Since 2008, James Hardie has discouraged the use of caulk where two pieces of lap siding come together on the side of a house. These such areas are called “field butt joints.”
In the case of James Hardie’s Color Plus siding, which has a pro-rated 15-year warranty, using caulk at field butt joints will flat out void your warranty!
So, what can you do to be sure your siding is not only the lowest in maintenance but also keep’s your warranty intact? Be sure metal joint flashing is used at every field butt joint. Don’t use caulk!
You can read more about this technical data directly on the James Hardie’s website.