[Greenbuilding] insulation vs. air sealing

Keith Winston keith at earthsunenergy.com
Mon Oct 4 00:42:26 CDT 2010


If the question of whether to ventilate, in this case, is being raised, 
let me add another layer: how much to ventilate?

Ventilation is being talked about like a binary decision, on/off, which 
presumably refers to IRC code-level ventilation requirements. But if 
most moisture intrusion has been eliminated with conscientious air 
sealing, perhaps much lower levels of ventilation would be adequate...

Keith

On 10/3/2010 1:27 PM, David Wentling wrote:
> Blower door saw the increase in "holes", because the roof was air tight (3" of
> asphalt) when we started and we added two 18" x 18" holes (venting caps) when we
> left! This was standard practice for many years and no one measured performance
> of the practice until we did a research project.
>
> If one plans to ventilate a roof, then be sure to airseal at the ceiling level
> COMPLETELY first. There are many photos of dirt lines, through the insulation,
> above top plates due to leakage along the sides of the plate, behind the wall
> surface (lath&  plaster, wall board etc.) and penetrations in the plate. Dr
> Joe's ADA approach highlighted this many years ago.
>
> 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<futureship0000 at hotmail.com>
>
>
> 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.
>
>
>
>
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>
>





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