Frame type
A multi-gable frame is two or more gable modules side by side, sharing interior columns. It covers great width with short spans, which is the cheapest steel in the section — and it creates a valley, which is the most demanding roof detail in it.
Practical span range
80–600 ft
Where this configuration is normally used
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.
Skip it when: Snow load is heavy. Valleys drift, and they are the first place a wide roof gives you trouble.
Each module is an ordinary gable frame at an ordinary span. Put two of them together and the inner columns are shared, so 300 ft of width becomes two 150 ft spans, or three 100 ft ones. Because moment grows with the square of the span, cutting the span in half cuts the demand on any one member by far more than half.
Where two modules meet, the two roofs slope down toward each other and form a valley: an interior gutter line running the length of the building, above the floor, carrying water from both roofs. Everything that makes multi-gable attractive structurally is spent again on that valley.
It is also the natural way to expand. A building framed as one gable can have another module added alongside later, matching the existing roofline, which is why multi-gable turns up on phased plants and on retrofits next to something that already exists.
The cheapest way to cover very large widths, and the reason widths past 300 ft are buildable at all — above the ceiling for a single span, multi-gable and modular are the only answers, and the frame selector switches to multi-gable automatically past 300 ft.
Against a modular frame of the same width the steel is comparable and the choice is usually about roof geometry rather than cost: modular runs one continuous roof over interior columns and has no valley, multi-gable has separate roof planes and does. If nothing requires matching an existing roofline or phasing the build, the valley is a reason to prefer modular.
Where multi-gable clearly wins is expansion and retrofit. Adding a module to match a roofline you already have is cheaper and looks better than any alternative.
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 |
|---|---|---|---|---|
| 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 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 →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.