Luba
MD
GL Collector – Technical manual
Version 1.0-EN-January 2012
© Enerconcept Technologies inc.
8
When 15
< 0.8 Select c
s
= 0.8
When 15
> 3 Select c
s
= 3
h= Roof level difference in ft
g= Ground snow load in lb/ft
Figure 7 : Diagram of snow overload swept by the wind in a multiple level roof (for more
details, see comment H of supplement no4 of the NBC)
In the case of sloped roofs with many levels, the snow sliding from a superior level can add a
considerable load to the triangular piles of snow on the inferior level. In comment H, it is
recommended to use half of the total overload calculation of the superior level of the roof.
Snow can also pile up behind obstacles on the roof, such as additional contructions of air
conditioning machinery, but since accumulation is not as great as real multi-level roofs,
reduced C values (up to C
s
= 2) are recommended.
Taking the preceding into account and although it is not specifically specified in the NBC,
Enerconcept proposes to sur-elevate (vertical clearance) the collectors from the roof line. The
Luba GL collector supports can therefore be adjusted in order to minimize the risk of excessive
snow accumulation on the roof which then avoids localised overloads on the existing structure.
As an example, for the city of Sherbrooke, Qc, Canada, the snow accumulation load used is of
44 lbs (20 kg) per square foot of roof. By calculating the snow height which would correspond
to this load, we can design clearance that will be sufficient to avoid excessive snow accumulation
on the existing structure, although this method is not required by the NBC.
