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Old 11-02-2008, 11:59 PM   #16
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Old home insulation woes


davitk: thanks for your input again.

I managed to illegally get my hands on the international building code and here is the real answer.

according to the 2006 international building code this is what the ventilation should be for an attic

Quote:
1203.2 Attic spaces. Enclosed attics and enclosed rafter spaces
formed where ceilings are applied directly to the underside of
roof framing members shall have cross ventilation for each
separate space by ventilating openings protected against the
entrance of rain and snow. Blocking and bridging shall be
arranged so as not to interfere with the movement of air. A minimum
of 1 inch (25 mm) of airspace shall be provided between
the insulation and the roof sheathing. The net free ventilating
area shall not be less than 1/150 of the area of the space ventilated,
with 50 percent of the required ventilating area provided
by ventilators located in the upper portion of the space to be
ventilated at least 3 feet (914 mm) above eave or cornice vents
with the balance of the required ventilation provided by eave or
cornice vents.
Exception: The minimum required net free ventilating area
shall be 1/300 of the area of the space ventilated, provided a
vapor retarder having a transmission rate not exceeding 1
perm in accordance with ASTM E 96 is installed on the
warm side of the attic insulation and provided 50 percent of
the required ventilating area provided by ventilators located
in the upper portion of the space to be ventilated at least 3
feet (914 mm) above eave or cornice vents, with the balance
of the required ventilation provided by eave or cornice
vents.
If you made it through the technical jargon, in laymens terms, i can put less vents in, and a vapor barrier, or more vents and no barrier. I'm pretty sure I'll be able to provide well over that 1/150 ratio.

I have approximately 1100sq ft of attic space. and about 35 viable eaves to put vents in. I just need to find a vent that provides at least 2.5 sq in. net free ventilating area (1100sqft/150sqft*12in/35eaves) = 2.5sqin NFVA

I'll prolly say screw the barrier at this point since I will have more than adequate ventillation. Sound good?


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