Rooftop Detention
Rooftop Detention
(OP)
Can detention of 2.8" of rain be detained on top of a warehouse roof without adding any additional cost?
We are trying to obtain city approval for development but there isn't a structural engineer on the team yet.
As part of standard structural calculations, the typical rain/snow loads (40psf as I am told in northeast) that are accounted for in the roof exceed the amount of water (15psf) that I need to detain. So, I would like to think that it is possible to include this detention in my stormwater calculations without adding cost to the roof.
Has anyone ever done this?
We are trying to obtain city approval for development but there isn't a structural engineer on the team yet.
As part of standard structural calculations, the typical rain/snow loads (40psf as I am told in northeast) that are accounted for in the roof exceed the amount of water (15psf) that I need to detain. So, I would like to think that it is possible to include this detention in my stormwater calculations without adding cost to the roof.
Has anyone ever done this?





RE: Rooftop Detention
In your case, the roof would need to be "flat" to within a couple of inches to avoid excessive loads in the low spots. Based on your average depth of 3" of water, a 6" low-spot would have 9" of standing water, producing a localized load of about 45psf.
This might introduce additional construction requirements for the flatness of the roof. Of course, you'll have to balance the flatness with whatever pitch you need in order to drain the roof completely.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Rooftop Detention
RE: Rooftop Detention
Hydrae
RE: Rooftop Detention