Building-related factors:
(1) an old building with a poor foundation or construction
(2) flat or low-pitched roof (snow does not slide off)
(3) L-shaped or T-shaped building
(4) presence of low buildings attached to a higher one (snow drops off the higher one to accumulate on the roof of the lower buildings)
(5) frozen or blocked drainage pipes and gutters
(6) pre-existing damage to the roof or structure
(7) canopy or overhang
(8) equipment or storage on the roof
Weather-related factors:
(1) heavy, wet snow, including
(1a) rain and sleet on top of snow
(1b) repeated storms with sequential accumulations
(2) high winds with drifting
(3) repeated episodes of thawing with refreezing
