b"THE OFFICIAL NFBA MAGAZINEcontinued from page: 27building designer worth his wages would confirmthe roof snow load his trusses were designed for, and that the snow and wind loads used in the roof trussthis still does not include the suggested increase and building design are appropriate for the locationadvisable for the valleys.before the trusses are manufactured. Building owners and their builders or building Besides the incorrect Ground Snow Load, thedesigners SHOULD have a crucial conversation truss should not have used a slippery roof surfaceon the design values for their building before any assumption because a large area of the barn wasmaterials are purchased and ensure that the roof tied into the milking parlor in a T-shape with twosnow load is not LESS than what the owner desires large valleys on the Freestall barn preventing snowafter they understand their options.This farmer POST FRAME DESIGNsliding from the roof through a wedging action of(along with many, many others) had no idea that the two roof slopes coming together.In addition,his building was designed for such a small amount they create a 3-dimensional pocket where snowof snow.commonly drifts in and accumulates in these valleysAccording to the Truss Plate Institute standard TPI-1, resulting in a roof snow load that is much more thanthe BUILDING designer (NOT the truss designer) the calculated roof snow load, possibly by a factor ofis responsible for establishing the proper building TWO (or more), based on my observations of snowdesign loads, confirming adequate connections and on roofs over many Northern Wisconsin winters.supports, provide truss bracing requirements (see Just changing the GSL to 50psf and removingTPI-1, Chapter 2Responsibilities). When you see a the slippery roof assumption would have raisedtruss design stamped with an engineers seal, they the sloped roof snow load from 20psf to 30.8psf,are NOT certifying the building design, only the something much more reasonable as a minimum design load appropriate for this area. design of the truss component to resist the specified loads if installed and supported and braced per the plans sealed by the Building Designer (a different engineer, typically).An engineered truss system supported by a NON-engineered building system will perform much like a building where nothing at all is engineered.When the farmer realized the trusses were designed for only 20psf snow, he jested that he wasnt sure if he was lucky his building was still standing or if he would have been better off with a collapse so he could have started over with a building designed for a better snow load.Assuming nobody would have gotten hurt in the collapse, I am not sure either.As it is, I will do my best to work with this farmer to reinforce his trusses before next winter arrives, but it is a much Figure 1A portion of Wisconsins Ground Snow Load Contours from ASCE 7more difficult process with less certain results than shows most of Jackson County is clearly in a 50 psf region (not the 35 psf used) a building designed correctly at the outset.In addition, this farmer should have consideredPlease keep in mind that this particular building increased safety factors by changing the risk categoryhad issues with the design snow load and a lack of from I (suitable for unoccupied buildings) totruss bracing, but if a competent engineer had been category II (suitable for occupied buildings) sinceemployed in the project, he or she would have verified he and his employees spend significant time in thismany other building design features, components, building and his livestock is continuously in thisand connections to ensure the constructed building building.This additional change would result in ais reliable for the owner's needs in the decades to calculated roof snow load of 38.5psf.Nearly DOUBLEcome.28 / FRAME BUILDER -JUN2021"