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Launch Slideshow

A Fiber-Cement Sunburst, Images 1-11

A Fiber-Cement Sunburst, Images 1-11

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    After stripping the old siding, I measured down perpendicularly from the peak to the base of the gable, and up the rake from the base flashing to the peak.

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    I snapped out the gable full-scale on some sheets of plywood.

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    With the steep pitch, the full semicircle looked right, so I cut a pattern out of 3/4-inch plywood.

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    In this case, the diameter of the half circle was about a fifth the length of the base of the triangle.

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    Next I marked out the clapboards along the rake, starting at the bottom and marking the exposure up both sides.

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    I marked the layout on the half-circle pattern.

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    Marking the layout on the half circle

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    Then I transferred the marks to the full-scale layout.

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    I now had endpoints for the rays marked on the sheets of plywood, so I snapped lines through the marks.

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    I laid out every ray from a couple of inches inside the half circle to a point several inches past the rake line.

Things have been a little slow this year, so I had time to help out a friend who’s refurbishing an old home. The siding had seen better days, and the gables were about the worst of it. After some brainstorming, we settled on adding a sunburst pattern for all four gables.

I looked around for some type of instructions, but to no avail. Because I had several gables to do, I thought it would be smart to think through the process and develop a systematic approach. Here’s what I came up with.

First, I needed accurate measurements. After stripping the old siding, I measured down perpendicularly from the peak to the base of the gable, and up the rake from the base flashing to the peak. This gave me what I needed to easily reproduce the gable triangle on the ground. I wasn’t concerned about being absolutely accurate, because I’d be reinstalling the bed molding under the soffit, which would give me about an inch of play.

View Drawing, p. 3

I snapped out the gable full-scale on some sheets of plywood. Then, by trial and error I came up with a half circle — the “sun” — that was pleasing to the eye. In this case, the diameter of the half circle was about a fifth the length of the base of the triangle. You can get a different look by cutting a few inches off the bottom of the half circle — use a shallower arc of the circle. This creates the impression of the sun rising over the horizon, and may look better with shallower pitches. With the steep pitch, the full semicircle looked right, so I cut a pattern out of 3/4-inch plywood.

Calculating the Exposure

I was using 8 1/4-inch fiber-cement siding and wanted to leave about a 7 5/8-inch exposure at the widest point (the rake). While 5/8 inch is not a big overlap, keep in mind that fiber-cement clapboards aren’t tapered, and I wanted to avoid the big buildup that would occur at the narrow end if the overlap was greater.

To fine-tune the layout, I added up the lengths of both rakes together (192 inches), then divided by 7 5/8 — my target exposure — to get a number slightly over 25. This was ideal: I wanted an odd number, to give me an even number of rays up each side and a cap piece at the top. (I’ve seen designs that have an even number of rays that meet at the top, with the joint covered by a mullion piece, but I preferred to make the cap look more like a natural part of the design.) To get the actual exposure, I divided the rake length (192 inches) by 25, for a final weather reveal of 7.68 — or 7 11/16 — inches.

Snapping Out the Rays

Next I marked out the clapboards along the rake, starting at the bottom and marking the exposure up both sides. I used a construction calculator to speed this step, adding the exposure number itself by pressing the “plus” button and marking the cumulative number on the tape measure.

To lay out the bottom of the rays, I measured the circumference of the plywood half circle, then divided that by the number of rays. I marked the layout on the half-circle pattern, then transferred the marks to the full-scale layout. I now had endpoints for the rays marked on the sheets of plywood, so I snapped lines through the marks, laying out every ray from a couple of inches inside the half circle to a point several inches past the rake line.