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RE: Cavity Width in Masonry Walls

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I can understand the structural concern.  The compression forces on the ties
can cause a buckling failure.  You could increase the tie gage or use a
coated / galvanized embedded bent rebar as a tie.  The "proper ties" would
have to be designed.  You would also probably have to increase the grouted
cells to anchor the ties (presuming a partially grouted wall).

I can also understand the architectural concern about eliminating mortar
bridging.  The 2 inch air space appears excessive.  Talk to the architect
about using "mortar net", or dropping a board on a wire into the cavity to
clean the cavity and maintain the air space.  The BIA has some literature on
this in their tech notes.

Harold Sprague
The Neenan Company

-----Original Message-----
From: WILLIAM R. KEEN [mailto:wrk(--nospam--at)]
Sent: Tuesday, September 29, 1998 3:37 PM
To: seaint(--nospam--at)
Subject: Cavity Width in Masonry Walls

Does anyone have any experience with large cavities (>3") in masonry cavity 
wall design and construction? UBC permits up to 4 1/2" with the proper ties,

but NAVFAC P-355 restricts cavity width to 3" unless spot mortar bedding is 
used to stiffen the ties. We have a project with CMU backup, 2" insulation 
and clay brick veneer. To get a clean cavity, the architect has specified a 
2" air space for a total cavity of 4". The Navy said no to any more than a

The project is located in Norfolk, Virginia (Zone 1).

Bill Keen
Clark Nexsen