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 of my fence will be 4x8x16 instead of the 8x8x16 full-size blocks. 

8x8x16 (left) and 4x8x16 (right) CMU

 

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.
8x8x16   2 openings are 5.5 x 4.75 = 52.25 sq in total
4x8x16   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.

2 comments:

Anonymous said...

Howdy! I could have sworn I've been to your blog before but after browsing through some
of the articles I realized it's new to me. Anyhow, I'm definitely pleased I
found it and I'll be bookmarking it and checking back often!

Thomas Gail Haws said...

Thanks for the kind words!