Caulk in trim that overlaps, lap siding


On the front of our house, we have masonite lap siding. Overlapping the lap siding on the edges, there is 1 x 6 inch wood trim. There are, thus, triangle gaps along the edges all the way down. My question is, should I caulk those in when I repaint? They seem like easy entry ways for moisture to get in behind the trim and most of the vertical trim boards are rotten at the bottom. I know the rot could have happened due to other reasons, but it leads one to think if the design of leaving the gaps un-caulked over masonite lap siding was ever a good idea. Much was found out about the problems with masonite a few years after our house was built. I have got both answers from professionals. The ones that said to caulk it in said two things. One, that annual inspections need to be done to ensure the seals are good to make sure you are not trapping water because of a breach in the caulk line. Two, that caulking them in is fine as long as you never caulk the underside of lap siding, as it needs to breath. The one that said leave them un-caulked said it was that way by design. Although I understand that theory and would find it applicable to stained wood siding, what we have is a different animal. Any suggestions? Thank you very much!

One Response

  1. Yes, caulk in the trim to the masonite siding, but never caulk in the siding drip edges (“underside of lap siding”). Caulking these gaps will help improve the weatherproofing of your home by preventing water infiltration, insects, and drafts. It will also enhance the aesthetic appearance of your house by creating a clean, finished look. When selecting a caulk, opt for a high-quality exterior paintable caulk that is flexible and durable to withstand temperature changes and movement in the siding. Before caulking, make sure to clean and dry the surfaces thoroughly to ensure proper adhesion.

    ** Most likely it was uncaulked by design, when a house is first painted the builder wants a cheap paint job and caulking this gap takes a lot of caulking and extra time = more money.

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