Roof framing for detached garage

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  #1  
Old 10-08-13, 12:32 PM
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Roof framing for detached garage

Hi, I am thinking to build a detached garage. I would like to fit an automotive lift into it; the city rules state I have to have the same roof pitch of the main building and the average height of the detached garage roof cannot exceed 14 feet; the lift alone would be 12 feet tall.

This said, I wonder if it possible, and in that case what are the "cons" of having a roof that does not take up precious space with trusses, maybe just beams that connect to the center line of the roof?

This might be a stupid question, forgive me, but I need to start somewehere

I have bought several books about garages and none of them really goes into the roof details.
 
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Old 10-08-13, 04:46 PM
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Oh I found out that what I like is probably called "ridge beam" roof construction. I would like to understand it better, especially what are the implications on the rest of the framing.
 
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Old 10-08-13, 04:55 PM
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Almost all residential structures have ridge beams. That is what your roof rafters are attached to. You must also have support for the span of the rafter, ie. trusses, or other middle support. The only way I can see you getting away with it is installing I Joists or Parralam from Weyerhauser Truss Joist or others. They don't require mid range support. You will pay through the nose for them, however. Go to their site and see if they have anything like what you need. Weyerhaeuser :: Trus Joist
 
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Old 10-08-13, 05:02 PM
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chandler, this is not my understanding. Maybe the technique you are describing is the "ridge board" construction? I am very confused.

I have found: "You use a heavy beam resting on supports at the gable end walls as the ridge and set the rafters on top of it down to the top of the walls."

An image search
shows more or less what I like, as you can see there are no horizontal elements.

Apparently the big central beam is often made with the "glulam" technique but otherwise it does not seem to require special materials.
 
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Old 10-09-13, 03:33 AM
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What is to keep the downward pressure of the rafters from pushing your walls out? You will need collar ties, at least, and substantial lumber for the rafters if you plan on an open space.
 
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Old 10-09-13, 05:55 AM
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It might help if you provided a description, or, better yet, a drawing, showing the size of your planned garage, intended wall height, orientation of the rafters or trusses in relationship to the doors, roof pitch, etc.
 
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Old 10-09-13, 06:47 AM
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Old 10-09-13, 12:43 PM
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chandler, from what I read, you are referring to a ridge board construction. In a ridge beam roof, there is no outwards pressure as the roof rests on the beam itself, that is a substantial piece of lumber, many times a "glulam". There is no need of space-wasting trusses and allows for a fully open space. In particular, I have found that you can use so called "structural insulated roof panels" (SIPs) with this method. I have found a short video:

Habitat for Humanity : Setting the Glulam Ridge Beam and Structural Insulated Roof Panels - Bob Vila

See how they just place the big beam first; then they add the panels. Those panels just make up for a very well insulated and quick construction; but one could use regular rafters like in the image search I have linked before.

With this kind of technique, why would anybody use regular trusses? Maybe if you want a flat ceiling (drywall) they are more convenient?
 
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Old 10-09-13, 12:51 PM
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Hi Pedro, the building would be simple: about 30x30 (I can go down few feet if necessary) and an height that allows this 12ft two post automotive lift to be installed freely. According to local regulations, the roof will have to match the one on the primary building that in my case is "4 in 12" (18 degrees).
 
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Old 10-09-13, 12:54 PM
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hi Joe, I do not wish to have trusses; my question is, what are the disadvantages of the construction techniques that do not use trusses and other horizontal elements?
 
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Old 10-09-13, 05:04 PM
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The ridge beam requires no cross framing as you discovered and others have learned. The point load for the lift/size of beam would require a SE stamp for local building department. Collar ties may not be required either, used only with rafters/ridge board; Removing collar ties - Fine Homebuilding Question & Answer

Extra cost for SE and beam compared to standard trusses. Figure if pitch rise is 6/12, inside rise is 3-4/12 without point load/extra trusses.

Gary
 
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