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Header Span Table Questions

Header Span Table Questions

Header Span Table Questions

(OP)
Good Morning All,

I'm from NY (PE-Civil). I am doing some design on my own attached garage and I am a bit stumped on my garage header as far as prescriptive code is concerned. IT doesn't appear that the prescriptive code accounts for openings larger enough for the 16' doors? Must these be an engineered beam, or spec's by LVL/Glulam, etc...

Thanks all for the help.

RE: Header Span Table Questions

This is quite common; Prescriptive codes are created with maximums as these then determine the loads to which columns, lintels, jack posts (etc) and the foundations are designed.

You need a local Structural Engineer's help.

RE: Header Span Table Questions

(OP)
Thanks for the response CEL.

I wouldn't call myself a "structural" engineer, but I do have a great deal of experience in structural design and analysis I am a NY PE (Civil). I just don't have much experience in residential design. I could sit here and design a beam specific for the overhead door, but I know that we have prescriptive code in place that handles the vast majority of residential specification.

It appears that most people use LVL's in this scenario (keeps engineering costs down I assume, and transferrs liability to LVL manufacturere and sealer/stamper) but I was hoping for somebody to shed a little more light on the process or alternate methods. I am a PE and I do have experience in the analysis; not just a homeowner posting a question on here.


Thanks all. I appreciate the help.

RE: Header Span Table Questions

If you know your snow load, there should be online calculators for glulam beams. LVL's can be calculated by downloading their software from RedBuilt (free).

Here in Phoenix, most 16' headers with 2' max roof trib (gable end truss condition) are (2)-2x10 or (2)-2x12.

RE: Header Span Table Questions

(OP)
Thanks AELLC. MY condition would be the truss bearing side (I'm drawing a blank on the terminology here), with a fairly significant GSL (I need to check, but I think that it is 60-65psf).

I'm probably going to spec an LVL, but I really wanted to see if there were any other options (i.e. built up 2x12's won't make the 16 ft).

Thanks all

RE: Header Span Table Questions

LSL's have less in the way of properties, but may work. Parallams are useful for larger loads. Glulam may be cheaper than LVL and are definitely cheaper than Parallam.

Be aware of the recent discussions regarding LVL deflections, there may be inferior product made by other companies.

RE: Header Span Table Questions

Typical local truss fabricator can supply the beam and engineering stamp.

RE: Header Span Table Questions

(OP)
I would expect the truss and LVL (or similar) manufacturer to stamp their product designs, but I will need to stamp the rest of the design (it is fairly simple design).

My real motivation here it to figure out how it is accomplished. Before composite materials was there not larger openings, or where they always steel?

Thanks again

RE: Header Span Table Questions

They were nearly always steel back in the day, but Timber beams can work on those spans (timber properties were previously much more stiff, old growth forrest being a big part of the reason why)

I see a great deal of steel beams doing this in older houses.

RE: Header Span Table Questions

(OP)
Thanks. That's what I was thinking. Engineered beam for large openings, or multiple smaller openings.

Appreciate all the help.

RE: Header Span Table Questions

I have never heard of a engineered lumber supplier providing any calcs or sealed drawings, you just specify what product you want on your drawing that is signed and sealed.

The tricky part of a garage is making the garage door walls/jambs work laterally and for in-plane shear, especially if the garage door(s) eat up most of the wall.

CELOttawa- Interesting comment about regional structural systems. I have never seen a steel beam used as a residential header in Florida, wood or CMU only. Rarely see steel at a house period, of course we also rarely have basements.

RE: Header Span Table Questions

Usually when there is a floor above the garage and then the wall up to the roof is load-bearing and snow loaded, then you have steel beam.

In fairly low-seismic areas like NY I understand in-plane lateral shear is not a big issue, assume 3-sided diaphragm but ignoring the stringent Code reqmts about diaphragm ratio and diaphragm deflection etc, as we mostly do here in Phoenix area.

RE: Header Span Table Questions

a2mfk: Regional differences are as amazing as anything else I've seen in this business. New Zealand was a lovely country, and I absolutely fell in love with the PFC "Parallel Flange Channel". Think of our W-sections being a modern update to the I or S sections, and then think why hasn't that been done to channels? They have in Australia and New Zealand. Makes fastening much easier.

Actually New Zealand had fairly similar construction techniques to Canada, but was architecturally very different. Australia surprised me by having a great deal of residential load bearing masonry (clay brick). Haven't seen that in a building built in Canada since 1920.

RE: Header Span Table Questions

a2mfk Bay County FL requires all truss plans and beams (outside the SBC code spans) to be stamped before permits are issued.

RE: Header Span Table Questions

More than likely, the size of the beam with those snow loads will not be stress governed, but deflection driven - I try to limit the vertical deflection to 1/4" or less for serviceability reasons under full snow load.

Mike McCann
MMC Engineering

RE: Header Span Table Questions

Apexpredetor,

I don't know of any practicing structural engineer who uses beam span tables. I'm not saying that they can't be useful but I am saying that if that's what you're relying on to proceed with caution. I wouldn't try to do civil or environmental engineering even though I work with people in those disciplines rather often. The problem would be, though, that I don't even know enough to know how much I don't know. I could get myself into trouble and not know it.

Some years back I reviewed drawings for some high-end residential structures. They had some very large and inefficient beam sizes, on the order of W10x54, maybe larger. Wondering why they used such a silly beam size I ran the numbers whereupon it became obvious: the designer apparently sized the beams from the moment capacity chart in the steel manual but didn't realize his beams were braced. I'm guessing the architect sized his own beams. The worst part was that this was a development so those beams sizes were repeated many times over. So, by saving a few hundred or a few thousand dollars by not hiring a structural engineer he cost many tens of thousands of dollars on inefficiently sized beams and unnecessarily-difficult installation labor.

But then, I suppose it could have been worse: he could have undersized them...

RE: Header Span Table Questions

I try to keep the deflection of roof supporting structure to Span/360. I just never want to have someone come back on me as having "too soft" a beam. Besides, it is cheap insurance in case the builder uses cheap caulking.

RE: Header Span Table Questions

CELinOttawa,

Are you referring to live load deflection or total deflection?

RE: Header Span Table Questions

Span tables are utterly useless anyway because there is always at least one case of concentrated load or uneven distributed load.

RE: Header Span Table Questions

Hi Archie: Total deflection. This is as per the recommendation of CWC Wood Design Manual, but note that NBCC permits it under live load.

I will vary from this if the job is clearly going to be able to sustain more movement, but rarely. The number one complaint one hears these days about all the McMansions is the lively floors and crappy roofs. I want our work to stand firm.

RE: Header Span Table Questions

Defections of long header beams over sliding patio doors needs to be looked at carefully.

Also, longer header beams where exterior wall is stucco. A beam w/ L/360 total may be adequate for a 16' span, but create a problem with a 35' span.

RE: Header Span Table Questions

We aren't talking about a 35' span, nor are we talking about stucco. Have I missed something?

RE: Header Span Table Questions

I'm am the unicorn. I'm an SE and I'm happy to use span tables every chance that I get. Headers, masonry walls, precast planks... you name it. I'm pretty sure that I only make money on the stuff that I don't design.

Back in the day, the vast majority of garage roofs were gable end roofs with the truss bearing on the walls not containing the 16' door. They were often constructed with 3-2x10 and, while likely not kosher by the numbers, seem to have been serviceable. Who knows, maybe the roof framing held up the header somehow.

Even in NY lateral will be an issue for the wall segments either side of the door. Think hurricane.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Header Span Table Questions

Sorry, CEL, don't get cross.
I was just suggesting additional considerations in a general sense for application in any other project.
It was implied, but you are right, it did sound a bit like I was contradicting you.

RE: Header Span Table Questions

KootK,

Yes you are generally correct, but I now do so many custom, wood constructed houses, for me it has become quicker overall to use my Excel workbook to churn out all my designs. The way it is set up, it makes it easier to just run the uniform loaded beams along with the beams with complex loading.

I am not saying everyone should be able to do this, I am saying it as advice for someone wanting to streamline the design process.

I use to submit a sheet or two with tabulated beam designs, ie B3, B7, B8 are 2-2x6 and B2, B13 are 2-2x8, etc, which was fine, but the way I set up my Excel shows 4 beam designs per sheet and showing simple uniform load desiogns along with the more complicated case works a bit better for me.

RE: Header Span Table Questions

Speaking of roof framing holding up the header, when I was working at a small consulting company located on residential street in an older neighborhood in Phoenix, and old house with a stick-framed roof and brick exterior walls was being demolished across the street, so we all took a break to check it out.

The demolition contractor started knocking down the right elevation wall (the house was rectangular in plan, longer in the left-right direction than the front to back direction), but leaving the roof. He got about 1/3 of the way into the house as he was knocking down the front and back walls alternatively, all the time the roof was cantilevering and sagging, then finally the unsupported roof collapsed. It made a more efficient demo because he didn't waste any time thrashing at the roof.

RE: Header Span Table Questions

I always design Garage Door headers at L/600 as even a small sag in the header is very apparent when you drive up to the house (at least to me anyhow). Also, don't forget about out-of-plane loads. You have to have enough king studs and enough attachment to the structure to resist the in/out wind pressure.

RE: Header Span Table Questions

Not cross, it is a good extra bit of info... Frankly I very strongly oppose anything that is too long to put up with a SPAN/360 total deflection. In terms of TOTAL deflection, you can't get much better in non-commercial construction. You need steel all the way to foundations, and very good foundations. Each case is different, but if the requirements are too strict the performance is rarely there.

RE: Header Span Table Questions

The usual header for 8' setback hip roof around here is a 3-1/8"x10-1/2" glulam (dead=22 psf, live=20 psf reduced for pitch, non-snow), and that yields about L/360 total. I haven't heard of any problems.

Years ago, before plans check, the tract home builders were always insisting the headers be 2-2x10, and those did sag a little.

RE: Header Span Table Questions

oops - I meant to say 16' garage door headers.

ps - for 8' plate height tract house, always 2 jack studs and 2 king studs, whether 2x4 or 2x6. If I took the time to design the kings per IBC 2012, the king probably wouldn't calculate, but I am of the opinion that the 2 lightly loaded jack studs, being just 1' short of the wall top plate, stiffen up the king studs considerably.

RE: Header Span Table Questions

KootK

I guess I wasn't thinking of things like lintels, precast planks, etc. Yes, I use tables for the likes of them too, as well as for metal decking, bar joists, and sometimes other types of joists as well. But I never use span tables for beams or girders. For such as that I always want some type of documentation of what loads I applied to it and what unbraced length I used. I.e., I would like to be able to check my files and quickly see whether the member in question carries a point load, a line load, does it carry a masonry veneer, etc. If it's guaranteed to include none of that then sure, a table will work, but I'd still rather have the full documentation. And yes, I have Excel spreadsheets and other software to help speed the process along.

What scares me, though, is the thought of people consulting span tables without considering all of the loads or circumstances that may apply. Just my opinion.

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