Frame type
A straight column is a constant-depth member: heavier than the tapered equivalent carrying the same load, and worth it whenever something has to sit flat against it. This is a usability premium bought on purpose, not an economy.
Practical span range
20–150 ft
Where this configuration is normally used
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.
Skip it when: Span is long and budget is tight. This is a usability premium, not an economy.
Constant depth means the section is sized for the moment at the knee and carries that depth all the way to the base, where the demand is close to zero. The surplus steel low down is the price, and it is unavoidable — that is what constant depth means.
What you get is a plumb, flat interior face for the full height of the column. Racking can stand tight against it, liner panel can run down it without a shadow gap, masonry wainscot can be built to it, and a partition can meet it cleanly. Girt connections are simpler because every girt frames to the same plane at every elevation.
On narrow buildings the penalty is genuinely small. The moment at the knee is modest, so the constant section is not much heavier than the tapered one would have been, and the simpler detailing can make it the cheaper building overall once fabrication and erection are counted.
Below about 60 ft, straight columns are the frame selector's default, and not as a compromise: the weight difference is small and the sidewall is easier to build.
Above that the premium grows with span, because the gap between a member that follows the moment diagram and one that ignores it widens as the moment grows. On a long span with a tight budget this is the wrong place to spend money unless something genuinely needs the flat face.
Practical spans run to about 150 ft. Past that, constant-depth columns on a clear span are hard to justify against almost any alternative, including furring out a tapered column where the flat face is actually needed.
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.
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 |
|---|---|---|---|---|
| 40 ft | 2.04 – 2.97 lb/sf | $13.45 – $16.33/sf | — | Light frames. Span is rarely the cost driver at this width - eave height and snow load matter more. |
| 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. |
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 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.
60–480 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 →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.