re: insulating/sealing walls from exterior
24 oct 2005
wayne whitney wrote:
>next month i'm going to be partially resheathing and residing an
>exterior wall, so it will be open to the studs from the outside. the
>wall currently has cotton batt insulation, and i understand batt
>insulation can be leaky where it meets the framing. so i'm wondering
>what i can do from the exterior to seal up the wall cavity better, and
>i'm thinking foam. i'm considering a few options:
>1) discard the batts and foam the entire wall cavity. probably too
> expensive given my climate (berkeley, ca).
>2) spray the perimeter of each batt to seal it to the framing...
>3) temporarily remove the batts and spray a thin layer of foam...
>which of these is the way to go?
4) staple black aluminum window screen into the south wall cavities to
compress 3.5" r11 batts to 1.5" r6.2 batts and screw clear corrugated
polycarbonate dynaglas or sun tuf "solar siding" over the wall to make
a thermosyphoning solar air heater which gains 0.9x1050 = 945 btu and
loses 6h(70-48.7)1ft^2/r1 = 128 btu by day and 18h(70-48.7)1ft^2/r6.2
= 62 by night, for a net gain of 945-128-62 = 755 btu/ft^2-day, vs the
original wall which loses 24h(70-48.7)1ft^2/r11 = 46 btu/ft^2 on an
average january day in berkeley.