This app allows you to easily and accurately size downspout and gutters using the methods and formulas covered in SMACNA’s Architectural Sheet Metal Manual (ASMM). The Rainfall Wizard allows you to select the closet city to use the information from the ASMM tables.

DOWNSPOUT SIZING In sizing downspouts, the following considerations apply: 1. Downspouts of less than 7.00 sq in.(4515 sq mm) cross section should not be used except for small areas such as porches and canopies. 2. The size of the downspout should be constant through-out its length. 3. Downspouts should be constructed with conductor

Oct 3, 2024 · Use this handy guide to make sure your gutter system is sized appropriately for even the heaviest storm. Properly sized gutters and downspouts help protect your home from water damage. They channel rainwater away from …

As with gutters, a downspout’s capacity must match or exceed the expected runoff. Use the chart below to figure out how many extra downspouts you need. Adding a 2 by 3 rectangular downspout, for instance, boosts your gutter’s capacity by 600 square feet of drainage area.

Aug 29, 2024 · Learn about our gutter and downspout sizes guide to find the right pair for you. Get expert advice on improvements to your home, including design tips, how much you'd expect to pay for a...

For SAF Perimeter Systems Commercial Gutter Designers, Contractors and Building Owners this Gutter Sizing section provides 4 Steps to properly size a Commercial Gutter & Downspout Configuration: Calculate roof area to be drained by your gutter system and note roof pitches.

This spread sheet will help you calculate the gutter width and maximum distance between downspouts based on your maximum rainfall, roof area, and style of gutter. There are two major factors to consider when deciding a gutter design.

Jan 18, 2024 · What Size Gutters Do I Need? Before knowing the minimum gutter size that you can install on your roof, let’s walk you through common gutter styles and sizes first. Standard Gutter Sizes. The two standard gutter sizes you’ll find on …

Use the tables below to size your gutters and downspouts according to your catchment area and potential maximum rainfall per hour. Note: I will err on the side oversizing gutters as I want all the rain I can get when it falls.

A printable PDF guideline when sizing your gutter for proper installation. Rules to follow when sizing outlets, sloping gutter, style considerations, and maximum lengths without expansion brackets. See RainFall Data PDF for Charts A and Charts …

Aug 1, 1999 · Determine the gutter needed to drain your watershed — Divide your favored gutter’s 1-in.-per-hour watershed (see the chart below) by the five-minute rainfall intensity (from the map above). This determines the maximum watershed level gutters can serve between downspouts.

DOWNSPOUT SIZING In sizing downspouts, the following considerations apply: 1. Downspouts of less than 7.00 sq in.(4515 sq mm) cross section should not be used except for small areas such as porches and canopies. 2. The size of the downspout should be constant throughout its length. 3. Downspouts should be constructed with conductor

Jul 21, 2023 · Knowing how to size gutters and downspouts means finding out how much water the roof will be able to drain during an intense downpour. The amount is usually the product of the drainage area, roof pitch factor, and the intensity of rain.

This app allows you to easily and accurately size downspout and gutters using the methods and formulas covered in SMACNA’s Architectural Sheet Metal Manual (ASMM). The Rainfall Wizard allows you to select the closet city to use the information from the ASMM tables.

Mar 16, 2024 · By dividing the total drainage area by the capacity of one downspout, you can estimate the number of downspouts needed. Can I use a larger downspout to reduce the number of downspouts needed? Yes, using larger downspouts can increase the drainage capacity, potentially reducing the number of downspouts required.

Feb 2, 2016 · Take the square footage of the drainage area and multiply it by the roof-pitch factor, as well as the maximum rainfall intensity. This number is called the adjusted square footage, and you can use it with the chart below to determine the recommended size of gutter for your home.

Mar 29, 2017 · “Gutters and Downspouts: Sizing Calculations” is the first of the AGS Online series and reflects the current standard of care in building design for this subject. It includes a step-by-step design process, ICC table and figures, and a sample design problem and solution.

Jan 31, 2025 · Assess your roof area, rainfall intensity, and downspout placement for the correct gutter size. Standard gutter sizes include 4-inch, 5-inch, and 6-inch options, with 8-inch gutters available for larger properties.

Knowing the effective area of your roof and the gutter flow capacity should enable you to go along to any guttering manufacturer or stockist and use their comparison charts to figure out what size guttering you need.

Dec 2, 2024 · In this guide, I’ll walk you through the process of sizing gutters and downspouts, covering all the factors you need to consider and providing actionable tips. Gutters and downspouts collect and direct rainwater away from your home. Here’s how they function: Gutters: Run horizontally along your roof edge, catching water as it flows down.

Your downspouts are one of your best defenses against prolonged water exposure. Without them, you’re at risk of developing a slab leak, mold infestation, or roofing failure. Definition and purpose of downspout drainage. Your drainage system is a multi-pronged structure that includes storm drains, drain lines, dry wells, and downspouts.

Mar 25, 2025 · Why Downspout Extensions Are Essential for Proper Drainage. Short or poorly placed downspouts often release water too close to your foundation, leading to moisture problems, basement leaks and erosion. Downspout extensions help by directing water at least 3–5 feet away from your home, reducing the risk of water pooling around your foundation.