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How far apart should the frames be?

Bay spacing is the cheapest decision on a metal building to get right and one of the easiest to leave on a default. At 20 psf of ground snow, the cheapest option for this building is 25 ft bays.

The building

Index is relative cost, with 25 ft bays at this snow load set to 100. Lower is cheaper.

Relative cost by bay spacing, 200 ft long building
Bay Cost index Frames Character
20 ft 104.1 10 Tighter frame spacing. More frames and more foundations, but the lightest purlins and girts.
25 ft 100.0 8 The industry default, and the optimum for most load cases.
30 ft 102.5 7 Fewer frames and fewer footings, paid for in deeper secondary framing.
35 ft 109.4 6 Rarely economical. Worth pricing only on long, lightly loaded buildings.

Why snow decides this. Primary framing and foundations get cheaper as bays get wider, because there are fewer of both. Secondary framing goes the other way: each purlin carries more roof, so it gets deeper and heavier faster than the spacing grows. Snow load sits entirely on the secondary side of that trade, so the more snow you have, the sooner wider bays stop paying.

Planning-stage estimate calibrated to published industry ranges. Not a substitute for a stamped design by a licensed engineer.

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Turn these numbers into real quotes

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Get engineered quotes for a 120 × 200 × 24 ft building

What bay spacing also decides

The cost index above is only half the reason to think about this. Bay spacing sets the rhythm of everything attached to the sidewall.

  • Door and window placement. Openings want to sit between frames. A dock door that lands on a column line needs framed-opening reinforcement, and a run of them wants the bay module to match the dock module.
  • Racking and mezzanines. If the interior grid and the frame grid disagree, one of them pays for it. Setting bays to a multiple of the rack bay is free at design time and expensive later.
  • Wind bracing. Bracing goes in specific bays. Wider bays mean fewer places to put it, which occasionally forces a braced bay into a wall where you wanted a door.
  • Erection. Fewer, heavier frames need bigger equipment. On a tight site the crane may decide the spacing before economics does.

Which is the short answer to why 25 ft became the default: it divides cleanly into common building lengths, matches typical rack and dock modules, and sits at or near the cost optimum for most of the country's snow loads.

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