Caulking Between Siding Boards

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.

Caulking between siding boards.

Seal a door frame in place and seal the subfloor at the bottom of a door frame. 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. Always caulk between the siding and the trim. Fill in gaps between crown moulding and baseboards.

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. Do not caulk between siding and any built in receiving channels located at or around windows. These siding joints can be caulked successfully if the gap is wide enough for the caulk to get into the crack.

Best for use with drywall wood and masonry. 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. Flashing acts as a waterproofing layer for this type of siding and caulking will prevent the flashing from doing its job. Sometimes known as acrylic latex caulk.

Vertical trim gap caulking. James hardie recommends the use of caulks and sealants that remain permanently flexible. Bottom of siding boards should not be caulked water is meant to exit through the bottom of each board. Placing caulk over large portions of wood siding prohibits the natural movement of the wooden panels and can cause extensive damage to the exterior of your home.

The siding expands and contracts with temperature and humidity. If the siding joint is so tight that the caulk only bridges the gap it may split. Also where the siding meets corner boards and corner board joints. While paint does tend to somewhat glue these pieces together caulking them is never advised and can cause permanent damage.

Use latex painter s caulk inside of doors and windows or to quickly fill cracks. Caulking them is a mistake and the caulking is likely to fail prematurely.