How to create a drywall arch

Use this skill to upgrade your rooms with interesting arches.

Back when labor was cheap and materials were plentiful, almost every room in a house featured decorative elements such as arches and dividers. But if the rooms in your newer home resemble unadorned boxes, don't let the plain-wall blues get you down. It's easier than you might think to add character to an otherwise dull room by building this drywall archway. Though it may look impressive, an archway requires little time and money: about one day and less than $100 in materials. Just follow these simple steps.


1. Determine and mark the position of the stub walls. Use a stud finder or a small nail to determine nailing points.


2. Cut away any baseboard and carpet that will interfere with the stub walls.


3. Build the stub walls from dimensional lumber using standard framing practices. We used two 2x4s side by side to give the walls a more substantial look.


4. Work in an area where you'll have enough room to draw the arch on the plywood. Lay a long board perpendicular to the plywood. (We used a drywall scrap.) Mark the center of the arch on the plywood; then measure down from that mark to accommodate the drop (4 to 6 in.) from the ceiling plus the radius of the arch (see "Designing an Arch," below). Have someone hold the tape at this point, and with a pencil, scribe the arch.


5. Tack the scribed plywood to an identical piece so you can cut both panels of the arch with one pass. Most arches can be cut with a circular saw, reserve the jigsaw for only the tightest of arches. Set the depth of cut as shallow as possible, and start the cut by watching the blade. Then shift to watching the buide on the front of the saw. Use a belt sander to smooth the arch if necessary.


6. Attach two 2x4s to the ceiling to support the plywood panels, and then nail the panels to the 2x4s. Use 8d nails or 2-in. screws to attach 2x4 blocks between the plywood panels to serve as backing for the drywall.


7. Gently press drywall into the curve starting at the center, it's best to get some help for this step. Screw it to the backer blocks, working your way out from the center. If the drywall breaks, all is not lost. As long as the paper doesn't tear on the front, it will usually work fine. If the arch is extremely tight, dampen the back of the drywall, or carefully score the paper on the back at 1-in. intervals. Clad the plywood panels in drywall, apply flexible corner bead; then tape, apply joint compound and sand (use extra joint compound to create texture that matches the ceiling and hides the seams). Your archway is complete, and you're ready to prime and paint.

DESIGNING AN ARCH
The main elements of an arch are span, rise and the radius of the curve. The span is the length of the curved portion of the arch. The rise is simply the distance from the top of the curve to the bottom of the curve. The radius is a line segment that starts at the center of a circle and ends at the circle's perimeter, in our case, the curve of the arch. Use the following formula to determine an arch's radius:

When designing the archway, you'll need to consider several factors, such as the length an radius of the curve, the thickness of the divider and whether to add stub walls or a horizontal header. Remember that an arch doesn't have to terminate at the perimeter walls of the room. We added a stub wall on each side and a horizontal header to give the appearance that the arch was supported by columns.

Leave a minimum of 4 to 6 in. between the ceiling and the top of the arch to allow for possible future crown molding. To maintain sufficient headroom, the bottom of the arch should be at least 7 ft. from the floor.