Once a structural engineer has calculated the loads on a new opening, the next question is what the beam is actually made from. Steel and engineered timber (glulam or LVL) both do the job, but they behave differently on site and suit different situations.
This isn't a matter of taste. The choice is driven by span, load, ceiling height and how the beam ends up sitting inside a finished room.
Section depth and span
Steel carries more load for a given depth than timber, which matters most where ceiling height is already tight or where the beam has to sit within an existing floor zone without dropping below it.
Over a genuinely long span — a full-width rear opening on a semi, say — steel usually wins on section size alone. Engineered timber can match it, but the beam gets deeper and heavier to compensate, and depth is often the one thing the room can't spare.
Getting it into the building
A steel beam for a long span is heavy and rigid. Getting one through a narrow hallway, up a staircase, or round a tight corner in a Victorian terrace can mean cutting and site-welding, or removing more of the structure temporarily than the job otherwise needs.
Engineered timber comes in lighter sections that two people can carry and manoeuvre by hand in most cases, which matters on restricted urban plots where a crane or gantry isn't an option.
What happens after it's in
Steel needs boxing in with plasterboard or timber to protect it from fire and to hide it, and stud walls or joists have to be mechanically fixed to it with brackets rather than simply nailed.
Timber beams take a nail or screw directly, which speeds up the follow-on carpentry — fixing joist hangers, studwork or ceiling battens straight to the beam without extra fixings.
Durability and site conditions
Steel corrodes if it's left exposed to damp before it's boxed in, so it needs protecting or painting where it sits near an external wall or a wet trade sequence runs late.
Engineered timber doesn't rust, but it does need keeping dry during storage and installation — a soaked glulam beam that isn't dried out properly can twist.
Common questions
Can a structural engineer choose either material for the same opening?+
Often yes, within limits — the engineer's calculation will usually give you a couple of viable options once the span and load are known, and the final choice comes down to depth, access and cost rather than one being structurally superior.
Is timber cheaper than steel?+
It depends on the span and section required — for shorter spans engineered timber can be competitive, but for long spans the depth needed to match steel's capacity can erase any saving. We'll only know once the calculation is done.
Does the choice affect Building Control approval?+
No — Building Control cares about the calculated capacity and the connection details, not the material, provided the beam and its bearings are correctly specified and installed.
Get a written quote for your new opening
We coordinate the structural engineer's calculation and fit the beam, whichever material it turns out to be. Free site visit, written itemised quote.