Horizontal blocking behind cement board necessary on edges(wonderlite specifically)
If the framing is 16&quot; on center or closer where the 2 long edges meet on the larger wall, I have never added any blocking. If the centers are 24&quot;, that is a bit of a stretch and needs to be blocked. I am presuming the narrow end walls are not an issue, since the sheet will go in vertically, and the seam will be above any reason to need blocking.