Expert: Bruce E. Johnson - 1/23/2011

Question
I wanted to add a bedroom to an existing pier and beam house.  This size of the bedroom will be 14ft by 15ft.  If I use a sonotube for this,  what should be under the sonotube?  I am in San Antonio Texas and they say we have bad soil here and homes/slabs are always moving.  I thought that there should be a 24"X24" mini slab under each 8 or 10 inch sonotube.  What is your opinion?  Also, how many sonotubes would you recommend?  Thank you.

Answer
hi Cee, yes there should be a footing pad under each pier.  The size of the pad depends on the soil conditions and the weight of the new addition.  A 24" x 24" x 12" thick pad would be a standard size for a typical wood post.  A sonotube pier may require a slightly larger pad to accommodate the added weight of the concrete in the pier.  Spacing of the piers will depend on the size of your beams.  A rule of thumb is one foot of span per inch of beam thickness..i.e. a 4x6 can span 6'..etc.   I hope this info helps please feel free to write again regarding this or other matters, sincerely, bruce e johnson..bejohnsonconsulting.com