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?

 

[Momgineer]

WHY NOT USE A STEEL HSS BENT TO SUPPORT THE ENDS OF THE RIDGE. I DO THIS IS MANY CASES WHERE I HAVE A VAULTED CEILING CONDITION. SEE MY ATTACHMENT.

 

[garpe]

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.

 

[taikos186]

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?

 

[bigmig]

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.

 

[msquared48]

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

 

[nac521]

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.

 

[MisterBill]

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.

 

[bigmig]

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.

 

[msquared48]

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

 

[BAretired]

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

 

[woodman88]

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.

 

[jdgengineer]

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.

 

[RFreund]

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