Futureship wrote:
<blockquote cite="mid:BLU0-SMTP1325DAFC4AB21C8288C030DC86C0@phx.gbl"
type="cite">
<pre wrap="">Good question ? What are the conditions in the attic that would
Merit ventilation after air sealing
And insulation ?
On Oct 3, 2010, at 1:27 PM,
David Wentling
</pre>
<blockquote type="cite">
<pre wrap="">
"With the airseal measures in place, and the moisture contribution from
ex-filtration to the attic eliminated, the question is do you need to ventilate?"
David Wentling
From: Futureship <a class="moz-txt-link-rfc2396E" href="mailto:futureship0000@hotmail.com"><futureship0000@hotmail.com></a>
I have a question with regard to
Your results:
In the first case you described that "Results were 15% higher energy usage with
10% greater leakage."
How does a blower door measurement
Tell you 10% greater leakage? The
Blower door measures holes in
The building envelope . Assuming no
Air sealing was done the blower door
Would not measure a 10% greater leakage. I would argue the increase in stack
effect In this case caused an increase in pressure thru the same holes therefore
causing more airflow thru the same holes.
</pre>
</blockquote>
<pre wrap="">
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</pre>
</blockquote>
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