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Accounting for unbraced length of LVL and qualifying existing ceiling joists for house renovation

Accounting for unbraced length of LVL and qualifying existing ceiling joists for house renovation

Accounting for unbraced length of LVL and qualifying existing ceiling joists for house renovation

(OP)
I'm working on a project where a single story residence is being converted into a two story residence. The roof was originally building with a steeper pitch (gable) to allow for a future renovation. Portions of the roof are being cut out with walls being erected in these areas (think four walls vertically punching through the roof).

The stair case will be leading up to a hallway that is open to below on both sides so you can look to the first story below. The joists supporting the hallway at the second story will be supported by LVL beams. The beam on one side is 15' and the other side is 11'. My question is regarding the unbraced length of the LVL beams. There is no much load here, as it's a 5' wide hallway with 40 psf, 100 PLF. The moment for the 15' s.s. beam is about 2800 LB*FT. The moment capacity of a single 7 1/4" deep LVL is 3580 Lb*ft. My question is whether the joist hangers/joists attached to the LVL are considered to brace the LVL or do straps have to be provided every several feet? I would probably use 2 LVLs to have a more robust section but at the same time the eccentrity from the joists increases, thus increasing torsion. How do you typically account for bracing of LVL? Do I just run the calcs in NDS?

The second question I have with respect to the renovation is qualifying the existing ceiling joists for the second floor occupancy loading. The ceiling joists are all 2x8s. What I have done so far is look at the IRC tables and determine the maximum allowable span for 2x8 for 40psf (#2 lumber) which is 12'-9". Any spans in the attic over then length, which is essentially all but one will requiring sistering of another 2x8 to the existing. I feel like this is sufficient. there are a couple of the new walls that will be supporting a new roof which has the potential of snow to accumulate. The "box" that will be cut into the roof is about 13'x13'. Does anyone see any issues with my approach here? Several of the ceiling joist bays span between bearing walls that are supported by steel beams in the crawl space.

AS for the roof framing, the ridge beam is a double LVL along with the hip rafters. The vertical supports for these members won't be modified so there is no issue with the roof framing. The collar/rafter ties will also not be modified as they are above the finished ceiling.

RE: Accounting for unbraced length of LVL and qualifying existing ceiling joists for house renovation

I would say your beam is braced by the joists. And if you double it up, which you should, buckling is usually not an issue with multi-ply members if they are properly interconnected. Eccentricity from the joists is negligible, the joist hangers will provide some torsional restraint to prevent the beam from twisting. If your ceiling joists are good for floor load, there’s no issue in using what’s there, but it’s probably worth checking the load path down to the crawl space to make sure everything checks out.

RE: Accounting for unbraced length of LVL and qualifying existing ceiling joists for house renovation

Better check deflection of the 7 1/4" LVL beams (I agree that the beam is braced though).

Also, they aren't growing 2x8's like they used to.... In other words, 12'-9" seems too far but the idea of sistering another 2x8 to the existing does seem right. Just be sure you account for any other loads on the 2x8's.

Overall I think the scheme is right but deflection compatibility is something to look closely at when going about this type of thing.

Steve

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