What spoils projects most is starting the design before requirements are fixed. Dimensions come first, because they are the item that, if it changes after fabrication begins, sends everything back to zero. This article explains how to state hangar dimensions in language an engineer understands and which cannot be read two ways.
Note: The figures and ranges here are common in practice and are not a substitute for an accredited structural calculation. Every project needs a design signed by a structural engineer under the building code in force at its location.
1. What is the difference between clear height and overall height?
This is the most repeated misunderstanding in the sector. Overall height is measured from floor to the apex of the truss or the highest point of the structure. Clear height is measured from floor to the lowest structural member or suspended service — and it is what your equipment actually needs.
The gap is not small: in a long-span hangar the depth of the truss at mid-span can be a metre or more. A client who measured to the apex and specified "8 metres height", then discovered their crane needed 8 clear metres below the lowest member, faces either a redesign or a crane that does not work.
The rule: always state the clear height you need, and say explicitly that it is clear. Let the designer work out the overall height.
2. How much does a wide clear span cost?
Clear span is the distance between columns with no intermediate support. It is the most expensive decision in the design: as span grows, member depth and steel tonnage rise faster than floor area does.
So the right question is not "what is the largest span possible?" but "what is the smallest span my operation can live with?". A single intermediate column can cut structural tonnage appreciably — if it does not obstruct equipment movement or racking layout.
Ask yourself: do you genuinely need a completely clear floor? Or would columns in calculated positions leave operations untouched? The answer moves the cost more than any other item.
From our projects: the widest span we have built is 40 m at the equestrian club hall — 5,000 m² over a 132 m length with no intermediate column, on perimeter concrete columns with steel lattice trusses. The industrial warehouse runs a 37 m span at 9 m clear height on steel portal frames.
3. Which structural system suits which span?
Tapered rigid frames: the most common system in pre-engineered industrial buildings. It spends material intelligently, deepening the section where moments grow and thinning it where they fall.
Trusses: economical for very large spans and lighter in weight, at the cost of many more connections and longer fabrication time — and every connection is another inspection point.
Arches and cold-formed sections: suited to small and medium spans, agricultural structures, and simple storage.
Between the frames sits a secondary system that matters no less: purlins, which carry the cladding and transfer its loads, and bracing, which resists horizontal forces and prevents lateral torsional instability. Cutting back bracing is the cheapest-looking error and in fact the most dangerous, because it threatens the stability of the whole building rather than one member in it.
4. When must an overhead crane be specified?
If the building has an overhead crane, its capacity and span change the design fundamentally: columns carry the crane runway, frames are calculated for moving and dynamic loads, and the foundations change accordingly.
And a crane cannot be added later to a structure that was not calculated for one. The remedy in that case is expensive structural strengthening, or a free-standing crane that eats into usable floor area.
If there is even a distant possibility of a crane, say so while requirements are being fixed. Calculating for it now is a small fraction of the cost of strengthening a standing structure.
5. How do openings and gates affect the structure?
Openings are not holes in a wall. Every large opening — a truck door, a wide ventilation opening, a strip of rooflights — interrupts the load path and forces the stiffening members around it to be redistributed.
Opening positions and sizes therefore belong to the design stage, not after it. Cutting a door into a completed wall means local strengthening at a cost far above designing it in place from the start.
Specify: the number and position of personnel doors; truck doors with their clear dimensions and type; ventilation openings; and the area of natural lighting required.
6. How do you design a hangar for future expansion?
Extendability is one of the strongest advantages of steel: adding new bays is possible and relatively cheap — if it was allowed for at design stage.
The practical difference is that the end wall is designed either as a final wall or as one that can be opened. The first is slightly cheaper today; the second saves you demolition and rebuilding in a few years.
If expansion is likely, say so explicitly and name the probable direction and approximate area.
7. Which dimensions must be fixed before design starts?
These items should be written down before anyone starts drawing:
- Intended use: storage, production, showroom, agricultural, sports.
- The clear width required between columns.
- Overall length, and the number of bays if already set.
- The clear height below the lowest structural member.
- Any overhead crane: capacity, span, and hook height.
- Positions and sizes of personnel and truck doors.
- Ventilation openings and the area of natural lighting.
- Suspended loads: services, lighting, fire systems, ductwork.
- Site conditions: soil, groundwater, wind, snow, proximity to the coast.
- Regulatory constraints: setbacks, permitted height, civil-defence requirements.
- Any likely expansion plan.
An hour spent filling in this list saves a week of changes during fabrication, and a month of them during erection.
- Clear span
- Clear height
- Overhead crane
- Fixing requirements
Have a project like this?
Send the requirements and we will come back with a preliminary study and clear quotation items.
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