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Community and Q&A

Wood siding 101

user-788447 | Posted in Green Building Techniques on

This is follow up to a question I posted before about not using caulk when installing cedar lap siding.

When not using caulk and trying to minimize rainwater infiltration to the WRB can cedar siding be pressed tight against window casings, corner boards, etc. or is a ~1/16″ gap necessary for lateral expansion/contraction? (I’m in Minnesota with a sizable temperature and humidity range)
I neither want to add a batten nor route out the window casements. I will just be butting the siding into any exterior trim. I did create a 1/4″ drainage plane behind the siding.

On a related note I’m using D&Btr cedar. The knots that some of the wood has are nickel sized and crusty black around the edges of the knot. Some have already popped out. Can I use two part wood filler to lock in knots or replace the knots that have fallen out? Or are these knots inevitably going to fail in the outside conditions?


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  1. GBA Editor
    Martin Holladay | | #1

    J Chesnut,
    1. Just butt the siding against the trim, without leaving a deliberate gap.

    2. If you notice the loose knots before you install the siding, then by all means cut out the knots before installing the length of siding.

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