Framing an Elliptical Arch Doorway: Complete Step-by-Step Carpentry Guide

Elliptical arches offer a graceful, sophisticated alternative to circular segmental openings. They provide maximum headroom at the center while smoothly sweeping down to the vertical side jambs.

Here is how professional finish carpenters lay out, frame, and finish an elliptical archway.

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1. Calculating the Ellipse Axes

For an elliptical opening:

• Semi-major axis (a): Equal to half the clear opening width: a = Span / 2
• Semi-minor axis (b): Equal to the total arch rise: b = Rise

Finding the Focal Pin Distance (c)

To draw the ellipse using two pins and a loop of string:

c = sqrt(a² - b²)

Drive two small finish pins at distance c to the left and right of the centerline on your springline.

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2. Cutting Plywood Ribs & Spandrel Blocks

1. Lay a sheet of 1/2” CDX or OSB plywood on your sawhorses.
2. Scribe your elliptical cut line using the two-pin string loop method.
3. Cut along the pencil line using a jigsaw with a fine-toothed blade.
4. Use the first cutout as a pattern to trace the duplicate rib for the opposite wall face.
5. Fasten 2x4 wood blocking ribs spaced every 6” to 8” on center between the two plywood faces.