Window Header: (2-2x8s) VS (2-2x6s + 2-2x4s)?

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Old 11-13-13, 04:42 PM
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Window Header: (2-2x8s) VS (2-2x6s + 2-2x4s)?

I have a bunch of 2x6s that I need to use, but the spanning chart says to use 2-2x8s. If I put a 2x4 above and under, can I use 2-2x6s instead? If not, is there an acceptable way to use 2x6s instead of 2x8s? Thank you for your answers :-)

In case it is relevant: I'm spanning 60" on a small(16' wide) single story house with a snow load of 35.
 
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Old 11-13-13, 05:14 PM
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http://www.duluthmn.gov/building_saf...ial%20Code.pdf

Even though 16' widths aren't listed in the charts above, I'm pretty sure the answer is no.
 
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Old 11-13-13, 07:18 PM
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Strict interpretation of the linked code would tell you not to do it. Especially if the work is being done under permit, with a required framing inspection performed by the building department before you button things up.

However, from an engineering/mathematical standpoint, sandwiching the 2 x 6s between flat 2 x 4s results in a member that will actually be somewhat stronger than the "pure" double 2 x 8 header. This is because the built-up member will have 17% greater depth than the standard 2 x 8 header (8.5" vs. 7.25"), and the extreme fiber-to-centroid distance is squared when computing the section modulus (the measure of a member's strength in bending). The foregoing is based on a presumption that the flat 2 x 4s will be properly attached (glued and screwed) to the 2 x 6s, meaning the assembly performs as a single unit with no chance of separation.
 
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Old 11-14-13, 12:48 PM
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Ask the "Man" at the BD. IMO, you are fine; Chapter 5 - Floors At 30#snow; 5'5" -----------at 50#sn.;4'8"------------middle of those two is 5' at 40# snow, not even figuring in you are only 3/4 the total span of 20' and less snow load.

Gary
 
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Old 11-14-13, 03:52 PM
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Ah.... I see the problem. Duluth's snow load is 70#. glad I don't live there! LOL
 
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