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roof ridge beam support

roof ridge beam support

roof ridge beam support

(OP)
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?

RE: roof ridge beam support

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
 

RE: roof ridge beam support

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

RE: roof ridge beam support

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.

RE: roof ridge beam support

Nightmare time!!

RE: roof ridge beam support

Nothing like accidental stability.

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

RE: roof ridge beam support

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.

RE: roof ridge beam support

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
 

RE: roof ridge beam support

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.  

RE: roof ridge beam support

(OP)
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.
 

RE: roof ridge beam support

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

RE: roof ridge beam support

(OP)
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.
 

RE: roof ridge beam support

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
 

RE: roof ridge beam support

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?

RE: roof ridge beam support

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.

RE: roof ridge beam support

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
 

RE: roof ridge beam support

(OP)
Thanks to everyone who has put their input into this.

 

RE: roof ridge beam support

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.

RE: roof ridge beam support

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

RE: roof ridge beam support

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.  

RE: roof ridge beam support

Looks like a flitch beam may be the best and easiest way to go. I would follow the profile of the two ridges, begin at the post between the windows on the left, up the first slope, overlap the lower flitch beam with the one at the high ridge and come back down along the roof slope to the bathroom wall. Check for deflection. Might be better to just bight the bullet and go with a wide flange section since you have to spend the money on steel anyway. A moment connection in wood is going to be huge and I wouldn't count on it being stiff enough.

RE: roof ridge beam support

(OP)
momgineer, and garpe like your idea, thank you!
Garpe, I'm not sure about "overlap the lower flitch beam with the one at the high ridge..." Can you explain more, or sketch it?
 

RE: roof ridge beam support

It should be done in steel, ridge beam included. Trying to do a moment connection between two beams of differrent materials with different planes with a skew.....good luck with that.

There is no thrust at the bottom of the hips if you do moment welds at your ridge beam/hip beams. And if there was you have no way to resist it (vertial 10' wall x 5 1/2" thick with a horizontal point load at the top). Size your structure stiff enough to resist lateral deflections otherwise your finishes will develop a nice big crack right at your valleys.

You will most likely have to field weld or create a moment splice joint because the shape looks a little akward to be shipping down a 10' road. Coordinate with the contractor regarding his ability to fly steel through the air (i.e. assembly methods)

And before you go to all the trouble of designing this, call your architect and tell him that his requirements are leading to more difficult structure i.e. more $ which might make him rethink the flat ceiling and collar ties. After you get approval, then proceed.

RE: roof ridge beam support

As BA and I have pointed out, you do not need steel, collar ties, or moment connections here.  You all are making the solution way too complicated.  It's your call though.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: roof ridge beam support

I agree with msquared and BA. Cantilevered hip beams to support the left side of the ridge beam. On the right side, I would drop a post down to the top of the bathroom door header directly under the ridge beam and be sure to carry the loads down through the structure.

RE: roof ridge beam support

I think the single dashed line in the loft space represents where the ceiling goes from sloped to flat. The architect did not fully clarify this but I think a lot of the ceiling is flat.

The dormer on the left shows single dashed lines and there is a single dashed line where the stair is.

I would call the architect and ask to confirm.

RE: roof ridge beam support

The cantilever distance on the hip idea would produce cantilevers of nearly 9' in length based on some rough estimations on room width. The stiffness of member it would take to satisfy deflection requirements would make these members quite deep.

A 9' cantilever in wood with an equal backspan on a residential house.....I wouldn't feel comfortable doing that. Let us know what you ended up doing.

RE: roof ridge beam support

I would if the members were sized right and the connections adequate.  I have done this before.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: roof ridge beam support

bigmig,
 
A nine foot cantilever is equivalent to an eighteen foot simple span.  And there are two of them to carry the reaction of the ridge beam.  I believe that cantilevering the hip beams may be the most economical solution to the problem.

There may be other equally good solutions but the introduction of structural steel is not likely to be a winner.

BA

RE: roof ridge beam support

I am with bigmig. I would not feel comfortable doing the 9' cantilevers/9' backspan for this ceiling with wood.

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.

RE: roof ridge beam support

I guess I'm just conservative. I think e 9' cantilever to support the roof is crazy. We try and always have a 2:1 backspan for cantilevers except in rear circumstances. Where I am in California nobody would bat an eye at the steel. I guess other parts of the country are different.  

RE: roof ridge beam support

FWIW - If I had to build it I'd probably end up going w/ wood solution cantilevers or similar and maybe gusseting the rafters at the ridge just to give me that warm, cozying feeling.

EIT

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