Calculate maximum attachment spacing for roof-mounted PV based on rail section modulus and wind loads.
Input Parameters
Results
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Max Attachment Spacing
ft
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Allowable Moment
in-lbs
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Stress at Max Span
psi
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Recommended Spacing
ft
Note: Typical attachment spacing is 3-5 ft for standard aluminum rails. Use manufacturer span tables when available. Account for both uplift and gravity load cases.
Reference
M_allow = Allowable Stress × Section Modulus
L_max = √(8 × M_allow / w_total)
w_total = (wind + dead) in lbs/in
Recommended = 80% of max span (rounded)
σ = M/S for rectangular beam