Re: [GBlist] attic ventilation

["Clark" <cellis1@texas.net>]

Robert, the reason you vent the attic is not for cooling it is to remove
moisture. If your architect told you this and this is not something you
derived from what they said, run as fast as you can to a competent
architect. I believe this information comes from asking friends while
leading the questions with the heat removal statement and then we end up
with the right answer to the wrong question.
DO NOT REMOVE THE PASSIVE VENTS.
In fact you normally have to make sure they will still have air passage with
new insulation.
When insulation soaks up the moisture from the air it decreases its ability
to insulate. Even fiberglass insulation will absorb moisture from the air.
The layer of insulation that sits just above your ceiling in the attic is
there to insulate against the heat and cold. This the area that absorbs the
most heat.  If you seal it off during the day warm moist air will still get
in, in fact it is already there, and then at night when you pump in cool air
the moisture will condense and you will have the biggest mess you can
imagine. Ever heard of Black Mold?
Living in Berkley you are in a high humidity area, you must have the flow of
air. Get as much passive air flow as you can, if you can not get enough then
look at electric fans with a temperature control.
Boost your insulation in the attic to R30 or R38. I live in Texas, hot and
humid, and once I pass R30 the results from the extra insulation never
really pay off, R38 seems to work better against cold.
If heat in the attic is still a major problem then look at a reflective
barrier insulation applied to the rafters. Do you have a metal roof, there
is a ceramic insulation that can be applied to the outside that will
dramatically reduce the heat penetration, stay away from the exterior foams
applied to the roof.
Dollar for dollar the best return will be with a white roof, lots of
insulation with a lot of good passive ventilation.
Clark


> I am about to insulate my attic.  My architect has suggested that I
install a fan connected to a solar panel to vent out the hot air.  The idea
being one only needs to exhaust hot air when it is hot.  It was recently
suggested to me that while this seems logical it basically does very little.
The idea being one is not replacing the heating attic air with cooler air,
as the air outside is hot also. The alternative suggestion was to have the
fan blow cooler night air in (with a cross vent installed)- dramatically
cooling the attic.
>
> I live in Berkeley CA which is a temperate climate.
>
> It was also suggested to remove the passive attic vents. Simply insulate
the attic - having the passive vents does nothing to keep the attic cooler
during the day as the temperate outside is also quite hot.
>
> Ay great insights.  Thanks,
>
> Robert Seelig



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