I’m working on an old house, they replaced the old siding with new preprimed ceder lap siding. The carpenter told us that it would be great if we would caulk all the laps, so we did on two sides of the house. I told this to a friend at the paint store, he said this might be a problem; The siding won’t be able to breath or move and may cause a mildew problem latter!! What do you think?
Do not caulk underneath the lap. More problems than mildew can be caused by this. I do not need to discuss the humidity issue with someone from your part of the country, as I will assume you understand how penetrating that is.
The siding needs to be able to breathe and allow moisture to escape.
Never, never caulk the bottom edge of lap siding. I've seen this done time and time again. Some painters do it thinking it will make a better finished product. They are right at first, it looks awesome. Give it a few years and it will be twisted, a pulled apart. The siding moves through the seasons, and even the very best elastomeric caulk will pull away from the siding. You will have to cut away the caulking and re-do it forever. It is ugly and a huge pain, and a major mistake. Please listen to this warning, you will be sorry.