Eric's suggestion is a good one; I agree that cavity construction on a
3-wythe 100-year old brick wall would be an unusual situation. But to
answer your question, Drew, the purpose of the space in modern cavity
wall construction is to provide a path to direct condensation out of the
wall. It allows you to control where the dew point occurs in the system
and where condensation happens, and through the use of weep holes and
proper flashing, direct the water out of the wall to the exterior. When
sloppy masons fill the space with mortar, it affects the performance,
obviously. The air space is also given consideration in analyzing the
energy performance of the wall; it adds an insulation value.

__________________________________________________
Dan Becker,  Exec. Dir.    "Oh joy!  Rapture!  Now
Raleigh Historic            I have a brain!"
Districts Commission                   - Scarecrow
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919/890-3678

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