But without designing the snow retention based on accurate testing, you could be wishing you had that steep slope and metal roof (which was always intended to shed snow). Medeek Design assumes no liability or loss for any designs presented and does not guarantee fitness for use. Roof slope = 0 degrees Slope Factor . obstruction that might not be considered by looking at the design of the roof Use a handy tool like snow load calculator to help you determine if your roof can handle the weight of snow-based on its pitch. However, in my practice, I typically use the horizontal run of the roof for both types of load. Residential roof with asphalt, wood shingles or shakes would use Fig. 24 in. So in general, the shallower pitch can be more dangerous with bigger slides. This translates a vertical load from the roof surface to a vector load parallel to the panels’ surface. I have found that if you want to stop damage to the roof from snow and ice, you must stop movement. One for Sloped roof snow loads are assumed to be acting on the horizontal projection of the surface. roofs. Another factor would be your training. discount that actual snow loads may exceed them, only that the risk of snow-load-induced failure is reduced to an acceptably low level. Is the roof warm or cold? Designers there want the architectural freedom to have access around the building. slid off the roof. Each graph relates to one of the three thermal factor values If these issues are addressed during the design stage and the roofing contractor does his job, these systems will almost always … A 4/12 is a roof slope that rises by … The resulting melt water flows downslope toward the cold eave, where some refreezes if the ambient temperature is below 32°F. Low-slope Roof Spans (115% Snow Load) for PWI Joists. Sloped Roof Snow Load, p s. Last Revised: 11/04/2014. This manual promotes the cold roof system and snow retention. These are also the most common pitches for shed roofs. There are also factors such as deflection, elasticity and wood species that come in to play. (This compares to our weekly union program that involves very little training on sloped roofs in snow climates.) e = 1.2 , flat roof load > p g 10 Outline Minimum Roof Snow Load Thermal Factor Unbalanced Load Drift Load on Adjacent Roof Parapet Wall & RTU drift Sliding Load on Adjacent Roof Ponding FAQ’s 11 Unbalanced Loads-Gable Roof Upper Limit Roof Slope - change Lower Limit Roof Slope - simplify Small Eave to Ridge Distance -change 12 The sloped roof snow load, ps, is found by multiplying the Minimum roof snow load. In buildings with Frost Depth. system. Once they know this, they engineer charts which help the consultants calculate how many snow stops are needed from eave to ridge based on roof slope and snow and ice loads to effectively hold the snow and ice on the roof. You can also find the load per square meter or square foot of roofing by opening the advanced mode. 7-2b with a C s =1.0 p f = Flat Roof Snow Load in psf The primary reason is a fear of having the building collapse under a heavy snow load. In my research, I have found different conditions which require snow fences and/or snow brackets. The sloped roof snow load, p s, shall be obtained by multiplying the flat roof snow load, p f, by the roof slope factor, C s: p s = C s p f The thermal factor, C t , from Table E-3 determines if a roof is “cold” or “warm.” “Slippery surface” values shall be used only … They would say “use a low slope (approximately 5/12) and keep the snow on.”. Then I install snow brackets and snow fences on the roof per manufacturer’s engineering design from eave to ridge. per 2003 IRC and 2003 IBC. This information is found in the code book. For dead loads, you are correct. Dead load is also a gravity load, but if the dead weight of deck plus roofing materials weighs 'w' psf and the slope is θ … *Advertisements: This web based application is made freely available courtesy of the advertisements displayed on this page. Calculate sloped roof snow load p s using the following equation: p s = C s p f where: p s = Sloped Roof Snow Load in psf C s = Roof Slope Factor, as determined by ASCE Sec. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off. Exposure. A German apprentice’s training includes classroom and onsite work. Live Load. Ice dams may be effective in preventing sliding on otherwise slippery Once you know these values, our snow load calculator automatically finds the total weight of snow on your roof. If you are from North America you would probably respond “shed it off.”  Our approach in North America is to use a metal roof with a steep slope that will allow the snow and ice to slide off. To complete this roof system, snow stops (or snow brackets) are used to stop all snow movement. (The SMS load will not be applied if it is less than the Calculated Sloped Roof Snow Load.) Manufacturers sponsor training and provide detailed reference books and manuals. What is a 4/12 roof pitch? This may not be reduced for slope or any other conversion factor, and may be only modified where applicable by a rain-on-snow surcharge.Oregon Structural Specialty Code … For further information, phone WSRCA at (650) 548-0112. The sloped roof snow load, also called the balanced load, is the basis for determining the snow load for all structures. C b = 0.8. In an effort to solve the problems associated with moving snow and ice, I have heeded the experience and resources of European construction industry and have implemented their ideas with great success. The minimum design roof snow load for all structures in Oregon is 20 pounds per square foot (psf). Consult local building codes for snow load capacity and reference the Span Tables for Joists and Rafters published by the American Wood Council (AWC) As a general rule, roofs that have a high human occupancy rate should be framed with rafters every 16." Wind Load. On each graph are two curves. Snow Loads, cont’d • Minimum snow load p m – ASCE 7 Section 7.3.4 – For slope < 15o p m = 20 I S • Sloped roof snow loads – ASCE 7 Section 7.4 • Partial loading – ASCE 7 Section 7.5 • Unbalanced snow loads – ASCE 7 Section 7.6 Chicago Department of Buildings 2019 Self Certification Training Class 27 Snow Loads, cont’d I follow Austrian venting charts for duct work size from eave to ridge. A cold roof system which controls these factors is ideal roof system. Sloped Roof Snow Loads, \({I}_{s}\) When the roof slope is greater than 5°, the roof is considered sloped. I also pay close attention to air intake and exhaust size because many screens reduce air flow by up to 70%. Here are some of the key factors in their approach to keeping snow on the roof. Figure 8.4.1 shows an obstruction on a slippery roof that turns out to be a If you attach only to the metal, the metal sheets can be torn off because of the use of expanding sheet clip system and the weight of the snow being held on. For instance, a roofer in Germany must apprentice before he can become a journeyman. Slopes greater than 6/12 will tend to shed snow regardless of the texture of the material on them, so roof slopes should be configured to avoid shedding anywhere people might be walking or exiting. Roof Snow Load Snow Drift Load (Step) Snow Drift Load (Obstruction) Wind. I vent the roofs for many reasons: If you lived in Europe, however, you training and experience would be notably different. If unbalanced snow loading isn’t required or specified, the Truss Designer may enter the 25 psf snow load as a top chord live load (TCLL), set the load duration factor to 1.15 for snow, and turn snow loading off completely. The loading defined in this edit box will only be combined with Dead and Collateral gravity loads for frame, purlin, and panel design. The higher the roof pitch, the more often the snow slides off. It makes sense when designing a metal roof to shed snow, not to keep it on. The existence of obstructions to sliding. The sloped roof snow load, p s, is found by multiplying the flat roof snow load, p f, by a slope factor, C s. The value of C s depends on such factors as . Snow Loads for Structural Design in Montana (Revised 2004) Gregory P. Theisen Michael J. Keller Jerry E. Stephens Fred F. Videon James P. Schilke December 2004 They also plan to use the snow as an insulation blanket and design a cold roof system to stop ice dam concerns at the eave. The manual helps determine the climate type and explains what design factors are important in the given zone. It also explains essentials such as ice damming, vapor drive, and ventilation for cold roofs and includes venting charts. This allows the snow to stay on while venting the roof system. jabacus - online snow drift load calculator. The snow load calculations provided by this online tool are for educational and illustrative purposes only. If it is 20 psf, then the total snow load acting on plan area A is 20*A, irrespective of roof slope (unless it is steep enough for the snow to slide off). Roof slopes between 4:12 and 6:12 are best for minimizing the wind uplift effects in high wind zones. that the snow will slide off the roof. With this I had great success in Sun Peak, Canada; Grand Targhee, Wyoming; Bear Creek, Colorado; Sundance, Utah, and many more. Metal Roof Slope Snow Load Requirements Slope requirements for metal roofs take into account snow load – theoretically. Leeward snow drifts occur when wind blows snow off of a higher elevation roof down onto an adjacent lower roof. Per ASCE 7-05, Section 7.10: For locations where 0< pg <= 20 psf, all roofs with a slope < W/50 (with W in ft.) shall have a 5 psf rain-on-snow surcharge. One factor would be your experience as a roofing expert. C s = 1. Loads (NBCC 2015) Snow. "unobstructed slippery surfaces" and one for all other types of surfaces. Phone: 877-290-8669, Phone Hours: 7:00 AM – 6:00 PM (MT) M-F It is determined based . Calculators. Snow and Ice on Sloped Roofs: Shed it or Keep it on? Snow brackets stop the movement of the snow on the entire roof. In the U.S., there is a manual on roof applications in heavy snow areas prepared by the Western State Roofing Contractors Association (WSRCA) and the National Tile Roofing Manufacturers Association (NTRMA). To provide an insulation blanket on the roof. Slope Correction. Germans in general are not concerned with snow loads because they design the structure to hold the live load. Note: this year a manual called Concrete and Clay Tile Roofing Design Criteria Manual for Cold and Snow Regions was commissioned by NTRMA and WSRCA. This rain-on-snow augmented design load applies only to the balanced load case and need not be used in combination with drift, sliding, unbalanced, or … (See German chart, page 25.). One key difference in industry’s approach to snow on roofs is that keeping snow on the roof is something that they desire-quite the opposite from the trend in North America. Density = γ = 3 kN/m 3 [Structural Commentaries Note that show up slope Snow Bracket Engineering: Is It Really Worth It, Join us for a chance to win a $50 gift card in this FREE webinar, Get 1 Hour of AIA & HSW Continuing Education Credits, ASTM’s Latest News on Creating Standards for Roof Snow Retention Devices. 7.4.1-7.4.4 and ASCE Figure 7-2 below. ASCE 7-05 7.4.1 provides some minimum insulation values for warm roofs that Figure 7-2. Roof slope, roof sheathing materials, the thermal characteristics of the structure, and exposure to wind all have an impact on the amount of snow that may be present on a roof over the course of a winter season. The slope of the roof. If you want to calculate these values by hand, use the following formulas: snow load = … Another would be where you live and work. Metal roofing systems have a good track record of performance in harsh winter environments, as long as they are properly designed. Calculate sloped roof snow load: ps pfCs where psis in pounds per square foot of horizontally projected roof area 3 Check for unbalanced snow load assuming wind can blow from any direction Hip and gable roofs Curved roofs, multiple folded plate roofs, sawtooth roofs, barrel vault roofs and dome roofs, see Section 7.6 of ASCE 7. Refer to beam calc software for specific design considerations. High Pitch (slope > 70o) and Curved Roofs. ASCE 7-05 accounts for each of these factors. flat roof snow load, pf, by a slope factor, Cs. They then have the option of putting dormers on the roof without damage to the valleys, penetrations, lower roofs, and property below due to sliding snow and ice. It is critical that a designer specify enough snow retention devices based on the slope and snow load. With sloped metal roofs, the load of interest is that which might drag the metal panels downslope. Why do we design this way? In Europe the majority of roofs are tile. One key difference in industry’s approach to snow on roofs is that keeping snow on the roof is something that they desire-quite the opposite from the trend in North America. For roof slopes exceeding 70o, of any surface type, it is assumed (See tile photo.) See Figure 7-7 from ASCE 7-10 below for a succinct depiction: Lets assume our project is in Madison, Wisconsin and we have already calculated our balanced, roof snow load here . (2) The basic roof snow load factor, C b, shall be 0.8, except that for large roofs it shall be, (a) 1.0 – (30/l c) 2, for roofs with C w = 1.0 and l c greater than or equal to 70 m, or (b) 1.3 – (140/l c) 2, for roofs with C w = 0.75 or 0.5 and l c greater than or equal to 200 m, where, l c = characteristic length of the upper or lower roof, defined as 2w-w²/l, in metres, are to be considered to be unobstructed and slippery. Engineering. on multiple factors, including: n. Ground snow load value. How would you answer this question? Again, the most important consideration is the weather. So consider a simple gable roof on a 24-foot wide ranch framed with 2×6 exterior walls and a 1 1/2 ridge: the span would be 11’5 3/4″. These snow fence brackets normally attach to the rafters on two-foot centers. 2015 TRA Snow and Sun, Inc., All Rights Reserved. For non-slippery roof: Slope <= 30 degrees. 90 mph for both 2003 IRC and 2003 IBC. They would say “use a low slope (approximately 5/12) and keep the snow on.”. Sloped Roof Snow Load (p s) p s = C s p f = (1.0)(20 psf) = 20 psf Warm Roof Slope Factor (C s) C s = 1.0 (asphalt shingle not slippery) Unbalanced Roof Snow Load (p u) Since the roof’s eave to ridge distance ≤ 20 ft, unbalanced uniform snow loads shall be applied as follows: P windward = 0.3 p s = 6 psf P leeward.1 = p s = 20 psf P Heat flow from poorly insulated roofs melts some of the roof snowpack. The basis for ASCE 7-05 snow load computations is the ground snow load, p g. Load limit calculations assume loads are pushing downward uniformly on the roof's horizontal surface area. With this information, European designers create roofs that effectively hold the snow and ice in place, as well as preventing roof damage and breakage. 1657 South 580 East They are typically installed over the entire roof. This is one reason keeping the snow on the roof is such a widely accepted practice-the roof are planned for it and installed correctly. insufficient insulation, ice damming on eaves is common, resulting in an If the eave-to-ridge length is over 20 feed, European designers usually place another snow fence row mid-span. These factors will make a difference in the roof design. As I design roofs today in ski resort areas, I use one of the above types of roofs and plan to keep the snow on. from the obstruction is still on the roof while all the rest of the snow has When snow blankets a roof, a strong adhesive bond occurs between the snow blanket and the metal panels. The slope that works best seems to be 5/12. 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