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Ornamental archway: new flexible moldings and old-time carpentry tricks create this classic passageway.

Square rooms, square doorways, square furniture--don't all those straight lines make you feel like breaking out of the box sometimes? Well, here's a project that will help round out your home's interior and your carpentry skills.

Not long ago, you would have needed the tools and talents of a skilled craftsperson to shape the moldings for this arch. Building it is still an exacting endeavor, but synthetic flexible moldings put this project within the grasp of adventurous DIYers. To find a dealer near you, contact: Flex Trim, 11479 Sixth St., Rancho Cucamonga, CA 91730 (800-356-9060); or Ultra-Flex, 207 N. Las Posas Road, San Marcos, CA 92069 (800-344-5293). The moldings can be ordered in an array of shapes and dimensions. What's more, they can be cut and nailed with conventional tools.

We rounded out the opening between a hallway and our eating nook. Openings between a living room and dining room, an entryway and hallway--really any two rooms with an opening--are good candidates. You don't need to mess around with the main structure of your home either, just add the arch below the structural framework already there.

Here's the lowdown.


Synthetic flexible moldings are "flexible" only to a degree. They'll bend easily across their thickness (for example, when used as jamb material, as shown in Photo 6) but with difficulty across their width (for example, as decorative casing around a curved window or door, as shown in Photo 7). Therefore, except for all but the most gentle curves, the manufacturer needs to preform your casing molding to fit the profile of your arch. If your arch is a true semicircle, most manufacturers can bend the molding knowing only the radius. But for ellipses (like ours) and other oddball shapes, they'll want a pattern. This requires drawing or tracing the ellipse onto a large sheet of paper--continuous computer paper works well--then sending it to the manufacturer. It can take up to four weeks for your molding to be manufactured and sent--so plan ahead.

Flexible moldings are available in paintable and (at least from some companies) wood-grained, stainable surfaces. For consistency, order a molding close to that of your existing trim. Unless your moldings are very old, ornate or custom-made, you should be able to get a good match.

We spent $300 for the materials in our project. The flexible moldings are expensive ($8 per linear foot or more, whether curved or straight), so if possible, special-order only the curved jambs and casing sections and use standard wood moldings for the straight legs of the opening. This is where corner blocks (Photo 9) prove their value; not only do they add visual richness, but they create a break in the moldings so the profiles and widths of the curved and straight pieces don't need to match exactly.


Arches come in a variety of shapes and sizes. We chose the ellipse because it kept the passageway's open feeling yet provided a continuous, graceful curve.


Begin by determining your passageway's rough opening or width. Remove a small piece of plaster or drywall from each side, then measure from framework to framework to determine the rough opening. Since you'll be adding 1-1/2 in. thick trimmers to each side of the opening (see Photo 4), subtract 3 in. from the rough opening. This gives you the span or "spring line" of your arch (Figs. B and C).


Lay out the ellipse on a piece of 1/2-in. plywood as explained in "Drawing an Ellipse," p. 66. Cut the curved and straight sections as shown, then hold this piece up to the opening to check for mental errors. If all looks well, trace your ellipse onto paper and bring or send it to the manufacturer or retail outlet for forming. Order one section of flexible jamb and two sections of precurved casing (Photo 7). Order corner blocks and straight lengths of trim at this time too, if you choose.

Ornamental Archway


An ellipse combines a gentle, upper arc with tighter, down-curving arcs at each end. Drawing an ellipse is simple--once you know the trick.

On a sheet of plywood, mark the "spring line" or opening width of the archway (in our case, 72 in.). Since we added 1-1/2 in. thick trimmers to each side, the spring line is 3 in. narrower than the 75-in. rough opening shown in Photo 1. Find the center of the opening and draw the "rise" or height of the ellipse (16 in. in our case). Then take half the spring line (in our example, 36 in.) and from the top of the rise, measure 36 in. and make a mark where it crosses the spring line (Fig. B). These marks are the focus points.

Install drywall screws at the two focus points and at the top of the rise, then tighten a length of picture-hanging wire from focus point to rise point to focus point. Picture-hanging wire is flexible, yet won't stretch. Remove the rise screw and position a fine-tipped marking pen in its place. Maintain tension on the wire and sweep the pen down, first in one direction, then the other (Fig. C). Let the wire guide the pen to form the ellipse.

Once you've received your moldings, verify they're correct, then remove the metal corners and drywall or plaster from the inside face of the opening (Photo 1).


Use the arch you just cut as a pattern to trace the second arch, then cut out the second arch and sandwich the two. Make a series of layout marks every 3 in.; blocks will be installed between them. Position 2x2 blocks where the arch makes a tight curve and 2x4 blocks along the gentle curve and straight sections. Accurately cut these spacer blocks to length (in our case, 2-1/2 in.). We used an electric miter box saw for accuracy. Secure the blocks to the layout marks along the edges of the plywood form (Photo 3). The finished thickness of the arch--outside of plywood to outside of plywood--should be as thick as the wall framing of your home; that's 3-1/2 in. for most houses built within the last 40 years.

Position your arch in the opening and secure it with 3-in. drywall screws (Photo 4). Cut and nail 2x4 trimmers under each leg of the ellipse. Place shims behind them if necessary to make them perfectly flush with the legs of the arch.

Cover the plywood form with the same thickness of drywall or plaster as on the rest of the wall. You'll be tempted to forge ahead to the fun part--applying the trim--but wait. Do your final drywall taping, sanding (or plastering) and painting first; it will be easier and less messy in the long run.


Test-fit your flexible jamb for length, allowing it--if long enough--to lap onto the new trimmers an inch or two. This overlapping allows the cut ends of the trimmers, jambs and casings to fall a few inches apart. This "locks" the individual members of the archway firmly together.

Secure the jamb to the 2x2 and 2x4 blocks of the form, using 8d finish nails and adhesive (Photo 6). Start in the center and work outward in both directions. Predrill all nail holes and sink nailheads below the surface with a nail set (so you don't dent the flexible moldings). Add the straight legs of the jamb. You may need to slightly angle-cut the end that butts the flexible jamb or sand the edges to make them align perfectly.

Next drive 4d finish nails along the edges of the curved jamb, drape the precurved flexible casing over them and clamp it to the jamb (Photo 7). Use a torpedo level to mark level lines where the curved casing will meet the corner blocks. Cut both ends with an electric or hand miter saw, making the pieces a little long on the first cut, then adjusting them as needed and making your final cuts.

Apply construction adhesive along both edges of the casing back, then nail it in place. If you drive nails close to the edges of the flexible casing, they'll make little bulges, so keep your nails at least 3/8 in. away from the edge. I found it helpful to "leapfrog" three bar clamps just ahead of where I was nailing to hold the flexible moldings exactly where I wanted.

Install the corner blocks (Photo 9), then cut and install the straight lengths of molding that fit below. If you have plinth blocks (blocks where the casings end before they hit the floor, as shown in the photo, p. 64) install them, then install the vertical casings.

Fill nail holes and small gaps with wood putty. Sand out any dimples along the flexible molding edges. Prime the moldings, if recommended by the manufacturer, then paint.

Give yourself a round of applause--you're done!
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Title Annotation:construction directions; includes directions for drawing an ellipse
Author:Carlsen, Spike
Publication:The Family Handyman
Date:Feb 1, 1995
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