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