Replies

1. GBA Editor
   Martin Holladay | Sep 28, 2014 04:46am | #1

   George,
   According to building scientist Bill Rose, who set up some test equipment to try to measure whether the calculation methods used by ridge vent manufacturers and soffit vent manufacturers was accurate, the method used by manufacturers hardly matters -- because it isn't accurate.

   Rose never got around to publishing his research; he reported what he learned in a telephone conversation.

   He said an accurate measurement method would show lower numbers than the numbers reported by the manufacturers.

   For most purposes, however, these exaggerations hardly matter -- because attic ventilation is less useful than most people think. For more information, see All About Attic Venting.

2. 
   user-741168 | Sep 29, 2014 09:37am | #2

   Martin is right, the values supplied by the manufacturer are wacky, but that's ok because the target value of 1/300 is wacky. The research was largely done by my colleague Jeff Gordon. We didn't publish it anywhere because why waste precious publication space on something of so little consequence. If a manufacturer-rated number gets the job approved, why bother with a real number?

   Maybe we should find a way to make our reports available. Ill check with Jeff Gordon.

   You can always measure the net free area of an existing attic, using add-a-hole zone pressure blower door techniques. Your local weatherization agency should be able to fill you in on how those measurements are made. Kudos to Michael Blasnik and team for showing how this is done.