Expert: Bruce E. Johnson - 6/6/2011

Question
I have a 15 ft by 65 ft slab 6 inches thick. I am putting a six foot foundation wall around the slab 4 foot under ground 2 foot above ground. code states I have to attach foundation wall to slab. What is the best system to attach wall to slab

Answer
Hi Steven, what? I've never heard of a code like that.  Unless there is a specific reason for it most slabs within foundation walls are floating and not tied to the walls at all.  In fact there is a material called expansion material that is used to separate the slab from the wall which allows it to expand and contract without affecting the wall structure.  However if you want to connect the slab to the wall it can be done by drilling into the edge of the slab 6" and inserting pieces of rebar into the holes along with an epoxy.  It seems like you put the cart before the horse, usually you do the foundation first and then pour the slab after.  But if you really need to do this embed the new rebars 3-6" into the slab and 3-6" into the wall. If your wall is masonry then you need to pour a fill cell at each location so your dowels will be 16" apart and have a hook on the one end that ties into the wall.  I'm not sure how you will do a poured concrete foundation with the slab already in place (you won't be able to form or strip the inside forms underneath the slab after the concrete is poured). I hope this information helps please feel free to write again regarding this or other matters, sincerely bruce johnson..bejohnsonconsulting.com