Expert: Dan Griffin - 3/28/2008

Question
I am planning on putting in a suspended concrete patio in the back of my house.  It will be roughly 16x13.  I have 12 years experience in masonry and concrete so I am confident on how I will support the weight of the concrete but my question is how would you recommend I connect it to my house?  I thought of running some all thread through the base plate but feared if the slab pulled away from my house that it would rip the plate right out.  The slab will be supported by block pillars filled with concrete sitting on a foundation that will be at least 4 feet below grade.  I look forward to hearing your opinion.  Any questions feel free to e-mail me.  Thanks, Jason.

Answer
Jason,  I don't think you want the slab tied to the house, but rather, an independent slab designed to be stable without the house.  I did this for a front porch not as large as your plan, but a bit similar.  This is sounding ambitious as this will require more than a simple one way 4" slab IMO.  I know you can make the span with a 7" slab (perhaps thinner, but I don't know), but the weight goes up dramatically.  A system of steel or concrete beams can be created, but I would recommend working with a structural engineer for details.  Core slabs with a capping slab would be another possibility, but they still require substantial bearing at their end points.