[Greenbuilding] attic insulation in Seattle house

Sacie Lambertson sacie.lambertson at gmail.com
Mon Nov 14 06:55:32 PST 2011


 Back to the question of insulating an attic in the PNW (Seattle) I have
found nothing from Lstiburek specifically addressing this issue in this
area.  This 1906 house has those small mushroom vents high up the roof but
nothing down low.  No soffit vents.  The attic is currently nicely dry--it
does have some old loose material between some of the 2x4 joists, material
that was probably across the attic floor at that little depth before the
house was updated.  Those folks never got around to insulating the attic
floor except where a new ceiling was put in below, where they put in
fiberglass batts above. (We will take these out, but leave in the loose
stuff).

Without a clear context, below is what L. does say about ventilating.  I'm
inclined to seal the perimeter to the degree I can and then simply blow in
a foot of cellulose over everything.  Several of you have suggested this,
however I would love to hear from John Straube on this issue.

thanks, Sacie

*“Is it better not to vent a roof?” *

*Lstiburek’s response: “I like to vent whenever I can. But when roof
venting cannot be done so that it will be effective or when it is difficult
(e.g. with hipped roofs or multiple dormers) it is better to have an
unvented assembly.”*

And from cmhc:

*Attic computer models show that attics in damp coastal climates may
actually be drier with less ventilation.*
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