Janine- I might suggest that you at least consult with a certified JHardie installer. There is one in your area that only does replacement work, not new homes, and is very competent working with HardiPlank and cedar. Check the Better Business Bureau site, then give a call to the one with the initials ACAE. They use backer rod and flashing in the appropriate places and Sonneborn Sonolastic 150 caulk. You probably just have Tyvek for a moisture barrier. There is better technology available now, and this installer is on the cutting edge of the newest ideas. They are all about making a house "bomb proof" for the full length of Hardie's warranty when it comes to water penetration, and they are especially good at it because of their region of the country (yours). The Tyvek will have to do if you aren't doing a complete replacement of course, but a consult might at least get you some very useful insight as to what you are really up against in total. I'd also powerwash the siding after repairs are done and use only Miller Paint. It protected our LP siding for 17 years before problems showed up, long after most others' LP had rotted and been replaced. Miller is also a company local to you and well-versed on water and mold repellency.
