Frame type
A single slope frame runs one continuous plane from a high eave to a low eave with no ridge at all. It is chosen for where the water goes, what the building looks like from the street, and what the zoning ordinance will allow — rarely for what the steel costs.
Practical span range
20–200 ft
Where this configuration is normally used
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.
Skip it when: Width is large. The high eave gets expensive fast because the whole frame grows with it.
Structurally it is still a rigid frame: moment connections at the knees, tapered members, the same secondary framing. Removing the ridge removes the symmetry, so the two columns are different heights and carry different loads, and the rafter is one long member rather than two meeting at a peak.
That asymmetry is the whole point. All the water goes to one side, so gutters, downspouts and any stormwater connection sit on one elevation and the other elevation has none. On a site that drains to one property line, or where a neighbour is close, that is worth more than the frame costs.
It also gives a tall, flat street face without a gable end, which is why it is the default for strip retail and small office buildings, and it fits under height limits a gable of the same clear height would break — the ridge is what usually violates a zoning envelope, and there is not one.
At modest widths a single slope costs about what a gable does. The high eave is the variable: because the whole frame is proportioned from it, raising the high eave grows the entire structure, and the taller sidewall carries more wall panel, more girt, and more wind load.
The cost therefore climbs faster with width than a gable does, because covering more width at a given roof slope forces the high eave up. Past roughly 100 ft that is expensive, and past about 200 ft it stops being offered — at that point a gable, or a modular frame, does the job for less.
Where a single slope genuinely earns its keep is at 40 to 80 ft: self-storage, strip retail and offices, where the frame is a minor line item next to the facade and the drainage and street presentation are what the building is actually being judged on.
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: Self-Storage, Retail / Office.
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. |
| 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. |
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 →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.