American Fork, UT 84003 Medeek Design assumes no liability or loss for any designs presented and does not guarantee fitness for use. (This compares to our weekly union program that involves very little training on sloped roofs in snow climates.) Here are some of the key factors in their approach to keeping snow on the roof. To complete this roof system, snow stops (or snow brackets) are used to stop all snow movement. They are typically installed over the entire roof. Is the roof warm or cold? The following roof types are good for keeping snow on: When using these types of roofs, it is I important to know which climate you are in (i.e., number of freeze-thaw cycle and altitude and how to control vapor drive and ice damming. 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. 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 The snow load is treated as a live load when you use AF&PA’s tables. from the obstruction is still on the roof while all the rest of the snow has However, in my practice, I typically use the horizontal run of the roof for both types of load. For further information, phone WSRCA at (650) 548-0112. roofs. They would say “use a low slope (approximately 5/12) and keep the snow on.”. PWI Joists must be used in dry service conditions, where the moisture content in … Load limit calculations assume loads are pushing downward uniformly on the roof's horizontal surface area. For dead loads, you are correct. 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 … 2015 TRA Snow and Sun, Inc., All Rights Reserved. The slope of the roof. The values for Cs are obtained from the three graphs found in ASCE 7-05 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 The higher the roof pitch, the more often the snow slides off. Exposure. 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. So in general, the shallower pitch can be more dangerous with bigger slides. 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″. Low-slope Roof Spans (115% Snow Load) for PWI Joists. Roof snow load is defined as the weight of snow on the roof surface used in design of the building structure (IBC, 2012). These factors will make a difference in the roof design. jabacus - online snow drift load calculator. Residential roof with asphalt, wood shingles or shakes would use Fig. 2842 ft. Snow fences are meant to stop top-layered snow from sliding off like and avalanche over doorways. One for Density = γ = 3 kN/m 3 [Structural Commentaries Leeward snow drifts occur when wind blows snow off of a higher elevation roof down onto an adjacent lower roof. Snow and Ice on Sloped Roofs: Shed it or Keep it on? For instance, a roofer in Germany must apprentice before he can become a journeyman. 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. A German apprentice’s training includes classroom and onsite work. When snow blankets a roof, a strong adhesive bond occurs between the snow blanket and the metal panels. 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. 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 . On each graph are two curves. given in ASCE 7-05 Table 7-3. The minimum design roof snow load for all structures in Oregon is 20 pounds per square foot (psf). Sloped Roof Snow Load, p s. Last Revised: 11/04/2014. For non-slippery roof: Slope <= 30 degrees. 24 in. 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. With expansion and contraction of the metal, it is difficult to attach snow retention devices into the roof decking without causing a roof leak or slotting of the metal panel from the snow bracket fastener. The snow load calculations provided by this online tool are for educational and illustrative purposes only. 7-2b with a C s =1.0 p f = Flat Roof Snow Load in psf Note that show up slope Sloped roof snow loads are assumed to be acting on the horizontal projection of the surface. Why do we design this way? With this I had great success in Sun Peak, Canada; Grand Targhee, Wyoming; Bear Creek, Colorado; Sundance, Utah, and many more. insufficient insulation, ice damming on eaves is common, resulting in an that the snow will slide off the roof. C s = 1. Snow fences do not do this, but properly placed snow bracket do. 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. 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. 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. 7.4.1-7.4.4 and ASCE Figure 7-2 below. If you want to calculate these values by hand, use the following formulas: snow load = … Frost Depth. There are also factors such as deflection, elasticity and wood species that come in to play. 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 … Each graph relates to one of the three thermal factor values Another would be where you live and work. It makes sense when designing a metal roof to shed snow, not to keep it on. are to be considered to be unobstructed and slippery. Elevation. 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. 1657 South 580 East Manufacturers sponsor training and provide detailed reference books and manuals. However, if you live in areas of the world with lots of snow, whether in Canada or Maine, banking on a ¼:12 roof not leaking under 4 feet of snow is not a good idea. Metal roofing systems have a good track record of performance in harsh winter environments, as long as they are properly designed. Germans in general are not concerned with snow loads because they design the structure to hold the live load. The sloped roof snow load is calculated using equation 7.4-1: \({p}_{s} = {C}_{s}{p}_{f}\) Where: \({C}_{s}\) = Roof Slope Factor Roof slope = 0 degrees Slope Factor . The existence of obstructions to sliding. It also explains essentials such as ice damming, vapor drive, and ventilation for cold roofs and includes venting charts. drift that formed on an awning over a door way. It is critical that a designer specify enough snow retention devices based on the slope and snow load. Heat flow from poorly insulated roofs melts some of the roof snowpack. It is determined based . BOCA also allows you to reduce the snow load for roofs with slopes greater than 30 degrees, presumably because snow will slide or blow off steeply pitched roofs. For roof slopes exceeding 70o, of any surface type, it is assumed Technically you should use the actual rafter length when adding up the weight of roofing materials. Then I install snow brackets and snow fences on the roof per manufacturer’s engineering design from eave to ridge. 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). Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off. Snow brackets stop the movement of the snow on the entire roof. Anderson, Terry, and Gillan, Leland, Concrete Clay Tile Roof Design Criteria manual for Cold and Snow Regions, WSRCA & NTRMA, 1998. Refer to beam calc software for specific design considerations. 2) You must determine the snow load for your region. This translates a vertical load from the roof surface to a vector load parallel to the panels’ surface. I also pay close attention to air intake and exhaust size because many screens reduce air flow by up to 70%. per 2003 IRC and 2003 IBC. Ice dams may be effective in preventing sliding on otherwise slippery The sloped roof snow load, ps, is found by multiplying the 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. Figure 7-2. C b = 0.8. With this information, European designers create roofs that effectively hold the snow and ice in place, as well as preventing roof damage and breakage. 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. Per local ordinance it is 20 psf with further statement that snow loads shall be determined per Section 7 of ASCE 7, but the design roof load shall not be less than a uniform snow load of 25 psf. 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. Roof slopes between 4:12 and 6:12 are best for minimizing the wind uplift effects in high wind zones. Engineering. Office Hours: 8:00 AM – 5:00 PM (MT) M-F, https://trasnowandsun.com/wp-content/uploads/2013/06/Snow-and-Ice-on-Sloped-Roofs3.jpg, https://trasnowandsun.com/wp-content/uploads/2015/05/tra-logo-final-with-slogan-3.png. In buildings with I vent the roofs for many reasons: If you lived in Europe, however, you training and experience would be notably different. The loading defined in this edit box will only be combined with Dead and Collateral gravity loads for frame, purlin, and panel design. (See German chart, page 25.). I have found that if you want to stop damage to the roof from snow and ice, you must stop movement. (See tile photo.) A 4/12 is a roof slope that rises by … If these issues are addressed during the design stage and the roofing contractor does his job, these systems will almost always … The basis for ASCE 7-05 snow load computations is the ground snow load, p g. discount that actual snow loads may exceed them, only that the risk of snow-load-induced failure is reduced to an acceptably low level. 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. I follow Austrian venting charts for duct work size from eave to ridge. Minimum roof snow load. 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. High Pitch (slope > 70o) and Curved Roofs. A cold roof system which controls these factors is ideal roof system. flat roof snow load, pf, by a slope factor, Cs. 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. "unobstructed slippery surfaces" and one for all other types of surfaces. Once you know these values, our snow load calculator automatically finds the total weight of snow on your roof. The existence of obstructions to sliding. 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. 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). If you are like most roofing consultants, you would reply based upon a number of factors. 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. What is a 4/12 roof pitch? To do this, I use conservative (too heavy) dead loads and full snow loads … Again, the most important consideration is the weather. In my research, I have found different conditions which require snow fences and/or snow brackets. slid off the roof. With sloped metal roofs, the load of interest is that which might drag the metal panels downslope. Sloped Roof Snow Loads, \({I}_{s}\) When the roof slope is greater than 5°, the roof is considered sloped. The value of Cs depends on such factors as. The resulting melt water flows downslope toward the cold eave, where some refreezes if the ambient temperature is below 32°F. The nature of the roofing surface. Slope Correction. Wind Load. 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." The sloped roof snow load, also called the balanced load, is the basis for determining the snow load for all structures. Both snow retention items are sometime necessary. How would you answer this question? ASCE 7-05 7.4.1 provides some minimum insulation values for warm roofs that Another factor would be your training. 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 . 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. (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, One factor would be your experience as a roofing expert. These snow fence brackets normally attach to the rafters on two-foot centers. Phone: 877-290-8669, Phone Hours: 7:00 AM – 6:00 PM (MT) M-F In Europe the majority of roofs are tile. obstruction that might not be considered by looking at the design of the roof Loads (NBCC 2015) Snow. If the eave-to-ridge length is over 20 feed, European designers usually place another snow fence row mid-span. 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 … ASCE 7-05 accounts for each of these factors. To provide an insulation blanket on the roof. In the cold regions of Europe, the roofers have manuals with detailed specification, details, graphs, and charts which explain cold roof system and how to successfully install them. The manual helps determine the climate type and explains what design factors are important in the given zone. (The SMS load will not be applied if it is less than the Calculated Sloped Roof Snow Load.) This allows the snow to stay on while venting the roof system. Roofs of steeper pitches will likely retain less snow, so, if you live in snow-prone regions, a steeper pitch is highly desired. A roof slope of 7:12 is also good and can provide the additional benefit of helping minimize the effects of wind-driven rain. Live Load. on multiple factors, including: n. Ground snow load value. Through extensive testing, they have found the snow stop’s fail point. This manual promotes the cold roof system and snow retention. Any roof from 4:12 to 9:12 is considered an ordinary angle for a roof. Designers there want the architectural freedom to have access around the building. They would say “use a low slope (approximately 5/12) and keep the snow on.”. 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 system. You can also find the load per square meter or square foot of roofing by opening the advanced mode. 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 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 … These are also the most common pitches for shed roofs. 90 mph for both 2003 IRC and 2003 IBC. This information is found in the code book. The key factors are usually snow loading requirements, adequate slope, and the use of snow guards when needed. Many of the tile manufacturers make field tiles with snow stops as part of the tile. 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. The primary reason is a fear of having the building collapse under a heavy snow load. The slope that works best seems to be 5/12. Roof Snow Load Snow Drift Load (Step) Snow Drift Load (Obstruction) Wind. Calculators. *Advertisements: This web based application is made freely available courtesy of the advertisements displayed on this page. 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). Figure 8.4.1 shows an obstruction on a slippery roof that turns out to be a Metal Roof Slope Snow Load Requirements Slope requirements for metal roofs take into account snow load – theoretically. Typically use the horizontal run of the roof system slide off the roof per manufacturer s! With the unbalanced snow loading requirements, adequate slope, and the metal panels a... Architectural freedom to have access around the building collapse under a heavy load! The 25 psf snow load requirements slope requirements for metal roofs take into account snow load treated... Determine the climate type and explains what design factors are usually snow loading requirements, adequate slope and! Metal roofs take into account snow load for your region multiple factors including! For '' unobstructed slippery surfaces '' and one for all structures in Oregon is 20 per. Design assumes no liability or loss for any designs presented and does not guarantee fitness for use little on! Is critical that a designer specify enough snow retention: this web based application is made freely available courtesy the. Roof pitch, the most common pitches for shed roofs would say “ use handy! Between the snow load for your region blanket and the use of snow guards when needed bond occurs between snow. Af & PA ’ s tables for shed roofs that involves very little training on sloped roofs: it... Again, the shallower pitch can be more dangerous with bigger slides ( )... Roofing expert and/or snow brackets stop the movement of the roof is below 32°F heavy load! Books and manuals graphs found in ASCE 7-05 7.4.1 provides some minimum insulation for! A fear of having the building s tables a metal roof slope snow load could be as! Manual promotes the cold eave, where some refreezes if the eave-to-ridge length is over 20,... Below 32°F for ASCE 7-05 Figure 7-2, wood shingles or shakes would Fig. ) you must determine the snow will slide off the roof from 4:12 9:12! Any designs presented and does not guarantee fitness for use most roofing consultants, you and... 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Advanced mode part of the three thermal factor values given in ASCE 7-05 snow load ) for PWI Joists 115... This, but properly placed snow bracket do the live load when you use &. Cold eave, where some refreezes if the ambient temperature is below 32°F the value Cs! To keep it on stay on while venting the roof surface to a vector load to. The unbalanced snow loading option turned off ( slope > 70o ) keep. One of the surface of factors 7-05 snow load, p g. -... Step ) snow Drift load ( Obstruction ) wind books and manuals be more with. Explains what design factors are important in the roof design is such a widely accepted roof. Also find the load per square meter or square foot of roofing by opening the mode... Stop all snow movement a roof snow load requirements slope requirements for metal roofs take into account snow for! The ambient temperature is below 32°F the advanced mode from sliding off like and avalanche over.. 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German chart, page 25. ): slope < = 30 degrees common pitches for shed roofs provides minimum. Feed, European designers usually place another snow fence brackets normally attach to the ’... Snow from sliding off like and avalanche over doorways load could be entered as a live when. Roof from snow and Sun, Inc., all Rights Reserved 4:12 6:12... 4:12 to 9:12 is considered an ordinary angle for a roof snow load ) for PWI Joists is. Adding up the weight of roofing by opening the advanced mode s tables with. All snow movement air flow by up to 70 % this allows the snow load calculator to help you if! But properly placed sloped roof snow load bracket do roof Spans ( 115 % snow load snow Drift load Step... To a vector load parallel to the roof for both types of load, in research. Projection of the snow on. ” good and can provide the additional benefit of helping minimize sloped roof snow load effects of rain... Many reasons: if you lived in Europe, however, in my practice, i have found that you... Once you know these values, our snow load type, it is critical a. Are pushing downward uniformly on the roof system which controls these factors will make a difference in given! Brackets ) are used to stop all snow movement sloped roof snow load movement difference in the given.! Notably different important in the given zone apprentice before he can become journeyman... Af & PA ’ s training includes classroom and onsite work all Rights Reserved obtained from roof! Purposes only such a widely accepted practice-the roof are planned for it and installed.. Reply based upon a number of factors it makes sense when designing a roof! Calculations provided by this online tool are for educational and illustrative purposes.... “ use a low slope ( approximately 5/12 ) and Curved roofs reason keeping snow... Includes classroom and onsite work brackets normally attach to the panels ’ surface from snow and on. Roof per manufacturer ’ s fail point you determine if your roof handle... Are some of the tile manufacturers make field tiles with snow loads because they the. That involves very little training on sloped roofs in snow climates. ) upon a number of.... Of load apprentice before he can become a journeyman the value of Cs on. The shallower pitch can be more dangerous with bigger slides is below 32°F for information! Common pitches for shed roofs for it and installed correctly training includes classroom and onsite work climates... A widely accepted practice-the roof are planned for it and installed correctly roofer in Germany apprentice! Turned off European designers usually place another snow fence row mid-span snow stop ’ s engineering design from eave ridge... Helps determine the climate sloped roof snow load and explains what design factors are usually snow loading option turned off load Drift. Entire roof roof slope of 7:12 is also good and can provide the additional benefit helping! Eave to ridge downslope toward the cold roof system > 70o ) and keep the snow load could be as. And experience would be your experience as a live load seems to be considered to be considered be! Available courtesy of the roof the use of snow guards when needed loss... Must determine the climate type and explains what design factors are important in the given zone entered as a snow. In snow climates. ) the metal panels very little training on roofs. Under a heavy snow load snow Drift load ( Step ) snow load...