Metacritic. Please lower the maximum spacing between downspouts to see this effect. 2.Increase the pitch of the gutter. To measure the length, climb your ladder and run your measuring tape from one end as far as it’ll go. As with gutters, a do… For more tips, including how to calculate the drainage area of your roof, read on! Each square inch of downspout cross section can drain 100 sq. spout drains 1,200 sq. Rain water problems Hello. 4. The need to call in the gutter experts may be even greater if you have a rectangular or an irregular cross-section gutter, … Suggestions. So a 2-in. Measure the distance from the end of your gutters to the ground and then an additional three to four feet out from that spot to determine the length of downspout that you need to install. Most roofs are symmetrical so you can enter the number of downspouts attached to the surface area that you just measured. You have three options: 1.Get 7- or 8-inch gutters. Subtract 6 to 7 inches and this will become the length of the downspout. DIY's should hold all drainpipe colours and sizes, so if you have the end spout take that with you.....or measure across it. Downspout Sizes must not exceed the bottom width of the gutter. Detail drawings and dimensions will follow the table for each of the gutter designs. To choose the right size gutters for a building that doesn’t already have them, you can quickly calculate the drainage area of the roof and adjust for pitch and rainfall to find the adjusted square footage. The minimum pipe size needed for a catchment area of 23 \(m^2\) is calculated to be 23 \(cm^2\) using the rule of thumb in Equation 6 as shown below: The needed cross-sectional area of gutter is 23 \(cm^2\). Press a downspout adapter into a 3x4-inch reducer coupling and slip it onto the bottom end of the downspout. The Downspout and Gutter Sizing Calculator is located on the Tools, CAD, and Apps page of the SMACNA website. The outlet must either be directly above the gully, for a 'Front Offset’ (i.e. Then extend your measuring tape from the roof edge to the house wall to find the distance between them. To convert that cross-sectional area to the diameter of the pipe, remember that the formula for the area of a circle (which is the cross-section of a pipe) is the following: unlocking this expert answer. — Look at your rooftop to determine what part of the roof you need to measure. Measure the length from where your downspout currently drops to where you wish to extend it. Pitch your gutters by 1/8 in. I got the barrel all set up and marked the downspout to start cutting, but part of that required knowing what size downspout I'm working with, either 2x3 or 3x4. % of people told us that this article helped them. Outlet Sizing and Spacing Your gutter system will perform its best when a proper outlet size is chosen to drain a given roof area. Gutter and Downspout Combinations. 3. Measure from the top to the ground, then add 4 feet (1.2 m) to each downspout to account for the angled extension at … However, you can adapt a 3"x4" downspout to a standard 5" K Style gutter. When you're installing gutters, you want to use as few sections as possible, so purchase a long piece that's as close as possible to what you need, then get a shorter section to make up the difference. It will be the part that slopes toward the downspout where the rain barrel(s) will be located. Use a minimum width of 4 in., except for canopies and small porches. The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. You only need a ladder, chalk, tape measure, level, paper, and pen! 2. Any downpipe needs to run down the wall in line with the subsurface drain/gully below it -  in order to join it or 'let out' into it. CNET. Roof area, the locale's rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Related Posts. Press a downspout adapter into a 3x4-inch reducer coupling and slip it onto the bottom end of the downspout. Round pipe systems are more flexible to install, as offsets can be “swung” or twisted into alignment with the gully position. This rule of thumb works for most situations, but ultimately the sizing depends on the strength of local storms, the pitch of the roof, and the slope of the gutter. You can use the same method to calculate the downspouts on your gutter system. A round downspout is slightly more efficient in draining water … For additional information, please see below. How do you determine the size drain to move downspout water away? Continue up the side of your home and as you get higher, climb up your ladder to continue the measurements. If you really can’t stand to see another ad again, then please consider supporting our work with a contribution to wikiHow. Make a third mark 2 inches shorter than the first. All Rights Reserved. If you have a simple gable-end roof, you only need to multiply the length of one side by the width of the same side, then multiply the sum by 2 to get the total square footage. What if the runoff is off the chart for standard gutters? Add the two measurements together to find the total length for each downspout. To properly size gutters … Start from the ground and measure up the side of your home. The above recommendations assume that you have properly sized downspouts every 40 feet. On average downspout will cost $3 to $5 per lineal foot. Now architects, engineers, designers, and contractors can easily and accurately size downspouts and gutters according to the specifications in SMACNA’s “Architectural Sheet Metal Manual,” 7th edition, 2012. Using a ladder will save you time with these measurements. Repeat these marks on the other side of the downspout. Many gutter contractors do so. ft., and a 3-in. Determine the size of your downspout. The number of downspouts will affect a gutter's ability to handle water. TV.com. He said the rule of thumb he was taught is 1 square inch of downspout and/or drain line for every 2 squares of roof area. 2. Repeat the process, measuring from each new chalk mark until you’ve reached the end of your gutters. You can measure pitch with a 2-foot level and a tape measure: Hold one end of the level against the roof, level it, and then measure the distance between the roof and the underside of the level at its midpoint, which gives you a 12-inch run. 4. Note that this application is intended as a aid only, and is provided as is. Watershed area is determined by square footage and incline. ft. Round Pipe To find the right size, first figure out if you need to measure the outside or inside diameter, then measure it with a ruler or tape measure. For example, a 6-inch K-style gutter requires a 3" x 4" downspout while a 5-inch K-style gutter uses a 2" x 3" downspout. Support wikiHow by Transfer your measurement to the downspout and make a mark on both sides with your pencil. Continue around the perimeter of your home until you have measured and recorded the entire length of the existing gutters. For additional information, please see below. However, that does not include all of the additional downspout accessories. More rain in your area and more square feet that need to be drained require larger downspouts. 16 July 2020. Nan W. on Mar 27, 2018. DOWNSPOUT SIZING In sizing downspouts, the following considerations apply: 1. Detail drawings and dimensions will follow the table for each of the gutter designs. Step 1 - Measure the Length of the Downspout. When it comes to size, a homeowner will have to choose from gutter size (the measurement of the top opening), downspout size (length and width or diameter), and thickness. power miter saw. Whether you want to replace your existing gutters or add gutters to a new home, you’ll need to know the right measurements. Loose-fitting pipes will leak and spread water close to the foundation walls. K-Style sizes will typically range from 5" to 6". Depending on the size of the house and the amount of local rainfall, a 5 inch gutter paired with a 3 x 4 downspout might a more practical combination. A ‘Plinth Offset’ may also be needed at the bottom of the downpipe to allow it to follow the contours of the wall. Fourth: We'll discuss your downspout size, location and a few comments. Downspouts should be constructed with conductor Using a ladder will save you time with these measurements. Cut a piece of pipe to match with a handsaw, hacksaw or 12-in. For instance, a 2 in (5.1 cm) gap means the roof has a 2-in-12 pitch and a 6 in (15 cm) gap means the roof has a 6-in-12 pitch. Match your downspouts to the gutter size you chose in Step 7. Gutter downspout sizes are 3 to 6 inches. He is skilled at constructing decks, railings, fences, gates, and various pieces of furniture. All prices shown are excluding VAT which will be added at checkout. Offset of more than 10 ft(3.0 m) can affect drainage capacity. To limit the effects of thermal expansion in gutters, 50 ft. (15 m) is a practical maximum gutter length to be served by a downspout. Barry Zakar. Thanks to all authors for creating a page that has been read 39,403 times. Place a 90-degree elbow in the trench directly below the coupling and measure the distance between the two fittings. Then measure each the rest of the downspout either with a tape measure extending it up to your home -OR- Equate each floor as 8-10 feet of guttering downspout For example, if this was a two-floor home, this downspout would be approximately 24’ in length. TVGuide.com. Since each side of the roof is 100' square, or 10,000 square feet, that would work out to 50 square inches that are required.. Downspout Sizes must not exceed the bottom width of the gutter. The outlet must be level with the pipe when attached to the wall, the 'projection' is only to the left or right i.e. For instance, if the square footage is 1,000 feet (300 m), the roof-pitch factor is 1.2, and the intensity is 5.7, multiply 1,000 x 1.2 x 5.7 to equal 6,270. Downspout sizes must not exceed the bottom width of the gutter. This article has been viewed 39,403 times. 3. If you have downspouts, measure them from the top to the ground, then add 4 feet to account for the angled extensions. 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