First time poster and new to industry:
I have a customer who wants a shallow cathedral ceiling on a porch. She does not want to see any truss members only the roof rafters and roof decking. I am concerned about support for the roof (i.e. the walls not falling outward) and was wondering what construction technique should be used to frame this type of roof.
I appreciate any leads, information, input or help.
Thanks for your time,
dlb
Replies
Presuming that you are describing a gable roof perpendicular to the main house, the solution is a structural ridge beam. With it supported at both ends, it holds the rafters up. You need to engineer it to support half the weight of the roof and live loads on it.
A structural ridge beam would definitely work, if there's something to set the end of the beam on.
What about scissor trusses? I know you said the customer didn't want to see truss members. But maybe you could add a ceiling and put up some fake beams/rafters.
I have a project like dale's. It's a single story family room with a gable end extending perpendicular to the existing structure. The ridge is 16' long and the roof has a 4/12 pitch and 2x12 rafters. The architect (who is not a structural engineer) prescribes a double 2x12 with 3/8" fitch plate for the structural ridge. I'd like to verify his work. Can anyone refer me to span tables for structural ridges?
FHB #145 (March) indicates a continuous ring beam could be used to eliminate cross ties. I can't find any information on how many 2x6 top plates need to be bolted together to eliminate the structural ridge. Does anyone have some references?
Where's the support for the ridge? Jeff * Jeff J. Buck/ Buck Construction/ Pittsburgh, PA *
2nd Generation Buck Const, 3rd generation Craftsman
A double 2X12 16' long has little value as a beam. I don't have design experience with steel flitch plates, so I don't know how much strength/stiffness that would add.
I've never worked with steel flitch plates, but it seems like they would be a pain. An engineered beam might be simpler to work with. A lumber yard or truss plant should be able to size one for you.
As for a "ring beam" - The 2X6 plates would have a great deal of horizontal thrust on them - probably 3 times the PLF a ridge beam would carry. There's no way you could get enough 2X6 plates in there to resist the forces involved unbless you had some sort of intersecting wall half way down that could be used as a shear wall. And the whole mess would probably have to be designed by an engineer.
I've got 2 porches like that. Yep, ridge beam worked great.
To get the ceiling nice, I sheathed the roof first with 11/32" BC plywood nice side down, then put on the regular sheathing. (Since my roof keeps going, I dropped the rafters for the porch enough so I didn't have to double sheath the whole roof.) Be real careful not to miss the rafters with your nails. If you do, you have to cut them off with a Dremel tool or something below the ceiling surface and putty in the hole with 2 part wood putty. Sounds sissified, I know, but I'm a girl so I'm allowed to do that. Don't miss.
My front porch has a little mildew buildup on the ceiling, so when I built the back porch the same way I ran the ridge vent out over the porch. I just finished framing it, so I don't know yet if that helped. Probably not necessary because that porch is on the South side and the mildewy one faces North. Something for you to think about, though.
B