Downspout and valley sizing 1

[texasrhb]

First post. I need to verify sizing of roof valley gutter and downspouts required. C=0.99 A=1(acres) I= 8.0 in/hr. I used the circular weir formula Q=CA(2gh)^0.5

I am not aware of any COde Requirment for this and am not sure that Q=CIA is applicable for roofing systems (although it would seem to apply).

Comments welcome.

THX

rhb

 

[cvg]

rational method can be used assuming you use a suitable intensity. Time of concentration should be fairly short, maybe 5 minutes or less. Verify if full circular weir is appropriate - does flow approach the downspout from both sides or is it located at the end, next to the gutter? If so, it may not function very efficiently as a full circle. Also, you may want to consider some degree of clogging with leaves, sticks, pine needles etc. If it happens (and eventually it will) then how deep does the water get and does it cause the roof to leak?

 

[texasrhb]

Good comments. I have a 6" deep valley located between 2 roof sections with a 1:12 roof slope. 4" Downspouts are placed every 12.5'. The downspouts (about 6" long) attach to a 12" PVC pipe set at a 1% slope for discharge. The 12"pipe eventually becomes vertical for street level discharge.

What year event would normally be used (if there is such a thing as normal)?

I also found an old SBC (southern building code) with sizing data. It looks as though the sbc uses a 10 yr event (100 yr 15 min precipitation curves) with an in/hr number of 8". 8" is what I got using ifd curve data for my state and county with a tc of 15minutes. Are these the same things?

THX for comments
RHB

 

[PEDARRIN2]

The plumbing code typically indicates requirements of how to size roof gutters.

Make sure you are looking at the applicable code.