Eurocode 1 Wind peak velocity pressure

Calculation of peak velocity pressure qp depending on the basic wind velocity and the terrain category at the location of the structure. The wind action on the structure (forces and pressures) can be derived from the peak velocity pressure.
According to:
EN 1991-1-4:2005+A1:2010 Section 4
Supported National Annexes:
In addition to countries that adopt the CEN recommended values for NDPs, the following National Annexes are also supported automatically: Finland, Portugal. The National Annexes of Germany, Norway, Spain, Sweden, Switzerland are NOT supported.
All Calculations
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.
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.
Wind terrain category 0 Wind terrain category I Wind terrain category II Wind terrain category III Wind terrain category IV
Illustration of terrain categories based on EN1991-1-4 Annex A (produced with AI, see original figure for details).
Terrain categories for wind according to EN1991-1-4 Annex A
TypeTerrain category
0Sea or coastal area exposed to open sea
ILakes or area with negligible vegetation and without obstacles
IIArea with low vegetation and isolated obstacles
IIIArea with regular cover of vegetation or buildings
IVArea on which at least 15% of the surface is covered with buildings with their average height exceeding 15 m
The appropriate reference height depending on the type of the structure is given in EN1991-1-4 Section 7. For buildings it is generally equal to the height of the building above ground, measured to the top, which may be a ridge or a parapet.

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.
Nationally Defined Parameters
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).
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.