A.Corresponding editor Paul Fisette responds: Clapboards should be installed tight against the trim boards, and the joints should be left uncaulked. Omitting the caulk allows any water that penetrates the joint to drain reasonably well and promotes drying.
Although the use of caulk does not cause any disasters, it can elevate the moisture level of the sheathing. I have taken moisture readings of sheathing on many homes, and on average the sheathing underneath caulked corners has a higher moisture content than that under uncaulked corners, and a higher moisture content than the sheathing a couple...
to read the full article.