Rain Water Deflection from Adjacent Buildings
Rain Water Deflection from Adjacent Buildings
(OP)
A 50-story building is proposed next to a 6-story building. The owner of the 6-story building hired an engineer who determined that rainwater could deflect (presuming it is coming down at some angle) off the side of the adjacent 50-story building onto their roof. They want to know how the owner of the 50-story building plans to mitigate this issue.
Is this really an issue? Is there any precedent for their claim? When I calculate roof runoff for designing building drainage systems, I assume the footprint of the building as the area for my calculation. I never consider runoff from taller adjoining buildings that may deflect onto my roof.
Does anyone out there have any experience with this?? Any advice would be appreciated....
Is this really an issue? Is there any precedent for their claim? When I calculate roof runoff for designing building drainage systems, I assume the footprint of the building as the area for my calculation. I never consider runoff from taller adjoining buildings that may deflect onto my roof.
Does anyone out there have any experience with this?? Any advice would be appreciated....





RE: Rain Water Deflection from Adjacent Buildings
Typically, I only use the bottom 30 feet of the wall area.
I would think the 50 story building would also intercept a lot of the rainfall falling the other direction.
Maybe they offset each other.
RE: Rain Water Deflection from Adjacent Buildings
RE: Rain Water Deflection from Adjacent Buildings
Here is the relevant section of the 2007/09 Florida Building Code
"1106.4 Vertical walls. In sizing roof drains and storm drainage piping, one-half of the area of any vertical wall that diverts rainwater to the roof shall be added to the projected roof area for inclusion in calculating the required size of vertical conductors, leaders and horizontal storm drainage piping."
Clifford H Laubstein
FL PE 58662
RE: Rain Water Deflection from Adjacent Buildings
You would likely be safe to account for the lower 50-60 feet of the other building in your calculations.