I am building a deck and was wondering how far doubled 2 x 6 joists can span at 16″o.c. I haven’t been able to find any info on any span charts I’ve looked at. Thank you in advance for your response
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I am sure someone will point you to a calculator somewhere but ...
If it is not in your code book, you hire an engineer.
You must be height-restricted to want to double them. Is that right?
Hi All,
Thanks for your responses. Had to change my account this morning for some reason. thus my log on name change.
I am heighth restricted and am wanting to span at least 10', 12' if doable.
What about hanging the joists off a beam, rather than the beam under the joists, to break up the span.?
"Bounciness" also comes from flooring choice (like 5/4 or man made materials), not just joists. By spacing closer together, you will lessen this effect.
According to charts (Sorry Boss), a 2X6 joist with fiber stress in bending of 1200 (mid grade) will span 10'-0" @12"oc, and 8'-8" @ 16"oc for 50 #/sq ft. This is based on a deflection of L/360 which is (0.33 " over 10').
Some areas will allow decks at 40#/sq ft, and limit deflection to L/240.
So.........2x6 @ 8" oc (instead of 2-2X6 @ 16" oc) will give a stiffer floor, and going 10' should not be a problem.
To go 12'.... how about clear spanning 10' to a beam, and cantilevering the last 2'?
""Bounciness" also comes from flooring choice (like 5/4 or man made materials), not just joists. By spacing closer together, you will lessen this effect."
I don't agree. Vibration is a function of the length/depth ratio of the floor member. And flex BETWEEN the joist will have a different feel.
The California state bird is the middle finger. [Jay Leno]
Hi there boss,
"Bounciness"....I was reading this as deflection, which is the movement of a framing member in a vertical plane when a live load is encountered.
You are correct (a function of the length/depth ratio of the floor member) . But, deflection can occur in all of the members in a floor system. If sized incorrectely, a beam, joist, or floor board can have deflection that exceeds the allowable (in my scenario) rate of L/360. It would be tantamount to sheathing a properly engineered truss roof (@24"oc) w/ 3/8 osb.
So all of the framing (beams, joists, and floor boards) have to be sized correctly for a floor not to have "bounciness".
Maybe we are discussing harmonic resonance? or the
You will note that no one asked you your loading. Most if not all of the advice given has been poor.Perhaps you should see your building permit office.
Edited 11/14/2005 1:59 pm by GHR
You will note that no one asked you your loading.
Actually 40#/sq ft, and 50#/sq ft mentioned in two separate posts. But you are correct.....no one asked him specifically.
Most if not all of the advice given has been poor.
Sorry you feel that way.
Perhaps you should see your building permit office.
He could, and still should, but he posted the question here. Just trying to help the guy out.
GHR likes to flaunt his claim that he's an engineer. But he never has once given useful advice to anyone or posted anything that would lead me to believe that he's an engineer. He likes making smart-a$$ed cracks instead of attempting to say anything useful. But say anything he doesn't like, and he runs to the moderators. It's best to ignore him.
Why do people who know the least know it the loudest?
Thank you boss. As always, words of experience.
I have a great deal of respect for guys like you who try to help people w/ questions. You are right about him not saying anything useful.
I really wanted to reply more strongly (but eloquently) to him, something like:
THREE lines of text, not ONE word of advise.
I guess we could all answer every question correctly w/ a statement like...
"ask your building dept"
Since I am a relatively newbie here, I did not feel it was my place to stir the pot.
But hey.......pass the spoon, will ya.
"ask your building dept"
I'm all for getting plans approved but don't depend on them to give building advice. For example, in another thread, the guy said building dept said to use 2x12 DF joists on 12" centers - or something to that effect. Then he is running all over the place trying to find DF. If I remember correctly, he lived in VA. They don't sell DF in VA - maybe you could special order it but who would want to pay for that? I think he ended up using 2x12 SPF to span 20'. What a joke!!
Thank you all for your insights and responses. I've decided to add another beam mid-span.
If you're looking to keep the deck as low as possible, you can trench out the line of the beam and set it in concrete at the correct elevation for your finish height. It goes without saying you're working with ACQ here... Just leave a little slope in the concrete itself for drainage. And a strip of 90# felt placed on top of the beam before you set your joists in place will aid in shedding water which could migrate to the joint between the beam members.
> I am heighth restricted and am wanting to span at least 10', 12' if doable.
> What about hanging the joists off a beam, rather than the beam under the joists, to break up the span.?
That's a very doable thing. It would be equivalent to having two copies of my existing deck side by side. Single 2x6 joists, 16" oc, spanning 6 ft. Mine's quite solid and comfortable.
I'd look at the hangers that have tabs on each side that go over the top of the beam. That seems stronger to me than the ones that just nail to the side, and it makes it easier to get all the joists at the same level.
When you lay out the actual decking, start with a plank centered over the center beam. You don't want a gap between planks over the beam, because it would catch crud and water, leading to rot and termite damage.
-- J.S.
An option to keep the span issue from being problematic would be to add another beam and line of posts beneath your proposed 2 x 6 structure.
First, welcome to BT.
You are right - span tables don't cover doubled joists. Wonder why that is? :-)
Some of it depends on what species of wood; SYP?, SPF? DF? Hemlock?. Another factor is what PSF LL (live load) your local code requires for decks.
Is this gonna be inspected? If not here is an educated guess: A quick Google found this span chart for SYP, 40 PSF LL: http://www.southernpine.com/pdf/table02.pdf
So for #2 2x6 the max spans are:
24" OC = 8'6"
16" OC = 9'9"
12" OC = 10'-9"
8" OC = ???
I used the visually graded #2 since that is more than likely what you are going to get, unless you live out west and I don't know what is customary out there. As far as I know all PT lumber is SYP in the eastern half of the US.
The idea being that 16" OC doubled is pretty similar to 8" OC... Now let's do a little extrapolation.
24" OC = 8'6" baseline
16" OC = 9'9" spacing reduced by 8" and length increased by 15"
12" OC = 10'9" spacing reduced by 8" and length increased by 12"
8" OC = 11'6" spacing reduced by 8" and length increased by 9"
Now, since I hate bouncy floors I'm gonna introduce a minor safety factor (for my project I might go with a larger safety factor):
8" OC = 11'3"
OK - not terribly scientific and I didn't do the math but you did get the benefit of the experience of someone who has built at least a few hundred decks. At any rate, there is one thing you can depend on here at BT: you always get your money's worth!! ;-)
Actually that should work even if it is being inspected just so you get your plans approved by the local building department first.
Good luck.
A 2X6 spanning 11' 3" has a length/depth ratio of almost 25/1. I don't like to go more than 18/1 on floors. For a 2X6, that means about 8' 3" max.
It is not from the benevolence of the butcher, the brewer or the baker that we expect our dinner, but from their regard to their own interests. [Adam Smith, "The Wealth of Nations"]
You are the expert.... although I didn't know you dealt with conventional lumber floor framing. So, you have no use for span tables what-so-ever? That is what your 8'3" span number seems to insinuate. Also, while I know that the OC spacing has a lesser effect of floor performance, the joist height being by far the major "player", spacing does have some effect. Your rule of thumb does not take that into account at all. And no, I don't want to look at your thread on floor vibration... :-)
Edited 11/14/2005 8:34 am ET by Matt
"So, you have no use for span tables what-so-ever?"
Not at all. Span tables are a starting poiint. I just have a different ENDING point than they do.
"I know that the OC spacing has a lesser effect of floor performance, the joist height being by far the major "player", spacing does have some effect. "
Right. Spacing changes have very little affect on vibration.
"Your rule of thumb does not take that into account at all."
My rule of thumb is roughly the point where you start having vibration problems regardless of spacing. It's not an absolute. But follow that and you'll almost never have problems.
"And no, I don't want to look at your thread on floor vibration..."
Dang! - That was gonna be the first thing I said. Am I that predictable ??? (-:
Any attack on a person or his property is a crime and punishable as such. Hate-crime laws add an extra penalty because the offense was spurred by malice toward a protected group. The additional punishment is for holding bad ideas. It's a short step from there to punishing pure advocacy. [Columnist Don Feder]
Ron:
I respect your points. My ending point is to come up with something that works reasonably well taking different factors into consideration, such as: cost, and a reasonably workable solution. For example I think we are assuming that the guy is space constrained and that is why he wants to use 2x6 floor joists but wants a fairly long span - or at least that is what I read into his Q so if that is what the project dictates, we need to find a workable solution. Personally I don't build anything with 2x6 floor joists except maybe a 4x4 stoop outside a back door. It seems like you are only looking at the vibration issue though. How important is limited vibration on a deck? By your method, let's say he wants to build an on ground deck that is 10' wide - he is SOL. I guess we could just tell him to use W6x15 I beams for joists. :-) Would the rule of thumb apply to those too ;-) Would those need to be bolted or welded? :-)
I'm not sure what your point is regarding a 10' wide porch. I don't change my recommendations based on whether the floor system is used for a porch, a house , or an office building. A bouncy floor is NOT a "workable solution", IMHO.Regarding steel - I don't yet have enough experience with it to give solid advice. But I do know the length/depth ratio can be much higher.
If you want to be great, you have to do things other people won't. [Dr. Rick Rigsby, Professor and assistant football coach, Texas A&M]
Why double?
As Homewright sugggest: Add a line of post in the middle and an under joist beam, usless your are "height restricted" as questioned by Stringer.
Here's something that maybe this HO can help with. We built a very low ground level deck and we set the beams right into the concrete piers and then hung the joists (using joist hangers) off the beams. We also dug out the area that would be under the deck so that the deck would be even lower. Between the bottom of the joists and the ground there is 2" and between the edges of the deck and the surrounding retaining wall there is 3-4". The grass height is just about the same exact height as the deck. Its pretty cool to walk from the deck to the grass and have there not be any step. I've included a pic of the rough framing.
Daniel Neuman
Oakland CA
Crazy Home Owner