Expert: Daniel Humphrey - 7/30/2010

Question
QUESTION: I am planning to build a 26' x 48' pole barn with a roof attic for light weight storage. The walls will be 9'8" with a maximum overall height of 18' (local code restriction). Can I use 6x6 posts on 6'centers and use 2x12s (in and out) to support the trusses? The posts holes will be 48" deep. At this point it appears my roof will be an 8/12 pitch. The local truss manufacturer tells me I will have a 6' high ceiling with a 10' floor. The sidewall material will be T-9 wood siding in lieu of metal.

Your help and advise would be appreciated.
Regards,
John

ANSWER: John,

The 6x6 on 6-foot centers is plenty of vertical support, but you will need to add some diagonal bracing, X-bracing, or long knee braces along the sides for shear strength. You cannot rely on the ground alone for holding the posts upright over time. Depending on the soil type, you get varying support from the soil itself, especially when you use only 6x6 posts, which don't have a lot of surface area and tend to cut through the soil to some extent. You can increase their surface area by pouring substantial concrete around them or by tamping them in with large, sharp stones.

The 2x12 doubled and bolted through the posts are also good support for the trusses and floor. My grandfather used to put sand into the joint before tightening the bolts, to increase the traction of wood to wood. The larger diameter the bolt, the better the support. For even more support, you can shoulder the 6x6; even a half inch is substantially stronger.

Remember to use hurricane ties to keep the trusses down in high winds. Alternate between the two 2x12s so that they both share the job.

One tip for building the roof is to build the framework on the ground and then raise it with wall jacks or other mechanical device, sliding it upward along the posts into position. This works very well and saves a lot of time, since you're always at the ground level instead of working up high.

Plywood siding is not good in our climate, since it doesn't repel water very well and turns into a kind of sponge that is slow to dry. It must be perfectly applied and waterproofed.

Daniel

---------- FOLLOW-UP ----------

QUESTION: Daniel,
Thank you very much for your fast response. I do appreciate it. A couple of other questions:

For the cross braces, can I use metal straps in lieu of 2x4s?

I have heard that I can use #53 stone to tamp into the holes and it would be better than concrete (I am not opposed to concrete). Is that true?

Would 5/8th carriage bolts or threaded rods be large enough?

I did plan to use the hurricane ties on each truss and each 2 x 12 but it sounds like you are recommending that I alternate them. Am I reading that correctly?

Finally, instead of wood siding would it be OK to use 1/2" composite board? I want to achieve the old barn look (board and batten).

Again, thank you very much. Your help is invaluable.

Regards,
John

Answer
John,

Yes, the strapping would work in opposing pairs, with tension strength only, of course. Knee braces and X-braces work mainly in compression.

Stone is very good around the posts. I concur that tamped stone in a fairly large hole is better than concrete in a smaller,  economical hole.

5/8 carriage bolts are all right. Use big washers and try to get a little indention when you tighten down. Try the sand in between for better grip.

Yes, the advantage of alternating hurricane ties between the two plate stringers is to share the loads. You get twice the uplift resistance that way and balance the stresses on the 5/8" bolts.

I would stay away from any composite board or plywood for exposed siding. Your climate may be more benign than ours. If you do use those products, make sure the wood is sealed well from the outside and has an air gap on the inside to dry out.

Metal can be purchased with board-and-batten appearance. And then there are real boards. The proper batten and trim details for board-and-batten, using real boards, makes for a very durable siding that can easily be renovated.

Daniel