Section SPS 362.1608 - Snow loads(1) UNBALANCED SNOW LOADS. This is a department alternative to the requirements in IBC section 1608.1: Unbalanced snow loads on a hip or gable roof may be calculated in accordance with the following equation: S = Ss(Is)(CbCwCsCa)
Where:
S = Alternate unbalanced roof snow load
Ss = Ground snow load from IBC Figure 1608.2
Is = Importance factor from IBC section 1608.1 [ASCE 7, Table 7-4]
Cb = Basic roof snow load factor of 0.8
Cw = Wind exposure factor of 1.0
Cs = Slope factor; see Tables 362.1608-1 and 362.1608-2
Ca = Accumulation factor; see Table 362.1608-3
Table 362.1608-1
Non-Slippery Roofa
Roof Slope, [ALPHA] | Factor, Cs |
[ALPHA] <= 30° | 1.0 |
30° < [ALPHA] <= 70° | (70° - [ALPHA]) / 40° |
70° < [ALPHA] | 0 |
Table 362.1608-2
Unobstructed Slippery Roofa
Roof Slope, [ALPHA] | Factor, Cs |
[ALPHA] <= 15° | 1.0 |
15° < [ALPHA] <= 60° | (60° - [ALPHA]) / 45° |
60° < [ALPHA] | 0 |
Table 362.1608-3
Accumulation Factor
Roof Slope, [ALPHA] | Factor, Ca |
[ALPHA] <= 15° | N/A. Analysis for balanced loading only. |
15° < [ALPHA] <= 20° | 0.25 + [ALPHA] / 20° |
20° < [ALPHA] <= 90° | 1.25 |
(2) EXISTING ROOFS. These are department rules in addition to the requirements in IBC section 1608.1: (a)Buildings on the same property.1. Where an existing roof, regardless of the date of its construction, is horizontally within 20 feet of a proposed, taller structure on the same property, IBC section 1608.1 or an alternate recognized engineering method shall be applied to the existing roof, to address any drifting or sliding of snow onto the existing roof, as caused by the taller structure.2. Where an analysis under subd. 1. shows that an existing roof or corresponding supporting elements will not be adequate to support the additional snow load caused by the taller structure, the existing roof or supporting elements shall be strengthened to support those loads, in accordance with chs. SPS 361 to 366. (b)Buildings on adjoining properties. Where an existing roof, regardless of the date of its construction, is horizontally within 20 feet of a proposed, taller structure on an adjoining property, the owner of the proposed structure shall notify the adjoining owner of the potential for increased structural loads on the existing roof, due to sliding or drifting of snow, as caused by the taller structure.Wis. Admin. Code Department of Safety and Professional Services § SPS 362.1608
CR 00-179: cr. Register December 2001 No. 552, eff. 7-1-02; CR 04-016: cr. (3) and (4) Register December 2004 No. 588, eff. 1-1-05; CR 06-120: r. (1) and (2), renum. (3) and (4) to be (1) and (2) and am. (1) (intro.), (2) (intro.) and (a) 1. Register February 2008 No. 626, eff. 3-1-08; correction in (1) made under s. 13.92(4) (b) 7, Stats., Register December 2011 No. 672.Amended by, CR 16-094: am. (2) (a), (b), Register April 2018 No. 748, eff. 5/1/2018