Drywall Arches: Simple, Segmented, and Elliptical

Arch 1: How to draw a radius arch

Points of reference:

• Height: top of arch above the floor. All arches in a house will typically share this number. The height will be two inches below the header.
• Rise: distance from a height down to where the curve begins. For a doorway that is 36 inches wide, the rise will be 18 inches, and the run will be 36 inches.
• Spring line: where the rise hits the outside edge. Where the curve becomes straight.
• Run: width of the arch.

Step-by-step guide for drawing a radius arch

• Mark the center of the opening
• Draw a plumb line up to the height mark.
• Measure down 18 inches from the height mark. This Mark will be the pivot point for drawing the radius.
• Partially set a drywall screw into the pivot point
• Use a piece of wire to bend to the correct length to draw the radius beginning at the top and swinging the pencil left and right.
• Draw a level line at the bottom of the arch — the spring line.

That is how to draw the simplest—and least common—arch.

Why is the easiest arch to draw the least used? Because it is hard to make a radius arch look like the other arches in the room if the widths are not all the same. Different spring lines in the same room look like after-thoughts.

A half-circle arch closes off a substantial amount of walking space, causing headache potential.

Arch 2: Drawing a segmented arch

A segmented arch is one that uses a portion of the radius from a larger circle. Segmented arches allow you to keep height and spring line consistent. In this example, the height will be the same as the radius arch was — two inches below the header.

• Mark the height
• Determine where the spring line will be (figure the rise). Myron chooses seven inches.
• Determine what the radius of the segment of the circle will be.

One way is with a construction calculator:

• Run=36
• Rise=7
• Radius = 26-3/4 inches.

Another way is to use the formula:

• Measure down from the height 26-3/4 inches
• Partially drive a drywall screw
• Prebend a piece of wire at 26-3/4 in
• Swing a line left and right from the center until the line intersects the spring line.
• This allows you to keep a consistent spring line height with slightly different radii
• This also provides a definite point of transition from curve to straight.

Arch 3: How to draw an ellipse:

Step by step for drawing an elliptical arch:

• Measure to find the center
• Plumb up
• Mark height
• Mark the rise (7 inches again)
• Draw the level spring line
• Get a piece of string with a knot at either end, 36 inches apart (or whatever the run is).
• On an elliptical arch, this is called the major axis.
• Half of 36 is 18 and that is called the minor axis