Take the roof’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.

## How big are roof drains?

According to the chart, for 1/8” slope per 12” of pipe, for 5,000 square feet of roof area, with a 6” per hour of rainfall, the required pipe size is 8”. To size the vertical roof drain for the same parameters – 5,000 square feet of room area and 6” per hour of rain – consult Table 1106.2(Figure 3).

## How do you calculate gpm for a roof drain?

To do this, we simply multiply across each row. The runoff, Q, for the roof area in drainage Zone A is: (1.00 x 1.5 x 500) / 96.23 = 7.79 gallons per minute. The runoff for the grass portion of drainage Zone A is: (0.35 x 1.5 x 900) / 96.23 = 4.91 gpm.

## How do you size a storm drain?

Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. The flow rate in storm drain piping shall not exceed that specified in Table 1106.2. For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m.

## How do you size a scupper?

To adjust this table for other than a 5-inch design rain fall rate, multiply the square footage on the table by 5 then divide by the local design rain fall rate. Example: For 4 inches of design rainfall rate, a 4-inch long scupper with a 1-inch head would accommodate 287 square feet. (230 x 5) ÷4 = 287.

## How many gallons run off a roof?

The answer is about 623 gallons. To calculate the runoff from any given rainfall: Take the dimensions of the footprint of your roof and convert them to inches.

## Are larger downspouts better?

When it comes to downspouts, bigger is better! The larger your downspouts are, the better they can dispel water away from your home. Having downspouts that are too small increase the risk of clogging from organic debris that becomes lodged in them.

## What is the minimum slope for drainage?

Regardless of surface characteristics, when it comes to surface drainage, slope is the most important issue to consider. For efficient drainage, paved surfaces should have a minimum 1-percent slope. Turf or landscaped areas should have a minimum slope of 2 percent.

## What is the design of a roof drain based on?

Historically, most primary and secondary roof drainage systems were designed based upon the 1hour duration, 100year rainfall rate. This 1hour duration, 100 year rainfall rate is the amount of rain that is likely to fall in one hour once every 100 years.

## How do you size a drainage swale?

When constructing a swale with known side slopes, the width of the swale can be defined in terms of the depth. For example, 3:1 side slopes on a swale indicates that for every 1 foot of depth, each side slope will be 3 feet wide, for a total swale width of 6 feet.

## How deep is a storm drain?

Sufficient depth shall mean the minimum cover from the top of the pipe to finish grade at the storm drain alignment. Under normal conditions minimum cover for most types of pipe shall be twenty-four (24) inches above the pipe in paved areas and thirty (30) inches at all other locations.

## How many gallons per minute can a 4 inch pipe handle?

4-inch pipe: 3,400 gallons per minute.

## What is a scupper on a roof?

Description: Scuppers are used to provide an outlet through parapet walls or gravel stops on flat and built-up roofs to allow drainage of excess water. They can be used in conjunction with gutters and downspouts to divert the flow to the desired location.

## Are overflow scuppers required?

Where roof drains are required, secondary (emergency overflow) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.

## What is an overflow scupper?

Overflow drainage scuppers are typically holes with no downspout or other intricate designs. This is because these scuppers are specifically designed to remove water when there is a blockage in the primary system. Overflow drains can be used with roof drains or with primary drainage roof scuppers.