A ATTIC AND CRAWL SPACE ( ^[5]) VENTILATION

1. When there is attic space under roof, venting of attic will:

   1. Reduce heat buildup.

   2. Provide escape route for moisture.

   3. In cold climates, help prevent ice dams from forming.

2. Even when there is no attic, the venting effect can still be achieved with at least a 1 ? air space above the insulation.

3. In some cases, the argument can be made for having no venting at all. This can be done in dry climates and building types where vapor is less of a problem or if the "wet" side of the roof is sealed against vapor migration. Because the codes require venting but often are not enforced, this needs to be checked with building officials.

   

4. Venting can be done by:

   1. Cross-ventilation

   2. Stack effect

   3. Fans

5. The IBC requires that where climatic conditions warrant, attics or enclosed rafters should have net free ventilating area of at least 1/150 of the plan area ( should be upper ventilators at least 3 ? above eaves). This can be reduced to 1/300 if a vapor barrier is on warm side of attic insulation.

6. Under-floor crawl space should have a net free vent area of 1 SF for each 150 SF of crawl space (or 1/1500 when ground has a vapor barrier).

7. Area required to provide 1 SF vent:

   ? Screen	1SF
   ? Screen w/louvers	2SF
   ? ? Screen	1.25 SF
   ? ? Screen w/louvers	2.25 SF
   1/16 ?