The single light French Doors on the basement patio are both sagging, resulting in a torn weatherstrip on the active door and a significant gap between the doors near the center bottom. The doors are sagging because each door weighs 64.5 lbs and is a bit too heavy for the standard grade residential door hinges. I plan to replace the door hinges with heavy-duty models – the subject of a forthcoming How To article. The topic of this article is replacing the unexpected surprise of a rotted bottom frame and installing a new weatherstrip.
Patio French Door Construction
The patio doors are metal skins folded over a wood frame with a foam core. The door hinges, dead bolt and door handle are fastened with screws to the wood frame. When I removed the door to replace the hinges and weatherstrip, I discovered the wood frame inside the bottom of door had dry rotted and was nearly gone!
Door Jig
In anticipation of replacing the hinges on both doors, I made a jig out of scrap 2×4 lumber and 3 inch wood screws to hold the doors. French doors are expensive and I didn’t want to take a chance on breaking the glass panes.
Door Jigs and Wedges
My doors are 1-3/4 inches thick. Therefore the vertical 2×4 blocks are spaced 2-1/4 inches apart to form a slot about 6 inches deep to hold the door. Wedges are used to take up the slack. The other jig dimensions are not critical, but sized such that the can’t tip over. I found these to be rock solid.
If you’re worried about scarring the door faces, just lay an old towel inside the jig to protect door finish.
Rotted Door Bottom Repair
This is bottom of the french door before I removed the old weatherstrip. I thought it would be quick to remove the old weatherstrip and install a new one. Little did I know the “fun” was just about to begin!
Patio Door - Torn Weatherstrip
Most of the bottom frame had rotted away when I pulled off the old weatherstrip. I scraped out chunks of what was left of the old wood. My first thought was termites, but the sides of the door frame were solid and untouched. I saw no evidence of termite tunnels and the door jamb was also OK. Closer inspection revealed the tendrils and spider-veins of fungi due to dry rot.
Rotted Door Bottom Found after Removing the Weatherstrip
The basement patio doors are shaded by the wood deck. This apparently created a cool moist environment that promoted fungi. Surprisingly the fungi only ate the bottom section and didn’t attack the side frames. My guess is the side frames are made of a different species of wood to take stresses of the door hinges and locks.
Here’s a closeup of the rotted wood. The bright area near the bottom left is the exposed foam core. I gave the inside a good spraying with bleach and water to kill any spores.
Dry Rotted Door Bottom
It was necessary to unbend the folded edge of the metal door skin to insert a new piece of wood. A pair of duck-billed sheet metal pliers would have been ideal for the job. A large adjustable wrench did the job just as well, if not more slowly. To minimize metal fatigue, I first bent the edge out 45 degrees along the entire length, then made a second pass to straighten it out flat as shown here. The lip on both sides was unfolded this way.
Unfolding the Metal Edge of the Door
The dimensions of the replacement frame section is 1-11/16 inches wide by 3/4 inches thick by 31 inches long. The closest thing I could find was a 1 in x 4 in x 8 ft pressure treated board at Home Depot. A nominal 1 inch board is actually 3/4 inches thick. To get a 1-11/16 inch wide board, I asked the Home Depot guy to rip it for me on the plywood saw because I don’t have a table saw. (Of course, you still buy the whole board, which is fine.) It was then a simple job to hand saw a 31 inch length when I got home. The new board fits in between the two end frames as shown in a notch that not too apparent in this photo.
Pressure Treated Replacement Door Frame Section
The bottom of the door frame is filled with GREAT STUFF expanding foam insulation. GREAT STUFF expands to several times it’s initial volume and is very sticky. This will fill in all the voids in the door bottom and press the new wood frame tightly against the metal door edge. Here I’ve just applied the GREAT STUFF.
GREAT STUFF in the Bottom Door Frame
The new pressure treated wood section is pressed into the door bottom. The GREAT STUFF is already expanding and trying to push it back out.
I used a rubber mallet to bend the lip of the metal door skin over the new section wood. The outer corners of the wood strip acted as a sheet metal brake to accurately bend the metal just like the original construction. The GREAT STUFF is expanding and squeezing out nicely. This will hold the wood tightly against the door skin.
Larger view of the new wood frame in the door bottom. The GREAT STUFF at the red arrows completely filled the end gaps and is trimmed flush with the bottom.
Replacement Door Bottom Frame Section
Now I’m finally ready to install the new weatherstrip.
Install the New Weatherstrip
The old weatherstrip attached by two ribs that fit into matching kerfs, or slots, in the door bottom. The new door bottom lacked these slots so I used a U-Shaped B79/35H Vinyl weatherstrip by Frost King. It attaches to the outside of a metal door with screws.
The weatherstrip is tested fitted on the door and marked to cut the length to fit the door. The installation was simple – fit, cut the length, test fit again, mark the screw locations, drill pilot holes and attach with screws.
End view of the U-shaped weatherstrip showing how it slides over the door bottom.
This is the new U-shaped weatherstrip installed on the door.
The new weatherstrip sealed well against the door sill, but a couple of things bothered me:
- The screws might rust.
- Water could seep in along the top of the weatherstrip and pool along the door bottom.
- The appearance didn’t match the other door.
I recommend caulking the screw heads and along the top edge of the weatherstrip. However, I decided to take the door off and cut slots on the door bottom to install the original style kerf-mount weatherstrip in Part 2 of this project.
Thanks for reading,
Bob Jackson
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I just found this website when I was searching for information on how to repair our exterior doors which have rotted on the bottom. Your explanation and pictures are amazing and are exactly what we needed to help us through this project. Our doors were ruined by the hurricane and insurance would not pay to replace them. With five doors we were looking at a very expensive problem. Now we have your how-to in hand, we are ready to tackle this project and will be doing so in the next week. Thank you, thank you, thank you for your wonderful article.
You’re welcome!
Excellent article, and I’ve been around!
I have wondered about that expanding sealant — didn’t realize it keeps expanding after it’s out of the can. Not sure how to use it in any other situation.
But mainly great practical details on how you pulled it all together.