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Patio beam span bfry 01-28-2007
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Posted by bfry on January 28, 2007, 9:10 am
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.


Posted by RicodJour on January 28, 2007, 10:22 am
bfry wrote:
> 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).

No. Beam strength increases much faster with increased depth than
increased width.

R


Posted by bfry on January 28, 2007, 10:57 am
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.



Posted by Michael Bulatovich on January 28, 2007, 12:14 pm

> 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.

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?
--


MichaelB
www.michaelbulatovich.ca



Posted by RicodJour on January 28, 2007, 12:22 pm
bfry wrote:
> 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.

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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