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Author Topic: Question for 2x and anyone else with carpentry skills.
Drako
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posted 05-31-2005 12:46 PM     Profile for Drako   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
What is the longest unsupported span I can safely build with a pair of 2x6 stringers on a non-load bearing structure? I'm building a shade structure in my back yard and want a 15 foot open span between my 4x4 uprights. I know that wood can begin to twist when the pieces get too long, so I was thinking that I'd run two of them (one on each side of the uprights) and place one or two spacers inside to keep them square with each other and increase its rigidity.

Since this thing won't carry anything heavier than a wind chime I think it will work, but I want to make sure it isn't going to come crashing down on me if I try.

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Cacophonous
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posted 05-31-2005 02:23 PM     Profile for Cacophonous   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Are the 'stringers' going to cantilever any distance?

I think you should be fine. I don't know of any engineering charts for that type of structure since there is basically no load. The closest may be a chart for ceiling or even rafter joists but they account for a load.

Do you want this structure to looks good too?

If so the way you want to install the 'stringers' may look the best but by doubling them up without spacers and setting them right on top of the posts will be stronger and help prevent twisting.

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Drako
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posted 05-31-2005 03:50 PM     Profile for Drako   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Slightly. They'll extend about 12" beyond the 4x4's, but it's more of an aesthetic flourish than a functional part of the span.

I was thinking that my spacer idea would give it a structural strength nearly equal to doubling the wood up directly. By slipping 6" tall 4x4 spacers in between the 2x6's at several points, and then securing those spacers with bolts through both the 2x6's and the spacers, I should be creating a "box" effect which should make it behave more like three 5 foot spans than a single 15 foot span. These shorter "boxes" should make it fairly twist resistant.

Of course, my biggest worry is sag, not twist. My statement that there would be no load wasn't entirely correct because this beam-pair will carry weight from both the crossbeams extending outwards from the house AND from the smaller 2"x1/2" slats that will overlay the whole thing. By my math, these beams will carry about 75lbs of load at their centerpoint in addition to their own weight.

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Cacophonous
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posted 05-31-2005 04:25 PM     Profile for Cacophonous   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
The wood back to back is stronger because it sits on the post. The other method relies on the shear strengh of the fasteners.

Since you are not putting much load on it the method you suggest will work. However I am uncertain about sag. Let's see what 2X thinks. He may have more experience with this type of structure.

For sure it would look better your way Drak, and looks has a big factor in that type of structure.

Another thought is use a single 2 X 10 or 2 X 12 to prevent sag.

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Drako
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posted 05-31-2005 04:34 PM     Profile for Drako   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Yeah, I was looking at some 2x12's yesterday, but they're way out of scale for the size of the structure. This thing is supposed to provide some shade while still staying open, light, and unobtrusive. Putting foot tall beams in place would require me to upgrade my 4x4's to at least 6x6's and would make the entire structure much larger and heavier than I'd like.

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doublefresh
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posted 06-01-2005 08:16 AM     Profile for doublefresh   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
If it is non load-bearing you can buy 16' 2 x6's and it should be no problem.

The "twist" you mention is often caused by wet wood. Go to the extra effort to buy KILN DRIED lumber or Pressure treated wood that has set for a while. I guarantee if you buy it sopping wet like they sell it at home depot it will warp like hell. I typically don't cantaliver more than 24" or 2 feet.

I'm building a Pergola next week out of Cedar and I'm using 6 x 6 posts, 2 x 10 stringers and 2 x 6 cross members with 2 x 2 rails on top of everything else to block the sun. I'm also wrapping some of it in copper which will age nicely over the next few years.


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doublefresh
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posted 06-01-2005 08:27 AM     Profile for doublefresh   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote


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doublefresh
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posted 06-01-2005 08:31 AM     Profile for doublefresh   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
The 2 x 2's on top will keep the 2 x 6 crossmembers from moving/warping.

If you were to do something like this I would step up to 2 x 8's to support all the additional weight up top.

The span on my project is 18 feet.

20 foot 2 x 10's in Cedar are EXPENSIVE!!!


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Drako
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posted 06-01-2005 10:56 AM     Profile for Drako   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Thanks!

It turns out I may have another problem though. I was told yesterday that I have to pull a building permit for this thing, and the California Building Code specifies a maximum unsupported beam length of 12 feet without steel reinforcement to prevent earthquake related failures. Since I don't live in an earthquake zone, that leaves me with two choices: 1. Ignore the law and build the thing how I want it knowing that it will be fine. 2. Pay the city several hundred dollars in fees and redesign the entire structure to meet a building code designed for natural disasters that don't occur here.

At the moment, I'm leaning towards number 2.

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doublefresh
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posted 06-01-2005 05:03 PM     Profile for doublefresh   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
I could weld some steel brackets for you :-)

If it's as small as you say it's only a couple of hundred dollars to build. I'd say F the police and build it. The worst anyone could say is "sorry you have to take it down"

What type of neighborhood do you live in? If you have a home owners association with A-holes that live and die by neighborhood codes you may be better with #2 but otherwise I'd say just build it.


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doublefresh
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posted 06-01-2005 05:08 PM     Profile for doublefresh   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Earthquake or not, pressure treated lumber bolted together will NOT fall down. The wood itself would crack long before the bolts would fail.

If you can avoid attaching it directly to the house you would avoid a number of potential problems. Rather than attach to the house just use four 4 x 4 post to support it.

Sink each 4 x 4 two feet into the ground and fill with concrete. Your hole in the ground should have a diameter of 12"


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Flux
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posted 06-01-2005 10:18 PM     Profile for Flux   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
quote:
Originally posted by Drako:
Quis est porro intolerabiliter span EGO can tutus constructum per iugum of 2x6 ligamen in a non - sarcina gestum compages? I'm aedificium edificium a umbra compages in meus tergum yard quod volo a 15 pes patefacio span inter meus 4x4 rectus. EGO teneo ut wood can suscipio torqueo ut pieces adepto diutius , sic EGO eram reputo ut I'd run duos of lemma ( unus in utriusque of rectus ) quod locus unus vel duos tractus inside ut servo lemma quadratus per invicem quod proventus suus austerus. Utpote is res won't veho quisquam graviter quam a ventus chime EGO reputo is mos opus , tamen Volo facio certus is isn't iens ut adveho fragosus down in mihi si Conor.

Good luck. Post pics when its done.

[ 06-01-2005: Message edited by: Flux ]

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Obsidian
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posted 06-02-2005 04:03 PM     Profile for Obsidian   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
I am assuming you mean it is Greek to you...

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Flux
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posted 06-02-2005 04:27 PM     Profile for Flux   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
I see this thread is intellectually stimulating enough to bring you out of the woodwork.

Close. Latin.

[ 06-02-2005: Message edited by: Flux ]

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J0SH
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posted 06-02-2005 04:27 PM     Profile for J0SH   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
killer sig obsidian.

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I am.


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burble
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posted 06-02-2005 04:42 PM     Profile for burble   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
needs more christopher walkin.

and cowbell.


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Cacophonous
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posted 06-03-2005 09:43 AM     Profile for Cacophonous   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
and queens of the stone age

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burble
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posted 06-03-2005 11:58 AM     Profile for burble   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
more like queens of sucky music.

AMIRITE?


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doublefresh
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posted 06-03-2005 07:47 PM     Profile for doublefresh   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
The cow bell kicks ass!!!

I just started my project similar to yours today. The cedar all arrived and I picked up the copper I'm wrapping some of it with. I also cut the first template for the 15 other similar pieces. I'll post pics tomorrow.


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Cacophonous
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posted 06-03-2005 09:51 PM     Profile for Cacophonous   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
queens of the stone age rock!

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Headstone
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posted 06-03-2005 10:31 PM     Profile for Headstone   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
How did they get a video of you on their site Cac?

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Yep it really is me.


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Cacophonous
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posted 06-04-2005 07:24 PM     Profile for Cacophonous   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
FM - It's a long story that involves a case of cheap beer, date rape drug and guy that looks like Ned Flanders.

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D2
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posted 06-05-2005 05:57 AM     Profile for D2   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
Drako, Let me look at it and i'll give you some ideas. Dont forget, i have a friend the draws up plans and can have them aproved by his engineer (that i am currently painting his house). Gotchya covered on the mass$$$
Call me bone head and we can get this strated. Dont forget, plans can take a few weeks to a feew months to get pushed through the planning department.

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Drako
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posted 06-06-2005 07:11 PM     Profile for Drako   Author's Homepage     Send New Private Message   Edit/Delete Post   Reply With Quote
D2~ Thanks for the offer, but I'm not going the permit route. I want the long span and it isn't legal here...the plans will be rejected the moment I try to pull the permit and I'm NOT going to screw up my open patio by adding a center beam. Rather than waste the time and money fighting a losing battle, I'm just going to build the damned thing.

Just remember, if you're ever in my back yard when an earthquake hits, run for the lawn or get inside the house

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