2x6 span question

[Koldham]

is a 12ft span for a 2x6 unreasonable? it will just be holding up plastic corrugated roofing to keep the leaves and sticks off my truck and trailer, no osb sheathing. no snow load. I can draw up a simple print of what im trying to build if that helps. its just a 10x12 pergola style 4 post pole barn.

 

[Jlbc212]

It is not unreasonable. Many houses have roofs framed with 2x6 rafters that span 12 feet in areas where there's lots of snow.

 

[Koldham]

all the websites I visited referenced deck construction so i wasn't sure. im no engineer. thanks. all the pergola kits i found with 12 ft spans used much much larger boards. Must just be for looks.

 

[DFB]

According to my bible or reference manual...
Carpentry (Koel) I got all those years ago in trade school

Maximum Rafter spans for 2X6 is dependent on both "spacing" and "slope"

Under 4/12 pitch with 16" spacing the allowable span is 14'6",

with 24" spacing the span decreases to 12'.0"

A steeper pitched roof angle 4/12 and over will gain some slight value but not much...

Using the same 2x6" rafter it be 15' 6" @ 16 o.c. and 12' 6" for 24" o.c.

Even larger distance increase using 12" centers up to 16' 6" under a 4/12 and 17'6" max over 4/12 roof slope

 

[mike93lx]

It will be fine. With almost no load, there isn't much sag to worry about.

Crown the boards up, git er done and move onto the next project

 

[Koldham]

Crown the boards up,

i thought boards had crowns laying flat. whats the crown sitting upright?

 

[mike93lx]

i thought boards had crowns laying flat. whats the crown sitting upright?

Looking down the edge of a board, you will almost always see some curve. There is also the curve from the growth rings when looking at the end. The first is what I am talking about

 

[Marctrees]

Crown is the convex edge, always place up when you do joists, beams, rafters etc so downward weight force will tend to make the member straight, rather than sag.

So it like counteracts any future sag, rather than ADDING to sag.

Not all boards have crown, most do, and some minimal and some alot more.

When you go to yard and pick your beam, find one w a bit of crown... Common in a 2x6x12 maybe like 1/4" - 5/16 or so.

For your purpose it would be better than a straight one.

Putting loose wood shelves in a bookcase, you put any warped arched sides up, and put your heaviest books on that .

And you could always double up/ laminate two slightly crowned 2x6's... not as strong as a single 2x12, but better than single2x6.


Marc

 

[Marctrees]

Thing is though, OP was asking about a beam, not a joist or rafter.

His proposal is for a single 2x6 12' long BEAM to carry at least 50% of a 120 ft sq load.

Seems shy to me even everything here considered.

I would at least double laminate two 2x6, choosing boards w no large knots along bottom edges.... or a single 2x8... but that is logical for me, BUT I am NOT a framing carp.

** - Koldham - Are you asking about the BEAM, OR about the individual Joists ?

Marc

 

[Koldham]

yes i was talking about the beam, the depth of the carport between posts will be 12ft (was planing on using a 16ft 2x6 for overhang). the posts will be 10 ft apart width wise with 2x6 "rafters" (or whatever they are called) at 24in spacing and corrugated plastic roofing running down the depth of the building. 2/12 pitch towards rear of building. 8 ft high at the front 6 ft at the rear. with 45 degree angle braces at all four corners keeping everything square.

 

[Marctrees]

So realize how much more your beam is carrying compared to your SAME size rafters.

I know you said you have no snow, but don't forget about wind.

And, if you ever need to walk on it.

I suggest you use a stronger beam, at least.

If you want, draw a hand sketch and post... also showing how you are incorporating a 16 footer.

Marc

 

[Koldham]

i want to build 2 of these 10ft apart. i was planing on using the deck joist hangers to hang the "cross beams" that the roof will sit on but now that i see the drawing on paper instead of my head the cross beams should sit on top of the 2x6 so i can rest them on 4 boards instead of 2. like a normal pergola. wiht the plastic roofing on top of that.

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[Marctrees]

So the 16' w 2' overhang cantilevers on both ends is fine. but now w a roof area of 160 sq ft you DEFINATELY need more than single 2x6 beam at each end of your structure.

In my opinion if you have a double beam as you show at both ends it's OK.

I also say now at this decent size structure you really should be using 6x6 or similar for posts.

Lastly, the ribs on your plastic roof i think run the 14' length. meaning PARRALLEL with your joists, meaning the plastic will sag AFAIK.

So, you may need to install 2x4 purlins like 30" oc on top of your rafters.

So you said at the begin "like a pole barn", you know what I mean.

Go look again at a newer decent build one and look at spacings, sizes of lumber used, etc.

Not sayin you need to make it quite THAT good, but you want to do it halfway decent anyway.

My opinions, having done similar stuff.
Marc

 

[Koldham]

the roofing is to run perpindicular to the cross beams. beams go left to right, roof goes front to back. if i rested the cross beams ON TOP of the 16ft 2x6 beams as to spread the load over all four like an actual pergola, not just to the inside 2, would that be sound? I also just looked at the cost of going to a 2x8. not a crazy amount more. i will only need 4 of them.

 

[Marctrees]

Do and do not understand you.

The 10 long post sandwiching 2x6's are "Beams"

The 14' 2x6 are "Rafters"

So that rain runs down, aren't your plastic ribs parrallel w your rafters?

So if they are parrallel, not across, that means your plastic will sag.

Clarify

Marc

 

[Marctrees]

Yes, FOUR 2x6x10 as beams should be OK good enough.

Of course you would arrange so each rafter bears on ALL 4 beams.

Marc

 

[Koldham]

looking at the front of the structure the beams run front to back, 2 on each side. the rafters run left to right between the beams. the roof panels then run front to back on top of the rafters. my dad built something similar (but smaller) under his deck to keep rain off his jeep stored under it. with 24in spacing between the beams and the plastic running perpendicular to the beams it did not sag with the weight of the water.

 

[Koldham]

Yes, FOUR 2x6x10 as beams should be OK good enough.

Of course you would arrange so each rafter bears on ALL 4 beams.

Marc

well yes but no. the span between poles is 12ft. so 4 2x6x12 as beams.

 

[Marctrees]

Now I understand.,, So your plastic ribs will be 90 degree to the rafters,,, Good.

Ok, sounds fine.

Another benefit of 6x6 posts at least 3' in ground is you will lessen or eliminate bracing.

Marc

 

[Marctrees]

"well yes but no. the span between poles is 12ft. so 4 2x6x12 as beams."

Got it, ya ok.

Marc

 

[Marctrees]

So I keep thinking its all turned 90 from how you have it,

So, this below does not count,, meaning they will automatically land on all four.

"Of course you would arrange so each rafter bears on ALL 4 beams."

Marc

 

[Koldham]

yes. the first image i posted was the side view. im trying to make this thing kinda modular so if my fleet grows i can bury 2 more posts, put up another beam, and put up some more roof to add another berth.

 

[Marctrees]

I guess your design is fine, but odd turned 90.

If you look at photos of pergolas w a pitched top, the beams are normallly at top and bottom ends of roof, not left right.

OK

Marc

 

[Koldham]

i want something like this but with no walls and built like a pergola.

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[Marctrees]

Make sure you use HOT DIPPED Galvanized hardware, NOT Electro Galvanised.

And any and all nails get Ring Shank style.

Marc

 

[Koldham]

iv got boxes and boxes of the 3in grey primer deck screws left over from my garage build. didnt have air to run a nail gun so the entire building was going to be built with screws. my neighbor came over laughing at me and gave me an old harbor freight compressor. Ran that thing into the ground but it lasted the job.

 

[Marctrees]

I suppose you can get by using those to toe nail the rafters onto the beams, but that alone would be not real strong w/o also like Simpson H8's or similar.

edit -H 11, NOT H 8.

If you don't want to throughbolt beams to posts, at LEAST use HDG 4 1/2" Ring Shank "Pole Barn Nails" NOT your 3" ers.

Also, if you look at your "deck screws" hopefully you will see they ARE approved for treated lumber cause your "primer" is a ceramic coating.

Marc

 

[Koldham]

bolts for the beams sounds like a good idea, i will look into that.

 

[Marctrees]

Anytime anyone builds almost anything, certainly something like this, there is a whole range of how good do ya wanna do it?

At one end, this could be done w 4 bamboo poles, guy line, and a cheap harbor freight tarp.

Or, built to Miami Dade county inspections approval for Hurricane area.

What I've given you is what I myself would do, and it's better FOR SURE than the average done around me.

Marc

 

[Marctrees]

bolts for the beams sounds like a good idea, i will look into that.

That is what is normally done, but in MY opinion the large long PB nails OR GRK RSS screws are good enough for this.

Some will say not only bolts, but to also cut a dado step on the posts to "let in" the beams.

I REALY think you will be VERY happy if you do the 6x6 posts 3 ft minimum in ground.

I would NOT use 4x4 for this size, nor this height above ground.

NOT.

Marc

 

[Marctrees]

I have been assuming this whole time this is NOT building permit Inspected.

In practical terms, you have decent specs now.

Marc

 

[Koldham]

ya i followed the code book when i built my garage, mainly because it had a permit and had to be inspected a few times during construction. im not getting a permit for this project. thats one reason its being built so low. you wont be able to see it over the fence. but I also dont want the thing falling over. I want one step above "good enough"

 

[Marctrees]

Make sure you have seen the below link VIDEO, AND photos.

Don't bother w the legal talk, but READ and SEE what fastenings failed.

Take your time w it ... Go through it sloww, and twice...you will NOT see everything that caused failure w a quick glance through.... I guarantee benefits to you.

Marc

https://www.garagejournal.com/forum/showthread.php?t=436901

 

[Marctrees]

This was an insanely defficiently fastened building in numerous ways.

Marc

 

[Marctrees]

Do not miss the link at very bottom of post #1 for still photos.

Scroll alll the way down for damage photos

 

[Koldham]

yeah my takeaway from that failure was to make sure your posts are in the ground and anchored deep enough to prevent deflection. nails are great for sheer loads but not tension loads. screws are far superior. also why did they skip purlins(?) when screwing the metal down. any place there could be a screw, there should be a screw.

i also will not have any walls on my structure. i know it will trap air, but not nearly as much as a 3 sided building.

 

[Marctrees]

OK so your'e in better shape now than earlier this eve w more info.

Marc

 

[Koldham]

i usually tend to over build everything i make. as this is by far the largest thing iv ever built without plans, the material costs is keeping the overbuilding in check.

 

[Marctrees]

I'll just leave you toninght w -

Most shed roof (Single plain "Lean to" roofs )covered pergola like structures and like Pole Barn shed roof porches have the beams level, and the rafters pitched .

You are thinking the opposite.

I never thought why "They" do it that way, rather than your way, but it may be wise to look at a bunch and just consider it.

One reason they do it their way is a ledger or hanger joist is on the building supporting upper end of joists... It seems you are free standing, so, I guess?? you could do it either way.

I dunno, just doublecheck this question.

I'll keep an eye out here.

Marc

https://www.google.com/search?tbm=i...s0KHT4kAvoQ4lYIPigL&biw=1229&bih=604&dpr=1.56

https://www.google.com/search?biw=1...hUKEwi_8PnvmtXmAhXHLs0KHSeBAWIQ4dUDCAc&uact=5

 

[Marctrees]

I may be misunderstanding how you're turning this thing... like which side you drive in to.

Draw out more fully if you want.

Marc