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:
   1. the Static Procedure described in Article 4.1.7.3.,
   2. the Dynamic Procedure described in Article 4.1.7.8., or
   3. the Wind Tunnel Procedure described in Article 4.1.7.12.
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:
   1. the Dynamic Procedure described in Article 4.1.7.8., or
   2. the Wind Tunnel Procedure described in Article 4.1.7.12.
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 4.1.7.12., 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:
   1. the Static Procedure described in Article 4.1.7.3., or
   2. the Wind Tunnel Procedure described in Article 4.1.7.12.
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).)

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
   1. its lowest natural frequency is less than 1 Hz and greater than 0.25 Hz,
   2. its height is greater than 60 m, or
   3. its height is greater than 4 times its minimum effective width, where the effective width, w, of a building shall be taken as

      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 hi; 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
   1. its lowest natural frequency is less than or equal to 0.25 Hz, or
   2. its height is more than 6 times its minimum effective width as defined in Clause (2)(c).

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:

   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.

   
   

   Table 4.1.7.3.
   Importance Factor for Wind Load, IW
   Forming Part of Sentences 4.1.7.3.(1) and (3)

   

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:
   
   where
   p_i = specified internal pressure acting statically and in a direction normal to the surface, either as a pressure directed towards 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
   1. (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,
   2. 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
   3. 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:
   1. for buildings whose height is less than or equal to 20 m and less than the smaller plan dimension, h shall be the mid-height of the roof above grade, but not less than 6 m,
   2. for other buildings, h shall be
      1. the actual height above grade of the point on the windward wall for which external pressures are being calculated,
      2. the mid-height of the roof for pressures on surfaces parallel to the wind direction, and
      3. the mid-height of the building for pressures on the leeward wall, and
   3. 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 pressures, C_ei, shall be determined as follows:
   1. 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
   2. 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:
   1. 2.0 for the building as a whole and main structural members, or
   2. 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_pC_g, the values of C_p and C_g 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:
    where
    V₀ = internal volume, in m³, and
    A = total area of all exterior openings of the volume, in m².
    (See Note A-4.1.7.3.(10).)

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 a 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:

   where
   

   

   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 = height of 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.

   Figure 4.1.7.4.
   Speed-up of mean velocity on a hill or escarpment
   Forming Part of Sentence 4.1.7.4.(2)

   

   Note to Figure 4.1.7.4.:
   (1) V(z) = wind speed
   

   Table 4.1.7.4.
   Parameters for Maximum Speed-up Over Hills and Escarpments
   Forming Part of Sentence 4.1.7.4.(2)

   

   Notes to Table 4.1.7.4.:
   (1) For H_h/L_h > 0.5, assume H_h/L_h = 0.5 and substitute 2 H_h for L_h in the equation for ΔS.

1. Applicable values of external pressure coefficients, C_p, are provided in
   1. Sentences (2) to (5), and
   2. 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:
   1. on the windward face,
      C_p = 0.6 for H/D < 0.25
      = 0.27(H/D + 2) for 0.25 ≤ H/D < 1.0, and
      = 0.8 for H/D ≥ 1.0,
   2. on the leeward face,
      C_p = -0.3 for H/D < 0.25,
      = -0.27(H/D + 0.88) for 0.25 ≤ H/D < 1.0, and
      = -0.5 for H/D ≥ 1.0, and
   3. 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:
   1. for H/D ≥ 1.0, C_p = -1.0, and
   2. for H/D < 1.0,
      C_p = -1.0 for x ≤ H, and
      = -0.5 for 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:
   1. on walls, C_p shall be taken as ±0.9, except that within a distance equal to the larger of 0.1D and 0.1W from a building corner, the negative value of C_p shall be taken as -1.2,
   2. 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 0.2W from a building corner, the negative value of Cp shall be taken as -1.4, and
   3. on roofs, C_p shall be taken as -1.0, except that
      1. within a distance equal to the larger of 0.1D and 0.1W from a roof edge, C_p shall be taken as -1.5,
      2. in a zone that is within a distance equal to the larger of 0.2W and 0.2D from a roof corner, C_p 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
      3. 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. 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 0.1W and 0.1D from a building corner, C_p shall be taken as ±1.2.

1. For the design of buildings with a height, H, that is both less than or equal to 20 m and less than the smaller plan dimension, the values of the product of the pressure coefficient and gust factor, C_pC_g, provided in Sentences (2) to (9) are permitted to be used.
2. For the design of the main structural system of the building, which is affected by wind pressures on more than one surface, the values of C_pC_g are provided in Figure 4.1.7.6.-A.

   
   Figure 4.1.7.6.-A
   External peak values of C_pC_g for primary structural actions arising from wind load acting simultaneously on all surfaces of low buildings (H ≤ 20 m)
   Forming Part of Sentence 4.1.7.6.(2)

   

   Notes to Figure 4.1.7.6.-A:
   (1) The building must be designed for all wind directions. Each corner must be considered in turn as the windward corner shown in the sketches. For all roof slopes, Load Case A and Load Case B are required as two separate loading conditions to generate the wind actions, including torsion, to be resisted by the structural system.
   (2) For values of roof slope not shown, the coefficient (C_pC_g) can be interpolated linearly.
   (3) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface.
   (4) For the design of foundations, exclusive of anchorages to the frame, only 70% of the effective load is to be considered.
   (5) The reference height, h, for pressures is the mid-height of the roof or 6 m, whichever is greater. The eave height, H, may be substituted for the mid-height of the roof if the roof slope is less than 7°.
   (6) End-zone width y should be the greater of 6 m or 2z, where z is the width of the gable-wall end zone defined for Load Case B below. Alternatively, for buildings with frames, the end zone y may be the distance between the end and the first interior frame.
   (7) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
   (8) For B/H > 5 in Load Case A, the listed negative coefficients on surfaces 2 and 2E should only be applied on an area whose width is 2.5H measured from the windward eave. The pressures on the remainder of the windward roof should be reduced to the pressures for the leeward roof.

3. For the design of individual walls and wall cladding, the values of C_pC_g are provided in Figure 4.1.7.6.-B.
4. For the design of roofs with a slope less than or equal to 7°, the values of C_pC_g are provided in Figure 4.1.7.6.-C.
5. For the design of flat roofs with steps in elevation, the values of C_pC_g are provided in Figure 4.1.7.6.-D.
6. For the design of gabled or hipped, single-ridge roofs with a slope greater than 7°, the values of C_pC_g are provided in Figure 4.1.7.6.-E.
7. For the design of gabled, multi-ridge roofs, the values of C_pC_g are provided in
   1. Figure 4.1.7.6.-C for roofs with a slope less than or equal to 10°, and
   2. Figure 4.1.7.6.-F for roofs with a slope greater than 10°.
8. For monosloped roofs, the values of C_pC_g are provided in
   1. Figure 4.1.7.6.-C for roofs with a slope less than or equal to 3°, and
   2. Figure 4.1.7.6.-G for roofs with a slope greater than 3° and less than or equal to 30°.
9. For sawtooth roofs, the values of C_pC_g are provided in
   1. Figure 4.1.7.6.-C for roofs with a slope less than or equal to 10°, and
   2. Figure 4.1.7.6.-H for roofs with a slope greater than 10°.
      
      

      Figure 4.1.7.6.-B
      External peak values of C_pC_g on individual walls for the design of cladding and secondary structural members
      Forming Part of Sentence 4.1.7.6.(3)
      

      
      Notes to Figure 4.1.7.6.-B:
      (1) These coefficients apply for any roof slope, α.
      (2) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
      (3) Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
      (4) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
      (5) Pressure coefficients generally apply for facades with architectural features; however, where vertical ribs deeper than 1 m are placed on a facade, a local C_pC_g of -2.8 applies to zone e.
      

      Figure 4.1.7.6.-C
      External peak values of C_pC_g on roofs with a slope of 7° or less for the design of structural components and cladding
      Forming Part of Sentences 4.1.7.6.(4), (7), (8) and (9)
      

      Notes to Figure 4.1.7.6.-C:
      (1) Coefficients for overhung roofs have the prefix "o" and refer to the same roof areas as referred to by the corresponding symbol without a prefix. They include contributions from both upper and lower surfaces. In the case of overhangs, the walls are inboard of the roof outline.
      (2) s and r apply to both roofs and upper surfaces of canopies.
      (3) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
      (4) Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
      (5) Positive coefficients denote forces toward the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
      (6) For calculating the uplift forces on tributary areas larger than 100 m2 on unobstructed nearly-flat roofs with low parapets, and where the centre of the tributary area is at least twice the height of the building from the nearest edge, the value of C_pC_g may be reduced from -1.5 to -1.1 at x/H = 2 and further reduced linearly to -0.6 at x/H = 5, where x is the distance to the nearest edge and H is the height of the building.
      (7) For roofs having a perimeter parapet with a height of 1 m or greater, the corner coefficients C_pC_g for tributary areas less than 1 m2 can be reduced from -5.4 to -4.4.

      
      Figure 4.1.7.6.-D
      External peak values of C_pC_g for the design of the structural components and cladding of buildings with stepped roofs
      Forming Part of Sentence 4.1.7.6.(5)
      

      Notes to Figure 4.1.7.6.-D:
      (1) The zone designations, pressure-gust coefficients and notes provided in Figure 4.1.7.6.-C apply on both the upper and lower levels of flat stepped roofs, except that on the lower levels, positive pressure-gust coefficients equal to those in Figure 4.1.7.6.-B for walls apply for a distance, b, where b is equal to 1.5h1 but not greater than 30 m. For all walls in Figure 4.1.7.6.-D, zone designations and pressure coefficients provided for walls in Figure 4.1.7.6.-B apply.
      (2) Note (1) above applies only when the following conditions are met: h1 ≥ 0.3H, h1 ≥ 3 m, and W1, W2, or W3 is greater than 0.25W but not greater than 0.75W.

      Figure 4.1.7.6.-E
      External peak values of C_pC_g on single-span gabled and hipped roofs with a slope greater than 7° for the design of structural components and cladding
      Forming Part of Sentence 4.1.7.6.(6)

      
      Notes to Figure 4.1.7.6.-E:
      (1) Coefficients for overhung roofs have the prefix "o" and refer to the same roof areas as referred to by the corresponding symbol without a prefix. They include contributions from both upper and lower surfaces.
      (2) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
      (3) Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
      (4) Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
      (5) For hipped roofs with 7° < α ≤ 27°, edge/ridge strips and pressure-gust coefficients for ridges of gabled roofs apply along each hip.

      Figure 4.1.7.6.-F
      External peak values of C_pC_g on multi-span gabled (folded) roofs with a slope greater than 10° for the design of structural components and cladding

      Forming Part of Sentence 4.1.7.6.(7)

      
      Notes to Figure 4.1.7.6.-F:
      (1) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
      (2) Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
      (3) Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
      (4) For α ≤ 10°, the coefficients given in Figure 4.1.7.6.-C apply, but for cases where α > than 7°, use α = 7°.

      Figure 4.1.7.6.-G
      External peak values of C_pC_g on monoslope roofs for the design of structural components and cladding

      Forming Part of Sentence 4.1.7.6.(8)

      
      Notes to Figure 4.1.7.6.-G:
      (1) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
      (2) Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
      (3) Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
      (4) For α ≤ 3°, the coefficients given in Figure 4.1.7.6.-C apply.

      Figure 4.1.7.6.-H
      External peak values of C_pC_g on sawtooth roofs with a slope greater than 10° for the design of structural components and cladding

      Forming Part of Sentence 4.1.7.6.(9)

      
      Notes to Figure 4.1.7.6.-H:
      (1) End-zone width z is the lesser of 10% of the least horizontal dimension and 40% of height, H, but not less than 4% of the least horizontal dimension or 1 m.
      (2) Combinations of external and internal pressures must be evaluated to obtain the most severe loading.
      (3) Positive coefficients denote forces towards the surface, whereas negative coefficients denote forces away from the surface. Each structural element must be designed to withstand forces of both signs.
      (4) Negative coefficients on the corner zones of Span A differ from those on Spans B, C, and D.
      (5) For α ≤ 10°, the coefficients given in Figure 4.1.7.6.-C apply, but for cases where α > than 7°, use α = 7°.

1. The internal pressure coefficient, C_pi, shall be as prescribed in Table 4.1.7.7.

Table 4.1.7.7.
Internal Pressure Coefficients
Forming Part of Sentence 4.1.7.7.(1)

1. For the application of the Dynamic Procedure, the provisions of Article 4.1.7.3. shall be followed, except that the exposure factor, C_e, shall be as prescribed in Sentences (2) and (3), and the gust effect factor, C_g, shall be as prescribed in Sentence (4), when determining the wind loads on the main structural system.
2. For buildings in open terrain, as defined in Clause 4.1.7.3.(5)(a), the value of C_e for the design of the main structural system shall be calculated as follows:

   (See Note A-4.1.7.8.(2) and (3).)
   

3. For buildings in rough terrain, as defined in Clause 4.1.7.3.(5)(b), the value of C_e for the design of the main structural system shall be calculated as follows:

   (See Note A-4.1.7.8.(2) and (3).)
   

4. For the design of the main structural system, C_g shall be calculated as follows:

   where
   

   g_p = peak factor calculated as , and
   
   where
   ν = average fluctuation rate calculated as ,
   T = 3 600 s,
   K = 0.08 for open terrain and 0.10 for rough terrain,
   C_eH = exposure factor evaluated at reference height h = H,
   B = background turbulence factor, a function of w/H determined from Figure 4.1.7.8.,
   s = size reduction factor calculated as ,
   F = gust energy ratio calculated as , where x₀ = (1 220 fn/VH), and
   β = damping ratio, which shall be determined by a rational method, or may be taken to be 0.01 for steel structures, 0.02 for concrete structures, and 0.015 for composite structures,
   where
   f_nD = natural frequency of vibration of the building in the along-wind direction, in Hz,
   f_n = lowest natural frequency of the building, in Hz, as defined in Sentences 4.1.7.2.(2) and (3),
   H = height of the building,
   w = effective width of windward face of the building calculated as , where
   w_i = width normal to wind direction at height h_i, and
   V_H = mean wind speed at the top of the structure, in m/s, calculated as ,
   where
   = reference wind speed at a height of 10 m, in m/s, calculated as ,
   where
   IW = importance factor,
   q = reference velocity pressure, in Pa, and
   ρ = air density = 1.2929 kg/m₃.
   (See Note A-4.1.7.8.(4).)

Figure 4.1.7.8.
Background turbulence factor, B
Forming Part of Sentence 4.1.7.8.(4)

1. Except where the wind loads are derived from the combined C_pC_g values determined in accordance with Article 4.1.7.6., buildings and structural members shall be capable of withstanding the effects of the following loads:
   1. the full wind loads acting along each of the 2 principal horizontal axes considered separately,
   2. the wind loads described in Clause (a) but with 100% of the load removed from any one portion of the area,
   3. the wind loads described in Clause (a) but with both axes considered simultaneously at 75% of their full value, and
   4. the wind loads described in Clause (c) but with 50% of these loads removed from any portion of the area.
      (See Note A-4.1.7.9.(1).)

1. In the design of interior walls and partitions, due consideration shall be given to differences in air pressure on opposite sides of the wall or partition which may result from
   1. pressure differences between the windward and leeward sides of a building,
   2. stack effects due to a difference in air temperature between the exterior and interior of the building, and
   3. air pressurization by the mechanical services of the building.

1. The effects of wind loads on exterior ornamentations, equipment and appendages, including the increase in exposed area as a result of ice buildup as prescribed in CSA S37, "Antennas, Towers, and Antenna-Supporting Structures," shall be considered in the structural design of the connections and the building.
2. Where there are a number of similar components, the net increase in force is permitted to be based on the total area for all similar components as opposed to the summation of forces of individual elements.

1. Except as provided in Sentences (2) and (3), wind tunnel tests on scale models to determine wind loads on buildings shall be conducted in accordance with ASCE/SEI 49, "Wind Tunnel Testing for Buildings and Other Structures."
2. Where an adjacent building provides substantial sheltering effect, the wind loads for the main structural system shall be no lower than 80% of the loads determined from tests referred to in Sentence (1) with the effect of the sheltering building removed as applied to
   1. the base shear force for buildings with a ratio of height to minimum effective width, as defined in Sentence 4.1.7.2.(2), less than or equal to 1.0, or
   2. the base moment for buildings with a ratio of height to minimum effective width greater than 1.0.
3. For the design of cladding and secondary structural members, the exterior wind loads determined from the wind tunnel tests shall be no less onerous than those determined by analysis in accordance with Article 4.1.7.3. using the following assumptions:
   1. C_p = ±0.72 and C_g= 2.5, where the building's height is greater than 20 m or greater than its minimum effective width, and
   2. C_pC_g = 80% of the values for zones w and r provided in Article 4.1.7.6., where the building's height is less than or equal to 20 m and no greater than its minimum effective width.