Water Flow Off Residential Roof

A downspout can be connected to one or more rain barrel s.

Water flow off residential roof.

How water runs off a roof depends on the amount of rainfall and how quickly it needs to drain. The answer is about 623 gallons. Use corrugated plastic tubing to direct overflow away from the foundation of your home. Anything less than one eighth of an inch may pool on the roof.

The roof is sloped toward the scuppers and water simply drains out through the scuppers. Measure along the length of the house or building and along the width of the house or building in feet. A scupper may drain into a downspout on the exterior of the building or it may have an extended chute or pipe that directs a stream of water away from the building. Spreading the flow over the roof in this way will not alleviate the damage that is caused.

However an ideal roof drop per foot should be at least one eighth to one quarter of an inch per foot. Multiply the two figures together to obtain the square footage of your roof step 2 determine the percentage of water collected from each downspout p. Step 1 determine the footprint of your structure f in square feet. Allowing the high volume of water to flow over the roof will damage the shingles and cause them to wear prematurely.

Count the number of downspouts coming from your roof. Divide 100 by the number of downspouts in order to obtain the percentage of water collected from each downspout. Even if you turn the spout adjacent to the slope it will still cause damage to the roofing. Rather rain barrels are most useful as an addition to other stormwater controls.

How much water can flow through a pipe gpm gph. We regularly get asked about the water flow capacity of different pipe sizes and which is the best roof drain for a specific pipe size. For a large roof it is recommended to have drains placed at multiple locations within the area of the roof. Anything with a slope of some kind will cause water to run off the roof.

Required roof drainage flow rate in gallons per minute 0 0104 x rainfall rate x roof area. While this is a normal aspect of roofing and gutters water that pours off of a roof and drenches an area like a door stoop or porch not only makes these spots slippery but water falling. The drainage system of any roof can be located at the edge or in the middle of the roof. Smith used a multiplier of 0 0104 in these calculations to convert inches of rain fall per hour into gallons of water per minute per square foot resulting in the following formula for calculating roof drain flow rate.

So a 50 x 20 roof is 600 x 240 multiply the roof dimensions by the number of inches of rainfall. Some building codes start at one quarter of an inch per foot or two percent. In this example 600 x 240 x 1 144 000 cubic inches of water divide by 231 to get the number of gallons because 1 gallon 231 cubic inches. An overflow device allows excess water to escape when the barrel or cistern is full.