Expert: Ted Barnhill (Principal, Design45 LLC) - 11/5/2007

Question
We are looking into adding onto the backup of our two story concrete block (vinyl sided) home.  The addition would be three stories, including the basement, which matches our current house.  We will likely choose concrete block for the foundation and typical stick framing for the two floors above the basement.  Q:  How can the wood framing be tied into the existing block wall?  Can they just insert wood floor joists into the existing block wall and go up?

Answer
Jack,

Wood frame construction and concrete block are routinely used together, and can be joined fairly easily.  Most likely you will bolt ledgers onto the block and tie in to those with your wood framing.  Keep in mind that it may be inadvisable and/or unnecessary to bear the new floor and roof loads on your existing block wall.  Whether to do so will depend on the geometry of your proposed addition, and the size and reinforcing schedule of your existing footings and CMU walls.  For example, if the addition is more-or-less square in plan, and/or you are unsure of the bearing capacity of the existing structure or soil, you can orient the new floor joists and roof trusses parallel to the existing adjoining wall, and bear on your new footings.

Good luck with your addition.