# Balcony Drainage



## ELLEN09US (Nov 27, 2019)

Hi All,

How can we calculate number of drain required per code for a balcony with 12" high parapet? 
Do we need overflow too?

Thank you!


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## mark handler (Nov 27, 2019)

*Step by Step Instructions*
There are 5 easy steps to figure out how many drains your  project will need.

*Step 1: Calculate total area*
Calculate the total area by multiplying its length by width. Example:  A 200 ft. x 250 ft. = 50,000 sq. ft. area.

*Step 2:  Determine leader size*
Determine leader or pipe size.
*Step 3: Find rainfall rate*
Find the rainfall rate for the building’s location. The most accurate and up-to-date resource for rainfall rates is going to be your local codes.
example
Los Angeles 2.1

*Step 4: Find the area handled by one drain*
Using the charts in the Plumbing Code, find the total square footage one drain can handle based on hourly rainfall rate.

*Step 5: Calculate drains needed *
Take the area’s total square footage and divide by the total square footage handled by one drain. The result is the number of drains needed.

For example: 50,000 / 4,400 = 11.36; or 12 drains required.


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## ELLEN09US (Nov 27, 2019)

Thank you!


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## Yikes (Dec 2, 2019)

ELLEN09US, I'm not sure what the parapet height has to do with it, other than to establish that stormwater is not sheet-flowing off the edge of the balcony..  Mark's instructions are correct, but I would add:
1.  Yes, you will need an overflow drain(s), since the parapet will trap any water that overflows when the main drain is clogged.
2.  You did not specify the type of "drain'" will be on the balcony.  For example, if the secondary drains are through-the-wall scuppers and downspouts instead of deck drains, note that (depending on the applicable plumbing code) scuppers may require much larger area than the initial calculation suggests for a round deck drain.  Here in California, our plumbing code 1101.12.2.1 1105.1 states:
(9) Scupper openings shall be not less than 4 inches (102 mm) high and have a width equal to the circumference of the roof drain required for the area served, sized in accordance with Table 1101.12.​
For example, if your calc showed that a 3" diameter deck drain was adequate, the code-required equivalent size for a regular scupper would not measure 3" high x 3" wide; it would be 4" high x 9.5" wide.


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## Bryant (Dec 5, 2019)

This is a residential question? If so then you would be in the  realm of the residential code, chapter 9 and what those scoping  requirements are, may Segway over to the commercial code. sounds like this may be an apartment building R-2 ?


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## mark handler (Dec 5, 2019)

Bryant said:


> This is a residential question? If so then you would be in the  realm of the residential code, chapter 9 and what those scoping  requirements are, may Segway over to the commercial code. sounds like this may be an apartment building R-2 ?


Because In CA, Plumbing, including Drains, are in the CA Plumbing code.


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## Bryant (Dec 5, 2019)

mark handler said:


> Because In CA, Plumbing, including Drains, are in the CA Plumbing code.


Always is amazing how we go about enforcing the international codes, but differ by state, But I get it. We in VA get our marching orders from the general assemblies adoption of the codes, hence our dialogue of codes with Virginia in front of the title. All about the scoping requirements, start there and if allowed Segway over the correct code book


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