300 ft clear span
Three hundred feet is the widest single span most manufacturers will quote at all. It is a bespoke frame, a long lead time and a heavy-lift erection. Above it, width is covered by putting more than one frame side by side, not by making one frame longer.
Priced as a 300 × 400 ft building at a 40 ft eave, 25 ft bays, 20 psf ground snow on the ASCE 7-16 basis, 115 mph wind, no crane — a case that matches what actually gets built at this width. Change any of it in the calculator.
Framing steel
21.76 – 31.28 lb/sf
Primary and secondary, 1,306 – 1,877 tons total
Building package
$39.53 – $55.11/sf
$4.74M – $6.61M over 120,000 sf
Installed
$61.28 – $104.71/sf
$7.35M – $12.56M, before interior buildout
Modular would save
33%
About $1.87M on the package
Outside the usual range. This width prices outside the $14–22/sf band commonly quoted for metal building packages. That band describes ordinary spans; a 300 ft clear span legitimately leaves it, and clamping the figure to look tidy would make it useless exactly where it is most needed. How these figures were derived.
At this span: The upper limit most manufacturers offer. Expect a bespoke frame design and a long lead time.
The short answer
If you need more than 300 ft of width you need multi-gable or modular framing. There is no single-span answer above here, and asking for one mostly buys you silence from bidders.
Planning-stage estimate calibrated to published industry ranges. Not a substitute for a stamped design by a licensed engineer.
Geometry that follows from the width alone, at this page's 40 ft eave. These are planning rules, stated so they can be argued with — the derivations are on the methodology page.
| Dimension | At 300 ft | Why it matters |
|---|---|---|
| Frame depth at the haunch | 144–180 in | Span/25 to span/20. The deepest point of the frame, at the knee, where the moment peaks. |
| Clear height at the sidewall | 25–28 ft | Eave height minus the haunch. The height you can actually use in the first bay in from the wall; clearance rises toward the ridge. |
| Rafter half length | 150 ft | Haunch to ridge. What has to get on a truck. |
| Shipping pieces per half | 4 | Past ordinary haul length, so the half arrives in bolted segments and each splice is a connection to make up in the field. |
| Deflection allowance, L/240 | 15 in | Allowable midspan movement with a non-plaster ceiling, per IBC Table 1604.3. The weight model behind this page checks none of it. |
| Engineering | Custom | Past the 150 ft ceiling for a standard frame. Project-specific engineering, fewer bidders, longer lead time. |
Nothing forbids a wider single span; it simply stops being a metal building. Weight per square foot has roughly quintupled from 60 ft, the haunch is 144–180 in deep, the members exceed what most PEMB shops are set up to fabricate and handle, and erection is a heavy-lift engineering exercise in its own right. At that point the honest comparison is against a conventional long-span steel truss or an arch, which are different buildings procured a different way.
The calculators on this site stop here too. They decline to answer above 300 ft rather than extrapolate, because the model is calibrated against a table that ends at this width and an answer past it would be invented rather than estimated.
Multi-gable framing: 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 that has to be detailed, drained and maintained, and that drifts snow. In a heavy snow climate that valley is the first place a very wide roof gives you trouble.
Modular framing does the same thing without the valley, running one continuous gable or slope over interior column lines. It saves 33% against clear span at this width and considerably more above it, which is why nearly every very large distribution building in the country is framed that way.
Then it is almost certainly aircraft, and the door is the real problem. A 300 ft opening is a structure of its own, the header over it carries load nothing else in the building carries, and door selection and frame design have to happen together rather than in sequence.
Framing runs about 21.76 – 31.28 lb/sf, so 1,306 – 1,877 tons of steel in this building alone. Rafter halves are 150 ft in roughly 4 pieces, deflection allowances are 15 in at L/240 and 20 in at L/180, and clear height at the sidewall is 25–28 ft under a 40 ft eave. Every one of those is a conversation with a manufacturer, not a specification you hand down.
The uses whose typical width covers 300 ft, and what drives the geometry in each. A use that does not appear here is not impossible at this width — it is just not where it usually lands.
| Use | Typical width | Typical eave | What sets the geometry |
|---|---|---|---|
| Aircraft Hangar | 100–300 ft | 24–60 ft | Door opening and tail height, not floor area. The clear span is set by the widest aircraft plus wingtip clearance. Usually clear span. |
| Warehouse / Distribution | 100–400 ft | 28–40 ft | Rack grid and dock count. A column is free if it lands on a rack line, so modular almost always wins. Usually modular. |
A modular frame at this width comes in around 33% lower on the building package — roughly $1.87M on the 120,000 sf building priced above. At that level clear span has stopped being an economic option and become a purchase: you should be able to name what the column-free floor is for.
The frame selector's own recommendation for this case, with interior columns permitted, is a Modular frame with tapered columns. Web-tapered members follow the moment diagram and are the lightest way to carry this span.
Next step
A dealer quoting your actual geometry and load case beats any estimator, including this one. Three of them, each carrying engineer-stamped drawings for your state, cost you nothing to ask.