Pricing structural steel on domestic jobs: more than a beam and a lift

Almost every extension and knock-through now carries steel, and it is one of the most consistently under-priced packages on domestic work. The beam itself is the cheap part. The money is in the fabrication, the handling, the bearings and the fireproofing, and quotes that miss those lines pay for them out of margin.

Start from the engineer's drawings, not the builder's guess

Steel on a domestic job is designed by a structural engineer, and their drawings and calculations are your pricing document. They give you the serial size of each member (say 203 x 133 x 25 UB), the length, the connection details, the bearing requirements and any plates or stiffeners. Never price steel from an architect's general arrangement alone, because "beam over" on a plan can turn into a box frame with moment connections by the time the engineer has finished.

The serial size hands you the weight for nothing. The last number in the designation is kilograms per metre, so a 203 x 133 x 25 UB at 4.2 metres weighs about 105 kg. Weight matters twice: fabricators broadly price supply by weight and complexity, and weight determines whether four lads can carry it or a crane has to.

What the package actually contains

A realistic steel package on a domestic job has seven or eight distinct costs. Miss any one and the line looks profitable until the week you do the work:

The access question decides the method, and the method decides the price

Before you price the install, answer one question honestly: how does this beam get from the wagon to its bearings? A 100 kg beam with clear side access is a morning's work with genie lifts or a strong gang. The same beam through a Victorian terrace, up a staircase with two turns and into a loft, is a different job entirely. It might need splicing into two pieces with a bolted connection (which changes the fabrication cost), or a mini crane over the roof, or a spider crane in the garden.

Walk the route on the survey. Measure the door widths and the head heights. If the beam is over about 150 kg or the route is tight, get a lift plan and a cranage price before you quote, not after. A crane visit on a domestic job commonly costs several hundred pounds to over a thousand once you include the appointed person and the road permit, and none of that is recoverable once you have signed a fixed price without it. Our site survey checklist has a section on exactly this.

Fire protection is a real line, not an afterthought

Building Regulations require structural steel in dwellings to achieve fire resistance, typically 30 minutes in most domestic situations, and the beam over your shiny new open-plan kitchen does not comply bare. The usual routes are fire-rated plasterboard casings (often two layers of 12.5 mm board, or a proprietary rated casing) or intumescent paint applied to the correct loading. Boarding is usually the economical choice on domestic work but adds framing, boarding, taping and decorating time. Intumescent looks cleaner where the steel is expressed but the paint and application cost more than people expect.

Whichever route, it is a measurable quantity: the exposed perimeter of the steel times its length. Put it on the bill as its own line. Building control will look for it, and pricing it after the plasterer has left site is the expensive way round.

Temporary works: the quiet risk

Between demolition and the beam taking load, the building stands on your props. That period costs money: needles through the wall, Strongboys under masonry, acrows both sides, hire for the full duration, and the labour to install and strike it all. On a straightforward opening this is routine. On a full-width rear knock-through with a pier removed, the temporary works can rival the steel package itself, and the engineer may specify a scheme you must follow rather than improvise.

Price the hire by realistic duration, not optimism. If the steel is late from the fabricator (two to three weeks lead time is normal, longer for galvanised), the props stay up and the hire keeps running. A modest allowance for programme slip here is cheaper than the alternative. For how delays ripple through the rest of your price, see how programme length quietly changes your price.

Putting the number together

A sensible pricing sequence for domestic steel: take each member from the engineer's schedule with its weight and connections; get a fabricator's supply price (or use your rate per kilogram for budget purposes, remembering that small one-off beams carry a premium over tonnage rates); walk the access route and choose the handling method; count bearing ends for padstones; measure the fire casing; and allow temporary works by duration. Then add your overhead and profit to the package like any other trade, as covered in setting a margin you can defend.

If you would rather not build that from a blank page every time, QS Quoter prices the full steel package from your job description or the engineer's drawings: beam supply, temporary works, labour, padstones, fire protection and making good, each on its own editable line at your rates. The lines you would forget at ten o'clock at night are already there, and you can still change every one of them.