Identifying the problem
The door between our garage and house has probably been in place since the house was constructed. However, last year we discovered that the same was not true of the rubber seal between the threshold and the door. It had been glued down to make up for the low clearance between the door and our hardwood flooring and the repeated friction of using the door had taken its toll. So, we removed the seal (it was getting annoying, flapping around every time we use the door and was entirely ineffectual) and proceeded to find a suitable replacement.
During my investigation into the various types of seal available, from simple door sweeps to threshold/door combinations, I found that part of our problem was the old door threshold. It had become worn and the saddle (the part that has an adjustable height on some types of threshold) was no longer adjustable. As I'm a bit of a DIY novice, I consulted a few Internet searches, a book, my dad while he was visiting and our wonderful neighbour (a local contractor). It seemed that the door was pre-hung including the threshold, so the right thing to do was to replace the whole door. Unfortunately, replacing the door is a pricey undertaking, so I decided to try replacing the threshold. In the worst case that I messed it up, I'd just be back to the original option of replacing the door.
Removing the existing threshold
The first thing I had to do was remove the old threshold. To do this, I used a reciprocating saw and cut the threshold down the middle. This was a little more difficult than I had anticipated due to both the uneven structure of the threshold and the hardwood floor in our house, both of which would catch the saw and jar it in my hands. After some trial and error, I was able to slice the threshold almost entirely in half.With the cut finished, I used a pry bar to lift the threshold and take out each half. This took some effort, lifting and pushing the threshold repeatedly to shear the remaining uncut portions. In fact, it took much more effort than I thought it would. Once the whole threshold was out and I had a chance to look, it became clear exactly why it was so difficult to remove. The threshold had been attached to the door frame on each side by three screws and I had sheared two screws on each side and torn the remaining screw out of the frame. I'm not sure that I could have avoided this as the door frame was overhanging the threshold, making it impossible for me to use the reciprocating saw to cut the screws. However, it's probably worth knowing should you try this yourself.
Before doing anything else, I cleaned up the edges that adjoined the threshold and swept up any remaining debris. This included getting rid of the flooring adhesive that had been used to seal the gap between the threshold and the floor.
Fitting the new threshold
With the old threshold removed, it was time to prepare the new threshold. I had shopped around and settled on a threshold that was mostly the same as the one I had removed except that it had a wooden saddle rather than a metal one and it was too wide for the door. I measured the width of the door frame (it seemed important) and the new threshold to determine just how much had to be trimmed.
To ensure that the saddle adjustment screws were properly positioned after trimming, I wanted to trim an equal amount from each end of the threshold and to ensure I didn't get the cuts wrong, I measured the two cut points in two ways. First, I measured from each end half the width of what was to be removed and marked it with a pencil, then I added the same amount to the door width and measured that from each end, again marking it with a pencil. Finally, with my trusty hacksaw, I made the cuts as marked.Once cut to size, I placed the threshold against the door frame to check the fit. Although the width was now correct, it was clear that the threshold was not going to just slip into place. After all, I had to cut the old one in half just to pull it out. In addition, the profile of the new threshold was different to that of the old one, which meant adjusting the door frame to fit. With several ideas coming to mind that all involved potentially irreversible actions, I was a little stumped on the right way to go so I consulted my awesome neighbour, Tim. He suggested flush-cutting the door frame so that the threshold would slide right in and then screwing the threshold down. He even lent me his flush-cutter to do the job, so after marking the door frame to show where the cut needed to go, I stacked up some things to give a platform for the flush-cutter to rest on. This turned out to be my first practical use of the Borders signs I had obtained when the beloved bookstore folded last year. With both sides of the frame cut and without the right tools to hand (a chisel would've helped here), I used my multipurpose paint-stripping tool to clean up the cut. It turns out that the part of the frame that needed cutting was thicker than expected so the finish was less than perfect, but it would be hidden once the job was done. To finish up this stage before actually getting the threshold into place, I checked the fit against the newly cut frame by using one of the pieces I had trimmed off.
With everything trimmed to size, it was time to install the threshold. On the advice of my neighbour, I removed the saddle so that I would be able to screw the threshold down once it was in place. I also marked the saddle and the threshold to ensure there was no frustrations when putting the saddle back on.With the saddle removed, I tapped the threshold into place. I added a bead of caulk to seal the gap between the inside floor and the threshold and pushed the threshold all the way home. It was now time for power tool number three. I drilled three pilot holes for the screws to fix the threshold in place. I also drilled countersinks to ensure the screws would be flush. Once all three screws were in and holding the threshold in place, I reattached the saddle and adjusted its height to fit against the bottom of the door (this involved a lot of opening and closing the door). To finish everything off, I caulked all of the edges.
I have learned a lot from this, had a lot of fun and saved quite a bit from not having to install a new door. When I started I wasn't entirely convinced it would work out and if I were to do it all again, I certainly might do things a little differently. That said, I am still very happy with the results and more importantly, so is my wife.