Q. What is the best way to tie a new block addition into an existing block building?

A. Dowel the new footing to the original building with at least two #4 rebars. You’ll need to dig to the bottom of the existing footing, drill it horizontally, and grout in rebars that extend about a foot into the new footing. The new footing should be at the same depth as the existing footing and on undisturbed soil.

At the wall connection, vertically fasten a 3x3x1/4-inch angle to the original wall with expansion anchors (see illustration below). Provide a bond breaker on each leg of the angle, and break out the end webs of the new blocks. Then, pack the cores with mortar around the angle, and seal the joint between the new blocks and the old wall with a good elastomeric caulk. This will provide lateral support to the wall, but will allow some minor vertical movement without cracking.