Documentation
This document contains all National annex values, which are used in SDF - Basic package
Clause 4.1 Characteristic values, paragraph (1)
The characteristic values of snow load on the ground sk in the United Kingdom should be obtained from the map and formula.
where:
Z is zone number from the map
A is altitude above sea level in meters
If the construction site is below 100 m above sea level, use altitude A = 100 m
Clause 4.3 Treatment of exceptional snow loads on the ground, paragraph (1)
Recommended value of the coefficient should be used, Cesl = 2,0
Clause 5.2 Load arrangements, paragraph (7)
Ce = 1,0 for all topographies
Clause 5.2 Load arrangements, paragraph (8)
Ct = 1,0 for all roof materials
Clause 5.3.3 Pitched roofs, paragraph (4)
Next drifted load arrangement is used instead of standard arrangement.
Table 1: Drifted snow load shape coefficient for duopitch roofs in the UK
| μ1 |
0,8 |
0,8 + 0,4(α - 15)/15 |
1,2(60 - α)/30 |
0,0 |
Clause 5.3.4 Multi-span roofs, paragraph (3)
Annex B should be used instad of standard load arrangement.
Annex B:
Shape coefficient μ1 is determined as the least value of:
Drift lengths are determined as:
Clause 5.3.4 Multi-span roofs, paragraph (4)
This clause is not used, because annex B is used.
Clause 5.3.5 Cylindrical roofs, paragraph (1)
μ3,max = 2,0
Clause 5.3.5 Cylindrical roofs, paragraph (3)
Special drifted load arrangement is considered in the UK.
δ is the angle between the horizontal and the tangent to the roof at the eaves.
α for δ ≤ 60° is the angle between horizontal and the line drawn from the crown to the eaves.
α for δ > 60° is the angle between horizontal and the line drawn from the crown to the point of the roof where the tangent to the surface, makes an angle of 60° with the horizontal.
The drifted load arrangement need only be considered for roofs where α is greater than 15°. For roofs with α lesser or equal to 15°, only undrifted load arrangement is considered.
Table 2: Drifted snow load shape coefficient for cylindrical roofs in the UK
| μ1 |
0 |
0,4 |
0,4 |
0 |
| μ2 |
0 |
0,8 + 0,4(α - 15)/15 |
1,2(60 - α)/30 |
0 |
| μ3 |
0 |
μ2(60 - δ)/30 |
μ2(60 - δ)/30 |
0 |
Clause 5.3.6 Roof abutting and close to taller construction works, paragraph (1)
Annex B should be used for determinate the drifted snow load case, therefore no range of values for μw is specified in the UK.
Clause 5.3.6 Roof abutting and close to taller construction works, paragraph (3)
Annex B should be used to determine the drifted snow load case.
Annex B can be used also for construction close to taller building, if constructions are less than 1,5 m away.
Annex B:
Drift length ls is the least value of 5h, b1 or 15 m.
Table 3: Shape coefficients for exceptional snow drift for roofs abutting and close to taller structures
| μ1 |
μ3 |
μ3{[30 - α]/15} |
0 |
0 |
| μ2 |
μ3 |
μ3 |
μ3{[60 - α]/30} |
0 |
μ3 is the least value of 2h/sk, 2b/ls or 8.
b is larger of b1 or b2.
ls it she least value of 5h, b1 or 15 m.
Clause 6.2 Drifting at projections and obstructions, paragraph (2)
Annex B should be used to determine the drifted snow load case.
Annex B:
If the vertical elevation against which a drift could form is not greater than 1 m2, the effect of drifting can be ignored.
This clause applies to:
- Drifting against obstructions not exceeding 1 m in height.
- Drifting on canopies, projecting not more than 5m from the face of the building over doors and loading bays, irrespective of the height of the obstruction.
- Slender obstructions over 1 m high but not more than 2 m wide, may be considered as local projections. For this specific case h may be taken as the lesser of the projection height or width perpendicular to the direction of the wind.
The shape coefficient is determined as the least value of:
μ1 = 2h1/sk or 5
μ2 = 2h2/sk or 5
In addition, for door canopies projecting not more than 5 m from the building, μ1 should not exceed 2b/ls1, where b is the larger of b1 and b2.
The drift length (lsi) is taken as the least value of 5h or bi, where i = 1 or 2 and h ≤ 1 m.
The shape coefficient is determined as the least value of:
μ1 = 2h/sk
μ1 = 2b/ls
μ1 = 8
The drift length ls should be taken as the least value of 5h, b1 or 15 m.
Clause 6.3 Snow overhanging the edge of a roof, paragraph (1)
Clause should be used for sites at altitudes greater than 800 m above sea level.
Clause 6.3 Snow overhanging the edge of a roof, paragraph (2)
Irregular shape of the snow k should be determined as recommended.