20’x12′ addition. with bearing 2×6 rafters 4/12 pitch on the 20′ exterior 2×4 wall. window openning is 96″ wide.
Lintel : double 2×10 sound adequate?
can’t make head nor tails of the span tables in code book. anyone know of a span calculator online for headers. Or know if the 2 ply 2×10 will fly.
seams to me last time I did a window that wide I was using a 3 ply. But it could have been 3 ply 2×8..I can’t remember. I know I’ve done big windows with P lams and strandboard before. But guy I’m doing this with was going to go with the 2 x10
Replies
What shows on the plans? ;-)
But seriously, OK, here's what I think you got -- header under roof and ceiling load with the building width being 20' or less. For code where i am . . . doubled 2x10 will serve as a header (need two jacks at each end) for a 8'5" span with a snow load of 30 psf or less. If it snows where you are, this may not work for you.
Tripled 2x10 (with two jacks at each end) will make it if the snow load hits 50 psf. More snow load than that, at least where I am you need the engineer.
"Let's get crack-a-lackin" --- Adam Carolla
Edited 4/12/2006 1:07 am ET by philarenewal
yeah..I'll have to check the plan more closely....
cept as you may have guessed..there is no plan.
yeah ...for sure the double jacks
In no snow country, my inspector once said, "....an inch of header for every foot of span.......rule of thumb....."
Grunge on.
I like your inspector. Practical rules that worked for decades are now suddenly horrendously dangerous. What happened? Trees -- guess they don't make 'em like they used to. ;-)
"Let's get crack-a-lackin" --- Adam Carolla
It's inches they don't make like they used to.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
>>It's inches they don't make like they used to.
Good point.
Reminds me of a rehab I'm working on. Young archy specs new 2x12 hem fir (what's common here) #1 or btr joists 16" OC (which would be oversizing anyway, span is 15'8"). More senior guy takes a look at the old existing 3x8s (that really are 3x8) and suggests they stay put. Guess whose opinion I preferred, plus the older guy is the one actually stamping the plans. ;-)
"Let's get crack-a-lackin" --- Adam Carolla
LOL
LOFL
LOL!!!!!!!
Grunge on.
I never heard that rule of thumb before. interesting.....so would that mean 2ft or even 3 ft openning would hypothetically be ok with a 2 ply 2x4 as header.
There's a similar rule of thumb for floor joists - 6" span/2x6, 8' span/2x8, 10' span/2x10, etc,
Of course, there's also an old saying "simple rules for simple fools", but I have always relyed on those beam and joist rules for common house work. Tipi, Tipi, Tipi!
http://www.asmallwoodworkingcompany.com
With all due respect, that rule of thumb is worthless at best and dangerous (possibly even criminal) at worst.As someone else said, does that mean a double 2x4 on edge can act as the header over a 42" window?Or if I need to span 12' in a basment of a house that is 32' wide with three habitable floors and rafters that are supported by a knee wall, can I use a double 2x12?I'm no PE, but I would dollars to donuts that the answer for both is a resounding NO.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Hey Jon, I must have had way too much coffee this am, so I got to stir the pot.
Double 2x4 will span 3'6" for roof and ceiling load on maximum 20' wide building with 30psf ground snow load (under IRC 2003).
>>"Or if I need to span 12' in a basment of a house that is 32' wide with three habitable floors and rafters that are supported by a knee wall, can I use a double 2x12?
Um, no. You have a point. Double 2x12 not even close. In fact under IRC 2003 looks like you need the engineer for that one. Ain't no ordinary wood that will hold. For less than what you describe (two clear span floors instead of three), a quadruple 2x12 with three jacks at each end would span 6'0" with a 50psf ground snow load.
"Let's get crack-a-lackin" --- Adam Carolla
Edited 4/12/2006 11:22 am ET by philarenewal
Edited 4/12/2006 11:23 am ET by philarenewal
Phil (or whoever you are),You're right, I made my statement too flippantly. See my post to Boss if you want the long explanation.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
Not flippant at all. You made your point. Sometimes rule of thumb works, sometimes the place would actually tumble. Makes one think about that.
Besides, if you can't be flippant, what fun would it be? ;-)
"Let's get crack-a-lackin" --- Adam Carolla
A rule of thumb isn't an absolute - It's just a starting point. Like if someone comes in here asking if an 11 7/8" LVL will span 20' carrying whatever, I pretty much no there's no chance it will work.If they ask what depth of a beam they need to span a 14' opening, I at least can give them an educated guess. But I would never SPECIFY a beam based on a rule of thumb.
Did you know...Captain Hook died from jock itch.
Boss,That's my point, if rules of thumb are just a good starting point, do they really have any benefit? I'm speaking especially to a "rule of thumb" that has absolutely no information about what loads will be carried.Maybe the guy who first brought the "one inch per one foot of span" rule lives in an area where all the homes are 24' wide ranch houses with no snow load. If that's the case, the rule of thumb is probably pretty decent.The problem arises (and I know you know this) when someone adds a clear span floor trusses and a second story on top of the header that meets the rule of thumb. Now you're grossly undersized.I myself often use the joist sizing rule of thumb, although I am a bit more liberal than JB. I multiply the nominal depth of the joist by 18 and figure that's about the max span allowed. A brief look at the 2003 IRC confirms that this is reasonable with 2x6 through 2x12 joists (#2 SPF, 16" o.co.; L/360, 40#LL & 10#DL).The main difference is that floor joists typically carry the same loading per square foot whereas any two headers in a given home could have a range of 300% (rough guess).
Jon Blakemore RappahannockINC.com Fredericksburg, VA
"That's my point, if rules of thumb are just a good starting point, do they really have any benefit?"
Sems to me that scentence both asks and answers the question - They're a starting point, but ONLY a starting point.
In the examples I gave, I said that rule of thumb could pretty much rule out a 12" deep LVL that spanning 20', for instance. The loading doesn't really matter - It just ain't gonna work.
So I'd say the answer is definitely yes - There is some value in having a starting point.
Change is inevitable, except from a vending machine.
Maybe the guy who first brought the "one inch per one foot of span" rule lives in an area where all the homes are 24' wide ranch houses with no snow load
Actually, it's a weird thing--for a material-less, solid, member, the moments & like correspond extremely well with 1" = 1' in span.
It's only when the material is significantly weaker, or stronger, for a given section that the rule gets caterwhumpus. Which is why an engineered "wood" I spans farther than a solid timber of equal length--the strengths of the parts are stronger than cut lumber. It's also why a high-strength steel section will span farther than a mild steel or iron beam of identical section.
It gets complicated quick--that's the failing of rules-of-thumb. Ok, stitch together 3 2xn--they will "act" like a 4x (mostly), but not like a 4.5" wide solid the same depth. (Making up the length out of big-box rejects 6-8' long won't help any, either.)
This is the trouble with putting span tables into code, too. The code writer has to "beat" the worst case scenario for their jurisdiction (which could be a fly-by-nighter parting together old apple crates and calling it framing). The code writers also have a lot of impetus to write "inspectable" code, too. "Ok, structural header from l to m; has to be at least n of z x at least q deep--done." Trying to remember if a #1 Hemlock 4 x 8 is "equivalent" tends to get pushed to the side.Occupational hazard of my occupation not being around (sorry Bubba)
" if rules of thumb are just a good starting point, do they really have any benefit?"sure do! A carp with no engineering training who is given a set of plans to build or estimate from should first review it to to see how buildable it is. A fourth to a third of what I've been handed has gone right back withion a day for redesign or confirmation of engineering because I had abasis from which to begin - a reference point to know where something looks rediculous.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
RRooster ---I like your rule of thumb. It is reasonable. It is based on engineering.As I recall the deflection ratio equation looks something like:w/L = constant * L^3/h^3 (H is the beam height, L is the beam length)At least the scaling for the rule is proper.I might differ with you about the proper constant.
> In no snow country, my inspector once said, "....an inch of header for every foot of span.......rule of thumb....."
I've heard that same rule of thumb, with the proviso that it's for a single story building, or the top floor, and spans up to 12 ft.
Of course that ain't gonna fly in the sub sub basement of the Empire State Building.
What can go very wrong with that kind of rule of thumb is forgetting its limits.
-- J.S.
Of course that ain't gonna fly in the sub sub basement of the Empire State Building.
Sure it does, we are just missing the variable of width, once we presume a span and depth.
Occupational hazard of my occupation not being around (sorry Bubba)
You don't say what your snow load requirements are or long long the rafters are
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
we deal with rain where I live. and rafters will be about 18' with truss design web at back bearing wall, which is at 12'. This will well exceed the 2x4 rafter design that has held up actually exceedingly well for past 40 or so years.
Edited 4/12/2006 7:43 am ET by alrightythen
Hey Piffin, just curious. What difference does it make how long the rafters are?
"Let's get crack-a-lackin" --- Adam Carolla
Edited 4/12/2006 9:47 am ET by philarenewal
Edited 4/12/2006 11:22 am ET by philarenewal
Well now, say with a ten foot wide window frame, and rafters that are tenn feet long. the load would be for fifty square feet, assumiong a bearing ridge beam or center load bearing wall.But if the rafters are spanning twenty feet over that ten foot window frame, the loading is based on a hundred square feet.In a typical 15# dead load and 40# live load area, 55#/sf for an extra fifty feet is an extra ton and a half of load the header has to bear - about the size of a pretty good sized automobile or a pallet of shingles delivered by boom right onto that spot of the window.That rule of thumb somebody mentioned is a good one - only in moderate snmow areas and when there is no second floor loading also added to the header
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Ah, I got you now. Of course.
The tables I use take building width into account to cover that. Leads to a lot of oversizing, but at least takes it into account.
"Let's get crack-a-lackin" --- Adam Carolla
We use a flavor of the IRC 2000 and the header span table is in the floor chapter.
BTW - is this header on the gable end or not? - sounds like not...
you are right. If it was gable end I wouldn't be asking.
No way to answer without knowing the loading requirements in your area.
Usually I would just take off all my clothes and go "whoops, I forgot to draw the curtains". [Caprice Bourret]
40.0 Live and 15.0 Dead
I was thinking yesterday about the compressive strength of a stud/plate/sheathed wall. There is a certain logic to the argument that header size is largely dependant on the load above it.
On the other hand, certain sized headers will support as much loading as the wall they are in. So in a sense, as long as there is a positive load path, the wall framing should be all the information we need to size a header, regardless of what's above it.
In fact, isn't that the point? That the header can carry at least an equal load as the wall it's in?
Tipi, Tipi, Tipi!
http://www.asmallwoodworkingcompany.com
Edited 4/13/2006 9:48 am ET by jimblodgett
I don't see any logic to that at all...
White people ought to understand, their job is to give people the blues, not to get them. [George Carlin, You Are All Diseased]
It's like you and a friend being chased by a bear.
If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison
"I don't see any logic to that at all..."
You don't see any logic to what, Boss?Tipi, Tipi, Tipi!
http://www.asmallwoodworkingcompany.com
In fact, isn't that the point? That the header can carry at least an equal load as the wall it's in?
I think I get at what you are saying. If the header can carry as much as the wall it is in, then by necessity it can carry the load above.
Trouble there is it could lead to grossly oversized headers unless the wall was actually carrying its rated load, for very large buildings or very wide openings.
Where I am a typical 2x4 16" OC stud wall is allowed to carry one clear span floor plus a roof and ceiling (a typical two story building). The headers on the first floor likewise have to support the same loads. What's a little wacky is there doesn't seem to be a limit on the width of the floor so theoretically the load on the wall could vary wildly. I guess the safety factors in wall framing are so high they don't care.
For headers, it's different. The tables (at least where I am) do take into account building width. A Piffin pointed out, the wider the building, the higher the load on the wall and header. If we sized all first floor headers for the maximum building width allowable for headers (where I am 36'), the headers would be oversized for narrower buildings.
The headers on the second floor could be oversized, if sized to support the same load the wall is capable of supporting. No clear span floor to support.
OTOH, as a practical matter, maybe it makes no difference as you suggest for most of the headers. Lets say all window RO in a typical two story building are 3'0". We size for the widest building allowed (36'0" -- that's what the wall can definitely support). The headers for the first floor would need to be two 2x6 with two jacks at each end. The headers for the second floor would need to be two 2x6 with two jacks at each end. You've convinced me. ;-)
"Let's get crack-a-lackin" --- Adam Carolla
Edited 4/13/2006 11:08 am ET by philarenewal
"If the header can carry as much as the wall it is in, then by necessity it can carry the load above."
Yeah, that's exactly what I'm asking.
"Trouble there is it could lead to grossly oversized headers"
Yeah, in some cases, but when we frame multi storey buildings we increase the compressive strength of the framing on the lower floors, right? So the header would then be sized to carry the load of THAT wall.
It's also totally possible that we way overbuild as a common practice and down size our headers to save lumber, I don't know. But I think there's something to this, in a "rule of thumb" kind of way. At least it is interesting to think about.Tipi, Tipi, Tipi!
http://www.asmallwoodworkingcompany.com
I see where you are going.
The sizing tables are already a digest version of the underlying engineering which leads to oversizing in most cases, but saves a lot of time and aggravation.
Ther is no reason to not digest the sizing tables even further, if you don't mind more oversizing (which I don't think is a real problem 'cause lets face it, except for tract builders, keeping track of an assortment of different headers can be more time and trouble than just sizing them alike, even if that does oversize them most of the time).
Here's a first go at it. All headers are doubled 2x's. Typical two story single family residential building, with bearing exterior walls framed 2x4, 16" OC. Maximum building width is 28'; maximum ground snow load is 50 psf.
2x4 will span 2'3".
2x6 with double jacks will span 3'4"
2x8 with double jacks will span 4'2"
2x10 with double jacks will span 5'1"
2x12 with triple jacks will span 5'11"
Except for the 2x12, it would work (under the limiting conditions described) if you said always double the jacks and span in feet is half the depth in inches (up to 5' opening). Could you live with that?
To really boil it down, make all headers doubled 2x10 on double jacks for up to a 5' opening (again assuming 28' max bldg. width, 50psf max snow).
"Let's get crack-a-lackin" --- Adam Carolla
Edited 4/13/2006 12:36 pm ET by philarenewal
Edited 4/13/2006 12:42 pm ET by philarenewal
Edited 4/13/2006 12:44 pm ET by philarenewal
> The sizing tables are already a digest version of the underlying engineering which leads to oversizing in most cases, but saves a lot of time and aggravation.
And so does the rule of thumb. Consider that this one is good for a maximum span of 12 ft. Take the price of two 2x12 by 12 ft., subtract from that the price of two 2x10 by 12 ft. At $150/hour, how much of an engineer's time can you get for that? Probably not enough to solve the problem, and even if you do engineer it, there's no guarantee that the answer will be the cheaper header.
-- J.S.
Do you really use double jacks on all your openings? that is 2 jacks plus your king studs making a three ply? I didn't realize doubling the jacks on most stuff under 6' was something necessary or desired.
Maybe I am missing something that you were trying to point out. a lot of basic header situations, it is the deflection we are dealing with and not so much the actual bearing. So having 3 plys for most small header situations seems a waste to me.
*footnote... I checked with the in house engineer at my local lumber yard to see about getting the beam sized. Got a beam schedule indicating the use of 3 1/2" x 9 1/2" timber strand. with bearing of 1 1/2" at either end. My buddy whom I'm doing the job with wants to go with 2x 12" if 2 x 10" isn't good enough. Now I don't know if the lumber yard is trying "push" the more expensive TJI product. But for $37 more bucks than 2x 12" I told my buddy to go with the timberstrand ... .in the end he still gets the better product.
and by the way....in spite of the schedule I will be doubling the jacks.
Edited 4/13/2006 3:23 pm ET by alrightythen
>>"Do you really use double jacks on all your oppenings?
No. What I was getting at is an interesting idea that Jim suggested maybe it would be possible to boil down a header size that is as strong as the wall it is in. So, if you got a 2x4 stud wall, use X as a header and go.
It kinda works. Very interesting idea.
Anyway, I'd definitely go with what your lumberyard engineered. They know your snow loads and I assume exactly what you've got going on in your building. Double jacks won't hurt anything for sure. IIRC, you don't get much snow. Must be coastal BC.
My better half is from Nova Scotia. Her folks are still in I think it's near St. John or anyway not too far from Frederickton. They get SNOW.
"Let's get crack-a-lackin" --- Adam Carolla
Edited 4/13/2006 3:37 pm ET by philarenewal
yup, lowermainland/Fraser Valley plenty of rain. We got lots of mountains around us that get snow ( actually ... even the local slopes seem to be getting less and less snow)
anyway....ok what do you think then about the 16" oc vs 24" oc framing then. It seems FHB likes to run these articles that push for 24" oc framing and I think there are a lot of supporters for it as well. ( the 'more insulation' issue gets brought up.) personally I still prefer 16"oc 2x6 construction.