Overflow scupper size = width?

[Yikes]

The old 2002 California Plumbing Code (2006 UPC) section 1101.11.2.1 stated that roof secondary drain / overflow scuppers needed to have "three times the size of the roof drains of the roof drains and having a minimum opening height of 4 inches".

I interpret this to mean that a 2" diameter drain has a nominal area of 3.14 sq. in., therefore the scupper needs to have an area of 9.42 sq. in., therefore a 4"x4" overflow scupper is OK.

The inspector interprets this to mean that for a 2" dia. main drain pipe, an overflow "3 times the size" is (2" x 3 =) 6 INCHES wide x 4 inches high.

Who is correct?

 

[ICE]

9.42 sq. in.

 

[mark handler]

2010 CALIFORNIA PLUMBING CODE

1101.11 Roof Drainage.

1101.11.2.1Scupper openings shall be not less than of four (4) inches high and have a width equal to the circumference of the roof drain required for the area served, sized by Table 11-1.

1101.11.2.2.1 Secondary roof drain systems shall be sized in accordance with Section 1101.11.1 based on the rainfall rate for which the primary system is sized

 

[Yikes]

2010 CALIFORNIA PLUMBING CODE1101.11 Roof Drainage.

1101.11.2.1Scupper openings shall be not less than of four (4) inches high and have a width equal to the circumference of the roof drain required for the area served, sized by Table 11-1.

1101.11.2.2.1 Secondary roof drain systems shall be sized in accordance with Section 1101.11.1 based on the rainfall rate for which the primary system is sized

Thanks, Mark, but my question was specificially referencing the previous code, not the today's code.

It does appear that the most current code would compel a newer project with a 2" main drain (which has a 6.28" circumference) to have a minimum 4 high x 6.28" wide overflow.

 

[pete_t]

Yikes

CA only adopted the 2006 UPC in their 2007 Plumbing Code, the prior code, 2001 CA Plumbing Code, was based on the 2000 UPC.

2001 CALIFORNIA PLUMBING CODE

October 1, 2002 Errata

1101.11 Roof Drainage

1101.11.1 Primary Roof Drainage. Roof areas

of a building shall be drained by roof drains or

gutters. The location and sizing of drains and

gutters shall be coordinated with the structural

design and pitch of the roof. Unless otherwise

required by the Administrative Authority, roof

drains, gutters, vertical conductors or leaders,

and horizontal storm drains for primary

drainage shall be sized based on a storm of sixty

(60) minutes duration and 100-year return

period (see Appendix D).

1101.11.2 Secondary Roof Drainage

1101.11.2.1 Where parapet walls or other

construction extend above the roof and

create areas where storm water would

become trapped if the primary roof drainage

system failed to provide sufficient drainage,

an independent secondary roof drainage

system consisting of scuppers, standpipes,

or roof drains shall be provided. Secondary

roof drainage systems shall be sized in

accordance with Section 1101.11.1 of this

Code. Overflow drains shall be the same

size as the roof drains with the inlet flow

line two (2) inches (51 mm) above the low

point of the roof and shall be installed

independent from the roof drains.

 

[David Henderson]

Agree with pete_t I don't read three times the size of the drain only circumference.

 

[David Henderson]

Yikes what mark posted is in the 2006 plumbing code also.

 

[Big Mac]

Another issue about roof scuppers that has recently come to my attention is with regard to the style of scupper that has the main drain and the overflow drain all rolled into the same unit. Typically the overflow is mounted 2" above the main drain so that it is not active until or unless there is a 2" buildup of rain water. However lately it seems, designers or installers have taken to recessing these drains 2" below the surface of the roof which means tha both the main drain and the overflow drain are working virtually all the time.

There are two significant issues with this approach.

1st the overflow drain is generally supposed to be directed to a location where it is very visible when the building occupants need to be alerted about excees water on the roof. In many cases this is even a nusiance location so as to bring immediate attention to make sure the condition is not ignored.

2nd, if this is an every time occurance when it rains, it won't be taken nearly as seriously when indeed there could be a problem. Another possible result is that the building owner my decide to solve the problem by either rerouting the line to a less conspicuous location or blocking it off altogether.

Has anyone else seen this? What other concerns may you have with this approach?

 

[Paul Sweet]

The overflow should have a collar outside the dome or a standpipe inside the dome if necessary to keep water out until it gets 2" or so above the main drain.

 

[BusiSussie]

like +++

I'm like this!