What a balustrade quote has to calculate

Ask a fabricator what balustrade costs and the honest answer is a question back: where is it going? A metre of the same glass and steel is a different product on a domestic landing, a balcony edge and the front of a bar, because each carries a different design load, and the load decides the post section, the post spacing, the glass makeup and the fixings before anyone gets to cut a length. A quote that starts from a price per metre has skipped the part of the job that was engineering.

The load case comes first

UK guarding design starts from where people are and what they might do there. Approved Document K sets the guarding heights and points at BS EN 1991-1-1 with its UK National Annex and BS 6180 for the loads: a horizontal line load at the rail, a distributed load on the infill and a point load on the infill, all three of which the design has to satisfy. The line load is the one that moves most.

Post spacing is an output, not a preference

Each post resists the line load collected from the bay either side of it, acting at the guarding height. The moment at the post base is therefore load times bay times height, and a bay that works at 0.74 kN/m and 1100mm does not work at retail or assembly loading. A section tabled at 1500mm centres under the office band has its bay roughly halved at 1.5 kN/m and cut to about a quarter at 3.0 kN/m, and the scaling only ever narrows: a lighter duty never licenses a wider bay than the section's own table, because that limit is also a fabrication and infill limit, not only a strength one. More posts means more base plates, more fixings, more welding and more time, which is how the load case reaches the price.

Glass is a makeup, not a thickness

Free standing glass protecting a drop is specified as a laminated makeup: two toughened leaves with an interlayer, written 8+8 with a 1.52 PVB for a 17.52mm build, 10+10 for 21.52mm, 12+12 for 25.52mm. The load case and the fixing method drive the choice, and the quote has to carry it as a makeup because the glass schedule, the weight the fixings see and the price per panel all follow from the build, not from a rounded thickness. A balustrade with a structural handrail and one without are different calculations for the same glass.

Then the boring lengths

Only after the engineering settles does the familiar estimating begin, and even that is bookkeeping with consequences: posts at the derated centres against stock lengths, rail runs with joints placed away from bays that carry gates, panel widths that respect the post setting out, base plates and fixings per post, and a cutting list that someone on the saw will actually follow. Get the spacing wrong at the start and every line after it is wrong too, which is why the order of operations is the whole game: loads, then spacing, then glass, then lengths, then money.