Do you always limit Header deflection to L/240 or better? 4

[Revv]

Hey guys, just wondering here if you guys always limit your header deflection to L/240(or higher)? I've read where it can be applied from the roof and floor limits provided in the code, but does it say that explicitly? Or do you use your own judgement on it?

 

[XR250]

I try to keep it to at least double that unless I am trying to get an existing condition to work.

 

[phamENG]

Depends. If it's supporting a wood floor, I go for L/600 (L/480 for the joists, L/600 for beams and headers). Combined flexibility can cause some pretty noticeable foot-fall vibrations and bounce. If it's supporting a roof, L/360. If it's over a sliding door (especially the really long, fancy ones), 1/8" hard limit.

 

[EngDM]

Typically L/360. However for longer spans I agree with phamENG that setting a hard limit is required to avoid damage to the framed window/door below.

 

[XR250]

@Pham,

Are you doing 1/8" LL or Total load for the big sliders?

 

[phamENG]

Usually total load. Most contractors put the doors and windows in to close up the building well before total dead load is in place. Granted, with entry doors they'll often use (and reuse) a $120 home depot special and put in the nice, custom door after the trades are done going in and out every day. But a 96" slider on the back of the house? Tough to fill that in a meaningful way for dry-in without using the spec'd door.

 

[XR250]

I usually go 1/8" LL. Many times with 20 ft. doors, I cannot get anything reasonable to work if I go tighter than that.

 

[phamENG]

I don't find 20ft doors to be reasonable, so I'm not the least bit worried when I tell them they need a steel beam.

To expand on this: if you can afford a house with a 20ft door, you can afford a better attorney than I can. So I'm not going to skimp on this and have your $19k door jamb up because I didn't make the beam quite stiff enough.

 

[XR250]

Some of the manufacturers are asking for 1/16"!

 

[jayrod12]

When they do that, I ask if we're building watches. Because the companies that ask for that sort of tolerance, have never swung a hammer or ran a saw in their life.

 

[phamENG]

jayrod - have you seen some of their cut sheets? They are building a watch. It's nuts. To get those massive things to slide effortlessly along the track while maintaining a virtually air tight seal is no small feat. So I get it - sort of. It's just a hassle. Most of them do require an oversized RO (vertically) to give plenty of room for shims.

In theory, they could always adjust the shims if the dead load deflection is too much, but the drywall will probably already be in place, and as long as the door works they won't realize the live load deflection is going to be too much for the shims. And you'll have an issue after 8 months of live loading and a bit of creep.

 

[jayrod12]

Fair point, I haven't seen those gigantic sliding doors on any of my projects yet.

Does anyone pay attention to the deflection of the floor below said large doors?

 

[phamENG]

Yes. I just did one recently - 3 floors with one of them on each floor, all stacked up. Between controlling drift for squareness tolerance and deflection for those sliders, just that 3 story moment frame cost almost as much as an entire house framed with steel down the street that didn't have such tight tolerance requirements. To say it raised some eyebrows is an understatement.

 

[RontheRedneck]

To paraphrase what phamENG said: "if you can afford a house with a 20ft door, you can afford a beam that will do the job".

Seems like as soon as one of those huge patio doors has trouble, they point fingers at the beam. That's not a place to skimp or do "value engineering".


As for the question in the OP - I don't like going to L/240 for anything but a pole barn in an agricultural setting.

 

[phamENG]

To paraphrase what phamENG said: "if you can afford a house with a 20ft door, you can afford a beam that will do the job".

Nailed it.