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Snow, rain and wind loads (4.1.6 and 4.1.7)

Snow and rain loads including drifting and accumulation factors, and wind loads (static, dynamic and wind tunnel procedures).

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Values this chapter turns on

roof slope up to which the snow slope factor is 1.0
30°
roof slope up to which the snow slope factor is 1.0
max specific weight of snow in drifts
4.0 kN/m³
max specific weight of snow in drifts
gap beyond which drift from a higher roof is ignored
5 m
gap beyond which drift from a higher roof is ignored
height that makes a building dynamically sensitive
60 m
height that makes a building dynamically sensitive

Snow and wind questions are mostly formula questions. You look up the climatic values for the town in SB-1, Table 2, pick the factors from Part 4, and multiply. The marks are lost on small things: forgetting the importance factor, dropping the rain load, or using the wrong slope formula.

Where the climatic values come from

Article 1.1.3.1 requires the climatic values used in design to come from Supplementary Standard SB-1 OBC Div. B 1.1.3.1.OBC Div. B 1.1.3.1. Climatic and Seismic Values(1) The climatic and seismic values required for the design of buildings under this Code shall be in conformance with the climatic and seismic values provided in MMAH Supplementary Standard SB-1, "Climatic and Seismic Data". (2) The outside winter design temperatures determined from MMAH Supplementary Standard SB-1…. SB-1 Table 2 lists each town's ground snow load S_s, its associated rain load S_r, and its 1-in-10 and 1-in-50 hourly wind pressures SB-1 Table 2OBC SB-1 Table 2: Climatic Design DataTable 2: Climatic Design Data Location | Elevation, m | Design Temperature — January — 2.5%, °C | Design Temperature — January — 1%, °C | Design Temperature — July 2.5% — Dry, °C | Design Temperature — July 2.5% — Wet, °C | Degree Days Below 18°C | 15 Min Rain, mm | One Day Rain, 1/50, mm | Annual Rain, mm | Moisture…. Some sample rows:

Location S_s (kPa) S_r (kPa) q 1/50 (kPa)
Ottawa (City Hall) 2.4 0.4 0.41
Sudbury 2.5 0.4 0.46
Kingston 2.1 0.4 0.47
Toronto (City Hall) 0.9 0.4 0.44

Part 4 uses the 1-in-50 values for both snow and wind. A common mistake is reading the 1/10 wind column.

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The snow load formula

The specified snow load is OBC Div. B 4.1.6.2.OBC Div. B 4.1.6.2. Specified Snow Load(1) The specified load, S, due to snow and associated rain accumulation on a roof or any other building surface subject to snow accumulation shall be calculated from the formula, S = I_s[S_s(C_bC_wC_sC_a) + S_r] where I_s = importance factor for snow load as provided in Table 4.1.6.2.-A, S_s = 1-in-50-year ground snow…:

S = I_s [ S_s (C_b C_w C_s C_a) + S_r ]

Factor Usual value When it changes
I_s ULS 0.8 / 1.0 / 1.15 / 1.25 for Low / Normal / High / Post-disaster; SLS 0.9 for all Table 4.1.6.2.-A
C_b 0.8 Large roofs, from Table 4.1.6.2.-B. It is 1.0 for low roofs with mean height under 1 + S_s/γ above grade
C_w 1.0 0.75 rural, or 0.5 north of the treeline, but only for Low and Normal buildings fully exposed to wind
C_s 1.0 up to 30° (70° - α)/40° from 30° to 70°, then 0. Slippery unobstructed roofs: 1.0 up to 15°, then (60° - α)/45°, 0 above 60°
C_a 1.0 Drifts, roof projections, gables, valleys and sliding snow (4.1.6.5 to 4.1.6.12)

S_r is capped: it may not exceed S_s(C_b C_w C_s C_a).

Wind exposure trap. C_w of 0.75 needs every condition in 4.1.6.2.(4): the building is Low or Normal Importance, it is exposed on all sides over open terrain and will stay that way, there are no significant roof obstructions, and there is no drifting from adjacent surfaces. A rural school is High Importance, so it stays at C_w = 1.0.

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Partial loading, drifts and special shapes

Flat roofs, shed roofs, gable roofs of 15° or less, and arch roofs must also be checked with full load on one part and half load on the rest OBC Div. B 4.1.6.3.OBC Div. B 4.1.6.3. Full and Partial Loading(1) A roof or other building surface and its structural members subject to loads due to snow accumulation shall be designed for the specified load given in Sentence 4.1.6.2.(1), distributed over the entire loaded area. (2) In addition to the distribution mentioned in Sentence (1), flat roofs and shed roofs, gable…. Gable roofs steeper than 15° add an unbalanced case: C_a = 0 on the upwind side, and on the downwind side 0.25 + α/20 for 15° to 20°, or 1.25 above 20° OBC Div. B 4.1.6.9.OBC Div. B 4.1.6.9. Gable Roofs(1) For all gable roofs, the full and partial load cases defined in Article 4.1.6.3. shall be considered. (2) For gable roofs with a slope of α > 15° , the unbalanced load case shall also be considered by setting the values of the accumulation factor, C_a , as follows: (a) on the upwind side of the roof peak, Ca shall….

For drifts at roof steps, the specific weight of snow is the lesser of 4.0 kN/m³ and 0.43 S_s + 2.2 OBC Div. B 4.1.6.13.OBC Div. B 4.1.6.13. Specific Weight of Snow(1) For the purposes of calculating snow loads in drifts, the specific weight of snow, γ , shall be taken as 4.0 kN/m³ or 0.43 S_S + 2.2 kN/m³, whichever is lesser.. For Bracebridge (S_s = 3.1), that is 0.43 x 3.1 + 2.2 = 3.53 kN/m³. Drifting from a higher roof can be ignored if the gap to an adjacent building is more than 5 m OBC Div. B 4.1.6.6.OBC Div. B 4.1.6.6. Horizontal Gap Between a Roof and a Higher Roof(1) Where the roof of one building is separated by a distance, a, from an adjacent building with a higher roof as shown in Figure 4.1.6.5.-A, the influence of the adjacent building on the value of the accumulation factor, C_a , for the lower roof shall be determined as follows: (a) if a > 5 m, the influence of the…. Drift next to a roof projection can be ignored if the projection's longest side is under 3 m OBC Div. B 4.1.6.7.OBC Div. B 4.1.6.7. Areas Adjacent to Roof Projections(1) Except as provided in Sentences (2) and (3), the accumulation factor, C_a , for areas adjacent to roof-mounted vertical projections shall be calculated in accordance with Sentence 4.1.6.5.(1) using the following values for the peak accumulation factor, C_a0 , and the drift length, x_d : (a) C_a0 shall be taken as…. Snow removal by any means can never justify a lower design snow load OBC Div. B 4.1.6.14.OBC Div. B 4.1.6.14. Snow Removal(1) Snow removal by mechanical, thermal, manual or other means shall not be used as a rationale to reduce design snow loads..

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Rain load

The roof is designed for the worse of snow with associated rain, or rain alone OBC Div. B 4.1.6.1.OBC Div. B 4.1.6.1. Specified Load Due to Rain or to Snow and Associated Rain(1) The specified load on a roof or any other building surface subject to snow and associated rain shall be the snow load specified in Article 4.1.6.2., or the rain load specified in Article 4.1.6.4., whichever produces the more critical effect. (See Note A-4.1.6.1.(1)). The rain load comes from the one-day rainfall in SB-1, over the horizontal projection of the roof and all tributary surfaces. It applies whether or not drains are provided. With scuppers as secondary drainage, use the lesser of the one-day rainfall and 30 mm of water above the bottom of the scuppers OBC Div. B 4.1.6.4.OBC Div. B 4.1.6.4. Specified Rain Load(1) Except as provided in Sentence (4), the specified load, S, due to the accumulation of rainwater on a surface whose position, shape and deflection under load make such an accumulation possible, is that resulting from the one-day rainfall determined in conformance with Subsection 1.1.3. and applied over the….

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Wind: which procedure

Article 4.1.7.1 sets out which procedure may be used OBC Div. B 4.1.7.1.OBC Div. B 4.1.7.1. Specified Wind Load(1) The specified wind loads for a building and its components shall be determined using the Static, Dynamic or Wind Tunnel Procedure as stated in Sentences (2) to (5). (2) For the design of buildings that are not dynamically sensitive, as defined in Sentence 4.1.7.2.(1), one of the following procedures shall be used…:

  • Not dynamically sensitive: the Static, Dynamic or Wind Tunnel Procedure.
  • Dynamically sensitive: the Dynamic or Wind Tunnel Procedure. This means a natural frequency between 0.25 and 1 Hz, a height over 60 m, or a height over 4 times the minimum effective width.
  • Very dynamically sensitive, or subject to buffeting or channelling from nearby buildings: the Wind Tunnel Procedure only.
  • Cladding: the Static or Wind Tunnel Procedure.

Computational fluid dynamics is not permitted. These classes are defined in OBC Div. B 4.1.7.2.OBC Div. B 4.1.7.2. Classification of Buildings(1) Except as provided in Sentences (2) and (3), a building is permitted to be classified as not dynamically sensitive. (2) A building shall be classified as dynamically sensitive if (a) its lowest natural frequency is less than 1 Hz and greater than 0.25 Hz, (b) its height is greater than 60 m, or (c) its height is….

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The static procedure

The external pressure is OBC Div. B 4.1.7.3.OBC Div. B 4.1.7.3. Static Procedure(1) The specified external pressure or suction due to wind on part or all of a surface of a building shall be calculated as follows: p = I_wqC_eC_tC_gC_p where p = specified external pressure acting statically and in a direction normal to the surface, considered positive when the pressure acts towards the surface and…:

p = I_w q C_e C_t C_g C_p

Factor Value
I_w (ULS) 0.8 / 1.0 / 1.15 / 1.25 by category; 0.75 for SLS (Table 4.1.7.3.OBC Div. B Table 4.1.7.3. Importance Factor for Wind Load, I_wTable 4.1.7.3. — Importance Factor for Wind Load, I_w Forming Part of Sentences 4.1.7.3.(1) and 4.1.7.8.(4) Importance Category | Importance Factor, I_w — ULS | Importance Factor, I_w — SLS Low | 0.8 | 0.75 Normal | 1.0 | 0.75 High | 1.15 | 0.75 Post-disaster | 1.25 | 0.75)
q SB-1, 1-in-50
C_e, open terrain (h/10)^0.2, not less than 0.9
C_e, rough terrain 0.7(h/12)^0.3, not less than 0.7
C_t 1.0 unless on a hill or escarpment (4.1.7.4.OBC Div. B 4.1.7.4. Topographic Factor(1) Except as provided in Sentence (2), the topographic factor, C_t, shall be taken as 1.0. (2) For buildings on hills or escarpments with slope, H_h/(2L_h) , greater than 0.1 (See Figure 4.1.7.4.), the topographic factor, C_t , shall be calculated as follows: C_t = (1 + (ΔS)/(C_g))(1 + ΔS) where ΔS = ΔS_max(1 -…)
C_g 2.0 for the building and main members; 2.5 for cladding and secondary members

For low buildings (20 m or less, and shorter than the smaller plan dimension), the reference height h is the mid-height of the roof but not less than 6 m. "Rough terrain" means suburban, urban or wooded terrain extending upwind for at least 1 km, or 20 times the building height, whichever is greater.

Internal pressure uses C_pi from Table 4.1.7.7.OBC Div. B Table 4.1.7.7. Internal Pressure CoefficientsTable 4.1.7.7. — Internal Pressure Coefficients Forming Part of Sentence 4.1.7.7.(1) −0.15 to 0.0 Building Openings | Values for C_pi Uniformly distributed small openings amounting to less than 0.1% of the total surface area of the building | Non-uniformly distributed openings of which none is significant or…:

Openings C_pi
Small, uniform openings under 0.1% of the surface -0.15 to 0.0
Non-uniform openings, none significant -0.45 to +0.30
Large openings likely to stay open in storms -0.70 to +0.70

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Chapter review

Chapter at a glance

One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.

  • Where the climatic values come from

    Article 1.1.3.1 requires the climatic values used in design to come from Supplementary Standard SB-1. SB-1 Table 2 lists each town's ground snow load S_s, its associated rain load…

  • The snow load formula

    S = I_s [ S_s (C_b C_w C_s C_a) + S_r ]

  • Partial loading, drifts and special shapes

    Flat roofs, shed roofs, gable roofs of 15° or less, and arch roofs must also be checked with full load on one part and half load on the rest.

  • Rain load

    The roof is designed for the worse of snow with associated rain, or rain alone.

  • Wind: which procedure

    Computational fluid dynamics is not permitted.

  • The static procedure

    For low buildings (20 m or less, and shorter than the smaller plan dimension), the reference height h is the mid-height of the roof but not less than 6 m.

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Questions on Snow, rain and wind loads (4.1.6, 4.1.7), in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.

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Code cited in this chapter

Based on the official 2024 Building Code Compendium on ontario.ca.

© King's Printer for Ontario, 2024. Reproduced with permission.

  • OBC Div. B 1.1.3.1. Climatic and Seismic Values

    (1)The climatic and seismic values required for the design of buildings under this Code shall be in conformance with the climatic and seismic values provided in MMAH Supplementary Standard SB-1, "Climatic and Seismic Data".

    (2)The outside winter design temperatures determined from MMAH Supplementary Standard SB-1, "Climatic and Seismic Data", shall be those listed for the January 2.5% values. (See Note A-1.1.3.1.(2))

    Open OBC Div. B 1.1.3.1. in the code viewer
  • OBC SB-1 Table 2: Climatic Design Data

    Table 2: Climatic Design Data

    Location | Elevation, m | Design Temperature — January — 2.5%, °C | Design Temperature — January — 1%, °C | Design Temperature — July 2.5% — Dry, °C | Design Temperature — July 2.5% — Wet, °C | Degree Days Below 18°C | 15 Min Rain, mm | One Day Rain, 1/50, mm | Annual Rain, mm | Moisture Index | Annual Total Precipitation, mm | Driving Rain Wind Pressures, Pa, 1/5 | Snow Load, kPa, 1/50 — Ss | Snow Load, kPa, 1/50 — Sr | Hourly Wind Pressures, kPa — 1/10 | Hourly Wind Pressures, kPa — 1/50

    Ailsa Craig | 230 | -17 | -19 | 30 | 23 | 3840 | 25 | 103 | 800 | 0.9 | 950 | 180 | 2.2 | 0.4 | 0.37 | 0.48

    Ajax | 95 | -20 | -22 | 30 | 23 | 3820 | 23 | 92 | 760 | 0.9 | 825 | 160 | 1.0 | 0.4 | 0.37 | 0.48

    Alexandria | 80 | -24 | -26 | 30 | 23 | 4600 | 25 | 103 | 800 | 0.9 | 975 | 160 | 2.4 | 0.4 | 0.31 | 0.4

    Alliston | 220 | -23 | -25 | 29 | 23 | 4200 | 28 | 113 | 690 | 0.8 | 875 | 120 | 2.0 | 0.4 | 0.28 | 0.36

    Almonte | 120 | -26 | -28 | 30 | 23 | 4620 | 25 | 97 | 730 | 0.8 | 800 | 140 | 2.5 | 0.4 | 0.32 | 0.41

    Armstrong | 340 | -37 | -40 | 28 | 21 | 6500 | 23 | 97 | 525 | 0.8 | 725 | 100 | 2.7 | 0.4 | 0.22 | 0.3

    Arnprior | 85 | -27 | -29 | 30 | 23 | 4680 | 23 | 86 | 630 | 0.8 | 775 | 140 | 2.5 | 0.4 | 0.29 | 0.37

    Atikokan | 400 | -33 | -35 | 29 | 22 | 5750 | 25 | 103 | 570 | 0.8 | 760 | 100 | 2.4 | 0.3 | 0.22 | 0.3

    Attawapiskat | 10 | -37 | -39 | 28 | 21 | 7100 | 18 | 81 | 450 | 0.8 | 650 | 160 | 2.8 | 0.3 | 0.3 | 0.41

    Aurora | 270 | -21 | -23 | 30 | 23 | 4210 | 28 | 108 | 700 | 0.8 | 800 | 140 | 2.0 | 0.4 | 0.34 | 0.44

    Bancroft | 365 | -28 | -31 | 29 | 23 | 4740 | 25 | 92 | 720 | 0.9 | 900 | 100 | 3.1 | 0.4 | 0.25 | 0.32

    Barrie | 245 | -24 | -26 | 29 | 23 | 4380 | 28 | 97 | 700 | 0.8 | 900 | 120 | 2.5 | 0.4 | 0.28 | 0.36

    Barriefield | 100 | -22 | -24 | 28 | 23 | 3990 | 23 | 108 | 780 | 1.0 | 950 | 160 | 2.1 | 0.4 | 0.37 | 0.47

    Beaverton | 240 | -24 | -26 | 30 | 23 | 4300 | 25 | 108 | 720 | 0.9 | 950 | 120 | 2.2 | 0.4 | 0.28 | 0.36

    Belleville | 90 | -22 | -24 | 29 | 23 | 3910 | 23 | 97 | 760 | 0.9 | 850 | 180 | 1.7 | 0.4 | 0.34 | 0.43

    Belmont | 260 | -17 | -19 | 30 | 24 | 3840 | 25 | 97 | 850 | 1.0 | 950 | 180 | 1.7 | 0.4 | 0.37 | 0.47

    Big Trout Lake (Kitchenuhmaykoosib) | 215 | -38 | -40 | 26 | 20 | 7450 | 18 | 92 | 400 | 0.75 | 600 | 150 | 3.2 | 0.2 | 0.31 | 0.42

    Borden (CBF) | 225 | -23 | -25 | 29 | 23 | 4300 | 28 | 103 | 690 | 0.82 | 875 | 120 | 2.2 | 0.4 | 0.28 | 0.36

    Bracebridge | 310 | -26 | -28 | 29 | 23 | 4800 | 25 | 103 | 830 | 1.0 | 1050 | 120 | 3.1 | 0.4 | 0.27 | 0.35

    Bradford | 240 | -23 | -25 | 30 | 23 | 4280 | 28 | 108 | 680 | 0.8 | 800 | 120 | 2.1 | 0.4 | 0.28 | 0.36

    Brampton | 215 | -19 | -21 | 30 | 23 | 4100 | 28 | 119 | 720 | 0.8 | 820 | 140 | 1.3 | 0.4 | 0.34 | 0.44

    Brantford | 205 | -18 | -20 | 30 | 23 | 3900 | 23 | 103 | 780 | 0.9 | 850 | 160 | 1.3 | 0.4 | 0.33 | 0.42

    Brighton | 95 | -21 | -23 | 29 | 23 | 4000 | 23 | 94 | 760 | 0.9 | 850 | 160 | 1.6 | 0.4 | 0.37 | 0.48

    Brockville | 85 | -23 | -25 | 29 | 23 | 4060 | 25 | 103 | 770 | 0.9 | 975 | 180 | 2.2 | 0.4 | 0.34 | 0.44

    Burk's Falls | 305 | -26 | -28 | 29 | 22 | 5020 | 25 | 97 | 810 | 0.9 | 1010 | 120 | 2.7 | 0.4 | 0.27 | 0.35

    Burlington | 80 | -17 | -19 | 31 | 23 | 3740 | 23 | 103 | 770 | 0.9 | 850 | 160 | 1.1 | 0.4 | 0.36 | 0.46

    Caledon | 425 | -21 | -23 | 30 | 23 | 4450 | 28 | 119 | 730 | 0.84 | 875 | 140 | 2.2 | 0.4 | 0.31 | 0.4

    Cambridge | 295 | -18 | -20 | 29 | 23 | 4100 | 25 | 113 | 800 | 0.9 | 890 | 160 | 1.6 | 0.4 | 0.28 | 0.36

    Campbellford | 150 | -23 | -26 | 30 | 23 | 4280 | 25 | 97 | 730 | 0.9 | 850 | 160 | 1.7 | 0.4 | 0.32 | 0.41

    Cannington | 255 | -24 | -26 | 30 | 23 | 4310 | 25 | 108 | 740 | 0.9 | 950 | 120 | 2.2 | 0.4 | 0.28 | 0.36

    Carleton Place | 135 | -25 | -27 | 30 | 23 | 4600 | 25 | 97 | 730 | 0.8 | 850 | 160 | 2.5 | 0.4 | 0.32 | 0.41

    Cavan | 200 | -23 | -25 | 30 | 23 | 4400 | 25 | 97 | 740 | 0.9 | 850 | 140 | 2.0 | 0.4 | 0.34 | 0.44

    Centralia | 260 | -17 | -19 | 30 | 23 | 3800 | 25 | 103 | 820 | 1.0 | 1000 | 180 | 2.3 | 0.4 | 0.37 | 0.48

    Chapleau | 425 | -35 | -38 | 27 | 21 | 5900 | 20 | 97 | 530 | 0.7 | 850 | 80 | 3.6 | 0.4 | 0.23 | 0.3

    Chatham | 180 | -16 | -18 | 31 | 24 | 3470 | 28 | 103 | 800 | 0.9 | 850 | 180 | 1.0 | 0.4 | 0.34 | 0.43

    Chesley | 275 | -19 | -21 | 29 | 22 | 4320 | 28 | 103 | 810 | 0.9 | 1125 | 140 | 2.8 | 0.4 | 0.35 | 0.45

    Clinton | 280 | -17 | -19 | 29 | 23 | 4150 | 25 | 103 | 810 | 0.9 | 1000 | 160 | 2.6 | 0.4 | 0.36 | 0.46

    Coboconk | 270 | -25 | -27 | 30 | 23 | 4500 | 25 | 108 | 740 | 0.9 | 950 | 120 | 2.5 | 0.4 | 0.27 | 0.35

    Cobourg | 90 | -21 | -23 | 29 | 23 | 3980 | 23 | 94 | 760 | 0.9 | 825 | 160 | 1.2 | 0.4 | 0.38 | 0.49

    Cochrane | 245 | -34 | -36 | 29 | 21 | 6200 | 20 | 92 | 575 | 0.8 | 875 | 80 | 2.8 | 0.3 | 0.27 | 0.35

    Colborne | 105 | -21 | -23 | 29 | 23 | 3980 | 23 | 94 | 760 | 0.9 | 850 | 160 | 1.6 | 0.4 | 0.38 | 0.49

    Collingwood | 190 | -21 | -23 | 29 | 23 | 4180 | 28 | 97 | 720 | 0.9 | 950 | 160 | 2.7 | 0.4 | 0.3 | 0.39

    Cornwall | 35 | -23 | -25 | 30 | 23 | 4250 | 25 | 103 | 780 | 0.9 | 960 | 180 | 2.2 | 0.4 | 0.32 | 0.41

    Corunna | 185 | -16 | -18 | 31 | 24 | 3600 | 25 | 100 | 760 | 0.9 | 800 | 180 | 1.0 | 0.4 | 0.37 | 0.47

    Deep River | 145 | -29 | -32 | 30 | 22 | 4900 | 23 | 92 | 650 | 0.8 | 850 | 100 | 2.5 | 0.4 | 0.27 | 0.35

    Deseronto | 85 | -22 | -24 | 29 | 23 | 4070 | 23 | 92 | 760 | 0.9 | 900 | 160 | 1.9 | 0.4 | 0.34 | 0.43

    Dorchester | 260 | -18 | -20 | 30 | 24 | 3900 | 28 | 103 | 850 | 1.0 | 950 | 180 | 1.9 | 0.4 | 0.37 | 0.47

    Dorion | 200 | -33 | -35 | 28 | 21 | 5950 | 20 | 103 | 550 | 0.8 | 725 | 160 | 2.8 | 0.4 | 0.29 | 0.39

    Dresden | 185 | -16 | -18 | 31 | 24 | 3750 | 28 | 97 | 760 | 0.8 | 820 | 180 | 1.0 | 0.4 | 0.34 | 0.43

    Dryden | 370 | -34 | -36 | 28 | 22 | 5850 | 25 | 97 | 550 | 0.7 | 700 | 120 | 2.4 | 0.3 | 0.22 | 0.3

    Dundalk | 525 | -22 | -24 | 29 | 22 | 4700 | 28 | 108 | 750 | 0.9 | 1080 | 150 | 3.2 | 0.4 | 0.33 | 0.42

    Dunnville | 175 | -15 | -17 | 30 | 24 | 3660 | 23 | 108 | 830 | 1.0 | 950 | 160 | 2.0 | 0.4 | 0.36 | 0.46

    Durham | 340 | -20 | -22 | 29 | 22 | 4340 | 28 | 103 | 815 | 0.9 | 1025 | 140 | 2.8 | 0.4 | 0.34 | 0.44

    Dutton | 225 | -16 | -18 | 31 | 24 | 3700 | 28 | 92 | 850 | 1.0 | 925 | 180 | 1.3 | 0.4 | 0.37 | 0.47

    Earlton | 245 | -33 | -36 | 29 | 22 | 5730 | 23 | 92 | 560 | 0.8 | 820 | 120 | 3.1 | 0.4 | 0.35 | 0.45

    Edison | 365 | -34 | -36 | 28 | 22 | 5740 | 25 | 108 | 510 | 0.7 | 680 | 120 | 2.4 | 0.3 | 0.23 | 0.31

    Elliot Lake | 380 | -26 | -28 | 29 | 21 | 4950 | 23 | 108 | 630 | 0.8 | 950 | 160 | 2.9 | 0.4 | 0.3 | 0.38

    Elmvale | 220 | -24 | -26 | 29 | 23 | 4200 | 28 | 97 | 720 | 0.9 | 950 | 140 | 2.6 | 0.4 | 0.28 | 0.36

    Embro | 310 | -19 | -21 | 30 | 23 | 3950 | 28 | 113 | 830 | 0.9 | 950 | 160 | 2.0 | 0.4 | 0.37 | 0.48

    Englehart | 205 | -33 | -36 | 29 | 22 | 5800 | 23 | 92 | 600 | 0.8 | 880 | 100 | 2.8 | 0.4 | 0.32 | 0.41

    Espanola | 220 | -25 | -27 | 29 | 21 | 4920 | 23 | 108 | 650 | 0.8 | 840 | 160 | 2.3 | 0.4 | 0.33 | 0.42

    Exeter | 265 | -17 | -19 | 30 | 23 | 3900 | 25 | 113 | 810 | 0.9 | 975 | 180 | 2.4 | 0.4 | 0.37 | 0.48

    Fenelon Falls | 260 | -25 | -27 | 30 | 23 | 4440 | 25 | 108 | 730 | 0.9 | 950 | 120 | 2.3 | 0.4 | 0.28 | 0.36

    Fergus | 400 | -20 | -22 | 29 | 23 | 4300 | 28 | 108 | 760 | 0.9 | 925 | 160 | 2.2 | 0.4 | 0.28 | 0.36

    Forest | 215 | -16 | -18 | 31 | 23 | 3740 | 25 | 103 | 810 | 1.0 | 875 | 160 | 2.0 | 0.4 | 0.37 | 0.48

    Fort Erie | 180 | -15 | -17 | 30 | 24 | 3650 | 23 | 108 | 860 | 1.0 | 1020 | 160 | 2.3 | 0.4 | 0.36 | 0.46

    Fort Erie (Ridgeway) | 190 | -15 | -17 | 30 | 24 | 3600 | 25 | 108 | 860 | 1.0 | 1000 | 160 | 2.3 | 0.4 | 0.36 | 0.46

    Fort Frances | 340 | -33 | -35 | 29 | 22 | 5440 | 25 | 108 | 570 | 0.7 | 725 | 120 | 2.3 | 0.3 | 0.23 | 0.31

    Gananoque | 80 | -22 | -24 | 28 | 23 | 4010 | 23 | 103 | 760 | 0.9 | 900 | 180 | 2.1 | 0.4 | 0.37 | 0.47

    Geraldton | 345 | -36 | -39 | 28 | 21 | 6450 | 20 | 86 | 550 | 0.8 | 725 | 100 | 2.9 | 0.4 | 0.22 | 0.3

    Glencoe | 215 | -16 | -18 | 31 | 24 | 3680 | 28 | 103 | 800 | 0.9 | 925 | 180 | 1.5 | 0.4 | 0.34 | 0.43

    Goderich | 185 | -16 | -18 | 29 | 23 | 4000 | 25 | 92 | 810 | 1.0 | 950 | 180 | 2.4 | 0.4 | 0.37 | 0.48

    Gore Bay | 205 | -24 | -26 | 28 | 22 | 4700 | 23 | 92 | 640 | 0.8 | 860 | 160 | 2.6 | 0.4 | 0.34 | 0.44

    Graham | 495 | -35 | -37 | 29 | 22 | 5940 | 23 | 97 | 570 | 0.8 | 750 | 140 | 2.6 | 0.3 | 0.22 | 0.3

    Gravenhurst (Muskoka Airport) | 255 | -26 | -28 | 29 | 23 | 4760 | 25 | 103 | 790 | 0.9 | 1050 | 120 | 2.7 | 0.4 | 0.28 | 0.36

    Grimsby | 85 | -16 | -18 | 30 | 23 | 3520 | 23 | 108 | 760 | 0.9 | 875 | 160 | 0.9 | 0.4 | 0.36 | 0.46

    Guelph | 340 | -19 | -21 | 29 | 23 | 4270 | 28 | 103 | 770 | 0.9 | 875 | 140 | 1.9 | 0.4 | 0.28 | 0.36

    Guthrie | 280 | -24 | -26 | 29 | 23 | 4300 | 28 | 103 | 700 | 0.8 | 950 | 120 | 2.5 | 0.4 | 0.28 | 0.36

    Haileybury | 210 | -32 | -35 | 30 | 22 | 5600 | 23 | 92 | 590 | 0.8 | 820 | 120 | 2.4 | 0.4 | 0.34 | 0.44

    Haldimand (Caledonia) | 190 | -18 | -20 | 30 | 23 | 3750 | 23 | 108 | 810 | 0.9 | 875 | 160 | 1.2 | 0.4 | 0.34 | 0.44

    Haldimand (Hagersville) | 215 | -17 | -19 | 30 | 23 | 3760 | 25 | 97 | 840 | 1.0 | 875 | 160 | 1.3 | 0.4 | 0.36 | 0.46

    Haliburton | 335 | -27 | -29 | 29 | 23 | 4840 | 25 | 92 | 780 | 0.9 | 980 | 100 | 2.9 | 0.4 | 0.27 | 0.35

    Halton Hills (Georgetown) | 255 | -19 | -21 | 30 | 23 | 4200 | 28 | 119 | 750 | 0.8 | 850 | 140 | 1.4 | 0.4 | 0.29 | 0.37

    Hamilton — Above Escarpment - West of John C. Munro Int'l Airport | 240 | -17 | -19 | 31 | 23 | 3460 | 23 | 108 | 810 | 0.9 | 875 | 160 | 1.5 | 0.4 | 0.36 | 0.46

    Hamilton — Above Escarpment - East of John C. Munro Int'l Airport | 200 | -17 | -19 | 31 | 23 | 3460 | 23 | 108 | 810 | 0.9 | 875 | 160 | 1.3 | 0.4 | 0.36 | 0.46

    Hamilton — Below Escarpment - West of Highway 403 | 90 | -17 | -19 | 31 | 23 | 3460 | 23 | 108 | 810 | 0.9 | 875 | 160 | 1.1 | 0.4 | 0.36 | 0.46

    Hamilton — Below Escarpment - East of Highway 403 | 90 | -17 | -19 | 31 | 23 | 3460 | 23 | 108 | 810 | 0.9 | 875 | 160 | 1.1 | 0.4 | 0.36 | 0.46

    Hanover | 270 | -19 | -21 | 29 | 22 | 4300 | 28 | 103 | 790 | 0.9 | 1050 | 140 | 2.6 | 0.4 | 0.34 | 0.44

    Hastings | 200 | -24 | -26 | 30 | 23 | 4280 | 25 | 92 | 730 | 0.9 | 840 | 140 | 2.0 | 0.4 | 0.32 | 0.41

    Hawkesbury | 50 | -25 | -27 | 30 | 23 | 4610 | 23 | 103 | 800 | 0.9 | 925 | 160 | 2.3 | 0.4 | 0.32 | 0.41

    Hearst | 245 | -35 | -37 | 29 | 21 | 6450 | 20 | 86 | 520 | 0.7 | 825 | 80 | 2.8 | 0.3 | 0.23 | 0.3

    Honey Harbour | 180 | -24 | -26 | 29 | 23 | 4300 | 25 | 97 | 710 | 0.9 | 1050 | 160 | 2.7 | 0.4 | 0.3 | 0.39

    Hornepayne | 360 | -37 | -40 | 28 | 21 | 6340 | 20 | 93 | 420 | 0.7 | 750 | 80 | 3.3 | 0.4 | 0.22 | 0.3

    Huntsville | 335 | -26 | -29 | 29 | 22 | 4850 | 25 | 103 | 800 | 0.9 | 1000 | 120 | 2.9 | 0.4 | 0.27 | 0.35

    Ingersoll | 280 | -18 | -20 | 30 | 23 | 3920 | 28 | 108 | 840 | 1.0 | 950 | 180 | 1.7 | 0.4 | 0.37 | 0.48

    Iroquois Falls | 275 | -33 | -36 | 29 | 21 | 6100 | 20 | 86 | 575 | 0.8 | 825 | 100 | 2.9 | 0.3 | 0.29 | 0.37

    Jellicoe | 330 | -36 | -39 | 28 | 21 | 6400 | 20 | 86 | 550 | 0.8 | 750 | 100 | 2.7 | 0.4 | 0.22 | 0.3

    Kapuskasing | 245 | -34 | -36 | 29 | 21 | 6250 | 20 | 86 | 550 | 0.8 | 825 | 100 | 3.0 | 0.3 | 0.24 | 0.31

    Kemptville | 90 | -25 | -27 | 30 | 23 | 4540 | 25 | 92 | 750 | 0.9 | 925 | 160 | 2.3 | 0.4 | 0.32 | 0.41

    Kenora | 370 | -33 | -35 | 28 | 22 | 5630 | 25 | 113 | 515 | 0.6 | 630 | 120 | 2.5 | 0.3 | 0.23 | 0.31

    Killaloe | 185 | -28 | -31 | 30 | 22 | 4960 | 23 | 86 | 680 | 0.8 | 825 | 120 | 2.7 | 0.4 | 0.27 | 0.35

    Kincardine | 190 | -17 | -19 | 28 | 22 | 3890 | 25 | 92 | 800 | 1.0 | 950 | 180 | 2.6 | 0.4 | 0.37 | 0.48

    Kingston | 80 | -22 | -24 | 28 | 23 | 4000 | 23 | 108 | 780 | 1.0 | 950 | 180 | 2.1 | 0.4 | 0.37 | 0.47

    Kinmount | 295 | -26 | -28 | 29 | 23 | 4600 | 25 | 108 | 750 | 0.9 | 950 | 120 | 2.7 | 0.4 | 0.27 | 0.35

    Kirkland Lake | 325 | -33 | -36 | 29 | 22 | 6000 | 23 | 92 | 600 | 0.8 | 875 | 100 | 2.9 | 0.3 | 0.3 | 0.39

    Kitchener | 335 | -19 | -21 | 29 | 23 | 4200 | 28 | 119 | 780 | 0.9 | 925 | 140 | 2.0 | 0.4 | 0.29 | 0.37

    Lakefield | 240 | -24 | -26 | 30 | 23 | 4330 | 25 | 92 | 720 | 0.9 | 850 | 140 | 2.2 | 0.4 | 0.3 | 0.38

    Lansdowne House | 240 | -38 | -40 | 28 | 21 | 7150 | 23 | 92 | 500 | 0.8 | 680 | 140 | 3.0 | 0.2 | 0.24 | 0.32

    Leamington | 190 | -15 | -17 | 31 | 24 | 3400 | 28 | 113 | 800 | 0.9 | 875 | 180 | 0.8 | 0.4 | 0.37 | 0.47

    Lindsay | 265 | -24 | -26 | 30 | 23 | 4320 | 25 | 103 | 720 | 0.8 | 850 | 140 | 2.3 | 0.4 | 0.3 | 0.38

    Lion's Head | 185 | -19 | -21 | 27 | 22 | 4300 | 25 | 103 | 700 | 0.9 | 950 | 180 | 2.7 | 0.4 | 0.37 | 0.48

    Listowel | 380 | -19 | -21 | 29 | 23 | 4300 | 28 | 119 | 800 | 0.9 | 1000 | 160 | 2.6 | 0.4 | 0.34 | 0.43

    London | 245 | -18 | -20 | 30 | 24 | 3900 | 28 | 103 | 825 | 0.9 | 975 | 180 | 1.9 | 0.4 | 0.37 | 0.47

    Lucan | 300 | -17 | -19 | 30 | 23 | 3900 | 25 | 113 | 810 | 0.9 | 1000 | 180 | 2.3 | 0.4 | 0.37 | 0.48

    Maitland | 85 | -23 | -25 | 29 | 23 | 4080 | 25 | 103 | 770 | 0.9 | 975 | 180 | 2.2 | 0.4 | 0.34 | 0.44

    Markdale | 425 | -20 | -22 | 29 | 22 | 4500 | 28 | 103 | 820 | 0.9 | 1050 | 160 | 3.2 | 0.4 | 0.32 | 0.41

    Markham | 175 | -21 | -23 | 31 | 24 | 4000 | 25 | 86 | 720 | 0.8 | 825 | 140 | 1.3 | 0.4 | 0.34 | 0.44

    Martin | 485 | -35 | -37 | 29 | 22 | 5900 | 25 | 103 | 560 | 0.8 | 750 | 120 | 2.6 | 0.3 | 0.22 | 0.3

    Matheson | 265 | -33 | -36 | 29 | 21 | 6080 | 20 | 86 | 580 | 0.8 | 825 | 100 | 2.8 | 0.3 | 0.3 | 0.39

    Mattawa | 165 | -29 | -31 | 30 | 22 | 5050 | 23 | 86 | 700 | 0.9 | 875 | 100 | 2.1 | 0.4 | 0.25 | 0.32

    Midland | 190 | -24 | -26 | 29 | 23 | 4200 | 25 | 97 | 740 | 0.9 | 1060 | 160 | 2.7 | 0.4 | 0.3 | 0.39

    Milton | 200 | -18 | -20 | 30 | 23 | 3920 | 25 | 125 | 750 | 0.9 | 850 | 160 | 1.3 | 0.4 | 0.34 | 0.43

    Milverton | 370 | -19 | -21 | 29 | 23 | 4200 | 28 | 108 | 800 | 0.9 | 1050 | 160 | 2.4 | 0.4 | 0.34 | 0.43

    Minden | 270 | -27 | -29 | 29 | 23 | 4640 | 25 | 97 | 780 | 0.9 | 1010 | 100 | 2.7 | 0.4 | 0.27 | 0.35

    Mississauga | 160 | -18 | -20 | 30 | 23 | 3880 | 25 | 113 | 720 | 0.9 | 800 | 160 | 1.1 | 0.4 | 0.34 | 0.44

    Mississauga (Lester B. Pearson International Airport) | 170 | -20 | -22 | 31 | 24 | 3890 | 26 | 108 | 685 | 0.8 | 790 | 160 | 1.1 | 0.4 | 0.34 | 0.44

    Mississauga (Port Credit) | 75 | -18 | -20 | 29 | 23 | 3780 | 25 | 108 | 720 | 0.9 | 800 | 160 | 0.9 | 0.4 | 0.37 | 0.48

    Mitchell | 335 | -18 | -20 | 29 | 23 | 4100 | 28 | 113 | 810 | 0.9 | 1050 | 160 | 2.4 | 0.4 | 0.35 | 0.45

    Moosonee | 10 | -36 | -38 | 28 | 22 | 6800 | 18 | 81 | 500 | 0.8 | 700 | 160 | 2.7 | 0.3 | 0.26 | 0.35

    Morrisburg | 75 | -23 | -25 | 30 | 23 | 4370 | 25 | 103 | 800 | 0.9 | 950 | 180 | 2.3 | 0.4 | 0.32 | 0.41

    Mount Forest | 420 | -21 | -24 | 28 | 22 | 4700 | 28 | 103 | 740 | 0.9 | 940 | 140 | 2.7 | 0.4 | 0.32 | 0.41

    Nakina | 325 | -36 | -38 | 28 | 21 | 6500 | 20 | 86 | 540 | 0.8 | 750 | 100 | 2.8 | 0.4 | 0.22 | 0.3

    Nanticoke (Jarvis) | 205 | -17 | -18 | 30 | 23 | 3700 | 28 | 108 | 840 | 1.0 | 900 | 160 | 1.4 | 0.4 | 0.37 | 0.48

    Nanticoke (Port Dover) | 180 | -15 | -17 | 30 | 24 | 3600 | 25 | 108 | 860 | 1.0 | 950 | 140 | 1.2 | 0.4 | 0.37 | 0.48

    Napanee | 90 | -22 | -24 | 29 | 23 | 4140 | 23 | 92 | 770 | 0.9 | 900 | 160 | 1.9 | 0.4 | 0.34 | 0.43

    Newcastle | 115 | -20 | -22 | 30 | 23 | 3990 | 23 | 86 | 760 | 0.9 | 830 | 160 | 1.5 | 0.4 | 0.37 | 0.48

    Newcastle (Bowmanville) | 95 | -20 | -22 | 30 | 23 | 4000 | 23 | 86 | 760 | 0.9 | 830 | 160 | 1.4 | 0.4 | 0.37 | 0.48

    New Liskeard | 180 | -32 | -35 | 30 | 22 | 5570 | 23 | 92 | 570 | 0.8 | 810 | 100 | 2.6 | 0.4 | 0.34 | 0.43

    Newmarket | 185 | -22 | -24 | 30 | 23 | 4260 | 28 | 108 | 700 | 0.8 | 800 | 140 | 2.0 | 0.4 | 0.3 | 0.38

    Niagara Falls | 210 | -16 | -18 | 30 | 23 | 3600 | 23 | 96 | 810 | 0.9 | 950 | 160 | 1.8 | 0.4 | 0.34 | 0.43

    North Bay | 210 | -28 | -30 | 28 | 22 | 5150 | 25 | 95 | 775 | 0.9 | 975 | 120 | 2.2 | 0.4 | 0.27 | 0.34

    Norwood | 225 | -24 | -26 | 30 | 23 | 4320 | 25 | 92 | 720 | 0.8 | 850 | 120 | 2.1 | 0.4 | 0.32 | 0.41

    Oakville | 90 | -18 | -20 | 30 | 23 | 3760 | 23 | 97 | 750 | 0.9 | 850 | 160 | 1.1 | 0.4 | 0.37 | 0.47

    Orangeville | 430 | -21 | -23 | 29 | 23 | 4450 | 28 | 108 | 730 | 0.8 | 875 | 140 | 2.3 | 0.4 | 0.28 | 0.36

    Orillia | 230 | -25 | -27 | 29 | 23 | 4260 | 25 | 103 | 740 | 0.9 | 1000 | 120 | 2.4 | 0.4 | 0.28 | 0.36

    Oshawa | 110 | -19 | -21 | 30 | 23 | 3860 | 23 | 86 | 760 | 0.9 | 875 | 160 | 1.4 | 0.4 | 0.37 | 0.48

    Ottawa (Barrhaven) | 98 | -25 | -27 | 30 | 23 | 4500 | 25 | 92 | 750 | 0.8 | 900 | 160 | 2.4 | 0.4 | 0.32 | 0.41

    Ottawa (City Hall) | 70 | -25 | -27 | 30 | 23 | 4440 | 23 | 86 | 750 | 0.8 | 900 | 160 | 2.4 | 0.4 | 0.32 | 0.41

    Ottawa (Kanata) | 98 | -25 | -27 | 30 | 23 | 4520 | 25 | 92 | 730 | 0.8 | 900 | 160 | 2.5 | 0.4 | 0.32 | 0.41

    Ottawa (MacDonald-Cartier Int'l Airport) | 125 | -25 | -27 | 30 | 23 | 4500 | 24 | 89 | 750 | 0.8 | 900 | 160 | 2.4 | 0.4 | 0.32 | 0.41

    Ottawa (Orleans) | 70 | -26 | -28 | 30 | 23 | 4500 | 23 | 91 | 750 | 0.8 | 900 | 160 | 2.4 | 0.4 | 0.32 | 0.41

    Owen Sound | 215 | -19 | -21 | 29 | 22 | 4030 | 28 | 113 | 760 | 0.9 | 1075 | 160 | 2.8 | 0.4 | 0.34 | 0.44

    Pagwa River | 185 | -35 | -37 | 28 | 21 | 6500 | 20 | 86 | 540 | 0.8 | 825 | 80 | 2.7 | 0.4 | 0.22 | 0.3

    Paris | 245 | -18 | -20 | 30 | 23 | 4000 | 23 | 96 | 790 | 0.9 | 925 | 160 | 1.4 | 0.4 | 0.33 | 0.42

    Parkhill | 205 | -16 | -18 | 31 | 23 | 3800 | 25 | 103 | 800 | 0.9 | 925 | 180 | 2.1 | 0.4 | 0.37 | 0.48

    Parry Sound | 215 | -24 | -26 | 28 | 22 | 4640 | 23 | 97 | 820 | 1.0 | 1050 | 160 | 2.8 | 0.4 | 0.3 | 0.39

    Pelham (Fonthill) | 230 | -15 | -17 | 30 | 23 | 3690 | 23 | 96 | 820 | 0.9 | 950 | 160 | 2.1 | 0.4 | 0.33 | 0.42

    Pembroke | 125 | -28 | -31 | 30 | 23 | 4980 | 23 | 105 | 640 | 0.8 | 825 | 100 | 2.5 | 0.4 | 0.27 | 0.35

    Penetanguishene | 220 | -24 | -26 | 29 | 23 | 4200 | 25 | 97 | 720 | 0.9 | 1050 | 160 | 2.8 | 0.4 | 0.3 | 0.39

    Perth | 130 | -25 | -27 | 30 | 23 | 4540 | 25 | 92 | 730 | 0.8 | 900 | 140 | 2.3 | 0.4 | 0.32 | 0.41

    Petawawa | 135 | -29 | -31 | 30 | 23 | 4980 | 23 | 92 | 640 | 0.8 | 825 | 100 | 2.6 | 0.4 | 0.27 | 0.35

    Peterborough | 200 | -23 | -25 | 30 | 23 | 4400 | 25 | 92 | 710 | 0.8 | 840 | 140 | 2.0 | 0.4 | 0.32 | 0.41

    Petrolia | 195 | -16 | -18 | 31 | 24 | 3640 | 25 | 108 | 810 | 0.9 | 920 | 180 | 1.3 | 0.4 | 0.37 | 0.47

    Pickering Zone 1 | 85 | -19 | -21 | 30 | 23 | 3800 | 23 | 92 | 730 | 0.9 | 825 | 140 | 1.0 | 0.4 | 0.37 | 0.48

    Pickering Zone 2 | 175 | -20 | -22 | 30 | 23 | 3900 | 23 | 92 | 730 | 0.9 | 825 | 140 | 1.5 | 0.4 | 0.37 | 0.48

    Pickering Zone 3 | 255 | -21 | -23 | 30 | 23 | 4010 | 23 | 86 | 770 | 0.91 | 850 | 140 | 1.9 | 0.4 | 0.35 | 0.45

    Pickering Zone 4 | 315 | -22 | -24 | 30 | 23 | 4200 | 23 | 86 | 770 | 0.91 | 850 | 140 | 2.3 | 0.4 | 0.35 | 0.45

    Picton | 95 | -21 | -23 | 29 | 23 | 3980 | 23 | 92 | 770 | 0.9 | 940 | 160 | 2.0 | 0.4 | 0.38 | 0.49

    Plattsville | 300 | -19 | -21 | 29 | 23 | 4150 | 28 | 103 | 820 | 0.9 | 950 | 140 | 1.9 | 0.4 | 0.33 | 0.42

    Point Alexander | 150 | -29 | -32 | 30 | 22 | 4960 | 23 | 92 | 650 | 0.8 | 850 | 100 | 2.5 | 0.4 | 0.27 | 0.35

    Port Burwell | 195 | -15 | -17 | 30 | 24 | 3800 | 25 | 92 | 930 | 1.1 | 1000 | 180 | 1.2 | 0.4 | 0.37 | 0.47

    Port Colborne | 180 | -15 | -17 | 30 | 24 | 3600 | 23 | 108 | 850 | 1.0 | 1000 | 160 | 2.1 | 0.4 | 0.36 | 0.46

    Port Elgin | 205 | -17 | -19 | 28 | 22 | 4100 | 25 | 92 | 790 | 0.9 | 850 | 180 | 2.8 | 0.4 | 0.37 | 0.48

    Port Hope | 100 | -21 | -23 | 29 | 23 | 3970 | 23 | 94 | 760 | 0.9 | 825 | 180 | 1.2 | 0.4 | 0.37 | 0.48

    Port Perry | 270 | -22 | -24 | 30 | 23 | 4260 | 25 | 97 | 720 | 0.8 | 850 | 140 | 2.4 | 0.4 | 0.34 | 0.44

    Port Stanley | 180 | -15 | -17 | 31 | 24 | 3850 | 25 | 92 | 940 | 1.1 | 975 | 180 | 1.2 | 0.4 | 0.37 | 0.47

    Prescott | 90 | -23 | -25 | 29 | 23 | 4120 | 25 | 103 | 770 | 0.9 | 975 | 180 | 2.2 | 0.4 | 0.34 | 0.44

    Princeton | 280 | -18 | -20 | 30 | 23 | 4000 | 25 | 97 | 810 | 0.9 | 925 | 160 | 1.5 | 0.4 | 0.33 | 0.42

    Raith | 475 | -34 | -37 | 28 | 22 | 5900 | 23 | 97 | 570 | 0.8 | 750 | 120 | 2.7 | 0.4 | 0.22 | 0.3

    Rayside-Balfour (Chelmsford) | 270 | -28 | -30 | 29 | 21 | 5200 | 25 | 92 | 650 | 0.8 | 850 | 180 | 2.5 | 0.4 | 0.35 | 0.45

    Red Lake | 360 | -35 | -37 | 28 | 21 | 6220 | 20 | 92 | 470 | 0.7 | 630 | 120 | 2.6 | 0.3 | 0.22 | 0.3

    Renfrew | 115 | -27 | -30 | 30 | 23 | 4900 | 23 | 97 | 620 | 0.8 | 810 | 140 | 2.5 | 0.4 | 0.27 | 0.35

    Richmond Hill | 230 | -21 | -23 | 31 | 24 | 4000 | 25 | 97 | 740 | 0.8 | 850 | 140 | 1.5 | 0.4 | 0.34 | 0.44

    Rockland | 50 | -26 | -28 | 30 | 23 | 4600 | 23 | 92 | 780 | 0.9 | 950 | 160 | 2.4 | 0.4 | 0.31 | 0.4

    Sarnia | 190 | -16 | -18 | 31 | 24 | 3750 | 25 | 100 | 750 | 0.9 | 825 | 180 | 1.1 | 0.4 | 0.37 | 0.47

    Sault Ste. Marie | 190 | -25 | -28 | 29 | 22 | 4960 | 23 | 97 | 660 | 0.9 | 950 | 200 | 3.1 | 0.4 | 0.33 | 0.44

    Schreiber | 310 | -34 | -36 | 27 | 21 | 5960 | 20 | 103 | 600 | 0.8 | 850 | 160 | 3.3 | 0.4 | 0.29 | 0.39

    Seaforth | 310 | -17 | -19 | 30 | 23 | 4100 | 25 | 108 | 810 | 0.9 | 1025 | 160 | 2.5 | 0.4 | 0.35 | 0.45

    Shelburne | 495 | -22 | -24 | 29 | 23 | 4700 | 28 | 108 | 740 | 0.9 | 900 | 150 | 3.1 | 0.4 | 0.31 | 0.4

    Simcoe | 210 | -17 | -19 | 30 | 24 | 3700 | 28 | 113 | 860 | 1.0 | 950 | 160 | 1.3 | 0.4 | 0.35 | 0.45

    Sioux Lookout | 375 | -34 | -36 | 28 | 22 | 5950 | 25 | 97 | 520 | 0.7 | 710 | 100 | 2.6 | 0.3 | 0.22 | 0.3

    Smiths Falls | 130 | -25 | -27 | 30 | 23 | 4540 | 25 | 92 | 730 | 0.8 | 850 | 140 | 2.3 | 0.4 | 0.32 | 0.41

    Smithville | 185 | -16 | -18 | 30 | 23 | 3650 | 23 | 108 | 800 | 0.9 | 900 | 160 | 1.5 | 0.4 | 0.33 | 0.42

    Smooth Rock Falls | 235 | -34 | -36 | 29 | 21 | 6250 | 20 | 92 | 560 | 0.8 | 850 | 80 | 2.7 | 0.3 | 0.25 | 0.32

    Southampton | 180 | -17 | -19 | 28 | 22 | 4100 | 25 | 92 | 800 | 1.0 | 830 | 180 | 2.7 | 0.4 | 0.37 | 0.48

    South River | 355 | -27 | -29 | 29 | 22 | 5090 | 25 | 103 | 830 | 1.0 | 975 | 120 | 2.8 | 0.4 | 0.27 | 0.35

    St. Catharines | 105 | -16 | -18 | 30 | 23 | 3540 | 23 | 92 | 770 | 0.9 | 850 | 160 | 1.0 | 0.4 | 0.36 | 0.46

    St. Mary's | 310 | -18 | -20 | 30 | 23 | 4000 | 28 | 108 | 820 | 1.0 | 1025 | 160 | 2.2 | 0.4 | 0.37 | 0.47

    St. Thomas | 225 | -16 | -18 | 31 | 24 | 3780 | 25 | 103 | 900 | 1.0 | 975 | 180 | 1.4 | 0.4 | 0.37 | 0.47

    Stirling | 120 | -23 | -25 | 30 | 23 | 4220 | 25 | 97 | 740 | 0.9 | 850 | 120 | 1.7 | 0.4 | 0.31 | 0.4

    Stratford | 360 | -18 | -20 | 29 | 23 | 4050 | 28 | 113 | 820 | 1.0 | 1050 | 160 | 2.3 | 0.4 | 0.35 | 0.45

    Strathroy | 225 | -17 | -19 | 31 | 24 | 3780 | 25 | 103 | 770 | 0.9 | 950 | 180 | 1.9 | 0.4 | 0.37 | 0.47

    Sturgeon Falls | 205 | -28 | -30 | 29 | 21 | 5200 | 25 | 95 | 700 | 0.9 | 910 | 140 | 2.4 | 0.4 | 0.27 | 0.35

    Sudbury | 275 | -28 | -30 | 29 | 21 | 5180 | 25 | 97 | 650 | 0.8 | 875 | 200 | 2.5 | 0.4 | 0.36 | 0.46

    Sundridge | 340 | -27 | -29 | 29 | 22 | 5080 | 25 | 97 | 840 | 1.0 | 975 | 120 | 2.8 | 0.4 | 0.27 | 0.35

    Tavistock | 340 | -19 | -21 | 29 | 23 | 4100 | 28 | 113 | 820 | 1.0 | 1010 | 160 | 2.1 | 0.4 | 0.35 | 0.45

    Temagami | 300 | -30 | -33 | 30 | 22 | 5420 | 23 | 92 | 650 | 0.8 | 875 | 120 | 2.6 | 0.4 | 0.29 | 0.37

    Thamesford | 280 | -19 | -21 | 30 | 23 | 3950 | 28 | 108 | 820 | 0.9 | 975 | 160 | 1.9 | 0.4 | 0.37 | 0.48

    Thedford | 205 | -16 | -18 | 31 | 23 | 3710 | 25 | 103 | 810 | 1.0 | 900 | 180 | 2.1 | 0.4 | 0.37 | 0.48

    Thunder Bay | 210 | -31 | -33 | 29 | 21 | 5650 | 23 | 108 | 560 | 0.8 | 710 | 160 | 2.9 | 0.4 | 0.29 | 0.39

    Tillsonburg | 215 | -17 | -19 | 30 | 24 | 3840 | 25 | 103 | 880 | 1.0 | 980 | 160 | 1.3 | 0.4 | 0.34 | 0.44

    Timmins | 300 | -34 | -36 | 29 | 21 | 5940 | 20 | 108 | 560 | 0.8 | 875 | 100 | 3.1 | 0.3 | 0.27 | 0.35

    Timmins (Porcupine) | 295 | -34 | -36 | 29 | 21 | 6000 | 20 | 103 | 560 | 0.8 | 875 | 100 | 2.9 | 0.3 | 0.29 | 0.37

    Toronto Metropolitan Region — Etobicoke | 160 | -20 | -22 | 31 | 24 | 3800 | 26 | 108 | 720 | 0.8 | 800 | 160 | 1.1 | 0.4 | 0.34 | 0.44

    Toronto Metropolitan Region — North York | 175 | -20 | -22 | 31 | 24 | 3760 | 25 | 108 | 730 | 0.8 | 850 | 150 | 1.2 | 0.4 | 0.34 | 0.44

    Toronto Metropolitan Region — Scarborough | 180 | -20 | -22 | 31 | 24 | 3800 | 25 | 92 | 730 | 0.9 | 825 | 160 | 1.2 | 0.4 | 0.37 | 0.47

    Toronto Metropolitan Region — Toronto (City Hall) | 90 | -18 | -20 | 31 | 23 | 3520 | 25 | 97 | 720 | 0.9 | 820 | 160 | 0.9 | 0.4 | 0.34 | 0.44

    Trenton | 80 | -22 | -24 | 29 | 23 | 4110 | 23 | 97 | 760 | 0.9 | 850 | 160 | 1.6 | 0.4 | 0.37 | 0.47

    Trout Creek | 330 | -27 | -29 | 29 | 22 | 5100 | 25 | 103 | 780 | 0.9 | 975 | 120 | 2.7 | 0.4 | 0.27 | 0.35

    Uxbridge | 275 | -22 | -24 | 30 | 23 | 4240 | 25 | 103 | 700 | 0.8 | 850 | 140 | 2.4 | 0.4 | 0.33 | 0.42

    Vaughan (Woodbridge) | 165 | -20 | -22 | 31 | 24 | 4100 | 26 | 113 | 700 | 0.8 | 800 | 140 | 1.1 | 0.4 | 0.34 | 0.44

    Vittoria | 215 | -15 | -17 | 30 | 24 | 3680 | 25 | 113 | 880 | 1.0 | 950 | 160 | 1.3 | 0.4 | 0.37 | 0.47

    Walkerton | 275 | -18 | -20 | 30 | 22 | 4300 | 28 | 103 | 790 | 0.9 | 1025 | 160 | 2.7 | 0.4 | 0.36 | 0.46

    Wallaceburg | 180 | -16 | -18 | 31 | 24 | 3600 | 28 | 97 | 760 | 0.9 | 825 | 180 | 0.9 | 0.4 | 0.35 | 0.45

    Waterloo | 330 | -19 | -21 | 29 | 23 | 4200 | 28 | 119 | 780 | 0.9 | 925 | 160 | 2.0 | 0.4 | 0.29 | 0.37

    Watford | 240 | -17 | -19 | 31 | 24 | 3740 | 25 | 108 | 790 | 0.9 | 950 | 160 | 1.9 | 0.4 | 0.37 | 0.47

    Wawa | 290 | -34 | -36 | 26 | 21 | 5840 | 20 | 93 | 725 | 0.9 | 950 | 160 | 3.4 | 0.4 | 0.3 | 0.39

    Welland | 180 | -15 | -17 | 30 | 23 | 3670 | 23 | 103 | 840 | 1.0 | 975 | 160 | 2.0 | 0.4 | 0.34 | 0.43

    West Lorne | 215 | -16 | -18 | 31 | 24 | 3700 | 28 | 103 | 840 | 1.0 | 900 | 180 | 1.3 | 0.4 | 0.37 | 0.47

    Whitby | 85 | -20 | -22 | 30 | 23 | 3820 | 23 | 86 | 760 | 0.9 | 850 | 160 | 1.2 | 0.4 | 0.37 | 0.48

    Whitby (Brooklin) | 160 | -20 | -22 | 30 | 23 | 4010 | 23 | 86 | 770 | 0.9 | 850 | 140 | 1.9 | 0.4 | 0.35 | 0.45

    White River | 375 | -39 | -42 | 28 | 21 | 6150 | 20 | 92 | 575 | 0.8 | 825 | 100 | 3.6 | 0.4 | 0.22 | 0.3

    Wiarton | 185 | -19 | -21 | 29 | 22 | 4300 | 25 | 103 | 740 | 0.9 | 1000 | 180 | 2.7 | 0.4 | 0.34 | 0.44

    Windsor | 185 | -16 | -18 | 32 | 24 | 3400 | 28 | 103 | 800 | 0.9 | 900 | 180 | 0.8 | 0.4 | 0.37 | 0.47

    Wingham | 310 | -18 | -20 | 30 | 23 | 4220 | 28 | 108 | 780 | 0.9 | 1050 | 160 | 2.6 | 0.4 | 0.36 | 0.46

    Woodstock | 300 | -19 | -21 | 30 | 23 | 3910 | 28 | 113 | 830 | 0.9 | 930 | 160 | 1.9 | 0.4 | 0.34 | 0.44

    Wyoming | 215 | -16 | -18 | 31 | 24 | 3700 | 25 | 103 | 815 | 0.9 | 900 | 180 | 1.6 | 0.4 | 0.37 | 0.47

    Open OBC SB-1 in the code viewer
  • OBC Div. B 4.1.6.2. Specified Snow Load

    (1)The specified load, S, due to snow and associated rain accumulation on a roof or any other building surface subject to snow accumulation shall be calculated from the formula,

    S = I_s[S_s(C_bC_wC_sC_a) + S_r]

    where

    I_s = importance factor for snow load as provided in Table 4.1.6.2.-A,

    S_s = 1-in-50-year ground snow load, in kPa, determined in accordance with Subsection 1.1.3.,

    C_b = basic roof snow load factor in Sentence (2),

    C_w = wind exposure factor in Sentences (3) and (4),

    C_s = slope factor in Sentences (5) to (7),

    C_a = accumulation factor in Sentence (8), and

    S_r = 1-in-50-year associated rain load, in kPa, determined in accordance with Subsection 1.1.3., but not greater than S_s(C_bC_wC_sC_a) .

    (2)The basic roof snow load factor, C_b, shall

    (a)be determined as follows:

    (i)C_b = 0.8

    for l_c ≤ (70/(C_w^2)) .

    (ii)C_rmb = 1/(C_rmw)[1 - (1 - 0.8C_rmw)exp( - (l_rmcC_rmw^2 - 70)/100)]

    for l_c > (70/(C_w^2)) .

    (b)conform to Table 4.1.6.2.-B, using linear interpolation for intermediate values of l_c C_w².

    (c)be taken as equal to 1 for any roof structure with a mean height of less than 1 + S_s/ γ, in m, above grade, where γ is the specific weight of snow determined in accordance with Article 4.1.6.13. (See Note A-4.1.6.2.)

    (3)Except as provided for in Sentence (4), the wind exposure factor, C_w, shall be 1.0.

    (4)For buildings in the Low and Normal Importance Categories as set out in Table 4.1.2.1., the wind exposure factor, C_w, given in Sentence (3) may be reduced to 0.75 for rural areas only, or to 0.5 for exposed areas north of the treeline, where

    (a)the building is exposed on all sides to wind over open terrain as defined in Clause 4.1.7.3.(5)(a), and is expected to remain so during its life,

    (b)the area of roof under consideration is exposed to the wind on all sides with no significant obstructions on the roof, such as parapet walls, within a distance of at least 10 times the difference between the height of the obstruction and C_bC_wS_s/γ in m, where γ is the unit weight of snow on roofs as specified in Article 4.1.6.13., and

    (c)the loading does not involve the accumulation of snow due to drifting from adjacent surfaces.

    (5)Except as provided for in Sentences (6) and (7), the slope factor, C_s, shall be,

    (a)1.0 where the roof slope, α , is equal to or less than 30°,

    (b)(70° − α)/40° where α is greater than 30° but not greater than 70°, and

    (c)0 where α exceeds 70°.

    (6)The slope factor, C_s , for unobstructed slippery roofs where snow and ice can slide completely off the roof shall be

    (a)1.0 where the roof slope, α , is equal to or less than 15°,

    (b)(60° − α)/45° where α is greater than 15° but not greater than 60° , and

    (c)0 where α exceeds 60° .

    (7)Unless otherwise stated in this Subsection, the slope factor, C_s , shall be 1.0 when used in conjunction with accumulation factors for increased snow loads.

    (8)The accumulation factor, C_a , shall be 1.0, which corresponds to the uniform snow load case, except that where appropriate for the shape of the roof, it shall be assigned other values that account for,

    (a)increased non-uniform snow loads due to snow drifting onto a roof that is at a level lower than other parts of the same building or at a level lower than another building within 5 m of it horizontally, as prescribed in Articles 4.1.6.5., 4.1.6.6. and 4.1.6.8.,

    (b)increased non-uniform snow loads on areas adjacent to roof projections, such as penthouses, large chimneys and equipment, as prescribed in Articles 4.1.6.7. and 4.1.6.8.

    (c)non-uniform snow loads on gable, arch or curved roofs and domes, as prescribed in Articles 4.1.6.9. and 4.1.6.10.,

    (d)increased snow or ice loads due to snow sliding as prescribed in Article 4.1.6.11.,

    (e)increased snow loads in roof valleys, as prescribed in Article 4.1.6.12., and

    (f)increased snow or ice loads due to meltwater draining from adjacent building elements and roof projections.

    (9)For shapes not addressed in Sentence (8), C_a corresponding to the non-uniform snow load case shall be established based on applicable field observations, special analyses including local climatic effects, appropriate model tests or a combination of these methods.

    Open OBC Div. B 4.1.6.2. in the code viewer
  • OBC Div. B 4.1.6.3. Full and Partial Loading

    (1)A roof or other building surface and its structural members subject to loads due to snow accumulation shall be designed for the specified load given in Sentence 4.1.6.2.(1), distributed over the entire loaded area.

    (2)In addition to the distribution mentioned in Sentence (1), flat roofs and shed roofs, gable roofs of 15° slope or less, and arch or curved roofs shall be designed for the specified uniform snow load indicated in Sentence 4.1.6.2.(1), which shall be calculated using the accumulation factor C_a = 1.0 , distributed on any one portion of the loaded area and half of this load on the remainder of the loaded area, in such a way as to produce the most critical effects on the member concerned. (See Note A-4.1.6.3.(2))

    Open OBC Div. B 4.1.6.3. in the code viewer
  • OBC Div. B 4.1.6.9. Gable Roofs

    (1)For all gable roofs, the full and partial load cases defined in Article 4.1.6.3. shall be considered.

    (2)For gable roofs with a slope of α > 15° , the unbalanced load case shall also be considered by setting the values of the accumulation factor, C_a , as follows:

    (a)on the upwind side of the roof peak, Ca shall be taken as 0, and

    (b)on the downwind side of the roof peak, C_a shall be taken as

    (i)0.25 + α/20 , where 15° ≤ α ≤ 20° , and

    (ii)1.25, where 20° < α ≤ 90° .

    (3)For all gable roofs, the slope factor, C_s, shall be as prescribed in Sentences 4.1.6.2.(5) and (6).

    (4)For all gable roofs, the wind exposure factor, C_w , shall be

    (a)as prescribed in Sentences 4.1.6.2.(3) and (4) for the full and partial load cases, and

    (b)1.0 for the unbalanced load case referred to in Sentence (2).

    Open OBC Div. B 4.1.6.9. in the code viewer
  • OBC Div. B 4.1.6.13. Specific Weight of Snow

    (1)For the purposes of calculating snow loads in drifts, the specific weight of snow, γ , shall be taken as 4.0 kN/m³ or 0.43 S_S + 2.2 kN/m³, whichever is lesser.

    Open OBC Div. B 4.1.6.13. in the code viewer
  • OBC Div. B 4.1.6.6. Horizontal Gap Between a Roof and a Higher Roof

    (1)Where the roof of one building is separated by a distance, a, from an adjacent building with a higher roof as shown in Figure 4.1.6.5.-A, the influence of the adjacent building on the value of the accumulation factor, C_a , for the lower roof shall be determined as follows:

    (a)if a > 5 m, the influence of the adjacent building on C_a for the lower roof can be ignored, and

    (b)if a ≤ 5 m, C_a for the lower roof shall be calculated in accordance with Article 4.1.6.5. for values of x ≥ a .

    Open OBC Div. B 4.1.6.6. in the code viewer
  • OBC Div. B 4.1.6.7. Areas Adjacent to Roof Projections

    (1)Except as provided in Sentences (2) and (3), the accumulation factor, C_a , for areas adjacent to roof-mounted vertical projections shall be calculated in accordance with Sentence 4.1.6.5.(1) using the following values for the peak accumulation factor, C_a0 , and the drift length, x_d :

    (a)C_a0 shall be taken as the lesser of,

    (b)x_d shall be taken as the lesser of 3.35 h and (2/3)l_0 , where h = height of the projection, and l_0 = longest horizontal dimension of the projection. (See Note A-4.1.6.7.(1))

    0.67(γh)/(C_hS_s)

    and (γl_0)/(7.5C_hS_s) + 1 , and

    (2)C_a is permitted to be calculated in accordance with Article 4.1.6.5. for larger projections. (See Note A-4.1.6.7.(2))

    (3)Where the longest horizontal dimension of the roof projection, l_0 , is less than 3 m, the drift surcharge adjacent to the projection need not be considered.

    Open OBC Div. B 4.1.6.7. in the code viewer
Show all 18 articles
  • OBC Div. B 4.1.6.14. Snow Removal

    (1)Snow removal by mechanical, thermal, manual or other means shall not be used as a rationale to reduce design snow loads.

    Open OBC Div. B 4.1.6.14. in the code viewer
  • OBC Div. B 4.1.6.1. Specified Load Due to Rain or to Snow and Associated Rain

    (1)The specified load on a roof or any other building surface subject to snow and associated rain shall be the snow load specified in Article 4.1.6.2., or the rain load specified in Article 4.1.6.4., whichever produces the more critical effect. (See Note A-4.1.6.1.(1))

    Open OBC Div. B 4.1.6.1. in the code viewer
  • OBC Div. B 4.1.6.4. Specified Rain Load

    (1)Except as provided in Sentence (4), the specified load, S, due to the accumulation of rainwater on a surface whose position, shape and deflection under load make such an accumulation possible, is that resulting from the one-day rainfall determined in conformance with Subsection 1.1.3. and applied over the horizontal projection of the surface and all tributary surfaces. (See Note A-4.1.6.4.(1))

    (2)The provisions of Sentence (1) apply whether or not the surface is provided with a means of drainage, such as rainwater leaders.

    (3)Except as provided in Sentence 4.1.6.2.(1), loads due to rain need not be considered to act simultaneously with loads due to snow. (See Note A-4.1.6.4.(3))

    (4)Where scuppers are provided as secondary drainage systems and where the position, shape and deflection of the loaded surface make an accumulation of rainwater possible, the loads due to rain shall be the lesser of either the one-day rainfall determined in conformance with Subsection 1.1.3. or a depth of rainwater equal to 30 mm above the bottom of the scuppers, applied over the horizontal projection of the surface and tributary areas.

    Open OBC Div. B 4.1.6.4. in the code viewer
  • OBC Div. B 4.1.7.1. Specified Wind Load

    (1)The specified wind loads for a building and its components shall be determined using the Static, Dynamic or Wind Tunnel Procedure as stated in Sentences (2) to (5).

    (2)For the design of buildings that are not dynamically sensitive, as defined in Sentence 4.1.7.2.(1), one of the following procedures shall be used to determine the specified wind loads:

    (a)the Static Procedure described in Article 4.1.7.3.,

    (b)the Dynamic Procedure described in Article 4.1.7.8., or

    (c)the Wind Tunnel Procedure described in Article 4.1.7.14.

    (3)For the design of buildings that are dynamically sensitive, as defined in Sentence 4.1.7.2.(2), one of the following procedures shall be used to determine the specified wind loads:

    (a)the Dynamic Procedure described in Article 4.1.7.8., or

    (b)the Wind Tunnel Procedure described in Article 4.1.7.14.

    (4)For the design of buildings that may be subject to wake buffeting or channelling effects from nearby buildings, or that are very dynamically sensitive, as defined in Sentence 4.1.7.2.(3), the Wind Tunnel Procedure described in Article 4.1.7.14., shall be used to determine the specified wind loads.

    (5)For the design of cladding and secondary structural members, one of the following procedures shall be used to determine the specified wind loads:

    (a)the Static Procedure described in Article 4.1.7.3., or

    (b)the Wind Tunnel Procedure described in Article 4.1.7.14.

    (6)Computational fluid dynamics shall not be used to determine the specified wind loads for a building and its components. (See Note A-4.1.7.1.(6))

    Open OBC Div. B 4.1.7.1. in the code viewer
  • OBC Div. B 4.1.7.2. Classification of Buildings

    (1)Except as provided in Sentences (2) and (3), a building is permitted to be classified as not dynamically sensitive.

    (2)A building shall be classified as dynamically sensitive if

    (a)its lowest natural frequency is less than 1 Hz and greater than 0.25 Hz,

    (b)its height is greater than 60 m, or

    (c)its height is greater than 4 times its minimum effective width considering all wind directions, where the effective width, w, of a building shall be taken as,

    w = (∑h_iw_i)/(∑h_i)

    where the summations are over the height of the building for a given wind direction, h_i is the height above grade to level i, and w_i is the width normal to the wind direction at height h_i ; the minimum effective width is the lowest value of the effective width considering all wind directions.

    (3)A building shall be classified as very dynamically sensitive if

    (a)its lowest natural frequency is less than or equal to 0.25 Hz, or

    (b)it contains a human occupancy, and its height is more than 6 times its minimum effective width as defined in Clause (2)(c).

    Open OBC Div. B 4.1.7.2. in the code viewer
  • OBC Div. B 4.1.7.3. Static Procedure

    (1)The specified external pressure or suction due to wind on part or all of a surface of a building shall be calculated as follows:

    p = I_wqC_eC_tC_gC_p

    where

    p = specified external pressure acting statically and in a direction normal to the surface, considered positive when the pressure acts towards the surface and negative when it acts away from the surface,

    I_w = importance factor for wind load, as provided in Table 4.1.7.3.,

    q = reference velocity pressure, as provided in Sentence (4),

    C_e = exposure factor, as provided in Sentences (5) and (7),

    C_t = topographic factor, as provided in Article 4.1.7.4.,

    C_g = gust effect factor, as provided in Sentence (8), and

    C_p = external pressure coefficient, as provided in Articles 4.1.7.5. and 4.1.7.6.

    (2)The net wind load for the building as a whole shall be the algebraic difference of the loads on the windward and leeward surfaces, and in some cases, may be calculated as the sum of the products of the external pressures or suctions and the areas of the surfaces over which they are averaged as provided in Sentence (1).

    (3)The net specified pressure due to wind on part or all of a surface of a building shall be the algebraic difference, such as to produce the most critical effect, of the external pressure or suction calculated in accordance with Sentence (1) and the specified internal pressure or suction due to wind calculated as follows:

    p_i = I_wqC_eiC_tC_giC_pi

    where

    p_i = specified internal pressure acting statically and in a direction normal to the surface, either as a pressure directed toward the surface or as a suction directed away from the surface,

    I_w , q, C_t = as defined in Sentence (1),

    C_ei = exposure factor for internal pressure, as provided in Sentence (7),

    C_gi = internal gust effect factor, as provided in Sentence (10), and

    C_pi = internal pressure coefficient, as provided in Article 4.1.7.7.

    (4)The reference velocity pressure, q, shall be the appropriate value determined in conformance with Subsection 1.1.3. based on a probability of being exceeded in any one year of 1 in 50.

    (5)The exposure factor C_e , shall be based on the reference height, h, determined in accordance with Sentence (6) for the surface or part of the surface under consideration and shall be

    (a)(h/10)^(0.2)but not less than 0.9 for open terrain, where open terrain is level terrain with only scattered buildings, trees or other obstructions, open water or shorelines thereof,

    (b)0.7(h/12)^(0.3) but not less than 0.7 for rough terrain, where rough terrain is suburban, urban or wooded terrain extending upwind from the building uninterrupted for at least 1 km or 20 times the height of the building, whichever is greater, or

    (c)an intermediate value between the two exposures defined in Clauses (a) and (b) in cases where the site is less than 1 km or 20 times the height of the building from a change in terrain conditions, whichever is greater, provided an appropriate interpolation method is used. (See Note A-4.1.7.3.(5)(c))

    (6)The reference height, h, shall be determined as follows:

    (a)for buildings with height less than or equal to 20 m and less than the smaller plan dimension, h shall be the midheight of the roof above grade, but shall not be less than 6 m,

    (b)for other buildings, h shall be,

    (i)the actual height above grade of the point on the windward wall for which external pressures are being calculated,

    (ii)the mid-height of the roof for pressures on surfaces parallel to the wind direction, and

    (iii)the mid-height of the building for pressures on the leeward wall, and

    (c)for any structural element exposed to wind, h shall be the mid-height of the element above the ground.

    (7)The exposure factor for internal pressure, C_ei, shall be determined as follows:

    (a)for buildings whose height is greater than 20 m and that have a dominant opening, C_ei shall be equal to the exposure factor for external pressures, C_e, calculated at the mid-height of the dominant opening, and

    (b)for other buildings, C_ei shall be the same as the exposure factor for external pressures, C_e, calculated for a reference height, h, equal to the mid-height of the building or 6 m, whichever is greater.

    (8)Except as provided in Sentences (9) and 4.1.7.6.(1), the gust effect factor, C_g, shall be one of the following values:

    (a)2.0 for the building as a whole and main structural members, or

    (b)2.5 for external pressures and suctions on secondary structural members including cladding.

    (9)For cases where C_g and C_p are combined into a single product, C_gC_p , the values of C_g and C_p need not be independently specified. (See Article 4.1.7.6.)

    (10)The internal gust effect factor, C_gi , shall be 2.0, except it is permitted to be calculated using the following equation for large structures enclosing a single large unpartitioned volume that does not have numerous overhead doors or openings:

    C_gi = 1 + 1/(sqrt(1 + (V_0)/6950A))

    where

    V_0 = internal volume in m^3 , and

    A = total area of all exterior openings of the volume in m^2 .

    (See Note A-4.1.7.3.(10))

    Open OBC Div. B 4.1.7.3. in the code viewer
  • OBC Div. B Table 4.1.7.3. Importance Factor for Wind Load, I_w

    Table 4.1.7.3. — Importance Factor for Wind Load, I_w Forming Part of Sentences 4.1.7.3.(1) and 4.1.7.8.(4) Importance Category | Importance Factor, I_w — ULS | Importance Factor, I_w — SLS Low | 0.8 | 0.75 Normal | 1.0 | 0.75 High | 1.15 | 0.75 Post-disaster | 1.25 | 0.75

    Open OBC Div. B Table 4.1.7.3. in the code viewer
  • OBC Div. B 4.1.7.4. Topographic Factor

    (1)Except as provided in Sentence (2), the topographic factor, C_t, shall be taken as 1.0.

    (2)For buildings on hills or escarpments with slope, H_h/(2L_h) , greater than 0.1 (See Figure 4.1.7.4.), the topographic factor, C_t , shall be calculated as follows:

    C_t = (1 + (ΔS)/(C_g))(1 + ΔS)

    where

    ΔS = ΔS_max(1 - (|x|)/(kL_h))exp( - αz/L_h)

    where

    ΔS_max = applicable value from Table 4.1.7.4.,

    x = horizontal distance from the peak of the hill or escarpment,

    L_h = horizontal distance upwind from the peak to the point where the ground surface lies at half the height of the hill or escarpment, or 2H_h (where H_h is the height of the hill or escarpment), whichever is greater,

    Z =height above ground, and

    k and α = applicable constants from Table 4.1.7.4. based on shape of hill or escarpment.

    Speed-up of Mean Velocity on a Hill or Escarpment Forming Part of Sentence 4.1.7.4.(2)

    Figure 4.1.7.4.

    Notes to Figure 4.1.7.4.:

    (1) V(z) = wind speed.

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  • OBC Div. B 4.1.7.5. External Pressure Coefficients

    (1)Applicable values of external pressure coefficients, C_p, are provided in

    (a)Sentences (2) to (9), and

    (b)Article 4.1.7.6. for certain shapes of low buildings.

    (2)For the design of the main structural system, the value of C_p shall be established as follows, where H is the height of the building and D is the width of the building parallel to the wind direction:

    (a)on the windward face,

    C_p = 0.6for H/D < 0.250.27(H/D + 2)for 0.25 ≤ H/D < 1.00.8for H/D ≥ 1.0

    (b)on the leeward face,

    C_p = − 0.3for H/D < 0.25 − 0.27(H/D + 0.88)for 0.25 ≤ H/D ≤ 1.0 − 0.5for H/D ≥ 1.0

    (c)on the walls parallel to the wind, C_p = - 0.7 .

    (See Note A-4.1.7.5.(2) and (3))

    (3)For the design of roofs, the value of C_p shall be established as follows, where x is the distance from the upwind edge of the roof:

    (a)for H/D ≥ 1.0, C_p = - 1.0 , and

    (b)for H/D < 1.0,

    C_p = − 1.0for x ≤ H − 0.5for x > H

    (See Note A-4.1.7.5.(2) and (3))

    (4)For the design of the cladding and of secondary structural elements supporting the cladding, the value of C_p shall be established as follows, where W and D are the widths of the building:

    (a)on walls, C_p shall be taken as ± 0.9 , except that within a distance equal to the larger of 0.1D and 0.1 W from a building corner, the negative value of C_p shall be taken as -1.2,

    (b)on walls where vertical ribs deeper than 1 m are placed on the facade, C_p shall be taken as ± 0.9 , except that, within a distance equal to the larger of 0.2D and 0.2 W from a building corner, the negative value of C_p shall be taken as -1.4, and

    (c)on roofs, C_p shall be taken as -1.0, except that

    (i)within a distance equal to the larger of 0.1D and 0.1 W from a roof edge, C_p shall be taken as -1.5,

    (ii)in a zone that is within a distance equal to the larger of 0.2D and 0.2 W from a roof corner, Cp shall be taken as -2.3 but is permitted to be taken as -2.0 for roofs with perimeter parapets that are higher than 1 m, and

    (iii)on lower levels of flat stepped roofs, positive pressure coefficients established for the walls of the steps apply for a distance b. (See Figure 4.1.7.6.-D for the definition of b)

    (See Note A-4.1.7.5.(4))

    (5)Except as provided in Sentence (6), for the design of balcony guards, the internal pressure coefficient, C_pi , shall be taken as zero and the value of C_p shall be taken as ± 0.9 , except that, within a distance equal to the larger of 0.1D and 0.1 W from a building corner, C_p shall be taken as ± 1.2 .

    (6)Where the top of the balcony guard is 2.0 m or less below the roof surface, the values of C_p shall be taken as equal to those determined for parapets in Sentences (7) and (8).

    (7)To determine the contribution from parapets to the wind loads on the main structural system, the values of C_p shall be taken as

    (a)on the outer faces, equal to those on the walls below,

    (b)on the inner face of the windward parapet, equal to that on the upwind edge of a roof surface at the level of the top of the parapet, and

    (c)on the inner faces of the other parapets, zero.

    (8)For the structural design of parapets themselves, the values of C_p shall be taken as equal to those specified in Sentence (7), except that the value of C_p on the inner face of the leeward parapet shall be taken as equal to that on the outer face of the windward parapet.

    (9)For the design of cladding on parapets, the values of C_p shall be taken as

    (a)on the outer vertical surfaces, equal to those on the cladding on the walls below, and

    (b)on the inner and top surfaces, equal to those on the cladding of a roof surface at the level of the top of the parapet.

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  • OBC Div. B Table 4.1.7.7. Internal Pressure Coefficients

    Table 4.1.7.7. — Internal Pressure Coefficients Forming Part of Sentence 4.1.7.7.(1) −0.15 to 0.0 Building Openings | Values for C_pi Uniformly distributed small openings amounting to less than 0.1% of the total surface area of the building | Non-uniformly distributed openings of which none is significant or significant openings that are wind-resistant and closed during storms | −0.45 to +0.30 Large openings likely to remain open during storms | −0.70 to +0.70

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