Finishing Exterior Door Threshold Gap

Question

We recently had an exterior door installed by a family friend. We raised the new door about 0.75" higher than the original rough opening using a 1x4 board so that we could comfortably fit a rug under the door sweep inside the house (previous owners installed a wood floor without fully removing the previous floor, so the original door had 0 clearance for any rug). The new door is hung well, but we neglected to determine how we were going to fully support and weather seal the new aluminum threshold.

Here are pictures of the situation:

https://imgur.com/a/hb4H9lF

Some other previous owner poured a large concrete porch thing directly against the side of the house. In the pictures you can see the rough door opening and the aluminum trim that was below the original door threshold.

We figure we need some kind of rot resistant composite board (maybe PVC?) to support the threshold and then some sealant to prevent water ingress off the concrete. Or maybe we can use another 1x4 and some kind of moisture barrier/flashing in addition to sealant?

I have no problem grinding away a small amount of concrete and backfilling it if it's important to get the old aluminum out first.

Any tips on how to handle this situation are appreciated! Thanks.

Answer 1

There are a few different ways to fill the gap.

My prefered method would be to apply polyurethane caulk in the gap first. Then insert a PVC trim that will fill in the void. Since your situation is unique, there isn't a standard moulding made for it. Something will need to be fabricated. A PVC brick mold ripped down on a table saw could work.

Insert the moulding backed with a generous amount of poly caulk. (No nails are used) Seal all the edges with poly caulk, wiping away the excess. Then paint to match the door trim. You have a very waterproof seal.