Glossary · Snow and wind
Snow shape coefficient μ
The conversion from ground snow to roof snow: μ = 1 up to 25°, 0 from 60°, linear in between (DBN V.1.2-2:2006, Annex Zh, scheme 1).
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Definition
The coefficient μ converts the weight of ground snow into a roof load. Clause 8.7 of DBN V.1.2-2:2006 refers to the snow load schemes by roof shape; intermediate values are interpolated linearly. For a monopitch surface — and a solar table is one — scheme 1 applies:
μ = 1 (α ≤ 25°); μ = (60° − α) / 35° (25° < α < 60°); μ = 0 (α ≥ 60°)Typical PV tilts
| Tilt α | μ | Sm, Kyiv (γfm = 1) |
|---|---|---|
| ≤ 25° | 1 | 1,550 Pa |
| 30° | 0.857 | 1,329 Pa |
| 35° | 0.714 | 1,107 Pa |
The Sm values in the table refer to the horizontal projection. Low-pitch roof systems at 10–15° get no reduction at all: μ = 1. A steeper table gets less snow but a larger wind aerodynamic coefficient, so the tilt is always a trade-off.
Clause 8.8 separately requires the variants with increased local snow loads (for example, at changes in roof level) for decking, purlins and those members whose section they govern.
How Solispec applies it
The Solispec engine applies scheme 1 as written: μ = 1 at α ≤ 25°, 0 at α ≥ 60° and linear in between, then converts Sm from the horizontal projection to the panel plane. The angle comes from the table geometry in the constructor.
Norms and clauses
- DBN V.1.2-2:2006, cl. 8.7, 8.8, Annex Zh, scheme 1
Related terms
- Limit design snow load SmThe snow load on the horizontal projection used for strength checks: S_m = γ_fm · S₀ · C under DBN V.1.2-2:2006.
- Characteristic snow load S₀The weight of snow cover per 1 m² of ground exceeded on average once in 50 years; under DBN V.1.2-2:2006 Kyiv has 1,550 Pa.
- Panel tilt angleThe angle between the panel plane and the horizontal; it affects yield, snow (μ), wind (c_f) and row pitch. Kyiv’s optimum is about 36°.
- Operating conditions factor CeThe snow load factor for clearing and melting; without data on how the roof is operated C_e = 1 (cl. 8.9).
- Aerodynamic coefficient Caer (cf)The multiplier turning wind pressure into force on a shape; for panels Solispec takes c_f from Table 7.6 of EN 1991-1-4:2005, as cl. 9.8 of the DBN allows.
- 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.