re: Replacing cedar board siding with Hardie Board

If your hardie boards rattle when you tap them, you have a terrible install. AND, if you’re that worried about it, hardie recommends face nailing in locations where required by code due to excessive wind (or I guess if you just want to) In this instance you would face nail only through two layers.

Hardie absolutely does not void the warranty if you caulk the bottom seam. Before I typed this I went back and read the specs that I downloaded when I built my house (I installed the hardie and flashed the shite out of every location I could). The only locations they specifically call to not caulk is the bottom row where trapped water would have to be flashed out (so above any windows, penetrations, or the bottom most run). But this should be a general no brainer. This is directly from the 2018 hz10 hardie plank lap siding spec(the latest spec offered on the James hardie website).

The only thing official I can find from hardie on caulking the horizontal joints is a 2014 bulletin about flashing that says it’s not recommended and could cause moisture buildup if you have an issue above. Nothing about warranty the being voided and again, no verbiage in the 2018 spec.