Rotten Wood Threshold

Teresa Schenck has a rotten wood threshold at her home in Bettendorf, Iowa.

Here's what she sent me:

"As you can see, this piece of wood at my back door is rotting.

It is about 1.5-2 " wide, and maybe 6-8" deep.

My deck is also there. I am replacing the wood decking.

I want to fix this piece of wood while I am working on the deck. I don't even know what it's called. How can I best fix this?"

The red arrows point to the rotten threshold. Photo credit: Teresa

Here's my answer:

Teresa, you've got a serious problem.

The threshold under the door is not treated lumber - at least I've never seen one before.

They're designed to be painted and have a drip kerf on the underside to shed water and stop it from rolling under the threshold.

The threshold is supposed to be able to dry out fast after each rain.

Whoever built the deck against it made a serious error.

Water is now trapped and the wood can't easily dry.

To do this the right way, you need to remove the deck band board and joists around the threshold.

You do this by building a header that connects to the joists on either side of the doorway.

I'd put this header about three inches away from the threshold.

Then I'd install a lead flashing over the wood threshold after allowing it to dry and painting it very well.

The lead would have to go under the aluminum door threshold I see in the photo.

Failure at any step in the process will just cause more rot in the future.