Author Topic: Engineered Attic Truss question?  (Read 265 times)

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Offline Rys

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Engineered Attic Truss question?
« on: November 18, 2017, 12:23:15 PM »
Seems like the more I read the less I know!
 Today's question is about attic trusses:
I'm wanting to use a raised heel parallel chord truss on my 20x40 1 1/2 build. In the loft area I'm planning a 10'-12' shed dormer. My question concerns attic trusses. Can they be made so that the shed roof is a couple of feet below the ridge line and can the "wall" part be inset slightly from the exterior wall. I'm afraid I know the answer but I'm still hopeful! I much prefer the look of a dormer that nestles into the roof.
Or would it be better to run a ridge beam over the loft area, tying it into the roof trusses?

Offline Don_P

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Re: Engineered Attic Truss question?
« Reply #1 on: November 18, 2017, 02:53:50 PM »
In that case I would probably have a common attic truss inboard from the end of the building to give you that return, which is visually th thing to do, then a stack of 2 or 3 attic trusses knitted together to make a girder truss, a gap of 10 or 12' then another group of ganged attic trusses. Across between them, floor joists are hangered perpendicular to truss direction and the floor sheathing switches directions across that area. Above there is a ridgebeam at the peak also carried by the girder trusses at either end. The ridgebeam carries common rafters from the backside of the roof and the shed either ties to that ridgebeam or there is a lower beam between girder trusses that the shed rafters tie into and short cripple rafters run from ridge down to shed... I've done it, it eats up a lot of time and adds more joinery in the metal, I understand, just sayin.

Offline Rys

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Re: Engineered Attic Truss question?
« Reply #2 on: November 18, 2017, 04:19:59 PM »
I kinda sorta think I know what you're describing.    ???

Offline Don_P

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Re: Engineered Attic Truss question?
« Reply #3 on: November 19, 2017, 03:05:26 PM »
 This is crude but basically how I've field framed a dropped shed dormer into an attic truss roof. The truss plant figured out their girder trusses and the beams then we built the dormer basically hanging from those stacked girder trusses.

Offline Rys

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Re: Engineered Attic Truss question?
« Reply #4 on: November 20, 2017, 05:43:19 PM »
Would it be possible to do the same thing using parallel chord trusses Don? I like the openness of the cathedral ceiling, especially in the open loft area that overlooks the great room.

Offline Don_P

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Re: Engineered Attic Truss question?
« Reply #5 on: November 21, 2017, 04:42:52 AM »
That is a question for the truss designer, I'm not sure of the depth they would need. I would frame it with a structural ridgebeam and common rafters. At 40' that would probably take 2 interior posts.

Offline Rys

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Re: Engineered Attic Truss question?
« Reply #6 on: November 21, 2017, 06:28:20 AM »
Thanks Don. Now that I have more concrete idea of what I want I'll talk to the truss guys.