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My roofing will have a drip edge that directs rainwater away from the subfasica and barge rafters. Is it still important to finish (paint) them to protect them?

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Yes, you should finish all exterior wood no matter whether it will get rained on or not as wood still can rot simply from ambient moisture in the air.

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Especially end grain. Wood is microscopically made of tubes which moves water by capillary action. Water getting into end grain migrates along the whole length of the piece of lumber if the rafter tail stays wet enough. I've watched this in action on our next door neighbor's house over the last 25 years. The final rafters were cut with decorative tails that project out from under the drip edge and have rotted up about 3 feet under the roof. Only a fool would expose rafter end grain to incessant winter rains in Oregon. –  Fiasco Labs Oct 2 '12 at 15:22
    
Why don't we paint floor joists, which are exposed to ambient moisture? –  Jay Bazuzi Oct 2 '12 at 16:10
    
@FiascoLabs: I am explicitly asking about wood that is protected from direct rain. –  Jay Bazuzi Oct 2 '12 at 16:11
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We are talking about wood exposed to weather. This is not the same as exposed to rain. Soffits are exposed to weather even though not exposed to rain. Think wind blown rain, not ambient moisture. Floor joists are typically covered by siding, so not exposed to weather. If not covered by siding or similar weather barrier, then they should be finished like any other exposed wood. Note that finish here does not necessarily mean paint, rather some sort of weather resistive finish, paint being a popular and effective choice. –  bcworkz Oct 2 '12 at 19:59
    
I can give you a really good example. When damp air hits anything colder than it is on the outside of your house, it condenses. Bare wood is a sponge, damp wood rots. You paint the wood exposed to these conditions to stop water absorption, promote shedding moisture to the outside and prevent deterioration. –  Fiasco Labs Oct 2 '12 at 21:59

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