Replies

1. 
   rjw | Nov 30, 2003 05:40am | #1

   D:

   Where are you located? That is a key piece of information because different areas have different needs, and what works in one area doesn't work in another. Also, the size of the openings doesn't mean much without knowing how many there are.

   As a very general rule of thumb (and one that isn't very precise) you need 1 sq inch of free vent space in the attic for every 300 sq feet of attic space if there is a vapor barrier on the ceiling, or for every 150 sg ft if not.

   Divide this 50/50 between the soffit vents and the through roof vents.

   Note: Free vent space isn't the rough opening - another inaccurate rule of thumb - with the slotted cover on, figure 1/2 of the rough opening for the "free vent space."

   Note also, if you question the builder, you might well get "We always do it this way." Ask how often he returns to see if "this way" actually works. Some do, so do not.

   For an impartial view, try asking an experienced home inspector in the area (someone with over, say 1,000 inspections.) S/he'll have seen what works and what doesn't work and won't have an ax to grind or fundament to cover.

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