Wasnt sure what the ideal depth for this space is. My architect is speccing an inch and a quarter, will that be enough to evaporate the moisture? My contractor likes 2.5 inches but that seems too deep to me. And why cant i put in paragraph break into these posts. I put 3 into this one but i doubt thet will show up. Thanks

Posted By drlebel on 08 Nov 2012 05:55 PM
Wasnt sure what the ideal depth for this space is. My architect is speccing an inch and a quarter, will that be enough to evaporate the moisture? My contractor likes 2.5 inches but that seems too deep to me. And why cant i put in paragraph break into these posts. I put 3 into this one but i doubt thet will show up. Thanks

Your architect is correct

And why cant i put in paragraph break into these posts.

Your browser settings.

Even an inch is plenty, especially when protective aspects of the vapor retardency of the foam is factored in. With any masonry or stucco cladding it's important to provide sufficient venting detail to the cavity, such as weep-holes at the bottom course and vent-slots at the top course (or better yet, a fully open bug- screened top to the cavity protected from rain intrusion by overhanging eaves &/or a back-vented facia board.)

Venting the masonry cavity into the attic is a common practice in some areas, but that requires a well-ventilated attic to work well and isn't necessarily a great option for a TN location.

A masonry cavity is exactly the same thing as a "rainscreen" back-ventilating other siding types, but since the masonry can store a lot of moisture then release that moisture in intense bursts when heated by the sun it's useful to have more air volume. For other types of cladding even 1/4" is enough for most climates, 3/8" is enough for very rainy areas like the western slope of the Cascades in B.C. (where 10mm minimum rainscreen is required by code), the AK panhandle, western WA, western OR etc.. But behind brick or stucco it's best to give it an inch or so.

I talked with my block layer who will eventually be my brick layer, and he said carpenters in our area (central Arkansas) generally set the frieze board 4-1/4" from the face of the sheathing. I have a king size brick here that I will be installing that is 2-7/8" from face to back. That would leave a gap between the brick and wall sheathing of ~1-3/8".