Half round and K-style gutters would be the two most frequent gutter types found on residential houses. Each gutter design comes in two dimensions and each has the capability to transfer a particular quantity of water from your roof. Correctly matching the size and style of a gutter to your house necessitates careful dimensions and exact calculations to ensure the gutters don’t float through heavy or prolonged periods of rain.
Set up an extension ladder from one border of your home’s roof. Be certain that the ladder extends at least three feet beyond its upper resting point against the roof edge. Place a torpedo level and tape measure in a tool pouch to keep your hands free. Climb the ladder, maintaining three points of contact at all times. For example, keep two feet and a hand or two hands and one foot on the ladder at all times.
Place the torpedo level on the roof together with the amount body sitting perpendicular to the roof peak. Adjust the amount until it reads degree. Hold an extended tape measure at the close of the level that isn’t touching the surface of the roof. Transfer the tape measure so that its blade is sitting right from the end of the degree. Measure the distance between the roof and the bottom of the level. The dimension will determine the pitch of the roof. For example, a distance of 6 inches would signify that the roof includes a 6-in-12-inch pitch.
Measure the length and width — distance from the eave to the peak of the roof — of one side of the roof. Multiply the 2 measurements to find the area of the roof section. For example, if the length of the roof section is 50 feet and the width is 25 feet, the area is 1,250 square feet. Determine the area of each roof section. When determining the area of a triangular hip roof, then use the formula: length times width divided by 2.
Locate the roof pitch — incline factor — for your pitch of your roof by consulting a roof pitch chart or using these values: For roofs involving horizontal and 3-in-12 in pitch, use a factor of 1. For 4-in-12 or 5-in-12, use 1.05. For 6-in-12 to 8-in-12, use 1.1. For 9-in-12 to 11-in-12, use 1.2. For 12-in-12, use 1.3.
Multiply the largest square footage from the corresponding roof pitch element. In the example, multiply 1,250 square feet from the corresponding roof factor of 1.1 for a drainage area of 1,375 square feet. Multiply the drainage area from the maximum rain for your area in inches per hour. For example, for the San Francisco area, you would multiply 1,375 square feet by 2.7 to get a entire drainage area of 3,713 adjusted square feet.
Compare the adjusted square footage to the two most frequent gutter types. K-style gutters possess the ability to move either 5,520 square feet for 5-inch gutters or 7,960 square feet for 6-inch gutters. Half-round gutters transfer less water and permit to get 2,500 square feet to get a 5-inch diameter or 3,840 square feet to get a 6-inch diameter gutter. For example, the 3,713 adjusted square feet in the previous example would allow you to use either a 5-inch K-style gutter or a 6-inch half-round gutter when installed with the typical pitch of 1/4 inch per 10 feet.
Decrease the necessary size of your gutters by installing more downspouts compared to normal spacing of one every 40 feet. The amount of additional downspouts needed to boost the gutters’ capacity will depend on the size of the downspout. For example, adding one 4-inch round downspout will raise the gutter capability by 1,255 square feet, and one 3-inch round downspout would boost capacity by 706 square feet. Rectangular downspouts move slightly less water, at 600 square feet for 2-by-3-inch or 1,200 square feet for a 3-by-4-inch downspout. Multiply the amount of downspouts by square footage of each downspout. For example, one 4-inch downspout would saturate 1,255 in the initial 3,713 and would reduce the drainage area to 2,538 square feet.