Solar & battery
Solar Racking Quantity Calculator
Rails, clamps and roof attachments for an array, from the panel count and layout.
Result
Attachment spacing is set by wind and snow loading and by the manufacturer's engineering tables, not by a rule of thumb. Four feet is a common residential figure; high wind zones and heavy snow regions require closer spacing, and the racking manufacturer publishes the span tables that govern it.
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About this calculator
What sets attachment spacing?
Wind uplift and snow load for the site, run through the racking manufacturer's span tables. It is an engineering requirement and frequently an inspection item.
Do attachments have to hit rafters?
On most pitched roofs yes, which is why locating rafters accurately matters. A missed rafter is both a structural failure and a leak.
The formula
rails = rail runs per row x rows; attachments roughly one every 4 feet of rail
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