Help, I am Going Crazy!
Reader DIRK in SPANISH FORK writes:
“I am planning to build a pole barn house. I get so confused with the different methods of doing things and the pros and cons of each. I plan to pour concrete piers with a post bracket. Not sure if a 6×6 post or 3 ply 2×6 is better? Maybe this is determined by the way trusses attach. My longest span is 50 ft on 10 ft o.c. If I need double trusses then I might not be able to sandwich the trusses between 2x6s on the laminated column unless i put four 2x6s. I have seen double trusses sitting in a notch. As far as the exterior walls I am not sure what method is better. Bookshelf/Commercial or Girts on outside and inside? Do I need sheathing on the exterior if I am doing a stone wainscot and LP type siding? Air/Water barrier details and how and where to install? Help me! I am going crazy!”
Help is on its way – so no need to go crazy!
Your best column is going to be a glulam, hands down.
Solid sawn columns (e.g. a 6×6) are unlikely to be found kiln dried. This means they are going to be prone to warp, check and twist as they dry.
Strength: bending strength is a product of Sm (Section modulus – depth squared x width divided by six) multiplied by Fb (Fiberstress in bending). Sm for a 6×6 is 5.5 x 5.5 x 5.5 / 6 = 27.729. Fb for #2 DFL (Douglas Fir-Larch) posts and timbers is 750.
27.729 x 750 = 20,796.75
If nailing together three 2×6 #2 DFL Sm = 3 x 1.5 x 5.5 x 5.5 / 6 = 22.6875 Fb for #2 DFL 2×6 is 1170 and 3 members together gets a repetitive member increase of 15%
22.6875 x 1170 x 1.15 = 30,526
Our 3 ply glu-lams have a Sm of 18.058. Take this value times 3000 = 54,173 or 177% of three 2×6 nailed up.
Nailed up columns have some of their own challenges, they are very flexible in weak axis bending (pushing against the 5-1/2″ face). If nails shorter than 4-1/2″ are used and members are nailed from each side, more force is transmitted to the center of the three plies. In testing to failure, this center member fails prematurely nearly every time. As these members still act independent from each other, they are still prone to warp and twist.
You really want to use doubled (2 ply) trusses. A true double truss system, such as used by Hansen Pole Buildings, features trusses physically attached face-to-face by means of mechanical connectors (structural screws). This allows for two members to actually load share, reducing probabilities of one weak single truss failing and pulling a roof system down with it. It also minimizes need for lateral bracing.
Trusses should be set into a notch cut into one side of the column. Trying to utilize a center notch makes setting trusses exceedingly difficult and requires heavy equipment.
Bookshelf girts are really your best design solution. An externally mounted wall girt, on 10 foot bays, deflects too much to adequately support your siding choices. Bookshelf girts are far stiffer against wind loads, provide a deep insulation cavity and allow for a single member to be used.
Your stone wainscot will require sheathing and I would not personally install LP siding without sheathing. An Omnidirectional water resistant barrier should be placed on exterior side of your sheathing (under siding).
Please reach out to me any time with questions. My goal is to assist clients in getting structurally sound buildings they will love forever.
For columns to be mounted into ICC-ESR Code conforming wet-set brackets there are other alternatives. Standard glulams for construction typically have a Fb (fiberstress in bending) of 2400 pounds per inch. This compares favorably to familiar pressure treated lower glulams, where most have a Fb rating of roughly 1900.
DEAR POLE BARN GURU: Hello Mike, Our monitor style home has been designed by your staff and we are putting together financing and logistics details edging closer to ordering our materials package. Still a bunch of questions to ask of the Guru. We will be using an AIB under the steel siding with rockwool insulation in the cavities. I believe we will need a vapor barrier on the inside. I will be working alone on a lot of this construction and don’t look forward to wrestling with plastic sheeting for our vapor barrier. I would like to use a rigid insulation board such as r-tech or r-max with taped seams to accomplish this. I’m thinking it will much easier to seal electrical boxes and such with something rigid. What’s your take on this approach? Do you feel it is a safe and effective way to accomplish this? Thanks as always for your great information! RUSS in TILGHMAN 
DEAR POLE BARN GURU: Looking to use laminated Gothic arch design trusses, 4 foot on center anchored to 1st floor continuous floor trusses 16 inch on center with two rows of support beams at 12 foot under floor trusses. 2nd floor planning on recreation and residential area. Need to have plans drawn up to meet codes. Would this style post framing be sufficient for truss kick out using a truss bass shoe and steel gusset plate at ridge? Possibly add some knee walls at 1st floor framing for added support. Help me out, kinda designing on my own until I get prints. Thanks, ROGER in SOUTH HAVEN 
DEAR POLE BARN GURU: I purchased a 24′ x 36′ pole barn from Hansen in 2016. I has an 8′ lean-to on one eave side making its total dimensions 32 x 36. I would like to add a 10′ enclosed lean-to on the other eave side. Since my building is one of yours, can you design and price it with the same siding colors and account for snow load and the pitch of the new roof? KEVIN in FORT WAYNE 
Most often steel truss post frame kits are being sold as ‘roof only’ structures – in order to drive prices down. I have seen some great prices advertised, however as prices get lower, so does usually quality and or service. Things tend to be not included, such as trims and condensation controls. Most of these buildings are not engineered, other than maybe trusses. However, even your best steel truss engineering is negated if quality controls are not present at wherever they are being manufactured. Use of steel of a lesser grade or thickness than specified can compromise strength. Pre-manufactured trusses are supposed to have in plant quality control and random quarterly third-party inspections, having spoken with a few of these (in hopes to find a reliable provider of steel trusses) – none of them appear to be aware of this requirement. Steel trusses should also be fabricated by certified welders. While I am sure there are some great steel truss providers, they are seemingly difficult to find.
My recommendation would be to use wood trusses. If you are trying to gain interior clear height, wood trusses can closely mimic what steel will do. Wood trusses are far easier to finish overhangs and if you want to have a ceiling finished at bottom chord height, wood trusses make it very easy to achieve. Wood trusses are subject to extremely stringent quality control standards. Every set of trusses we manufacture has to have extensive records kept to verify accuracy of members and connectors, plus – we have third party inspections.
