“Just make the beam smaller.” It sounds like the cheaper option.
Most of the time, it’s the expensive one.
Here’s the bit that catches people out with structural steel: a deeper beam is usually the smarter, cheaper beam — not the other way round. Let me show you why, in plain English.
Depth does the heavy lifting — literally
A beam’s strength comes mostly from its depth, not its width. Make a beam deeper and its stiffness shoots up — roughly with the cube of the depth. Double the depth and, very loosely, you’re in the region of eight times stiffer.
So a deep, “chunky” beam carries more load and sags less while using less steel by weight.
Try to force that same job into a shallow beam — because you want it hidden in the floor zone — and you’re fighting physics. You end up with a heavier, fatter section, or two beams bolted together, just to match what one deeper beam would’ve done on its own.
Heavier steel isn’t just more steel
Steel is largely priced by weight, so a heavier section costs more on day one. But it doesn’t stop there:
- Bigger supports. More load landing in one place means bigger padstones — or even columns — to spread it safely into the wall.
- Harder install. Heavier beams are harder to lift, prop and position — sometimes the difference between a couple of labourers and hiring a crane.
In short: shaving the depth often just moves the cost somewhere less obvious — and usually makes it bigger.
The trade-off: the downstand
There’s a catch with a deep beam, and it’s an honest one: it hangs below the ceiling line. That’s called a downstand. You can live with it, box it in as a feature, or recess it up into the floor above.
If you can accept a downstand — or you’re ripping the floor up in a full renovation anyway — a deep beam is a gift: fewer steels, lighter sections, simpler connections, easier install.
When bigger is genuinely cheaper
- Full-house renovations — the floor above is already coming up, so recessing a deep beam costs almost nothing.
- Long, open-plan spans — where a shallow beam would need a monster section or an extra column to break the span.
- Simplifying the steel count — one well-sized deep beam can replace a fiddly arrangement of several shallow ones.
When you can’t go deep (and that’s fine)
Sometimes head height is tight, there’s no appetite for a downstand, or the floor level is fixed. Then a shallow, flush beam is the right call — just go in knowing you’re paying a premium for it, not assuming “smaller” means “cheaper.”
It’s also why beam choice is an engineering decision, not just a drawing one: spans, deflection limits, and the load path down to the foundations all feed into it.
Not sure whether your project wants a deep beam or a flush one? WhatsApp us your questions and we’ll be able to assist.
Bottom line
Don’t reflexively ask for the smallest beam. Ask for the right one.
If you’ve got room for a downstand — or the floor’s up anyway — going deeper is often lighter, simpler and cheaper. Bigger isn’t the expensive option. Sometimes it’s the clever one.
Thinking about a knock-through or extension? WhatsApp us your questions and we’ll be able to assist.
