"Robin" pleaseaskinthegroup@becauseIhavegotfedupwithspama ndstuff.co.ru
wrote in message . ..
I am puzzled why the site says "Multiply the roof plan area by the
roof pitch factor" in order to get the actual roof area. Why do you
need to know the actual roof area for rainfall calculations? Surely
the plan area should be used.

Because rain does not always fall vertically? Then the actual roof area
matches the ground area from which the roof intercepts the rain (I think).
For example, imagine a very steeply pitched roof and driving rain.

I would have said that such calculations would have to assume "worst case".
Worst case here is maximum water, ie the rain hitting perpendicular to the
roof, whatever its pitch. Therefore the roof area is required rather than
the plan area.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)