Frame type
A modular frame refuses to let any single member span the full width. One or more interior column lines split the building into modules, each rafter covers a fraction of the width, and the whole structure steps back down the curve that makes wide clear spans expensive.
Practical span range
60–480 ft
Where this configuration is normally used
One or more interior column lines split the width into modules, so each rafter spans only a fraction of the building. The savings grow with width and become decisive past roughly 150 ft.
Skip it when: A column would land in a traffic aisle, a crane runway, or an arena floor.
Nothing about the steel is different — it is the same tapered members, the same moment connections, the same secondary framing. What changes is the span each member is asked to cover. Two 60 ft modules covering 120 ft of width carry a fraction of the moment one 120 ft frame does, because moment grows with the square of the span.
The cost of that is a column line: footings, base plates, a connection at each rafter, and something permanently standing in the floor. The saving grows with width because the column line is close to a fixed cost that gets amortised over a wider and wider building, while the clear span alternative keeps getting heavier.
Modular is the reason very large distribution buildings exist at the price they do. Practical widths run far past anything a single span reaches — 480 ft and beyond is ordinary — because you are simply adding modules rather than asking any one member to do more.
The crossover is around 80 ft. Below it, modular saves nothing: the column costs as much as the span relief is worth. At exactly 80 ft the two configurations should price within a percent or two of each other, which is inside the noise between two quotes.
Above the crossover the gap opens steadily — roughly 5% at 100 ft, 9% at 120 ft, 14% at 150 ft, 22% at 200 ft, 33% at 300 ft. Those are package percentages, so on a large building they are substantial absolute sums, and they are the reason the frame selector recommends modular at every width above the crossover unless something rules the column out.
A column that lands on a rack line, a demising wall, or a bay division you were building anyway is very close to free. That is the ideal case, and it is common enough in warehousing that modular is the default there rather than a compromise.
Planning-stage estimate calibrated to published industry ranges. Not a substitute for a stamped design by a licensed engineer. How the figures behind those percentages were derived.
Uses whose profile names this configuration by default: Warehouse / Distribution.
The widths this configuration reaches that have a page of their own, with what a clear span at that width costs and what a column line would save against it. Where the saving is meaningful, that number is the case for or against this configuration in one figure.
| Width | Clear span steel | Clear span package | Modular saves | What changes at this width |
|---|---|---|---|---|
| 60 ft | 3.00 – 4.20 lb/sf | $15.00 – $18.00/sf | — | The practical floor for commercial work. Below this width, small-building suppliers price better. |
| 80 ft | 4.07 – 5.57 lb/sf | $16.63 – $20.79/sf | — | The crossover band. Clear span and modular start to diverge in cost here - price both. |
| 100 ft | 5.26 – 7.32 lb/sf | $18.35 – $22.66/sf | 5% | Haunch depth begins to govern interior clearance. Check usable height, not just the eave. |
| 120 ft | 6.41 – 8.92 lb/sf | $19.43 – $24.82/sf | 9% | Deep haunches and heavier anchor-bolt patterns. Foundation cost stops being a rounding error. |
| 150 ft | 8.26 – 11.56 lb/sf | $21.98 – $28.57/sf | 14% | The practical ceiling for a standard single-span rigid frame. Past this you are buying custom engineering. |
| 200 ft | 11.55 – 16.42 lb/sf | $26.85 – $35.80/sf | 22% | Custom engineering, shipping splices, and heavier erection equipment. Modular usually wins on cost alone. |
| 250 ft | 16.10 – 22.54 lb/sf | $32.44 – $44.02/sf | 28% | Specialist territory. Justified by use, not economics - hangars, arenas, column-free process floors. |
| 300 ft | 21.76 – 31.28 lb/sf | $39.53 – $55.11/sf | 33% | The upper limit most manufacturers offer. Expect a bespoke frame design and a long lead time. |
Each row is priced at the case on that width's own page — the eave and length that actually get built there — so the rows are comparable to those pages rather than to each other. Planning-stage estimate calibrated to published industry ranges. Not a substitute for a stamped design by a licensed engineer.
A single rigid frame carrying the full width with no interior columns. Maximum usable floor area and total layout flexibility, paid for in steel weight that rises faster than the span.
20–300 ft →One continuous slope from a high eave to a low eave, with no ridge. Drains to one side, presents a taller street face, and fits sites where a gable would break a height limit.
20–200 ft →A single-slope module framed off an existing sidewall, with no independent ridge. The cheapest square footage on any project, provided the host frame can take the added load.
10–60 ft →Two or more gable modules side by side sharing interior columns, covering great width with short, cheap spans. The tradeoff is a valley - an interior gutter line you must detail and maintain.
80–600 ft →Built-up members whose web depth follows the moment diagram - shallow at the base, deep at the haunch. The standard configuration for clear span, and the reason a rigid frame is the lightest way to cover a wide bay.
40–300 ft →Constant-depth columns. Heavier than a tapered equivalent, but they give a flat plane for racking, liner panel, masonry wainscot, and interior partitions, and they simplify sidewall framing.
20–150 ft →Not sure which one you need? The frame selector takes width, eave height, crane load and whether a column can stand inside, and tells you which configuration fits — and what the runner-up would have cost. Or go straight to quotes.