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# Eurocode 1 Wind load on monopitch roofs (external and internal pressure coefficients)

Description:
Calculation of wind load action effects on monopitch roofs. The net effect of external and internal wind pressure for zones F, G, H, I on the roof surface are calculated from the corresponding external pressure coefficients
According to:
EN 1991-1-4:2005+A1:2010 Section 7.2.4
Applicable for:
Duopitch roofs with slope α of 5° ≤ α ≤ +75°, consisting of one skin, on buildings having permanent side walls.
Supported National Annexes:
A) Calculation of pressure coefficients: Only countries that adopt CEN recommended values for section 7.2.4 of EN1991-1-4 are supported. B) Peak velocity pressure: The value can be specified manually. Otherwise automatic calculation of peak velocity pressure is supported for countries that adopt the CEN recommended values for the related NDPs, and also for the following National Annexes: Finland, Portugal. The National Annexes of Germany, Norway, Spain, Sweden, Switzerland are NOT supported.
Input

Hint: Select 'Custom peak velocity pressure' in the terrain category dropdown in order to manually specify the peak velocity pressure.

The terrain categories are illustrated in EN1991-1-4 Annex A. The transition zones between terrain categories are specified in EN1991-1-4 §A.2. For a description of the terrain categories 0, I, II, III, IV see Calculation of peak velocity pressure.
m/s
The basic wind velocity is given as vb = vb,0cdircseason where the fundamental value of basic wind velocity vb,0 is defined in EN1991-1-4 §4.2(1)P and its value is provided in the National Annex. Altitude correction may also be specified in the National Annex for EN1991-1-4 §4.2(2)P. The directional and season factors are generally cdir = 1.0 and cseason = 1.0. For particular cases values smaller than 1.0 may be specified in the National Annex for EN1991-1-4 §4.2(2)P.
kPa
°
Direction of the wind θ = 0° corresponds to wind parallel or nearly parallel to roof slope direction from low eave to high eave. Direction of the wind θ = 90° corresponds to wind parallel or nearly parallel to the direction of low eave and high eave (i.e. perpendicular or nearly perpendicular to the slope direction). Direction of the wind θ = 180° corresponds to wind parallel or nearly parallel to roof slope direction from high eave to low eave. A figure is provided after the 'calculate' button is pressed.
m
m
m
°
For pitch angle smaller than 5° the calculation for Wind Load on Flat Roofs should be used.
Local coefficients cpe,1 are intended for design of small elements and fixings with an area per element ≤ 1 m2 (e.g cladding elements, roofing elements). Overall coefficients cpe,10 may be used for the design of the overall load bearing structure with loaded area ≥ 10 m2.

Orography factor larger than 1.0 may be applicable over isolated hills and escarpments. See EN1991-1-4 §4.3.3 and §A.3 for more details.
True when the area of openings at that face is at least twice the area of openings and leekages in the remaining faces. For more information on dominant faces see EN1991-1-4 §7.2.9.
Minimum value of internal pressure coefficient cpi to be used when unfavorable. For buildings without a dominant face and where it is not possible, or not considered justified, to estimate ratio μ the value cpi = -0.3 may be used. Otherwise more accurate value may be determined in accordance with EN1991-14 §7.2.9. Enter cpi,min = cpi,max= 0 to ignore internal pressure.
Maximum value of internal pressure coefficient cpi to be used when unfavorable. For buildings without a dominant face and where it is not possible, or not considered justified, to estimate ratio μ the value cpi = +0.2 may be used. Otherwise more accurate value may be determined in accordance with EN1991-14 §7.2.9. Enter cpi,min = cpi,max= 0 to ignore internal pressure.
A face is considered dominant when the ratio Ao,dom/Ao,rest is at least 2.
See the details of the calculation for the pressure coefficients corresponding to the different zones. Calculate manually the area weighted value of the pressure coefficient based on the area of openings for the different zoned of the dominant face. Negative values correspond to suction directed away from the surface i.e. pressure towards the exterior of the building. Press calculate to see external pressure coefficients.
Nationally Defined Parameters
kg/m3
According to EN1991-1-4 §4.5(1) and the National Annex.
According to the National Annex to EN1991-1-4 §4.1(1), §4.2(1)P, §4.2(2)P, §4.3.1(1), §4.3.2(1), §4.3.5(1), §4.4(1), §4.5(1).
According to the National Annex to EN1991-1-4 §7.2.4(3).
Note: Always verify the validity of the Nationally Defined Parameters (NDPs). Please inform us of any discrepancy using our Contact Form. The NDP value is left blank for all NDPs that we do not have this information available. Interested users who have access to the corresponding NDPs can notify us using our Contact Form to fill-in the missing information.