Sizing Methodology

  • Gutters

    Testimonials

    “We just wanted to thank you for taking care of our gutter replacement on our home. It was a pleasure to have you and your team on our property; they were conscious of our landscaping and your cleanup afterwards was superb. After years of watching the rain cascade over our roof outside our dining room window, it’s great to finally have a working gutter.
    William C.
    Wake Forest, NC

    • Sizing Methodology

    Sizing a gutter and downspout system to perform effectively requires the following information:

    1. The area of a roof to be drained
    2. Historical rainfall data
    3. Calculations of water flow during extreme periods of rainfall
    4. And water handling capacity of the gutter and downspouts selected

    As a safety factor, always design or select gutters and downspouts for worst-case conditions. For upper roof levels that drain onto lower roofs, the lowest roof elevation should include the area of roofs above, that drain onto it. For example, the first story roof if 1,000 square feet and the second story roof has an area of 500 square feet and drains onto the first story roof. The new total area for the first story should be calculated at 1,500 square feet.

    Roof Slope Historical Rainfall
    1.2” 1.3” 1.4” 1.5” 1.6” 1.7” 1.8” 1.9” 2.0” 2.1” 2.2”
    <1” 0.034 0.038 0.043 0.046 0.051 0.056 0.061 0.068 0.073 0.078 0.085
    Roof Slope Historical Rainfall
    2.2” 2.3” 2.4” 2.5” 2.6” 2.7” 2.8” 2.9” 3.0” 3.1” 3.2”
    <1” 0.085 0.088 0.093 0.098 0.103 0.108 0.113 0.119 0.124 0.129 0.134

    Gutter/Downspout Capacity Table

    Downspout Size Gutter Size
    5” 6” 7”
    2×3 40 95 100
    3×4 85 130 135
    4×4 125 165 170
    4×5 155 210 220
    GPM Capacity