Many homes between the 1920’s and the 1950’s were built with archways instead of a square opening as a room entry or transition. This is a nice architectural feature, but doesn’t always suit the new style of a project, or isn’t in the kind of condition that makes it an attractive feature. The plaster may have many cracks, or paneling might have been added in a way that doesn’t do a nice trim job justice.

Before
arch opening

After
arch doorway squared

Here is a quick step by step guide to replace the arched opening.

– We are assuming that you are keeping the opening the same width as it is now. If you are not, you will have some structural issues to contend with. It isn’t all that difficult if you follow the correct steps, but that is for a different how-to.

A-1: arched opening original

1) Cut the corner bead. The corner bead is very likely a metal bead that will be very tough. You will need to cut about an inch below the point where your arch meets the square section of your opening. A reciprocating saw with a metal cutting blade is perfect for the job. You will do this at each side of your arch. (see diagram A-2). This will allow you to tear out the arched portion of the door.

A-2: arched opening original A-2

2) Score or cut a the new corners. Now that you have made these cuts, you can score the outline of your new opening. You are essentially looking to square off the opening. I prefer using a circular saw (assuming you have the clearance) for this project. If you make cuts in the existing plaster, you will give it a place to break away. I make a cut about 1/2″ deep (see the darker outline in image A-3. Cut about 1/2″ to the inside of your opening. You will be trimming this out with door jambs, so you should cut away a bit larger area. This will be covered with casing (molding) later.

3) Tear out the corners. Once you have made cuts in your corner beads, and scored your plaster, you can remove the arched portion of opening. This is the messy part. Find what works for you, but a hammer is probably best tool for the job. These corners were probably formed with a few pieces of lumber cut to the shape of the opening. The actual rough framing should be square. Remove everything above your first cuts. Tear out the corner bead and the plaster. Knock out the wood used to shape the arch.

A-3: remove arched opening A-3

4) Attach the upper piece of your door jamb. Now that you have a clean slate, begin the process of building your new opening. Your jamb can be build out using a decent quality pine. You will attach the top piece first. Cut the piece to width and keep it about 1/4″-1/2″ short of your entire opening. Your jamb lumber needs to be ripped to the same with as the finished wall on each side. You might get lucky and have a 6″ piece of lumber that is the exact with of your walls. Attach the upper piece. Be sure that it is level. If it is not, shim to level the piece. This is important.

5) Attach the side Jamb Pieces. One the upper jamb is in place, measure and cut your 2 side pieces. Cut them about 1/8″ short so that you can fit them in well. Attach these side piece by making sure the are plumb, and that they are flush with each side of the wall. Since you cut away the upper section (where your arch used to be) you won’t fasten there first. You probably don’t need to at all. Nail these in with some finishing nails. Be sure that your nails are long enough to reach the lumber beyond the plaster.

6) Attach Your Trim/Molding. You are nearly finished, and it will really look that way once you have your trim attached. Measure and cut your upper trim piece first. Measure your opening and then add about 3/8″ to th inside length. This should be the total length of your trim measure from the shortest part of your 45″ miter cut. Attach the upper, making sure that it is square, leaving a reveal of about 3/16″. Once you have attached this upper piece on both sides of your opening, you can measure and cut your pieces for the side trim.

All that is left is some paint and/or stain. Please feel free to post a comment or a question in the comment section following this how to. We will be happy to elaborate on any part and provide better images to explain any steps along the way.