Structural steel is the one material on a building site where the order is placed in tonnes and the work is done in pieces. A beam that weighs 400 kg still has to be lifted, levelled, bolted and fire protected as a single item, and the crane time does not scale with the weight.
That is why a steel quote can look generous per tonne and still lose money. The tonnage is the easy part. The number of pieces, the connections, the crane visits and the fire protection are where the estimate lives or dies.
This guide covers how to get the tonnage from a schedule, how to count the connections, and what the erection and protection items actually are.
Steel is designed, not chosen. The sizes, the grades and the connections come from a structural engineer, and the drawings carry a steel schedule: member marks, sections, lengths and quantities.
Take the schedule at face value for the sections, then verify the lengths on the general arrangement drawings. Lengths on a schedule sometimes exclude the end plates and the haunch, and on a beam with a deep end plate that difference matters.
If there is no schedule, you can build one from the drawings, but the safe assumption is that the engineer will issue one before fabrication. Pricing fabricated steel from an architectural drawing is how a project ends up with a redesign after the order.
Weight = length x mass per metre for the section
Universal beams, columns and channels all have a published mass per metre, and the section designation tells you what it is. A 203 x 133 x 30 UB is 30 kg/m. A 254 x 254 x 73 UC is 73 kg/m.
Worked example. A small extension with a steel frame:
Total: 1,070 kg, or 1.07 tonnes of sections. Add cleats, end plates and base plates at 3 to 6 percent of section weight, so about 1.12 tonnes of steel.
For a two storey house extension with a steel frame, 1 to 3 tonnes is typical. For a small domestic opening, a single beam of 150 to 400 kg is more common, and it is often supplied as a lintel rather than a fabricated frame.
Steel is priced in two parts that are often combined into one rate, and the split matters when comparing quotes:
Fabrication is charged per tonne or per piece, and it is dominated by the number of connections. A beam with two simple end plates is a fraction of the work of a beam with moment connections, haunches and stiffeners.
Ask for a fabrication drawing before the order. It shows every plate and bolt hole, and it is the only way to price connections accurately.
Connections are counted, not weighed:
A fabricated frame with six members might have twenty plates and eighty bolts. Those are not expensive items individually, they are just numerous, and a quote built only on tonnage will have missed them.
Anchor bolts are the item that must be ordered before the concrete is poured. A base plate cast into the wrong position is a cutting and welding job on site, and it is the most common steel related delay on domestic work.
Erection is priced per tonne in theory, but what actually drives it is the number of lifts and the access.
A single 300 kg beam over a domestic opening can be a half day with a small crane or a telehandler, and the crane cost may exceed the steel cost. That comparison is worth showing a client, because it explains why a wider opening costs so much more.
Structural steel must be fire protected to the period the building requires. The options and their rough implications:
The key estimating point is that fire protection is measured on the steel surface area, not on the tonnage. A deep, heavy beam has more surface than a light one of the same length, and a schedule that gives no surface area needs one computed from the section perimeter.
Intumescent coatings also have a dry film thickness requirement that a single coat often cannot achieve, so two or three coats are normal, and the applicator needs the section factor calculation to know how much.
The 1.12 tonne frame above, with bolts, plates, crane and fire protection:
The steel is often less than half of this total. That is the honest shape of a steel line, and it is why a client's assumption that the beam costs what the beam weighs is almost always wrong.
A steel frame carries a design responsibility. The engineer designs, the fabricator produces drawings, and the contractor builds to them. If the contractor mixes those up, the liability lands on the wrong party.
For the estimate, three documents matter:
Without the middle one, the order is a guess. Without the third, an inspector may reject the steel.
Fabrication takes three to six weeks for a domestic frame, longer for anything with complex connections or a finish requirement. Erection is a day or two.
That means steel sits on the critical path twice: once for fabrication and once for the crane booking. Both are worth confirming in writing before a start date is given to a client.
On site, a two person gang with a crane erects 1 to 3 tonnes a day on straightforward domestic work, less where members must be threaded through an existing building.
A steel member is usually primed at the fabricator and finished on site. That order matters because anything welded on site has no primer and anything damaged in transit has to be touched up before the final coat.
Where the steel is exposed to weather, hot dip galvanising is often specified instead of a paint primer. It is priced per tonne and it adds to the lead time, because the member travels to a galvaniser and back before it goes to site. Galvanising also distorts thin members, so the sections chosen by the engineer may change if the coating is specified late.
Steel does not arrive on nothing. Every column base sits on a pad foundation, and those pads are part of the steel job in practice even though they are concrete.
A pad for a domestic column is typically 600 to 900 mm square and 300 to 400 mm deep, with a reinforcement cage and a cast in base plate or holding down bolts. The size comes from the engineer, not from a rule, because it depends on the load and the ground.
Quantities to count: the pad excavation, the concrete volume, the mesh or cage, the anchor bolts with their template, and the grout under the base plate after erection. On a four column frame that is four of each, and it is the line that most steel quotes leave to the groundworks, where it is often duplicated or missed entirely.
The sequencing point is that the bolts have to be set with a template and checked for level before the concrete sets. A pad that is 30 mm out is a base plate that will not fit, and the correction is either a re-drilled plate or a packer and a grout bed, both of which are site work nobody priced.
Most domestic steel does not stand alone. It sits inside an existing building, carrying a wall that has been removed or a floor that has been opened up.
That means connections into masonry or timber, which are the least predictable part of the job. A resin anchored plate into a Victorian brick wall behaves differently to one into a modern block. The engineer will specify a connection, and the site will discover that the wall is not what the drawing assumed.
Two allowances that make the difference between a good estimate and a difficult conversation: a provision for opening up and inspecting the existing structure before fabrication, and a provisional sum for the connections that will be detailed once the wall is exposed. Both are honest, and both are cheaper than a variation after the crane has been booked.
How much does a steel beam weigh? Length multiplied by the mass per metre of the section. A 203 x 133 x 30 UB at 5.2 m is 156 kg.
How much steel does a house extension need? Commonly 1 to 3 tonnes for a steel frame, or a single beam of 150 to 400 kg for one opening.
Do I need a crane? Above about 150 kg, or where the member cannot be handled manually, yes. A telehandler can substitute in some situations.
How long does fabricated steel take? Three to six weeks typically, from approved drawings to delivery.
How is fire protection measured? On the steel surface area, from the section perimeter, not on the tonnage.
Who is responsible for the design? A structural engineer. The contractor builds to the approved drawings and should not substitute sections.
The FRELUX structural steel calculator converts a schedule into tonnage by section, adds plates and bolts, and prices fabrication, delivery, crane time and fire protection from your market's price book.