Expert: Daniel Humphrey - 2/28/2009

Question
I am planning on building a 26' x 48' pole barn with 6x6 posts and perma columns. The walls will be 12' high  and I plan set the posts 12' and use a 6x6 beam sandwiched and between 2 2x12 and carriage bolted together. I will rest the 6x6' beams  on the post and carriage bolt thru the 2x12 and 6x6 posts.  For the roof I will use 10/12 attic trusses on 16" centers with a standard sheeted and shingled roof. I would need a 30 PSI live load and I live in snow country.

My question is are the beams proposed able to handle the load of the 2nd floor and roof. I have considered framing between the posts with conventional framing to make a hybrid building. Any info would be appreciated.

Answer
Dear Brian,

The 6x6 posts are too small for such a height and to carry a second floor. I would go up to 8x8 at least. If you stay with 6x6 for ease of construction, you should frame in between with conventional framing, as you said. You can use 24" on center to minimize the extra framing.

To span 26 feet, tie the posts together,  and support a floor load, you will need tie beams of at least a built-up 8 x 12 every 12 feet, approximately. This would mean a post every 12 feet, of course.

To support a roof system that large, your rafter plate must be substantial as well. With posts every 12 feet, you can get by with a built-up 8x8, or the 6x6 sandwiched between 2x12 would be enough. But if you frame in underneath, that rafter plate could be very slight.

I built a very similar structure last summer, using 6x6 also. I placed posts 10 feet apart on the sides and also down the center so that I could use smaller posts, beams, and plates. Since the building was to be divided anyway, the loss of the clear span was not a factor.

Your truss system will be very good on just 26 feet. You didn't mention braces; I would put them in even if you plan to sheathe.

--Daniel