Cathedral ceilings first appeared, of course, in cathedrals. Medieval masons crafted these marvels by hand 
(actually, thousands of hands) over decades. They worked their magic with stone (before steel and modern concrete) and stretched the architectural limits with flying buttress, pointed arches, and ribbed vaults to achieve impossible heights for the glory of God.
Cathedral ceilings need not be limited to churches. Even if you are not religious, you can raise your porch ceiling for the glory of… air and space and light. Make it a great porch by raising the ceiling from eight feet to eleven. Now you can install windows in the gable ends to bring in more light and, when screened, more cool breezes. And cost? I’ll give you that good news in a few paragraphs.
First, I need to explain just what a “cathedral ceiling” is. Unlike common flat ceilings, cathedral ceilings are angled, with a slope that follows the bottom of the roof rafters. Indeed, the ceiling finish is typically attached to the rafters. Compare a gable roof with a flat vs cathedral ceiling: 
And on a shed roof¹: 
Structurally, cathedral ceilings differ dramatically. Flat ceilings are formed by horizontal ceiling joists that perform an important structural function: they hold the walls from falling outward under the load from above. 
Roof rafters and ceiling joists form a rigid triangle. Strong.
But a cathedral ceiling has no ceiling joists. 
Without the tension strength of ceiling joists, cathedral ceilings need another strategy. They find it with a structural ridge. Change the simple ridge board to a beefy beam, support it on both ends, and that beam holds the roof load and eliminates the outward force to the walls. 
But take care. That structural ridge redirects thousands of pounds of roof weight to the front and rear gable ends. The ridge beam must be properly engineered and supported to transfer that load safely to the ground. Do not leave calculating and constructing this critical load path to amateurs, especially in snowy climates.² For best effect, the structures supporting the ridge should be hidden within the walls. When done correctly, the results can be dramatic. Eliminating those ceiling joists opens up the entire room. And adding glass or screen to the gable end captures even more light to further transform the room.
Even on a shed roof, a cathedral ceiling can be impressive. 
So, a cathedral ceiling adds space, light, and ventilation. And the cost? Compared to flat ceilings, cathedral ceilings cost less. Really. That sounds so good, I’ll say it again: cathedral ceilings — with their additional space and increased light — cost less than low, stuffy flat ceilings. A cathedral’s structural ridge beam adds some cost, as does the slightly larger ceiling area, but eliminating all those ceiling joists (10 joists on a 12 ft deep porch), saves even more.
So, what do you prefer: a flat ceiling or a cathedral?
Footnotes:
1. I use “cathedral” here in a generic sense. Some strict definitions limit “cathedral” to ceilings with two equally sloped sides with a central peak, and thus consider a sloped ceiling under a shed roof to be vaulted and not cathedral. The word cathedral is derived from the Greek noun καθέδρα (cathedra) which translates as “seat” and refers to the presence of the bishop’s (or archbishop’s) chair or throne. Without a bishop in residence, purist consider the building merely a church. (I know: this is probably more than you wanted to read about.)
- The weight of snow on a roof can be massive. Three feet of snow on a small (12′ x 14′) porch can bring the total roof load (including the dead load of the roof itself) to over 10,000 lbs. The ridge beam of a cathedral gable roof bears half that load, and the post under each end of that ridge beam must safely transfer over 2,500 lbs twelve feet down to Mother Earth. Make sure your porch or sunroom is structured properly. For more information about the weight of snow, see the last part of my blog article about snow on decks.
Links:
A. For more photos of cathedral ceilings, see our galleries of Porches, of Sunrooms, and of 3- and 4- Season Rooms.
B. For a discussion of the cost of sunrooms, see my blog article.
At Archadeck of Suburban Boston, we offer professional design and build services for clients west and north of Boston. Over the past 26 years we have designed and built over 950 projects, including over 240 porches and sunrooms. We have enhanced the depth of our expertise by limiting our work to decks, porches, sunrooms, and patios. To view some of these projects or see our design and service awards, visit our website. To learn how we treat our clients, check our ratings on Angie’s List or read about us in an article in Remodeling magazine. For a free design consultation and a relaxed and rewarding experience, contact us via e-mail, subboston@archadeck.net or by phone, 781-273-3500. 
© 2018 Advantage Design & Constr., Inc.
