5
Figure 6
– Roof Measurement
D. EXAMPLE #1
– EXAMPLE OF TYPICAL ESTIMATION
Consider a roof section (See Figure 4) that you want to treat that has:
• 32 feet of roof
• an overhang of 12 inches with a gutter
• 1 dormer (30 feet around)
• 1 valley
• 2 downspouts (each 10 feet long)
From Table 2, the multiplier for a roof with a gutter and an overhang of 12 inches is 4.
Using Table 1, the cable length needed = (32 x 4) + (1 x 30) + (1 x 6) + (2 x 10 x 2) = 204
Using Table 3, you would select the DR-9RC2200 (200 feet of cable). You would select the smaller cable because the difference between
the cable length and your calculation is less than 5 feet.
E. EXAMPLE #2
– EXAMPLE OF SPECIAL ROOF AREA ESTIMATION
This example shows how to estimate the cable length needed for a limited problem roof area
– a skylight (see Figure 6). For this
roof, you would like to treat only the problem area underneath the skylight.
This roof section has:
• 1 downspout (l0 feet long)
• 1 skylight (the distance from the bottom of the skylight to the roof edge is 12.5 feet, and the width of the ice dams that form beneath the
skylight is about 6 feet)
• 1 gutter
From Table 6, the special roof area multiplier for a roof with a gutter is 2.6.
Using Table 5, the cable length needed = (1 x 10 x 2) + (12.5 x 6 x 2.6) = 215
From Table 3, you would select the DR-9RC2250 (240 feet of cable) to ensure complete coverage.
Note: If you are only treating one special roof area and the problem area is a significant distance from the downspout, you may wish to add
extra cable to your estimation to account for the cable in the gutter.
