roof ridge beam support

[taikos186]

I need to frame attic floor roof. Cannot have color ties and no ceiling joists from below to connect roof rafters to resist outward thrust force. I’m using 3-1/2”x 14” LVL ridge beam but unfortunately cannot place support on each end of beam (architect showing open space). What options do I have?

 

[msquared48]

It can be done, but it will be difficult. You will have to use the four hips and make moment connections at the ends of the LVL to the hip beams, then take the thrust from the hips either into the walls they bear on, or the roof diaphragm and beyond.

Kinda sketchy solution, but I have done things like this before.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ztengguy]

God above what a mess. You could try a moment connection, how much load are we talking?

 

[jdgengineer]

In cases like these we have used a vaulted flitch beam to support the ridge beam. The flitch beam is basically a 3/4"-1" thick steel plate with threaded rods welded to it that is then covered with wood framing. The steel plate would be CJP welded at the kink.

 

[MiketheEngineer]

Nightmare time!!

 

[SteelPE]

Nothing like accidental stability.

I would also suggest doing it out of steel. This way you will know everything will work.

 

[woodman88]

I will second the steel idea.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

The steel idea occured to me too, but I would first try wood, or the Architect will likely not buy the steel solution, if you know what I mean. The sizes and connections for the wood will likely look and be ridiculous.

Just model the roof in RISA 3D.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[ToadJones]

Man, I miss framing these roofs...just a great challenge and incredibly satisfying.

I have an idea for one side of your problem.....

I framed a house once that had a similar situation and we used a steel cranked beam that formed the hip rafter on one side of the house and the valley on the other and landed on the walls.
I think this might work for you here with your valley being the valley of the dormer.
In your case the one side of the ridge could tie to this cranked beam and your ridge could also be a cranked beam that formed the slope of the roof that is above the toilet.

 

[taikos186]

jdgengineer I like your idea, but cannot span vaulted flitched beam from wall to wall on each end of the ridge beam because dormers. You can see roof plan in my attachment.
I think I need to do similar what msquared48 suggested, design moment connection for points where ridge beam meets with hip rafters. Simpson Connectors have similar solutions but thickness of the plates is too small, need probably min 7 gauge metal to fabricate these connectors.

 

[jdgengineer]

Where I practice in California, we wouldn't give the architect an option. It would be done in steel.

If they want a complicated roof framing system that won't allow you to have a ceiling beam to take the ridge reaction then in my opinion they bought a steel beam.

We introduce steel on a lot of our custom homes. Builders out here are used to working with it and I don't think the premium is all that significant compared to the total building cost.

Can you drop the ridge beam so that it doesn't daylight through the dormers and run it long to the cross-walls? Architect would either have to fur the ceiling down, box it, or expose the beam

 

[taikos186]

jdgengineer, cannot drop beam, attic ceiling height does not allow and cannot elevate it, we will exceed max roof height dictated by local ordinances.
More I think more I agree that STEEL is the way to go.

 

[msquared48]

The fact of the matter is, that when the budget numbers come in from the contractor pointing to the cost of the roof framing, a collar tie option is far more likely to be considered by the owner.

That redesign should be extra money in your pocket. Keep the faith!

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[4thorns]

Are the bathroom walls built up to the underside of the roof/ridge? If so, is there a way to support at least one end of the ridge using these walls and supports from below?

 

[EngineeringAdam]

I second jdgengineer's steel option. A steel flitch beam seems to be the best option.

It might cost more, but the roof plan indicates a somewhat expansive home. I would imagine that the architect and home owner would want the vault to remain intact to respect the design intent of the structure.

There are flitch beam design guidelines that are easy to find on the net.

 

[msquared48]

Actually, in looking at this harder, it looks like at least three of the four hips can be supported with two columns each.

That should render the hip members as simply supported members with cantilever ends supporting a simply supported ridge - no moment connections necessary at the LVL ridge. This could mean extra framing to pick up the point loads at the floor level though.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[taikos186]

Thanks to everyone who has put their input into this.

 

[TXStructural]

To resist thrust, why not make the top of the exterior walls a girt restrained by the intersecting interior and end walls. It looks like a hybrid may be needed.

 

[BAretired]

I don't think a steel beam is warranted. The hip beams can be supported on columns located in walls, as msquared suggested. The left end of the ridge beam is picked up by two cantilevered hip beams.

BA

 

[ToadJones]

I could be wrong but the inside of that ceiling is going to be all cut-up anyway....it don't think it will even look nice.
I'd talk to the Arch and see if you can make a portion of the ceiling flat.