Saturday, December 16, 2017

Size of CMU (concrete masonry unit) wall openings for drainage

An engineering client of mine passed along to me the following information that comes in handy for calculating flow through concrete walls that have turned-block openings:

Most all of fence will be 16 inches long and 4 inches wide instead of the 16x8 typical blocks.  The openings for water flow in the 16x4  have 14.8% more square inches.  It costs less and will allow about 15% more volume of water.  Good news.
16 x 8   2 openings are 5.5 x 4.75 = 52.25 sq in total
16 x 4   2 openings are 5 x 6          = 60  sq in total
Both of these are larger than the apparently conservative 4" x 4" opening dimension his wall builder gave me.

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