The more I inspect, the more I respect the challenge of constructing a home. Products, codes and best practices are constantly changing. Each system requires that the installer understand how it works. The slightest error gets compounded when it's repeated with a thousand parts. Partial knowledge is always dangerous, thus I always try to remain humble and ready to learn more.
Cement fiber board is a wonderful invention developed in Australia were wood is dissolved readily by water and insects. It replaces aluminum and vinyl siding: never a close substitute matching the character of wood. Its main weakness is that it fractures when punctured near boarders. I recently inspected a large condominium complex where many of the boards had their corners broken off.
So, about butts. My frequent clients are happy my wife gave me suspenders for Christmas thereby enhancing my claim for "no surprises". The gaps seen in the picture above are where the butt ends of the boards meet. With cement fiber boards there are supposed to be no gaps at the butts, only 1/8 of an inch at the ends near the flashing. Click on the image above for a link to Appendix A for Hardie Plank installation. In there is says the factory cut ends are supposed to be joined for the butt ends. Omitting this trick likely led to the gaps. It also tells you how to put flashing behind the gaps. I often see this flashing drooping down over the course below.
The directions also say to not caulk the gaps. There are a couple reasons for this. First, if the butt ends are tight the caulk has nowhere to go so it won't hold; second, there can be a color match problem with some of the products. However, if you have gaps between the boards that aren't supposed to be there, caulking is your only option.
If there are loose boards the Appendix also tells you what kind of nails to use and where to put them so the boards don't break.