Dividing the total "effective" roof catchment area by the catchment area for the gutter selected, will give the number of downpipes required. This is not normally a whole number, so it is rounded up to the nearest whole number.
Calculating Downspouts Based on Gutter Length
The general rule of thumb is one downspout for every 20-30 feet of gutter. This may vary depending on several factors such as the pitch of your roof, the volume of rainfall in your area, and the capacity of your gutters.
To calculate for heavy rainfall conditions, however, sizes should be based on a figure of 10cm² of gutter and 8 cm² of downpipe for 7 m² of root area. Conversely, if dry conditions prevail, calculations should be based on 10 cm² of gutter and 8 cm² of downpipe being sufficient for 14 m² of roof area.
Determine the number of drains needed
Finally, divide your total roof area by the square footage a single drain can handle to determine the required number of drains. Round up to ensure sufficient drainage capacity.
A good rule of thumb is one downpipe for every 9m (30ft) of guttering. However, you do need to mindful of how many drains you have around your home or business premises. If you are simply replacing an existing guttering system, we would recommend replacing like for like and having the same number of downpipes.
Drain Flow Rate Formula
To calculate a drain flow rate, multiply the coefficient of runoff, rainfall intensity, and area of drainage together, then divide by 96.23.
To calculate the minimum number of downpipes, divide the roof catchment area by the allowable maximum catchment per downpipe. To calculate the average catchment per downpipe, divide the roof catchment area by the number of downpipes.
At least one wastewater drain for each water fixture (sink, toilet, shower, etc.). Large homes with multiple bathrooms and a kitchen can result in several wastewater drains. Stormwater drains include gutters and downspouts for every roof section and underground pipes to direct rainwater away from the foundation.
1. With your flexible tape measure, measure all the way around the outside of the downpipe horizontally to get the circumference of the pipe. 2. Then divide that measurement by 3.14 (π pi) to get the outer diameter of the pipe.
An inch of rainfall on a square foot of surface area yields . 623 gallons. So, multiply . 623 gallons by the number of surface square feet of your roof.
The Volume of Pipe Formula is a mathematical equation used to calculate the volume of a pipe. It is the same formula used to calculate the volume of any cylindrical shaped object. The Volume of Pipe Formula is V = πr^2h, where V is the volume, r is the radius of the pipe, and h is the height of the pipe.
Dividing the total "effective" roof catchment area by the catchment area for the gutter selected, will give the number of downpipes required. This is not normally a whole number, so it is rounded up to the nearest whole number.
Size of the Gutter Drainage Area: As a rule of thumb, one downspout should be placed every 25-35 linear feet of guttering. Depending on the local climate and rainfall intensity, some homeowners may need more downspouts. Many homeowners add extra downspouts to boost the drainage capacity of their gutters.
Adding more downspouts is an effective way to increase your gutter system's capacity without changing the gutter size. The standard recommendation is one downspout every 40 feet.
The quantity of rainfall on a roof surface is determined by the effective roof surface in m² to be multiplied by the rain intensity (i) l/min. The dimensions of the rainwater-drainage system can be calculated by means of this quantity of rainfall to discharge per unit of time.
A maximum 12 m gutter length served by each downpipe is to ensure effective fall and adequate capacity to discharge all water anticipated during a storm having an average recurrence interval of 20 years.
The installation of downpipes, especially near valley gutters, is designed to ensure rainwater from areas on the roof that have concentrated water flows is adequately removed. Particular consideration needs to be given to box gutters, valley gutters etc. located above the internal areas of a building.
Use a level or plumb line to mark where the downpipe will sit against the wall. Ensure brackets are spaced no more than 1.2m apart and the first clip is a maximum of 200mm below the downpipe bend. Downpipe clips to be secured with two stainless steel screws.
It is expressed as Rh = H/L, where H is the difference in height between the highest and lowest points in the basin and L is the horizontal distance along the longest dimension of the basin parallel to the main stream line. The ratio can be positively correlated with the rate of sediment loss from a basin.