Practically speaking though, a common gutter size is usually selected and downspout spacing is equal for most buildings. Welcome to Gutter Supply, your online reference for gutters, gutter machines, gutter guards and accessories. To figure out the right roof gutter sizing, our experts have come up with some math done easy for you. For a … When you are completing a gutter replacement, the first point to note is that gutters come in different sizes. Note: When reviewing data from the NOAA Databases you will need 60 minute duration data to use our SAF GPM Calculation Tables. Roof area, the locale's rainfall intensity and gutter capacity determine how many square inches of downspout are needed. First you’ll need to calculate the square footage of the gutter’s drainage area. But this isn’t the whole story. The SAF Perimeter Systems Gutter/Downspout Capacity Table (click to enlarge) relates Downspout Size to Gutter Sizes. The IRC proposal is RB311-13, and can be found on page … Downspouts should be constructed with conductor heads every 40 ft(12.2 m) to admit air and prevent vacuum. Look up the value(s) applicable to your project and multiply by your total roof area(s) to be drained. The standards mentioned previously regarding container strength and size are standards set by the ISO organization and International Maritime Organization. I often receive requests to write a column on certain issues. Requirements for reroofing projects are found in both the International Building Code (IBC) and the International Existing Building Code (IEBC). The capacity of a sloped rectangular gutter may be approximated by using a gutter cross section area not less than that of a semicircular gutter and a depth to width ratio of at least 0.75. Roofing Contractors. Commercial roof structures can be complex, consisting of many areas, shapes, and configurations. Unfortunately, due to government budget constraints, mapping for all the U.S. has not been completed. Gutter Sizing … Metal Roofing Contractors. Water capacity values of a gutter & downspout system is calculated using the height (head) of water a gutter can hold, the outlet (orifice) size of the downspout, and the quantity of downspouts used.  It is possible to use a mix of gutter sizes, a mix of downspout sizes, and quantities to accommodate the theoretical gallons per minute draining from a roof during in-climate weather. Offset of more than 10 ft(3.0 m) can affect drainage capacity. K-Style 5-inch 5,520 square feet 6-inch 7,960 square feet Half-round 5-inch 2,500 square feet 6-inch 3,840 square feet For example: A house in Chicago has a roof whose actual drainage area is 1,000 square feet. Then use the chart below to see what size gutter you need. Total area for 1st story roof should be calculated as 15,000 square feet (see example 1, right). Continuing with our example in the last step, we know our gutter & downspout system may be subject to as much as 1,880 gallons per minute.  For design purposes and aesthetics, let’s assume you have selected an 8″ gutter.  Also assume our guttered eave is 335 linear feet.  From the table, we find that a 5″x5″ downspout will discharge 260 gallons per minute.  At 1,880 gpm’s, we will need 8 downspouts to handle the rainfall (1,880/260=8 downspouts, rounded up). 8370 Highway 78, Villa Rica, GA 30180 | Phone: +1-800-334-9823 | Fax: +1-770-942-4173 Their values are formulated on a roof’s pitch. 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: Gutter Sizing Step 1 – Determine roof area to be drained 3. Without question you will run into gray areas, when in doubt, please call us toll free 1-800-334-9823 and we will gladly assist you with your sizing requirements (see example 3, right). IBC Roofing. Although it is commonly believed the International Building Code (IBC) is consistent globally it is simply not reality. Calculator is based on Chapter 1 of SMACNA's Architectural Sheet Metal Manual 7th Edition (ASMM). 37 37The width at the top is 74 mm 100mm 37 51 mm 77mm. ... Gutters. (If a roof’s various drainage areas call for different size gutters, … HORIZONTAL GUTTER SIZING For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 gallon per minute = 3.785 L/m, 1 inch per foot = 83.3 mm/m. furthermore, the standard norm for gutters among many in the rain carrying industry is to allow 1 square inch of outlet opening in the gutter … You must use all of the requirements of the IBC or all of the requirements of the IEBC. Downspout sizes must not exceed the bottom width of the gutter. 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