Expert: Richard Taylor, AIA - 4/11/2008

Question
I have been asked by a client to build a simple portico over a front entry door. The house is a box colonial with enough room to attach a gable roof to the front facade. I am trying to figure out the best way to frame for an arched ceiling under a gable roof. Do I frame the roof as a typical gable then add plywood "rafters" that have been cut with an arch? The existing porch slab is approx. 8' long x 5' wide (from house to end of stoop).
Thank you in advance for your help.

Cordially, Bob

Answer
Bob - thanks for your question!

The way you frame this will depend on how high the arch is.  If it's a relatively "flat" arch, you can install collar ties partway up the rafters and frame the arch in underneath.  In such cases we usually design arched plywood bulkheads to create the arch shape (sometimes double 3/4" plywood) and to attach the ceiling boards to.

For a taller arch the method you've described is appropriate - as long as you make the ridge live and support it at both ends.  You can also block the arch shape in with 2x lumber and bend 1/4" plywood around it to create the arch.

An arched entry portico is a classic Colonial Revival detail and when it's properly built and designed adds great character to such homes.

For more information I recommend several books, all available inexpensively from www.doverpublications.com:

"Old House Measured and Scaled Detail Drawings" William A. Radford
"Architectural Details and Measured Drawings of Houses of the Twenties" William A. Radford
"Architectural Details from Old New England Homes" Stanley Schuler

Hope this helps!

Richard Taylor, AIA
www.rtastudio.com
www.rtaplans.com