Installing a pre-hung door

When we moved, the doors and trim in our house all had an oak finish. All except for one. For some reason, the main level bathroom door was white. This was a case where being unique wasn’t a good thing. While we were doing some work on that bathroom, it was time to make the door match all the others.

Doors are not complex (there are no hidden parts) but not easy either. A door is the largest moving part in your home and you use it every day, especially if it’s the bathroom door, so it has to be set up for the long haul.

The first step is to choose the correct door, and right there at the start I messed up. I carefully measured the width and height of the door and picked out a pre-hung oak replacement at Menards. I even checked out what’s called the handedness of the door. Doors can be left-handed or right-handed — this website explains in foolproof detail how to check.

What I never thought to measure was the thickness of the wall. Aren’t all walls the same? Actually, some of our walls are plaster instead of drywall, so they are a little thicker than the normal 4-1/2-inch depth. (The house was built in the 1960s, which seems a little late for plaster — I need to learn more about that.)

I looked into a few options. I could have added an extra piece onto the standard jamb to bring it up to the necessary thickness, but that seemed tricky, especially without a table saw. I also considered building my own custom jamb, including the cutouts for hinges. In the end, I ordered a custom door from Menards with the correct jamb thickness.

Now it was time to remove the old door. First I removed all the old trim — carefully, because I wanted to put some of it back up when I was done. I have a small pry bar that helped, but I did a lot by working a stiff putty knife between the trim and the wall. Then I popped the hinges and removed the door.

Finally, I got out the reciprocating saw I had borrowed. That tool can cut right through the nails holding the current jamb in place (along with anything else that gets in its way, so pay attention). After some noise and mess, the jamb was free.

A tip for removing the jamb: once it’s loose it won’t want to keep its square shape. That’s fine if you’re throwing it away, but the old door and jamb might have some value — I sold mine for $50 on Craigslist. To keep the jamb from collapsing, you can screw a thin board across the bottom, making the fourth side of your rectangle, so to speak. Place the screws such that they will be covered by the trim when the next person installs the jamb. Later you can put the door back in the jamb and that will help stabilize it as well.

With the door cut out, I now had a not-very-private bathroom. Time to get to work.

I won’t give a thorough description of installing the door, but I’ll outline the general process and share a few lessons learned. Here’s the first one: never trust. Or to make it more specific: do not assume that right angles exist. The wall cutout is not perfectly square. The floor is not level. Nothing is square or level or plumb or straight.

The goal is to have the jamb perfectly level and square in its place. The first thing to check is that the top is level — in other words, whether the floor is level. In my case, it was not. I propped up the low side with a shim, then measured and cut that amount off the high side using a jigsaw and straight-edge. Really, you have to cut a piece off your brand-new jamb? Yes. Keep track of which side is which! It’s surprisingly easy to get turned around and cut the short side instead of the long one.

Getting the top level is the easy part. The more difficult task is making the vertical parts stand straight up and down (technically this is called plumb). I had a two-foot and a four-foot level for this, along with a square that could show me a right angle. And then I just kept working at it.

One more thing: the jamb needs to stay aligned to the planes of the wall without sliding or tipping into or out of the room. To make this part easier, I screwed a scrap piece of trim into the wall near the bottom of the opening. Now the jamb could fit up against that piece and be perfectly aligned with the wall. The screw holes would be covered up when I put the molding back.

Cedar shims keep the jamb square and plumb. They are angled and you push one in from each side. In this way you secure the jamb and can even move it a little one way or the other by pushing the shims in deeper. Some areas may need more shims than others, but you can imagine putting them in every 18 inches or so.The shims will stick out from the jamb. This is expected, and you can snap them off later by hand, as a way of releasing frustration over how long this whole thing ended up taking.

Unfortunately, as you work on one side of the door, the shims will fall out of the other side. For this project, it’s good to have a partner to help, preferably one with patience and a good sense of humor.

Once the shims are in place, I checked that everything was level and square. And checked again. And again. When I felt ready, I used a nail gun to drive nails through the shims. I did a couple of those, then checked for level again, then drove the rest of the nails and snapped off the shims.

Some people add extra stability by removing one of the standard hinge screws for each hinge and replacing it with a long screw that goes all the way into the wall. I didn’t do that because my hinges were a dark color and I couldn’t find a matching screw head on short notice.

Finally, time to hang the door! Here again it’s ideal to have a helper, though one person can do it in a pinch. One trick is to close the door so that the latch helps hold it in place while you insert the hinge pins. Keep in mind that if you don’t have a doorknob attached yet it is possible to lock yourself in the room this way (I learned that the hard way).

Once the door was in place, I made sure it swung freely and hung level when closed. Honestly, I didn’t get everything perfectly aligned, but it wasn’t bad for a first try. I put the trim back up and — finally — privacy was restored.

If you want to see more, this YouTube video gives a pretty detailed description of the process (notice he has trouble with the shims too).

(Featured image by Erik Mclean on Unsplash)