Mikepier wrote:
....

If you use an oak sill, how do you protect it from the elements?
Stain, paint?

Typically, they're reasonably well protected by the eave overhang,
porch, etc., ...

You can stain to suit, then good exterior varnish. Not much point in
the oak if you're going to paint--the reason for oak beside it being
suitably hard is typically the appearance.

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