Shingling a curved roof? Prepare to improvise

Q. Destroyed by fire, my 1923 house is being rebuilt using red-cedar shingles. I want to duplicate the gambrel roof, and do not know how to bend shingles to curve. The roofer is steaming the shingles, but has difficulty with splitting. What is the proper procedure? A reader Mattapoisett, Mass.

A. The commercial art of bending wood shingles is virtually gone. Improvisation on the job has taken its place. It's a fussy process!

''To achieve the desired effect,'' writes a veteran roofer, ''the shingles were submerged in water for 24 hours, transferred to a steamer for 30 minutes, then to a brake (specially designed on the job) to form the shingles into the different pitches needed.''

He was describing reshingling a curved residence in Florida. They only had 10 seconds to get the shingles from the steam to the brake, and could only brake 16 at a time. Each shingle was then custom fitted and fastened in place. The reshingling took five months, including tearing off the old shingles. Sixteen-ounce copper was used for all flashing.

During the 1920s and '30s, when curved-eave architecture was popular, several shingle mills installed special steam-bending equipment for that market, principally in southern California.

When rolled-eave architecture lost favor, the market for steam-bent shingles all but ended. Mills removed and junked the specialty equipment. ''Therefore, none of our manufacturers have been in a position to market these special shingles for many years,'' says Marshall Ritchie, marketing manager of the Red Cedar Shingle & Handsplit Shake Bureau in Bellevue, Washington.

One intrepid couple who tackled shingle bending themselves reported that, before boiling, some shingles are more flexible than others. Some don't bend at all even after boiling. The whiter, pinker ones work the best, they said.

In the boiling process, the water must be changed several times to limit discoloration of the shingles. Sort shingles to find the proper grain pattern best suited for the bending needed. Straight grain is usually, but not always, chosen for boiling. Boiled shingles are submerged in a drum of cold water to ''set'' the shape of the shingle. Kept damp, they are fastened with copper nails. It may take 100 squares of shingles to fetch fifty usable squares.

Successful bending of shingles is almost a trial-and-error skill. Splitting is predictable. Careful preselection of the most likely shingles is recommended, the straight-grain units being the most likely candidates.

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