ft. of roof area. The answer is I was holding my angle level on the wrong scale. Egad! Tan (45 deg) = 1.00 - that is, we will travel 12" up for 12" of run. Dr. Butler received his PhD in General Physics in 2004. ISBN-13: 978-0471331728, Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) So really I could go just 9 degrees off of flat. But to understand how some people use a flat or horizontal projection of a roof to guess at roof area, here is the procedure. For more accurate angle or slope measurements, for example on a rough shingle surface outdoors, use a straight edge between the angle finder level and the roof surface to give a longer footprint for the sensor. A roof pitch multiplier, also known as a roof pitch factor, is a number that, when multiplied by the area covered by a sloped roof, gives the actual area of the roof. A long-standing use of the framing square that is missed by many new carpenters is the rafter table imprinted right on the framing square itself. How to Calculate the Roof Area Using the Building Square Footage & the Pitch of the Roof. 3. 81-50643. R4413.6.5 Parapet wall … EO: Measure or estimate the increase in footprint size given by the roof eaves overhang. Multiply by the square footage of a single floor of your house. Measure straight down to the roof surface from the mark you just made - the blue line in our sketch. Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Handbook of Building Crafts in Conservation, Jack Bower, Ed., projected roof area in accordance with Table 1106.3 . (25 mm/hr) rainfall that varies with diameter, for example, 3 in. Young, Wiley (March 21, 2008) Tan-1 (1.43) = 55 deg. Divide your roof pitch by 12. Cherilyn A. Hatfield, US Department of Agriculture, US Forest Products Laboratory, Research Note FPL-RN-0301, NRCA - National Roofing Contractors Association - Website: www.nrca.net 10255 W. Higgins Road, Suite 600, Frankly, as we illustrate beginning at ROOF MEASUREMENTS, there are some easy and accurate alternatives that can give a good estimate of roof area while making measurements only from the ground. Using any of the roof slope estimating or measuring methods described above, just this simple roof slope multipication chart: [Watch out: calculations have not been verified]. something's crazy here. For a 12-inch unit-length roof we calculate the hypotenuse dimension to obtain the roof true width for each roof slope. Jerrold E. Winandy This calculation will give a solid estimate for a single slope roof and a simple gable roof with a single pitch. The roof area (RA) is calculated easily: we multiply the Roof Length (c) (which is the sum of building length plus the gable end overhangs of the roof) by the Roof Width of slope (a) that we just figured out above when we computed the hypotenuse of the roof triangle (that's why we needed the roof rise number). 2 inches b. E.g. You need: a tape measure and, if there is no horizontal siding installed, you will need a carpenter's level. St. James Press, 1998. This problem has been solved! Hold the carpenter's level in a horizontal position with one end touching the roof surface. All of these examples work best for a simple gable end roof. You're in luck, because math can rescue you from pulling out that ladder and tape measure. If we start counting siding at a horizontal lilne even with the lower roof edge or eaves and count up to the ridge, we've got a close guess at the total roof rise. Griffin, Mcgraw-Hill (Tx); 2nd edition (July 1982), ISBN-10: 0070247838, ISBN-13: 978-0070247833, Concrete Folded Plate Roofs, C. Wilby PhD BSc CEng FICE FIStructE (Author), Butterworth-Heinemann, 1998, ISBN-10: 0340662662, ISBN-13: 978-0340662663. This would yield 1/3.) Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly. Where vertical walls project above a roof so as to permit storm water to drain to the roof area below, the adjacent roof area shall be permitted to be computed from Table 1101.12 as follows: For one wall - add 50 percent of the wall area to the roof area figures. Multiply the hypotenuse by the length of the roof. Remember to include in (a) the amount by which the roof extends out over the building walls - its eaves. There are 5 easy steps to figure out how many drains your commercial roofing project will need. A complete table of roof slopes expressed as rise / run, slope, and grade as well as roof walk-ability according to steepness is given. ft. roof area, the 3 inch rainfall will produce 18,700 gallons in one hour at the rate of 312 gallons per minute. For more complex roof lines with multiple pitch angles, it's a little more complicated but the same steps can be followed; just break down the roof into separate sections with a different square footage for each different pitch angle. Anderson, 1961 (hard to find), Corrugated Iron, Building on the Frontier, Simon Holloway. I can check this result against the rise per foot we got above. Tan -1 is the inverse of a Tangent which will convert any rise/run ratio back to degrees. The minimum slope of horizontal branches shall be one-eighth unit vertical in 12 units horizontal (1-percent slope) unless otherwise approved. Example: A 200 ft. x 250 ft. = 50,000 sq. ROOF MEASUREMENTS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice. To use the direct roof slope measurement procedure shown just abofe, in addition to safe access to a roof that won't be damaged by touching or walking on it, you need: a tape measure and a carpenter's level. While it is possible to estimate the amount of necessary materials using only the total roof area measurement, as can be seen from the table, depending how large the pitch of the roof, the actual area of the roof can differ by up to 2.236 from the measured total area at a pitch of 24/12. The result is the surface area of the sloping roof. Here we describe various methods for measuring all roof data: roof slope or pitch, rise, run, area, and other features. In sizing roof drains and storm drainage piping, one-half of the area of any vertical wall that diverts rainwater to the roof shall be added to the projected roof area for inclusion in calculating the required size of vertical conductors, leaders and horizontal storm drainage piping. lower roof projected roof area 50 × 50 = 2,500 sq.ft. Question: If The Mean Annual Rainfall Is 252 Cm .A Horizontal Projected Roof Area Is 460 M² . ISBN-13: 978-1405161039, Built-Up Roof Systems, Manual, C.W. Using a 10,000 sq. Historic Preservation Technology: A Primer, Robert A. Generally, roofing types and roofing products are typically divided up into two primary categories, steep slope roofing and low slope roofing. For example, if the sloping surface is 11.18 feet wide, and the roof is 30 feet long, the sloping area is 335.4 square feet -- 11.18 x 30 = 335.4. Storm drainage systems shall be permitted to be sized using the roof area served by each of the drainage system.Maximum allowable roof areas with various rainfall rates are listed in Table 110 1.8 and Table 1101.12, along with the required pipe sizes. Roof pitch is given as the number of inches in height change over the distance of one foot. Roof width (a): This data allows us to calculate the roof triangle as we know two sides (b) and (c) of the three sides of a right triangle (the red lines in our photo at above left). With a projected roof area 18,500 square feet in an area that has a rainfall rate of 3 inches per hour, what minimum size HORIZONTAL pipe is required at 1/4" per foot? Congress Catalog Card Nr. Time permitting Dr. Butler also enjoys volunteering as a science fair judge for the local high school and junior high school age competitions. 9" 12" 6" 4' 4' 6" 12" 19' 16' 26' 30' 5' 5' 5' 12" 20' 30' F I G U R E 2 - 3 Horizontal projection of a complex roof. This is a low slope roof, how can it be sloping 81 degrees? RA: Obtain the approximate roof slope to convert Roof Footprint to Roof Area - RA using the ROOF SLOPE MULTIPLIER TABLE given below. The Tangent of any angle expressed in degrees is nothing more than a ratio: I'll show that even if we screw up we can still come out ok finding the angle and then the rise and run of a roof using the angle finding level. A r = horizontal projected area of roof top structure or equipment, ft 2 (m 2) The components and cladding pressure on each wall of the rooftop structure shall be equal to the lateral force divided by the respective wall surface area of the rooftop structure and shall be considered to act inward and outward. Note: appearance of your Comment below may be delayed: if your comment contains an image, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. on my angle level. Roof length (c): Measure or step off building gable end width. The procedure is like the on-roof example above, but flipped upside down. This distance (green arrow in our photo) is the roof rise in inches per foot of run. Here, any means all. The third side of the triangle, its hypotenuse or the sloping surface of the roof, or side is (a) which is calculated as follows: a2 = b2 + c2 - the square of the length of the hypotenuse (a) equals the squares of the lengths of the opposite sides of a right triangle (b) and (c). The minimum size of a horizontal rain water pipe with a 1/8 inch per foot slope, serving a roof with a projected area of 10,700 square feet, and a rainfall rate of 2 inches per hour is _____. Tan -1 (1.73) = 60 deg.Put another way, a roof with a slope of about 27 in 12 has a Rise/Run of 27/12 = 1.73 (approximately), So Tangent in its simple use here is just the ratio of increase in unit height for travel in unit run. Then from that point on our level we measure the distance straight up to point of contact with the roof surface. RL = Roof Length = dimension of the roof from one gable end of the building to the other. Green Roof Plants: A Resource and Planting Guide, Edmund C. Snodgrass, Lucie L. Snodgrass, Timber Press, Incorporated, 2006, ISBN-10: 0881927872, ISBN-13: 978-0881927870. It helps to have a steady hand and to read the instructions on exactly where to read the inches on the bottom scale in the folding rule triangle that we show at left. Off (1963), ASIN: B0007FTV2Q, Tile Roofs of Alfred: A Clay Tradition in Alfred NY, "Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE, Wood Shingle Roofs, Care and Maintenance of wood shingle and shake roofs, (EC), Stanley S. Niemiec (out of print). We describe all of them here. 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