[Greenbuilding] insulation vs. air sealing

[Corwyn]

On 10/2/2010 10:03 AM, Futureship wrote:
> Corwyn and Nick,
>
> Do you have a suggestion on
> How to test the stack effect ?

You could use a hot air balloon.  If the balloon rises faster when the 
temperature difference is greater (e.g. when you turn on the burner), 
that would support a theory that stack effect increases with increased 
temperature difference.

> I could do a before and after.
> My hunch is that the stack effect decreases if you air seal attic before blowing insulation and increases
> If you do not air seal the attic before blowing insulation.

Stack effect is the pressure not the flow.  So air sealing doesn't 
affect the effect itself, just the results of that effect.


On 10/2/2010 12:49 PM, Kathy Cochran wrote:
 > Hi all,
 >
 > I am getting ready to have insulation blown in to my attic.  What 
exactly is
 > the "stack effect"

The stack effect is the tendency of warm air to rise with respect to 
cold air inside, or through, a building or chimney.
http://en.wikipedia.org/wiki/Stack_effect

 > And, now in my county anyway, it is required to have roof caps that are
 > ventilated.  So, how does this impact on sealing up all "leaks" in the
 > attic?

The sealing being discussed is at the thermal envelope boundary (usually 
the attic floor).  The ventilation is at the attic ridge line (and 
possibly outside the insulation at the soffits in the eaves).  In other 
words, above the insulation.  Sealing the air leaks in the attic floor 
will keep your expensively heated, and damagingly moist air, out of the 
attic, where it would (need to) be vented and/or condense causing problems.


Thank You Kindly,

Corwyn

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
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