In insurance coverage determinations, the question of causation
is generally the starting point. Did the house flood because of
heavy rainfall or a sewer blockage? Did the roof collapse because
of snow buildup or defective design?
While ideally, all claims would resolve with a satisfying reveal
of the cause of the loss, the reality is that there will be
scenarios where there is no straightforward causation theory and
there are multiple possible independent sources that may have
caused the loss.
The Supreme Court of Canada's 2001 decision of Derksen
v. 539938 Ontario Ltd is the leading case in Canada on
concurrent causation. The brief facts of Derksen are that
during the clean-up of a worksite, a heavy sign base was left
unsecured at the rear of a contractor's truck. As the truck was
driving on the highway, the sign base went through the window of an
oncoming school bus, killing one child and injuring three more. The
Supreme Court of Canada held that the accident
