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STRUCTURAL CRITERIA FOR RESIDENTIAL FLUSH-MOUNTED SOLAR ARRAYS
1. ROOF CHECKS
A. Visual Review/Contractor’s Site Audit of Existing Conditions:
1) Is the roof a single roof without a reroof overlay? Y N
2) Does the roof structure appear structurally sound, without signs of alterations?
or significant structural deterioration or sagging, as illustrated in Figure 1? Y N
B. Roof Structure Data:
1) Measured roof slope (e.g. 6:12): ________:12
2) Measured rafter spacing (center-to-center): _______ inch
3) Type of roof framing (rafter or manufactured truss): Rafter Truss
4) Measured rafter size (e.g. 13/4 x 33/4, not 2x4): ____ x _____ inch
5) Measured rafter horizontal span (see Figure 4): ____’ - ____”ft-in
6) Horizontal rafter span per Table 2: ____’ - ____”ft-in
7) Is measured horizontal rafter span less than Table 2 span? Y N Truss
2. SOLAR ARRAY CHECKS
A. Flush-mounted Solar Array:
1) Is the plane of the modules (panels) parallel to the plane of the roof? Y N
2) Is there a 2” to 10” gap between underside of module and the roof surface? Y N
3) Modules do not overhang any roof edges (ridges, hops, gable ends, eaves)? Y N
B. Do the modules plus support components weigh no more than:
4 psf for photovoltaic arrays or 5 psf for solar thermal arrays? Y N
C. Does the array cover no more than half of the total roof area (all roof planes)? Y N
D. Are solar support component manufacturer’s project-specific completed worksheets,
tables with relevant cells circled, or web-based calculator results attached? Y N
E. Is a roof plan of the module and anchor layout attached? (see Figure 2) Y N
F. Downward Load Check (Anchor Layout Check):
1) Proposed anchor horizontal spacing (see Figure 2): ____’ - ____”ft-in
2) Horizontal anchor spacing per Table 1: ____’ - ____”ft-in
3) Is proposed anchor horizontal spacing less than Table 1 spacing? Y N
G. Wind Uplift Check (Anchor Fastener Check):
1) Anchor fastener data (see Figure 3):
a. Diameter of lag screw, hanger bolt or self-drilling screw: _______ inch
b. Embedment depth of rafter: _______ inch
c. Number of screws per anchor (typically one): _______
d. Are 5/16” diameter lag screws with 2.5” embedment into the rafter
used, OR does the anchor fastener meet the manufacturer’s guidelines? Y N
Structural Criteria for Residential
Rooftop Solar Energy Installations