The choice is a calculation, not an opinion — and it is one that building control will want to see supported by an engineer's design.
When timber or concrete is enough
Short openings in non-loadbearing partitions, or modest spans carrying only a light load above, can be handled by a timber or precast concrete lintel with proper bearings each side.
As spans grow or the load above includes floors and roof, the depth of timber required becomes impractical and steel takes over.
How a steel beam is designed
An engineer works out the loads reaching the opening, selects a section that satisfies both strength and deflection limits, and specifies the bearing length and the padstones that spread the load into the masonry below.
Deflection often governs. A beam that is strong enough can still move enough to crack plaster above it, which is why the calculation matters more than a rule of thumb.
On site: propping, fire and finishes
The temporary works — needles and props supporting the structure while the wall comes out — are as important as the permanent beam, and the sequence should be planned before anyone starts breaking out.
Steel needs fire protection, usually boarding, and it needs to be positioned to allow for the finished ceiling. Flush beams look better but complicate the connections and cost more.
Common questions
Do I always need an engineer for a steel beam?
Yes. Building control requires calculations for the beam, its bearings and padstones, and the design also confirms the temporary propping requirement.
Can a steel beam be hidden in the ceiling?
A flush beam can be, with the floor joists hung from it. It costs more and takes more detailing than a downstand.
How long does removing a wall take?
The structural work itself is usually a few days, with making good, plastering and decoration taking longer than the beam installation.
Does building control need to inspect it?
Yes, at the point where the bearings and beam are in place and before they are covered up.