Glossary · Snow and wind
Height factor Ch
The wind correction for height above ground and terrain type, Table 9.01 of DBN V.1.2-2:2006: 0.7 at 5 m and 0.9 at 10 m for type II.
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Definition
Clause 9.9 of DBN V.1.2-2:2006 (as amended by Change 1) introduces Ch, which accounts for the growth of wind load with height above ground Z and with the surrounding terrain type. For structures with a fundamental period up to 0.25 s it is taken from Table 9.01, for all others from Table 9.02. Solar tables and roof systems fall into the first group.
| Z, m | I | II | III | IV |
|---|---|---|---|---|
| 5 | 0.9 | 0.7 | 0.4 | 0.2 |
| 10 | 1.2 | 0.9 | 0.6 | 0.4 |
| 20 | 1.35 | 1.15 | 0.85 | 0.65 |
Intermediate values are interpolated linearly. The table has no rows below 5 m.
Example: Kyiv
A ground table topping out at 2 m in terrain type II: Ch = 0.7, and 370 · 0.7 = 259 Pa instead of W₀ = 370 Pa. The same array on a 10 m high roof has Ch = 0.9 and 333 Pa. On an open reservoir shore (type I) a 2 m table gets Ch = 0.9, in dense city blocks (type IV) 0.2.
How Solispec applies it
The Solispec engine takes Ch from Table 9.01 for the array top height and the chosen terrain type (II by default), interpolating linearly. Below 5 m the 5 m row is used — the table gives no rule for lower heights, so this is the engine’s assumption. The snow and wind calculator shows Wm = γfm · W₀ · Ch · Calt at the building height you enter.
Norms and clauses
- DBN V.1.2-2:2006, cl. 9.9 (Change 1), Table 9.01
Related terms
- Terrain type I–IVThe wind classification of a structure’s surroundings under cl. 9.9 of DBN V.1.2-2:2006: from open water (I) to dense urban areas (IV).
- Characteristic wind pressure W₀The mean wind pressure at 10 m height exceeded on average once in 50 years; Kyiv has 370 Pa under DBN V.1.2-2:2006.
- Limit design wind load WmThe wind load used for strength checks: W_m = γ_fm · W₀ · C, where C covers aerodynamics, height, topography and dynamics.
- Peak velocity pressure qpA Eurocode term from EN 1991-1-4:2005 (cl. 4.5): wind pressure including gusts; DBN V.1.2-2:2006 uses W₀ and C_h instead.
- DBN V.1.2-2:2006 “Loads and actions”: what matters for a solar plantNorms explained
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.