Why Do Roof Collapses Occur?
A partial or complete roof collapse can occur for several reasons. Most of the causes are preventable if measures are taken beforehand to address roof design, snow removal and ensure that roof drains and gutters are clear and flowing freely. A few of the reasons that roof failures occur are:.
1. Incorrect roof live load design.
2. Problems with the installation of the roof steel.
3. Roof drains and/or downspouts become blocked or frozen and melting snow or rain can not
adequately drain from the roof.
4. Over time, additional dead load (weight) is added to the roof, which will reduce the available
live load or roof design.
5. Imbalance of snow load on roof.
Warning Signs of Potential Roof Collapse
Prior to a roof collapse, buildings generally exhibit signs that the roof is in distress and action should be taken to mitigate a roof collapse. The following are some of the symptoms that have been reported prior to roof failure:
sagging roof steel - visually deformed
cracked or split wood members
sprinkler heads pushed down below ceiling tiles
doors that pop open
doors or windows that are difficult to open
bowed utility pipes or conduit attached at ceiling
creaking, cracking or popping sounds
How Much Does Snow Weigh?
According to Winter Snow Loads. Curt Gooch, Sr. Cornell University. 2002:
1 FOOT of DRY SNOW = 3 LBS / FT
1 FOOT of "IN-BETWEEN-SNOW" = 12 LBS / FT
1 FOOT of WET SNOW = 21 LBS / FT
3 FEET of "IN-BETWEEN-SNOW" will often exceed the design load for many flat roofs in our area.