Are you trying to calculate the number of drains that your residential or commercial roofing project will require? A roof drain calculation can seem complicated, but this resource will break down how to size roof drains step-by-step. Here’s what you should know.
Why Is Roof Drain Calculation Important?
Proper roof drainage is so important. Without proper drainage, water collects around your home, seeps into the ground, and possibly enters your home if there are weak spots in the foundation.
Moisture buildup threatens your foundation, and therefore, having a system that diverts water away from your home will serve you well. This system is also helpful in removing both water and debris from your roof.
Steps for Roof Drainage Calculation
In just five simple steps, you’ll have your roof drain calculation.
1. Calculate the total roof area
Start by determining the total roof area of your building. This measurement can be found by multiplying the length of the roof by its width.
For example, if your roof is 300 ft by 300 feet, then the total roof area would be 90,000 sq. ft. area.
2. Determine the leader size
Establish the leader or pipe size that you need. A “leader” drain is a pipe that is installed to drain water from the roof gutters or catchment to the storm drain or other means of disposal. You may also hear it called a conductor, roof drain, or downspout.
ⓘ The standard sizes for top manufacturers are normally 2, 3, 4, 5, 6, and 8 inches. How do you know which size you need? It will depend on the area that one drain can handle and the hourly rainfall that you receive in your area. The next two sections will address this.
3. Learn the rainfall rate
You’ll need to determine the rainfall rate in your local area to understand which leader drain size is right for you. The local codes for your building or home’s location will offer accurate and updated information.
4. Find the area handled by one drain
Research the total square footage that one drain can handle based on the hourly rainfall rate. This will vary based on your area, so it’s important to have accurate information.
This ICC Appendix lists Rates of Rainfall for Various Cities. This can be a helpful reference as you’re doing this research.
5. Calculate the drains needed
To determine how many drains you need, you’ll need to take your roof’s total square footage that you found in the first step and divide the total square footage handled by one drain. This will give you the total number of drains that you need.
90,000 sq. ft. area ÷ 3,520 total sq. ft. covered per drain = 25.57, or 26 drains required.
Measuring Roof Drains
Measuring roof drain parts are an important part of roof drain calculation. You can find all of our specifications and technical drawings for drains here.
Safeguard your home and land today! A roof drain calculation is a key step in making sure your property doesn’t get water damage when heavy rain or flooding occurs. Learning how to size roof drains properly is a big step in making sure your home is protected.
Shop Thunderbird Protects for roof drains today.