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.
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.