I am in the process of designing a Cape Cod style house. I want a 12/12 pitch on the front roof and a shed dormer across 90% of the back (leaving a 6/12 pitch on the rear roof).
According to a recent article dealing with design/construction problems, using a collar tie that will attach to the front rafters at mid-span is a poor idea, it puts considerable load at this point.
Does anyone have specificinformation, a book or manual as to how this can be properly framed? Are there framing tables for just this situation?
Thanks for the help
JDC
Replies
I've done cape cod houses with trusses before. The major drawback to this is that you have to come up with beams in the 2nd floor system to support the ends of the trusses at the front 2nd floor walls.
I could probably do some sort of drawing, if that isn't clear........
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Have you thought about using a ridge beam? This means cutting the roof yourself and foregoing trusses. It is not that difficult. The height above the ridge will be less for the 6/12 shed so you will have to block under the rafters with a block ripped at the 6/12 angle to raise the rafters to meet the 12/12 roof. Offset the layout so the rafters can overlap and nail to each other at the ridge. Collar ties are optional with a ridge beam system. You may want to have collar ties anyway if you have enough ceiling height to make the ceiling a little easier to finish.
Thanks for the quick response.
I had not planned to use factory made trusses. I had assumed that the roof framing would be constructed on site.
I am unfamiliar with the ridge beam concept. Does the ridge beam carry the roof load at the middle of the structure (through a central support wall or series of posts)?
Do you know of a book that thoroughly describes this method? It sounds promising.
Thanks again
JDC
A structural ridge beam is sized to carry half the load of the roof. Actually, in your case that percentage might vary if the ridge is off center. It is more proper to describe it as that it carries half the load that each individual roof rafter carries and the total of all those halves.
It is the best way to support loads on this asymetrical roofline (some call it a saltbox) because your short kneewall is not resisting lateral forces well if you transfer all the roof loads to that.
Essentially, the ridge beam is supported on stud posts in the end gable wall that transfer that weight to the foundation. If you happen to have a window or door openning there in that load path, the header over the window must be sized to carry half the load the ridge beam is putting on it.
Trusse leave that load off the end gable walls.
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Edited 1/16/2003 3:39:26 PM ET by piffin