Patio beam span

I'm extending an existing patio. My question is; will (4) 2x6's be sufficient for a beam (given the following) ?
- Beam will span 13'-6" between posts. - Rafters are 2x6 @ 24" O.C. and will be attached to a ledger on the other end. - Rafter span is 7'-0" with 1'-0" of overhang. - Roofing to be 1/2" OSB, tar paper and asphalt type roll roofing. - The underside will be finished and will be 1/2" sheetrock with plaster finish. - Each colums is 12" square and constructed from 2x4's and 1/2" OSB sheathing (2 2x4's at each corner and OSB on each side).
Thanks in advance.
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bfry wrote:

No. Beam strength increases much faster with increased depth than increased width.
R
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Can you show the calculations to back up your answer ? I am matchting the existing patio and can only use the depth of a 2x6 but can go as wide as 12".
What I was thinking was to construct (2) double 2x6 beams by gluing & nailing them together or bolting them together with carriage bolts. Then space them 6" apart and attach 6" long pieces of 2x6 at 24" OC to create a 12" wide beam. Also 1/2" OSB will be nailed to the underside of the beam.
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Like Rico said, beam depth is what you want...You want your as many of your working fibers as far from the neutral axis of the beam. Just look at an I or W beam. Lots of meat above and below the center line. Why are you trying to skimp on a beam?
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MichaelB
www.michaelbulatovich.ca
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bfry wrote:

Can I show my calculations? Do you want fries with that? ;)
Based on a boat load of assumptions - since you didn't mention where you are, what design loads code requires, whether the roof is to be flat of pitched (not clear on that one), species and grade of wood, etc. - I came up with a failure in bending with 1.5" deflection. Your loads and actual situation might ameliorate that, but shallow longish beams are prone to creep (that's not deflection under load, rather slow settling of the wood fibers - you know, sag).
Might be easier to use a better suited beam, read deeper, and add a bit to the existing so everything matches up nicely. If you must keep the 2x6 depth, check out a flitch beam - store-bought version at betterheader.com Greater strength = more money.
R
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Yeah, sure I'll have fries with that.
Kidding aside, I'll provide some more info that I inadvertantly left out.
- No snow loads (south-central Arizona). - No live load. - 2x6's will be DFL #2 - Roof pitch is 3/8" per foot.
All of the span tables that I have looked at do not show spans (rafters) of only 7' so I need some help here with the calculations. Also since the rafter span is only 7' I should be able to get away with 32" spacing vs 24 if that makes a difference.
The existing patio has a stucco finish so the overall size (height of beam) cannot be changed unless I tear down and rebuild the patio with a larger beam height.
One more thing to consider. Since the posts are 12" square I could use up to (8) 2x6's for the beam. Will this make much of a difference ?
All things considered, I would like to match the existing patio for asthetical reasons.
Thanks for taking the time to answer my post and I look forward to hearing from you again.
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Factor your load by the ratio of the given rafter span to your 7' span...
12" posts?!
I thought 6x6 were pretty massive
btw 3/8" in 12 is pretty shallow
cheers Bob
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If your really dead set on using 2x6's, then you may want to consider installing a couple of 1/2" steel plates in between each 2x6. It will be extremly heavy so you will want to build it inplace. Lou
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The depth of the beam is inadequate for the 13' 6" span...it will sag noticeably & you won't be happy with it. You need more depth.
I built a patio cover from salvaged timber...I used a 4x6 for the beam the span was just under around 11 or 12 ft (cannot remember exactly) I was too cheap to buy a new 4x8....& I had convinced myself via calcs that it would "be fine" .....it sagged slightly but not all that noticeable. But still I'm pissed for going cheap when I "knew better" :(
I just built another patio cover
beam is a rough sawn 6x6 (yeah, kinda weird but headroom & I replacing an 80 year old exisitng design)
beam total length 22' with post at center.....yielding two 10.5' spans rafters ~9' roof deck 3/4 with membrane roof, rafters exposed
Your built up beam has approx 1/2 the stiffness of my 6x6....based on the increased span
Spacing two builtup 2-2x6's apart another 6" isn't going to buy you anything unless you skin it; top & bottom...you need increased depth.
You could create a "box beam" by block & spacing your 4 2x6's & then skinning the top & bottom with plywood.
Skinning just the bottom will help but I'm too lazy to find the neutral axis & calc stiffness.
I rough guess is that 8" wide with 1/2 plywood top & bottom is close (~ double the stiffness)
Oh, if you decide to do this.....
glue (water proof) & nail (.113" dia nails) the 2x6's together....forget the bolts glue the plywood as well as nail
but you what really need a deeper beam (which is where you're headed with the box beam)
or shorter span
cheers Bob
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I have built the beam, but have not installed it yet.
This is how I built it: I built the beam using (8) 2x6's. I used Titebond II (extior grade, waterproof) wood glue and applied an even thick coat using a foam roller applicator. The glue was applied to both facing members to ensure full coverage. I used 3" long exterior grade deck screws 12" O.C. at the top and bottom of each 2x6 while alternating the pattern from one 2x6 to the next. After letting the glue cure for 3 weeks, I glued and nailed 1/2" OSB using #8 galvanized nails at 6" O.C. to the bottom side of the beam.
Also I calc'd the beam strength using "ConstructionCalc ProBeam". I entered a custom member size of 12" width and 5.5" height. The deflection overdesign for this beam calcs at 91.2% overdesign.
Any comments ?
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Just one for now....
if it was built from 2x6's & you added 1/2" OSB to the bottom face, how is the beam only 5.5" deep?
oh, and.....

what does this mean? what LL & DL did you do the calc with?
time will tell if your numbers are correct.......8 - 2x6's is a cheers Bob
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Originaly I was not going to add the OSB, untill I read your earlier reply about skinning the top and bottom. So the 5.5" (depth of the 2x6) was used for the calculation.

The "ConstructionCalc ProBeam" program uses this term (overdesign). The 91.2% refers to the deflection overdesign. The bending overdesign calc's at 157.4%. And the shear overdesign calc's at 1151.5%.

These are all of the values used in the program for the calculation; Span: 13.5' Allowed Live Deflection: L/360=.45" Allowed Total Deflection: L/240=.68" Pitch: .4/12 Load Duration: 7 Days (worst case live loading will be from short term construction loads) Load is uniform only and weight of beam is included. Roof loads with no snow: LLpsf, DLpsf, Tributary width=5.5ft Custom member size and weight: Width", Height=5.5" height, Weight.7 lbs/ft Custom Member Material: Douglas Fir #2 Custom Member Bending Strength: 1,170 psi Custom Member Shear Strength: 180 psi Custom Member Perpendicular Comp. Strength: 625 psi Custom Member Modulus of Elasticity: 1,600,000 psi

given the information above, is it correct ? and what about the 8 - 2x6's ?
Cheers to you also,
Brian
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I have built the beam, but have not installed it yet.
This is how I built it: I built the beam using (8) 2x6's. I used Titebond II (extior grade, waterproof) wood glue and applied an even thick coat using a foam roller applicator. The glue was applied to both facing members to ensure full coverage. I used 3" long exterior grade deck screws 12" O.C. at the top and bottom of each 2x6 while alternating the pattern from one 2x6 to the next. After letting the glue cure for 3 weeks, I glued and nailed 1/2" OSB using #8 galvanized nails at 6" O.C. to the bottom side of the beam.
Also I calc'd the beam strength using "ConstructionCalc ProBeam". I entered a custom member size of 12" width and 5.5" height. The deflection overdesign for this beam calcs at 91.2% overdesign.
Any comments ?
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