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Wind on canopy roofs

What are canopy roofs ?

A canopy roof is defined as the roof of a structure that does not have permanent walls, such as petrol stations, dutch barns, etc.
The wind on a canopy roof is calculated differently from the climatic action on a closed or partially enclosed building.
For a building with walls, when in at least two sides of the building, the total area of openings in each side is more than 30% of the area of that side, the actions on the roof should be calculated as for a canopy roof.
Photovoltaic shelter - Monopitch canopy roof monopitch canopy roof
Photovoltaic shelter - Duopitch canopy roof duopitch canopy roof
Photovoltaic shelter - Multibay canopy roof multibay canopy roof

How to calculate the wind pressure on the main structure of a canopy roof ?

Extract of the standard EN 1991-1-4 §7.3 Canopy roofs

(2) The degree of blockage under a canopy roof is shown in Figure 7.15. It depends on the blockage φ, which is the ratio of the area of feasible, actual obstructions under the canopy divided by the cross sectional area under the canopy, both areas being normal to the wind direction.
NOTE: φ=0 represents an empty canopy, and φ=1 represents the canopy fully blocked with contents to the downwind eaves only (this is not a closed building).
(3) The overall force coefficients, Cf, given in Tables 7.6 to 7.8 for φ=0 and φ=1 take account of the combined effect of wind acting on both the upper and lower surfaces of the canopies for all wind directions. Intermediate values may be found by linear interpolation.
(4) Downwind of the position of maximum blockage, values for φ=0 should be used.
(5) The overall force coefficient represents the resulting force. The net pressure coefficient represents the maximum local pressure for all wind directions. It should be used in the design of roofing elements and fixings
(6) Each canopy must be able to support the load cases as defined below:
  • for a monopitch canopy (Table 7.6) the location of the centre of pressure should be defined as a distance from the windward edge.
    NOTE: The location may be given in the National Annex. The recommended location is in Figure 7.16.
    NOTE 2: The document 'BNCM/CNC2M N0380 / REC EC1-CM : July 2017 §5.3' proposes a transformation of the force coefficients cf into a distribution of pressure coefficients along the slope of the roof, whose resultant is compliant, in size and position, to that defined by standard NF EN 1991-1-4 and the French National Annex.
  • for a duopitch canopy (Table 7.7) the center of pressure should be taken at the center of each slope (Figure 7.17). In addition, a duopitch canopy should be able to support one pitch with the maximum or minimum load, the other pitch being unloaded.
  • for a multibay duopitch canopy each load on a bay may be calculated by applying the reduction factors ψmc given in Table 7.8 to the values given in Table 7.7.
(8) The reference height should be taken as :
  • the top edge of monopitch canopy roof
  • the bottom edge of duopitch canopy roof
Representation of airflow over canopy roof from the standard
Figure 7.15 - Airflow over canopy roofs

Example of results given by the software

See the features of Canopy Roofs
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B - Data

B1 - Roof

α Bs
Type Angle α Slope length Bs
monopitch 8.0° 12.492m

B2 - Wind - Peak velocity pressure

Wind from left qp1 Wind from right qp2 Wind from gable qp3
55.76daN/m² 55.76daN/m² 55.76daN/m²
French flag

B3 - Degree of blockage under the roof

Position At left At right Profile
Blockage ratio φ 0.33 0.23 0.25

C - Loadings calculation - EN 1991-1-4 §7.3

cf distribution from BNCM/CNC2M N0380 / REC EC1-CM : July 2017 Figure 22
Left wind - sag 82.52daN/m2(on 1.249m) 45.39daN/m2 -7.47daN/m2
Force coefficient cf 0.46 Table 7.6
Location of cf 3.123m Figure 7.16
Left wind - uplift -110.4daN/m2(on 1.249m) -99.36daN/m2 21.97daN/m2
Blockage ratio φ 0 no increase of the blockage at the right downwind eave - §7.3(4)
Force coefficient cf -0.82 Table 7.6
Location of cf 3.123m Figure 7.16
Right wind - sag -7.47daN/m2 45.39daN/m2 82.52daN/m2(on 1.249m)
Force coefficient cf 0.46 Table 7.6
Location of cf 9.369m Figure 7.16
Right wind - uplift 28.15daN/m2 -124.35daN/m2 -131.93daN/m2(on 1.249m)
Blockage ratio φ 0.33 increase of the blockage at the left downwind eave - §7.3(2)
Force coefficient cf -1.011 Table 7.6
Location of cf 9.369m Figure 7.16
Gable wind - sag 25.65daN/m2 25.65daN/m2
Force coefficient cf 0.46 for roof slope angle α = 0° - BNCM/CNC2M N0380 / REC EC1-CM : July 2017 Table 3
Location of cf 6.246m cf is uniform on the whole roof - BNCM/CNC2M N0380 / REC EC1-CM : July 2017 §5.3
Gable wind - uplift -39.03daN/m2 -39.03daN/m2
Blockage ratio φ 0.25 increase of the blockage under the building - §7.3(2)
Force coefficient cf -0.7 for roof slope angle α = 0° - BNCM/CNC2M N0380 / REC EC1-CM : July 2017 Table 3
Location of cf 6.246m cf is uniform on the whole roof - BNCM/CNC2M N0380 / REC EC1-CM : July 2017 §5.3