Water readily enters the end grain of posts, joists and decking. The end grain is what you look at when you cut down a tree and can see the concentric growth rings.

Here is what I see in Amber’s photo. First, there are two joists at the end of the deck. The first one, no doubt, is nailed into the end grain of the ledger board.

Here’s what I see in Amber’s photo. First, there are two joists at the end of the deck. The first one, no doubt, is nailed into the end grain of the ledger board.

This is a close-up shot of the top of a 2-by-10-inch treated wood deck joist. You can clearly see the rot happening around the corroding screw.