This Wednesday the Pole Barn Guru answers reader questions about what best installed between ceiling liner and trusses and insulation recommendations in a new shop, advice on sidewall column size for use with double trusses, and the structural stability of a pole barn second floor.
DEAR POLE BARN GURU: Just built a 40x60x11 pole barn on the eastern shore of MD. Approx. 20×40 will be garage workshop, the rest will have a kitchen and bathroom etc. going to use liner panel for ceiling, what do I, if anything needs to use between the liner and the trusses? Insulation recommendation? Product recommendations are appreciated! Thank you, LYNN in SHARPTOWN
DEAR LINN: There is not a Code requirement for a barrier between trusses and liner panels in your climate zone. If you are considering blowing in cellulose, chemicals in cellulose can react with steel panels to cause premature deterioration, so a barrier should then be used. My first choice would be blown granulated rockwool, second would be fiberglass. Make sure to have adequate eave and ridge ventilation, in correct proportions.
DEAR POLE BARN GURU: Went reading your blog on double truss system, if wanting to erect a pole barn 30×78. Would using 4×6 be ok going 12 ft high post spaced every 8 foot other then 2 16 openings. BRIAN in PADUCAH
DEAR BRIAN: Thank you for being a reader of my articles. Even with a very low design wind speed, low risk occupancy and a well-protected site, it is unlikely 4×6 columns would be adequate to properly carry design loads, given your eave height. As you are possibly considering utilization of ganged (double) trusses, and will need larger columns anyhow, you may want to consider increasing column spacing to 12 feet on center. Fewer holes to dig, fewer columns to set and your budget will be much happier. In any case, I would encourage you to invest in a fully engineered building – any possible savings you might believe you would attain without engineering, will be quickly eaten up when you have a failure.
DEAR POLE BARN GURU: I’m wondering if this would be structurally sound with a top floor on it? It would be meant as a home/business. I work in the commercial construction industry I guess the other question is do you have any of these in New Hampshire? Please let me know what you think and Thank you. JOE in HUDSON
DEAR JOE: My own post-frame building has a 48′ x 60′ main center section. Downstairs has a clearspan floor (yes, spanning 48 feet), with a 16 foot high ceiling. Upstairs is a full living area, again with 16 foot high ceilings. A portion of this upper level also has a small mezzanine. Overall building height at peak of roof is 44 feet. So, in answer to your question – fully engineered post-frame construction lends itself very well to multiple stories (up to three stories and 40′ tall sidewalls, or four stories and 50′ tall sidewalls with fire suppression sprinklers). We have provided over 100 of our buildings to clients in New England states, including a dozen or so in New Hampshire.
DEAR RON: Lots of possible design solutions available. To begin with, I would recommend wood trusses – should you ever want to finish a ceiling, or if you want to have a product fabricated under strict quality control standards, then wood trusses are your best choice. On to options…. #1 My favorite. Make your building tall enough to have a full second floor. This will give you greatest usable space and best resale value. By using prefabricated wood floor trusses, you can still have a clearspan floor (no posts below) and it provides an unencumbered space below without columns to dodge. Yes, it will be a greater investment, but one you will probably never regret. #2 Prefab wood ‘bonus room’ trusses. With a steep enough slope (roughly 8/12) you can end up with an eight foot ceiling height at center and a room roughly 10-12 feet in width. For amount of space being gained, this is a fairly costly design solution. #3 Increase sidewall height and use scissor trusses to allow for a central mezzanine supported by columns. While likely to be your least expensive design solution, you will be faced with columns below (unless opting to again add in floor trusses.
DEAR ANNIE: As you get closest to square, your costs per square foot will decrease slightly. This is due to having less exterior wall surface, although it does not necessarily lend itself best to layout of rooms. For post frame construction, your most efficient use of materials typically comes from multiples of 12 feet in width and length. Work from inside out – do not try to fit your wants and needs within a pre-ordained box just because someone said using a “standard” size might be cheaper. Differences in dimensions from “standard” are pennies per square foot, not dollars. Post frame will always be your most cost effective structural design solution: 
DEAR JEFF: If erecting a roof only “pavilion” style post frame building, column dimensions are often dictated by L/d ratio as there is no wind load on totally open sidewalls. “L” is unsupported length of column (grade or top of concrete slab to bottom of truss connection), divided by least dimension of column. Playing a part in this is a factor known as Ke. Ke is determined by fixity of columns. On a roof only structure, columns act as cantilevers (think of a diving board), so Ke = 2.1. Looking at your 5-1/2″ square 6×6, 5.5″ x 50 / 2.1 = 130.95″ (or just under 10’11”). This means at an unsupported length of 11 feet, a 6×6 would fail. Obviously, truss span, spacing, and loads from dead, wind and any snow must be properly factored into equations to be verified by your building’s engineer. Adding an eave sidewall (or sidewalls) with open endwalls will cause bending forces to fail most 6×6 columns at lesser heights.
Me, “You would have to write one and they will be very complex due to the tremendous number of variables involved. I’ve thought about having a Wall Girt calculator on our website for Building Officials to use and the reality is, it is a huge undertaking. For it alone, requires all of the building dimensions including roof slope, is building enclosed or partially enclosed? Which means one has to know if doors are wind rated, and where they are placed. Also makes a difference as to where girts are located on building as wind forces are greater at corners. If girts are barn style on outside of columns, do they span a single bay or multiple bays? Then one has to account for lumber species differences as well as visual vs. machine grading.
