Do I Need a Structural Engineer for a Steel Beam?

If you're putting a steel beam into a building — removing a wall, forming an opening, building an extension — then yes, in practically every case you need a structural engineer. It isn't red tape for its own sake: their calculations are what makes the work approvable, and what the steel is made from.

What the engineer actually does

• Works out the loads coming down onto the opening: roof, floors, walls above, and anything concentrated.
• Specifies the beam — the exact section, its grade, and how deep and heavy it needs to be.
• Designs the bearings — what the beam sits on at each end, including padstones, posts, or a goalpost frame where the masonry can't take it.
• Details the connections — bolt positions, cleats, base plates, and how the steel ties into the existing structure.
• Issues calculations and a drawing that building control can check and a fabricator can work to.

How it fits with building control

Building control's job is to confirm the work is structurally safe. They do that by reviewing the engineer's calculations, then inspecting the installed steel and bearings before anything is covered up. Without calculations there's nothing to assess, so the application stalls. See do I need building regs for a steel beam? for how that process runs.

Engineer vs fabricator — who does what

These are two different jobs, and you generally need both:

	Structural engineer	Steel fabricator (us)
Decides the beam size	Yes	No
Calculates the loads	Yes	No
Cuts, drills and welds the steel	No	Yes
Supplies the finish (primed / galvanised)	No	Yes
Delivers, and can install	No	Yes

We fabricate to the engineer's design — we don't replace it. Working the other way round (making the steel first and asking questions later) is how jobs end up being cut out and redone.

What to do first

Get the engineer involved early, before you've committed to a layout. A small change to where an opening sits can substantially change the steel needed, and it's far cheaper to move a line on a drawing than to re-make a beam.

Frequently asked questions

Can my builder size the beam instead? An experienced builder will have a good instinct for it, but building control wants calculations from a qualified engineer — and instinct isn't a calculation.

Do I need one for a small internal opening? If the wall is load-bearing, yes. If it genuinely isn't structural you may not — but confirming that is itself worth having checked.

What do you need from the engineer? The calculations and the drawing showing sections, lengths and connection details. Send them over and we'll quote from them.