I had a new paver patio installed and the installers removed the flat stones that were previously between the landing and the sliding doors (about 4-5" of height). I purchased some white PVC fascia board that I wanted to rip down and screw in to fill the gap, but before I do what is the best way to waterproof this to prevent rotting under the door? Right now there is just the original tar paper. Do I need to apply some sort of flashing?

 

It's pretty hard to flash it correctly when the door is already installed but what you could do is get some waterproofing membrane like Grace Vycor or ProtectoWrap, make a small flap, and stick it to the bottom of the door threshold. But that stuff doesnt stick to felt paper too well so you "might" want to remove some of the felt. But if the felt is in good shape, leave it... just tack the membrane with a few cap nails to hold it until you put the trim on. You should really be putting a z flashing under the siding... and over the pvc.

 

what is behind/under the door. wood or part of the foundation

 

Marq1 - There is wood behind/under the door (it is above grade). The foundation starts a few feet below.

XSleeper - good call on the membrane. I've seen Tommy use that a bunch when installing doors/windows on This Old House but couldn't figure out what the product was called.

Now when I install it, should I flair out the bottom so that it sits like an "L" shape on top of the pavers (below the PVC)? That way any water that gets behind the PVC will then flow out to the paver instead of along the wall behind the paver. The paver landing is pitched away from the house. Also this area is under a soffit so does not get significant water anyway.

Like this: