Caulking Between Siding Boards

Seal a door frame in place and seal the subfloor at the bottom of a door frame.

Caulking between siding boards.

When james hardie siding products butt into wood based materials a 1 8 gap will allow for expansion and contraction of the wood based product. Do not caulk between siding and any built in receiving channels located at or around windows. Use latex painter s caulk inside of doors and windows or to quickly fill cracks. Sometimes known as acrylic latex caulk.

While paint does tend to somewhat glue these pieces together caulking them is never advised and can cause permanent damage. Best for use with drywall wood and masonry. It needs to move and breathe. Always caulk between the siding and the trim.

Another critical place is where the siding butts together in the middle of the wall. Also where the siding meets corner boards and corner board joints. These siding joints can be caulked successfully if the gap is wide enough for the caulk to get into the crack. Think of a wood home as a living thing.

If the siding joint is so tight that the caulk only bridges the gap it may split. Bottom of siding boards should not be caulked water is meant to exit through the bottom of each board. Flashing acts as a waterproofing layer for this type of siding and caulking will prevent the flashing from doing its job. Leave a 1 8 gap between the siding and the trim or other materials to allow for structural movement.

The hypothesis that if it is properly sealed with caulk no moisture will get behind the boards has not only been proven wrong by building scientists it s dangerous and could lead to problems such as sick building syndrome and mold. In my opinion caulking between the seams in any lapped siding either horizontal or vertical is not good practice but not just because of any potential vapor barrier effect. The siding expands and contracts with temperature and humidity. Caulking them is a mistake and the caulking is likely to fail prematurely.

Many professionals like those at james hardie also agree that you should not use caulk on fiber cement siding unless there is no metal flashing underneath. Fill in gaps between crown moulding and baseboards.