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Re: Rafter/ridge board
Let's visualize a 2x12 rafter against a 1x6 ridge board, leaving over half of it unsupported.
The part which *is* supported against the ridge board will transfer its loads to the other, opposite, ridge board.
The part which *is not* supported will likely split away from the upper part which is supported. This is because the roof load (dead load) is a gravity load, working against the rafter vertically, trying to push the rafter down, the unsupported part of the rafter end complies, the supported part of the rafter end does not comply - causing the rafter to split.
Now, add snow loads, wind loads, etc., to those roof loads and the forces trying to deflect that rafter is even greater. And the force trying to split the rafter at the unsupported end is even more concentrated.
I'm sure someone has a good photo of a rafter splitting because it was unsupported by a too-small ridge board.
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