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wayneb 05-25-2011 12:43 PM

How to build a 2x8 beam
I am building a small storage loft (about 10'x10') in my shop and want to build a beam to span 9'6", made from 2 - 10' long 2x8's with 1/2" OSB sandwiched between and fastened together with Liquid Nails and 16d nails every 8" or so. The 2x8's are 9'6" long but the OSB is only 8' long.
My question is: do I sandwich the 8' OSB piece in the middle of the span and add a short 1'6" piece to one end OR a short 9" piece to each end OR does it matter as long as the longest piece of OSB is mainly in the middle area of the span between the 2x8's?

dpach 05-25-2011 01:32 PM

Personally, I'd put the joint between OSB pieces closest to the end of the beam (so one 8 foot piece and on 18 inch piece). The further away from the two side supports the joint is (so the more in the middle the joint is), the more stress there will be on the joint.

But, if you are using a good quality construction adhesive and spiral nails to put this together, there shouldn't be any problems.

I'm assuming you meant to say 4x8 beam in your post title instead of 2x8 beam (2-2x8's would be 3.5 inches plus the 1/2 inch OSB = 4 inches wide).

wayneb 05-25-2011 02:14 PM

4x8 Beam
Thanks for the reply. Yes, it will be 4x8 when built not 2x8, I messed that up, I should have said a 4x8 beam made from 2x8's. I had heard that the most stress on the beam would be in or near the middle so there shouldn't be a joint near that area. Thanks for confirming that. Will this 4x8 beam be strong enough for the 10 foot span? Thanks again.

Daniel Holzman 05-25-2011 02:33 PM

Whether the beam is strong enough for the span depends on the loading (what are you planning to store up there?), the tributary area to the beam, and the allowable stress of the beam (depends on species of wood and grade of wood). For example, if the beam is a center beam designed to support joists perpendicular to the beam, the tributary area is probably half the floor area (the walls support the other half). You also have to look at whether any roof loading is carried down to the beam. If there are point loads, they need to be included as well.

wayneb 05-25-2011 04:33 PM

Loft beam
I will be storing misc. garage junk in boxes, maybe 1500 pounds of stuff. The 4x8 beam would be across one end (from a vertical 4x4 to a vertical 4x6 in the wall of pole building shop) and there would be 2x8's attached to the beam with Simpson tie brackets, the 2x8's would be perpendicular to the beam and run about 9-1/2 feet to a 2x8 mounted on the end wall, where they would be mounted with simpson tie brackets on 16" centers. The loft floor will be 3/4" plywood sheets. Thanks.

chrisBC 05-26-2011 12:09 AM

remember to stagger your joints too

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