The International Code specifies design snow loads are to be determined according to Section 7 of a document called ASCE 7. We use ALL of this information in the design of your new Hansen Pole Building. From our example, our ground load and flat roof snow load were found to be 30 psf and 21 psf, respectively. ASCE I is a structure which is a low hazard to life in the event of a failure. Site designed and … This document provides for all roof snow loads to be calculated from ground snow loads, however not every Building Department follows this procedure. • Alameda County, CA: 0 psf • Dallas County, TX: 5 psf The National Building Code of Canada requires buildings to be designed to carry uniformly and nonuniformly distributed snow loads and the "Commentary on Snow Loads" in Supplement No. “Modern buildings are designed with snow load in mind,” said Dr. Edwin Nagy at the University of Maine Department of Civil and Environmental Engineering. Higher Loads in Steps in Geographic Regions of Low Ground Snow – The basic ground snow is now a major part of the 1995 NBCC calculation in the form of the non-dimensional roof length (γl*/ S s). This is considerably less than the 25 psf that the old codes required. My last caution is to be careful when asking your building department about snow load. The ANSI snow load subcommittee took advantage of this new information to update and improve calculation of roof snow loads. 2. To calculate Roof Snow Load per Residential Building Code: 0.7 x pg (ground snow load) = pf (roof snow load) Roof Snow Load Examples: Above line: 0.7 x 60 psf = 42 psf Below line: 0.7 x 50 psf = 35 psf . The value used for the ground snow load should represent the snow load that has a 50 year mean recurrence interval, or, in other words, a 2% probability of being exceeded in any given year. Compact Kitchen Remodel - Common Code Mistakes - Installing an Endless Pool, JLC Online: Best practices for professional builders and remodelers. Another type of load that code addresses is snow, where accumulation can concentrate extra weight in smaller areas for periods of time. Often changes of five or 10 pounds per square foot result in minimal differences in cost. There is also a Minimum Roof Live Load (known as Lr) of 20 psf (defined by Code) (psf = pounds per square foot) which accounts for weights such as construction loads, when Pg values are very low. to help guide you in the design of your new pole building. However, a South Roof Load Zone home cannot be installed in either a Middle or North Roof Load Zone. Roof snow load is a much more important statistic and is computed from the ground load in a region. The Ground Snow Load data along with the Building Geometry will generate factors that convert this Load into the applied Roof Snow, Snow Drift or Sliding Snow Loads. The basis for the snow load computation in ASCE 7-05 is the ground snow load. Trust me, I know all too well, and my character analysis consistently reads “does not like numbers”! psf (pounds per square foot) ABOVE LINE 60 PSF . This is based upon a once in fifty year (probability of event greater than design loads happening is 2% in any given year). Pf is FLAT ROOF SNOW LOAD – If, as a consumer, your concern is snowfall and you want to upgrade the ability of your building to carry it, THIS is the value to increase. Table R301.6 also takes into account that the steeper the roof, the less chance higher concentrated loads will occur. A: Victor Staley, a building official in the town of Brewster, Mass., responds: This issue of Live Load vs. From Pf, Pr (Pressure on the roof) values are calculated depending upon whether the roof is a slippery surface or not, whether building is heated or not and the slope of the roof. When using Figure 1608.2 for sites at elevations above 1,000 feet (304 m), the ground snow load shall be increased from the mapped value by 2 psf (0.095 kN/m 2 ) for every 100 feet (30.48 m) above 1,000 feet (304 m). Yes I know, it is white (at least it starts out that way). If you have any concerns as you are determining your flat roof snow load, consult with a structural engineer or roofing specialist. While this may be more intuitive for flat or even gable/hip type roofs, the determination of snow loads is increasingly more difficult for arch roofs due to complex geometry. In our case, let’s assume that our structure has a flat roof (roof slope ≤ 5°). For an Exposure B or C for Wind; Fully Exposed = 0.9; Partially Exposed = 1.0; for fully sheltered (e.g. In the past, design snow loads were often considered to be equal to the ground snow load with reductions allowed for sloped roofs only. Your email address will not be published. Some Examples of this include Higher elevations in Utah and Kittitas County, WA where the BO has declared DOL = 1.0. The snow load that is applied to our structure is not the ground snow load, but in most cases, the flat roof snow load. In other words, on a steep roof, less material would be stacked in a concentrated area at one time, to avoid having it slide off. Be sure you keep “roof” and “ground” snow loads separate. Ice density is around 57 pcf. 260plf combined uniform load = 140plf, or 54% of 260, snow (S) load portion and 120plf, or 46% of 260, dead load portion; 650lbs combined point load = 350lbs, or 54% of 650, snow (S) load portion and 300lbs, or 46% of 650, dead load portion. This may also be true in some more moderate climates as well. (University of Arkansas Division of Agriculture) If using the heaviest wet snow value for roof designed to sustain 40 psf of snow load then it can be viewed that it should be capable of supporting nearly 24" inches of wet heavy snow. Code requires roofs to be built strong enough to carry more than just their own weight including live loads such as the weight of workers and stacked up materials concentrated in small areas. Roof snow load calculation. 1. Ground Snow Load, pg: psf: Figure 7-1, pages 84-85 and Table 7-1, page 92: Length of High Roof, Lu: ft. Measure the horizontal distance from eaves to the ridge -- the point where the roof is tallest -- and record the result labelled as "run." GROUND SNOW LOAD (otherwise known as Pg). The ground snow load is pretty much what it sounds like: A predictable load situation that is derived from snowfall records over the years in a particular region (photo 2). Snow load is the downward force on a building’s roof caused by the weight of accumulated snow and ice. (2) The roof design live load should be 40 psf; but 30 psf could be used for flat roof up to 2%. 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This Load is measured in Pounds per Square Foot (English). Pg = ground snow load Pf = flat roof snow load = Pg*I*Ce*Ct Ps = sloped roof snow load = Pf*Cs Ground Snow Load Values for Ontario and Quebec. 2010 Ground Snow Load Table for Quebec. These figures are established by the local jurisdiction, in my case the state of Massachusetts, which lists ground snow loads for each town in the state. Snow loads acting on a sloping surface shall be assumed to act on the horizontal projection of that surface. from Eave to Ridge, W: ft. Horizontal Distance from Eave to Ridge: Type of Roof Farm Storage Buildings and Equipment Sheds, More High Wind News – Pole Buildings Can Withstand Strong Winds. You need to use a snow load formula for flat roofs. 1995 Ground Snow Load Table. In colder regions the design snow load represents snow deposited by multiple snow events. 5. Use our Roof Snow Load Calculator to determine your design roof snow loads. When discussing snow load with anyone, it is crucial to have a clear understanding as to if the load is a ground or flat roof snow load. In my region on Cape Cod, we have a ground snow load design of 25 psf, which is a greater design load than the live load (12 psf to 20 psf) over an entire roof system. Doing the math, it would be unusual, using the laws of physics, for Pf to be greater than Pg – however, some jurisdictions have established Lr values which defy the laws of physics (e.g. Our recommendations on ground-to-roof conversion factors incorporates what we consider to be the most accurate information on the topic. All these numbers and “code requirements” are why we not only ask, but insist you must take the page of our quote with the Design Criteria to your building department to get their blessing on it, and ask if there is anything else they require. Ct is the effect of temperature (building heating), where: Ct = 1.0 for heated structures (climate controlled), Ct = 1.1 for Structures kept just above freezing and others with cold, ventilated roofs in which the thermal resistance (R-value) between the ventilated space and the heated space exceeds 25h – ft^2 – degreesF/Btu. Posted at December 21, 2014, in Technical. 2005 Ground Snow Load Tables. downward) and Sn (the rare negative acting snow loads). Ground Snow Load might seem somewhat confusing until you read the basic premise that is identified in IRC Section R301.6, which states: “The roof shall be designed for the Live Load indicated in Table R301.6 or the Snow Load indicated in Table R301.2(1), whichever is greater.”. This guru will grant you the answer to one pole barn question! 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