So far I've been taking off sections of the old floor and replacing them. I'm at the point where I'm about to work in the doorway so I thought I'd write a bit about the doors.
This barn is of a style known as a "bank barn." It has a cellar, and the floor of the cellar is at the original grade. When the foundation was built a stone wall was built and then dirt was piled around it to make a ramp to the first floor. The first floor has a door on each side, my understanding is that hay would be brought into the barn in wagons, unloaded into the lofts and then driven out through the opposite door. Here's a picture:
When I got the barn the sills were even with the ground, the previous owner used to drive tractors in. On the south side the sill was quite rotten. One of the things I did, years ago, was to use the tractor and box blade to take almost a foot of soil off of the ramp on each side so that the sills are now up off the ground.
The picture above is of the north door, looking south. I built these doors five years ago. They look just like the doors that were there which were badly rotten. The doors on the south side are vertical cedar tongue and groove, which is probably more historically accurate. When I built these doors I wanted them to last so the bodies are made of a sheet of MDO and the trim is Azek.
Each door is 8'8" high and 4'8" wide -- bigger than a sheet of MDO. To make up the extra space I added 4" strips along each side and an 8" strip along the bottom. Across the top is a 1x8 piece of Azek, along the sides are 1x6 pieces and the bottom is 1x12. A piece of 1x4 is attached to the left door to cover the gap where they meet.
I beveled the top of the bottom edge to prevent water from pooling:
On the back the joints are covered with a layer of 1/4" plywood. The whole sandwich is 1-1/2" thick and held together with glue and 1-1/4" deck screws from the back. The Azek is glued together with Azek glue. Along the outside edges and the top there is a piece of 1x2 Azek to cover the seam.
There is a wooden box that covers the track. I have replaced both the north and south sides. On the north side I used Azek and on the south side I used pressure-treated trim boards, an experiment in which is more durable. We'll see.