VAULTED CEILING UNCONVENTIONAL DESIGN

[Skiffguy]

Hey guys. I wanted to share this to get your thoughts. The build concept and thought process is this;

The inner exposed yellow pine beams will tie the 2x6 walls together...The concept spawned from the simular beam concept in above picture...the scissor trusses design is posted to ask if perhaps would be easier to engineer...but other is preffered

Construction would be in order - Frame walls, install tension rods, install roof rafters (typ engineered wood I beams @ 16" centers) insulate, sheetrock..... THEN install the exposed beams, bold into place.... remove temp tension rods.

Looking at the drawing you can see the welded steel tube brackets at peak ridge, and there are 2 acting as tie beams. The bottom of beam will bolt to a double or triple top plate to tie walls together.

This is for construction in Florida so no snow load.

FOR BETTER VIEW SEE UPLOADED PDF

 

[GeorgeTheCivilEngineer]

That's a trussed roof, not a vaulted roof.

 

[phamENG]

I don't think you can cut a birdsmouth in I-joist rafters like that. Could be wrong, but I usually see the adjustable bearing clips from Simpson in those situations. Though, I don't see that situation often...most framers despise I-joist rafters around here.

 

[Eng16080]

So, effectively the structural roof is I-Joist (not I-Beam btw) rafters joined at the top with a ridge board and resting on the wall top plate at the eaves. The rafters will want to spread outward which will be resisted by the wall top plate, which effectively spans between your yellow pine and tube steel trusses, which appear to be about 7 or 8 ft on center. My concerns would be:
[ol 1]
[li]I doubt the double 2x6 wall top plate is adequate to resist the outward thrust. You should check that, analyzing it like a beam turned sideways. Also, you want to be sure that the top plate won't be broken between the horizontal supports.[/li]
[li]I wouldn't use I-Joists for this, but rather conventional framing. Since the rafters will be in both bending and compression, I'm not sure I-Joists are meant to be used in compression. Also, the birdsmouth cut, as noted above, looks questionable.[/li]
[/ol]

 

[IceNine]

The rafters will want to spread outward which will be resisted by the wall top plate, which effectively spans between your yellow pine and tube steel trusses

If the ridge board is stiff enough, it will span between trusses, eliminate the thrust concern at the typical rafters. I would size this ridge board to act as a ridge beam.

 

[Skiffguy]

Eng16080 I have seen Ibeams used as rafters in quite a few builds online and on a manufacturer website but not at 12/12 pitch... but your concern is noted ..ill send detail to I-beam manufacturer
I joist chosen for depth to allow build in place venting soffit to ridge and use of batt insulation to R-38.
Top plate also noted...could be tripled.

 

[Skiffguy]

Icenine could a gluelam span 36 feet and carry the load ?

 

[IceNine]

Icenine could a gluelam span 36 feet and carry the load ?

Sure, if the beam is large enough.

 

[phamENG]

Top plate won't see thrust in this. Your truss-frame thingy is 8' o/c...By the time you have a ridge deep enough, it'll likely be able to span 8'. Just make sure your truss-frame thingy can take the reaction from the ridge beam.

 

[Skiffguy]

Icenine perhaps I should look into the glulam... that would take a lot of outward thrust away...

 

[Eng16080]

If the ridge board is stiff enough, it will span between trusses, eliminate the thrust concern at the typical rafters. I would size this ridge board to act as a ridge beam.

This is true. I was assuming that the trusses were mostly just aesthetic and not taking vertical load. I was thinking that the rafters/ceiling would be sheetrocked and finished before the "trusses" were installed. And supporting the trusses on those tiny ledgers seems really questionable if there will be any significant load. But typically, when I've had similar designs to this before, I designed it exactly as you mention.

 

[phamENG]

Missed IceNine's comment in there.

 

[Skiffguy]

Eng16080....

So you like the idea of a ridge beam vs board... be a big glue lam...

With that approach u have other concerns?

 

[IceNine]

For what it's worth, I wasn't suggesting a ridge beam spanning the entire length (though you certainly could do this).
I was suggesting a ridge beam spanning 8' between trusses. As phamENG mentioned, based on the depth of the rafters, the ridge board will likely accomplish this.

 

[Skiffguy]

Phameng.... I spoke to I joist manufacturer he said we can use but needs to see some drawings but its been doe he said

 

[Eng16080]

Skiffguy,
Same as IceNine, I think spanning between trusses not the full length is probably the best solution. I would prefer to build the trusses first, not last, though. I would also do something other than the ledger connection you currently show to support the trusses.

 

[Skiffguy]

ENG16080..... The reasoning in the build order like I posted is so sheetrock can be installed and painted BEFORE... so we have a sealed barrier to insulated vented roof...
Understand?

 

[Eng16080]

Maybe it's possible to construct in that order, but you'll need to somehow connect the trusses to your ridge beam.

 

[Skiffguy]

Eng16080 you mean attach the yellow pine truss ??

 

[phamENG]

Prioritizing painting and insulation over structural efficiency and safety isn't going to win you many fans around here....

You have a truss that is probably more than strong enough to do an actual job rather than just look pretty. Build the walls, set your trusses, make the connections, set a ridge beam, install rafters, install sheathing, then worry about making the building watertight and insulating it. The little bit of prep work required to protect the trusses from paint is going to be child's play compared to trying to erect those trusses inside a completed building.