sloped roof snow load


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

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