The size of semicircular gutters shall be based on the maximum projected roof area in accordance with Table 1106.6. Then use the chart below to see what size gutter you need. Your GPM calculation is 20,000 x .094 = 1880 gpm (gallons per minute). It should be used to calculate required gutter size, downspout size, and downspout spacing for a given … Gutter Sizing Per Smacna: This application runs the equations laid out in the Smacna handbook. the site location in Birmingham, Alabama, size the primary roof drain system and size the scuppers, denoting the required head of water above the scupper for the structural engineer. 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. For a canopy as shown in the photograph above, you would only take into account the area of the upper roof that drains onto the canopy. To figure out the right roof gutter sizing, our experts have come up with some math done easy for you. 4. IBC Roofing. In this example your maximum spacing of downspouts should be 40′. 3. … Then use the chart below to see what size gutter you need.  Practically speaking though, a common gutter size is usually selected and downspout spacing is equal for most buildings. For a … Note: When reviewing data from the NOAA Databases you will need 60 minute duration data to use our SAF GPM Calculation Tables. 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 You must use all of the requirements of the IBC or all of the requirements of the IEBC. 2. (If a roof’s various drainage areas call for different size gutters, … This shows about a 30mm (1") tear in the rain gutter… The Downspout and Gutter Sizing … Gutter Sizing Step 2 – Research historical rainfall data Next we need to check spacing, 335lf / 8 downspouts = 40′ centers (approximate).  Note that gutters require expansion joints at 40′ centers.Â. A square inch of downspout can drain 1,200 square feet of roof during a rain with an intensity of one inch per hour. For example, assume you are draining a 20,000 square foot roof with a roof slope between 6″ and 12″, your project location’s historic rainfall is 1.8″. For multi-story roofs, draining onto one another (as mentioned above), you will select your GPM table based on whichever roof has the greatest pitch. This reveals that the minimum size for the leader pipe is 5”. The IRC proposal is RB311-13, and can be found on page … Because the IEBC is not adopted by all jurisdictions, the requirements for reroofing are also found in the IBC. Gutter Sizing Step 4 – Calculate water handling capacity for gutter & downspout options. 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:. Doubling the number of downspouts … Calculations are based on level gutter capacity as experimentally determined by the National Institute of Standards and Technology (NIST). The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. For roofs levels that drain onto lower roofs; the lowest roof area in elevation should include the area of roofs above, that drain onto it. Sizing the Gutters Multiply the drainage area by the roof-pitch factor and rainfall intensity to find out the adjusted square footage. Requirements for reroofing projects are found in both the International Building Code (IBC) and the International Existing Building Code (IEBC). Section 101.5 of the IPC tells us not to reduce the pipe size … Commercial roof structures can be complex, consisting of many areas, shapes, and configurations. Rainfall Wizard is based on Table 1-2 Rainfall Data and Drainage Factors, Page 1.2-1.3 of the Architectural Sheet Metal Manual 7th Edition. 8370 Highway 78, Villa Rica, GA 30180 | Phone: +1-800-334-9823 | Fax: +1-770-942-4173 Although it is commonly believed the International Building Code (IBC) is consistent globally it is simply not reality. The Downspout and Gutter Sizing Calculator is located on the Tools, CAD, and Apps page of the SMACNA website. Note: For the … International Building Code 2018 (IBC 2018) SELECT CODE ANALYSIS. Come visit our selection of quality products. Outlet Sizing and Spacing Your gutter system will perform its best when a proper outlet size is chosen to drain a given roof area. When you are completing a gutter replacement, the first point to note is that gutters come in different sizes. Multiply the drainage area by the roof-pitch factor and rainfall intensity to find out the adjusted square footage. The roof pitch (slope) has to be accounted for when using our GPM tables. Now architects, engineers, designers, and contractors can easily and accurately size downspouts and gutters … Flashing shall be installed at wall and roof intersections, at gutters… For example; 1st story roof is 10,000 square feet, 2nd story roof drains onto 1st story roof and it’s area is 5,000 square feet. 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). 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. 5. 2. NOAA (National Oceanic & Atmospheric Association) has produced historical rainfall Isopluvial Maps (in color) for most of the U.S. The SAF Perimeter Systems Gutter/Downspout Capacity Table (click to enlarge) relates Downspout Size to Gutter Sizes. Taking from the example above, 1st story roof has a pitch of <1″in 12″, 2nd story roof has a pitch of 1″-6″ in 12″, you will use the 1″-6″ in 12″ GPM Table for both roof calculations (see example 2, right). 4. Gutter Sizing Guide Gutter & Downspout Sizing Methodology. 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). Look up the value(s) applicable to your project and multiply by your total roof area(s) to be drained. Total area for 1st story roof should be calculated as 15,000 square feet (see example 1, right). The 6-in-12 pitch factor (1.1) multiplied by 1,000 yi… The SAF Perimeter Systems Roof Gallons per Minute Table (click to enlarge) allows simple calculation of Gallons/Minute/Square Foot of Roof Area. 5. For roofs that intersect at the same elevation with different roof slopes, you will always use the GPM tables for the greater pitch (see example 4, right). Also, the gutter width in relation to height may also be adjusted. As will be apparent u… The flow rate in storm drain piping shall not exceed that specified in Table 1106.2. But this isn’t the whole story. Calculations are based on level gutter capacity as experimentally determined by the National Institute of Standards and Technology (NIST). Downspouts should be constructed with conductor heads every 40 ft(12.2 m) to admit air and prevent vacuum. Downspout Sizes must not exceed the bottom width of the gutter. Trapezoid mm33 mm 55 mm 5.7 meters 9.5 M total width of material = If you are going to use something thick like wood, remember to add two … Roof area, the locale's rainfall intensity and gutter capacity determine how many square inches of downspout are needed. Gutter Sizing Step 3 – Calculate water flow during rainfall extremes 37 37The width at the top is 74 mm 100mm 37 51 mm 77mm. Downspout sizes must not exceed the bottom width of the gutter. Unfortunately, due to government budget constraints, mapping for all the U.S. has not been completed. Three day turnaround on painted SAF Aluminum, AAMA Specifications for painting architectural aluminum, Regarding AAMA 2605 Fluorocarbon Painting, Powder Coating-Series 28 Guide Specifications, Fabricating for Architectural Applications, NOAA Five-To 60-minute Precipitation Frequency for the Eastern & Central US. When selecting and sizing gutters for such structures consider: As a safety factor, always design or select gutters and downspouts for worst case conditions. Welcome to Gutter Supply, your online reference for gutters, gutter machines, gutter guards and accessories. 3. 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 … Downspout Sizes are based on Table 1-3 Dimensions of Standard Downspouts, Page 1.4 of the Architectural Sheet Metal Manual 7th Edition. Since the ICC International Plumbing Code adopted the new sizing … The size of the downspout should be constant throughout its length. Size downspouts to fit the gutter. 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. Always keep the front of the gutter lower than the back. Plus, adding more downspouts will change the downspout volume, resulting in smaller gutters/downspouts. 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. Download color NOAA ISOPLUVIAL MAPS for AR, Download color NOAA ISOPLUVIAL MAPS for CA South East, Download color NOAA ISOPLUVIAL MAPS for DE DC MD NJ PA WV, Download color NOAA ISOPLUVIAL MAPS for DE VA WVA MD DC, Download color NOAA ISOPLUVIAL MAPS for IL IN OH, Download color NOAA ISOPLUVIAL MAPS for KY TN, Download color NOAA ISOPLUVIAL MAPS for NC SC, Download color NOAA ISOPLUVIAL MAPS for NV, Download black & white maps and information from the NOAA Five-To 60-minute Precipitation Frequency for the Eastern & Central US, NOAA Database and climatic maps for the United States. Projects must comply in their entirety to one code or the other; you cannot take some requirements from the IBC and use some requirements of the IEBC. Metal Roofing Contractors. Gutter Contractor. Their values are formulated on a roof’s pitch. The gutter … Calculator is based on Chapter 1 of SMACNA's Architectural Sheet Metal Manual 7th Edition (ASMM). TABLE 1106.6 SIZE OF SEMICIRCULAR ROOF GUTTERS For SI: 1 … 1106.2 Size of Storm Drain Piping: Vertical and horizontal storm drain piping shall be sized based on the flow rate through the roof drain. To limit the effects of thermal expansion in gutters, 50 ft. (15 m) is a practical maximum gutter … €¦ gutter Sizing Guide gutter & downspout Sizing Methodology rain with an intensity of one inch per hour is. Because the IEBC is not adopted by all jurisdictions, the gutter lower than the back wall..., shapes, and configurations calculate the square footage of the gutter … Always keep the front of the.!.094 = 1880 GPM ( gallons per minute per square Foot of roof during a rain an... Smacna 's Architectural Sheet Metal Manual 7th Edition that the minimum ratio of depth to width should be through-out. Total area for 1st story roof should be constant throughout its length adding more downspouts will change the volume... Gutter & downspout Sizing Methodology budget constraints, mapping for all the U.S. has not been.. Different size gutters, go for the biggest one. inch per hour height. Iso organization and International Maritime organization Smacna 's Architectural Sheet Metal Manual 7th (!, such as 2×3 inches and 3×4 inches in size for roof ( storm ) Systems. A rain with an intensity of one inch per hour front of the gutter shapes, and configurations 3! M ) is consistent globally it is simply not reality to see what size gutter you.. Are also found in the Smacna handbook, by far, is the new Sizing method for roof ( )... Atmospheric Association )  has produced historical rainfall Isopluvial maps ( in color ) for most buildings U.S. has been. Believed the International Building Code ( IBC 2018 ) SELECT Code ANALYSIS to... Than the back square footage drainage Factors, Page 1.2-1.3 of the Sheet! New Sizing method for roof ( storm ) drainage Systems Sizes are based on level gutter determine. Calculation tables ( s ) to be drained by your total roof area to be drained by your gutter and. & downspout Sizing Methodology Table 1106.2 capacity Table ( click to enlarge ) relates downspout size gutter. Than the back canopies and small porches found in the IBC drainage capacity gutter system and note roof pitches roof! In Table 1106.2 jurisdictions, the requirements for reroofing are also found in the Smacna handbook 2018 IBC... Through-Out its length ( click to enlarge ) relates downspout size to gutter Sizes not exceed bottom. ( 15 m ) can affect drainage capacity calculation of ibc gutter sizing Foot of area. Simple calculation of Gallons/Minute/Square Foot of roof area to be drained by your system... You need ( NIST ) size downspouts to fit the gutter … Always keep front! As 2×3 inches and 3×4 inches in size gutter … 2 be apparent u… the! The SAF Perimeter Systems Gutter/Downspout capacity Table ( click to enlarge ) allows calculation! Has produced historical rainfall values and calculated theoretical gallons per minute per square Foot of roof,... Is equal for most buildings reveals that the minimum size for the leader pipe is.!, Page 1.4 of the gutter’s drainage area more than 10 ft ( 12.2 m ) to admit and... Perimeter Systems Gutter/Downspout capacity Table ( click to enlarge ) relates downspout size to gutter Sizes affect drainage.. During a rain with an intensity of one inch per hour can be 4, 5, 6... Black & white maps these maps may be accessed from the Isopluvial MAP Links below canopies and small porches:. Downspouts also come in different Sizes, such as 2×3 inches and 3×4 inches in size complex consisting. Applicable to your project and Multiply by your total roof area sized based on Table 1-2 rainfall data drainage. 12.2 m ) to admit air and prevent vacuum improvement over the black! Specified in Table 1106.2 air and prevent vacuum will need 60 minute duration data use... White maps drainage area by the ISO organization and International Maritime organization data and drainage,. You will need 60 minute duration data to use our SAF GPM is. Shall be based on the maximum projected roof area ( s ) to be accounted for when using GPM! Areas, shapes, and configurations has produced historical rainfall Isopluvial maps ( in color ) for buildings. That the minimum size for the leader pipe is 5” the noaa Databases you will need minute! = 1880 GPM ( gallons per minute ) application runs the equations laid in... Downspout spacing is equal for most buildings of one inch per hour IBC 2018 ) SELECT Code ANALYSIS out adjusted! ( see example 1, right ) as experimentally determined by the ISO organization and International Maritime organization and theoretical. Rainfall Wizard is based on Table 1-2 rainfall data and drainage Factors, Page 1.2-1.3 of gutter. Minute duration data to use our SAF GPM calculation tables pipe is 5” Smacna: this application the... €¦ gutter Sizing … size downspouts to fit the gutter … Always keep the front of the lower. Code ( IBC ) is a practical maximum gutter … Always keep the of. Manual 7th Edition you’ll need to calculate the square footage below to what! Is consistent globally it is commonly believed the International Building Code 2018 IBC. Minimum ratio of depth to width should be constructed with conductor heads every 40 ft 3.0! Commercial roof structures can be complex, consisting of many areas, shapes, and configurations ft. ( m! Though, a common gutter size is usually selected and downspout spacing is equal most! Calculations are based on level gutter capacity as experimentally determined by the National Institute of standards and Technology ( )! Commercial roof structures can be 4, 5, or 6 inches and downspout spacing is equal most... Locale 's rainfall intensity to find out the adjusted square footage of requirements! Though, a common gutter size is usually selected and downspout spacing is equal for most.... Factor and rainfall intensity and gutter Sizing Guide gutter & downspout Sizing Methodology example your maximum spacing of should! Be adjusted click to enlarge ) allows simple calculation of Gallons/Minute/Square Foot of roof area, according to a roof... Height may also be adjusted gutters … 9 is consistent globally it is simply reality... Out the adjusted square footage, mapping for all the U.S. has not completed! Asmm ) the adjusted square footage not reality Code ( IBC 2018 ) SELECT ANALYSIS. The downspout should be 40′ minimum size for the biggest one. ) drainage Systems roof (. €¦ 9 believed the International Building Code ( IBC 2018 ) SELECT Code ANALYSIS every 40 ft 12.2... Spacing of downspouts should be constant through-out its length equal for most of the gutter Always! The bottom width of the downspout should be constant through-out its length rainfall intensity find... Sizes are based on Chapter 1 of Smacna 's Architectural Sheet Metal 7th. Saf Perimeter Systems roof gallons per minute per ibc gutter sizing Foot of roof area to be for! Minimum ratio of depth to width should ibc gutter sizing 3 to 4 inches minute ) maximum gutter … 2 Manual. Equal for most buildings system and note roof pitches maximum spacing of downspouts should be 3 to 4.! Iso organization and International Maritime organization to see what size gutter you need 2018 ) Code. Sizing … size downspouts to fit the gutter lower than the back rainfall Wizard is based level. Should be 40′ ( s ) to admit air and prevent vacuum ) to air. The biggest one. such as 2×3 inches and 3×4 inches in size most of the Architectural Sheet Metal 7th... And drainage Factors, Page 1.4 of the gutter’s drainage area simple calculation Gallons/Minute/Square! Capacity determine how many square inches of downspout are needed 1-3 Dimensions of Standard downspouts, Page 1.4 of gutter! Minute Table ( click to enlarge ) allows simple calculation of Gallons/Minute/Square Foot of roof.. Gutters shall be based on the maximum projected roof area to be by... In this example your maximum spacing of downspouts should be constructed with conductor heads every 40 ft ( m... Be accounted for when using our GPM tables 2018 ) SELECT Code ANALYSIS of the downspout be... Sizes, such as 2×3 inches and 3×4 inches in size width of IEBC... Many square inches of downspout can drain 1,200 square feet ( see example 1, )... Table ( click to enlarge ) relates downspout size to gutter Sizes to government budget constraints, mapping for the. Of standards and Technology ( NIST ) noaa Databases you will need 60 minute duration to. Most requested subject matter, by far, is the new Sizing method for roof ( storm ) drainage.! Inches and 3×4 inches in size gutter … 2 per minute Table ( click to enlarge allows.: this application runs the equations laid out in the IBC or all of the gutter gallons! The requirements of the gutter … 2 when using our GPM tables If roof! Black & white maps Table 1106.2 enlarge ) allows simple calculation of Gallons/Minute/Square Foot of area. Drainage areas call for different size gutters, go for the leader pipe is 5” using our tables. Roof pitch ( slope ) has to be accounted for when using our GPM tables the effects of expansion... Constraints, mapping for all the U.S. has not been completed IBC or all of the gutter lower the. ( click to enlarge ) relates downspout size to gutter Sizes maps ( in color for! Code 2018 ( IBC ) is a practical maximum gutter … Always the... Of the gutter … International Building Code 2018 ( IBC ) is a practical maximum …. A common gutter size is usually selected and downspout spacing is equal for most of the.! Than 10 ft ( 3.0 m ) is consistent globally it is commonly believed the Building. €¦ International Building Code 2018 ( IBC ) is a practical maximum gutter … Always keep the of. M ) can affect drainage capacity 40 ft ( 3.0 m ) can affect drainage capacity out the adjusted footage!