Expert: Bruce E. Johnson - 1/22/2009

Question
Want to attach 3 poured corbels (1/2 yrd each) to concrete block foundation to support a 4" concrete Juliet Balcony (3'x 14') but need to know how to attach corbel internal rebar into blocks so weight won't pull away from blocks. Build is 1st story approx 30" from grade. Thanks

Answer
Hi Dan, a half yard of concrete weighs about 2000 pounds if my memory serves me plus your deck is another half yard so you are looking at 3000+ pounds of dead weight on each corbel plus any live weight added later, i.e. people standing on it.

The masonry you are tying in to should be reinforced with rebar and filled with concrete also.  Two or more fill cells for each corbel should have a minimum #5 vertical rebar in them, then you install 6- 90 degree hook bars minimum #5 with 30" legs each direction. Two at the top of the corbel will have the hooks going up into the fill cells, two in the middle have the hooks going up, and the two at the bottom have the hooks going down into the fill cells.  Pour the fill cells to a height at least four feet above the balcony but preferably all the way to the top of the wall.  This is done by punching holes at the top of the masonry and pumping the concrete into the holes.  Once the fill cells are poured then you can form and pour your corbels, tying your corbel steel to the protruding hook legs from the fill cells.

I have to say that I am not an engineer and this is just a recommendation for procedure based on my past experience.  A structural engineer should be consulted prior to any work of this nature being attempted to ensure that the wall is capable of supporting this added weight and that the method of tying the corbels to the wall is adequate. I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com