Metal Works · 9 September 2026

Fire Protection for Structural Steel: The Line Item Steel Quotes Keep Missing

Steel is the reason a mezzanine can be thin, a loft can be open, and a second storey can go on without doubling the size of everything below it. It is also the material with the least patience for heat. Concrete carries its own insulation in its bulk; a steel beam is thin, conductive and works close to its limit by design, so when it gets hot it loses strength quickly.

That is the whole reason fire protection exists as a line of work. And it is the line most often absent from a steel quotation, most often discovered late, and most often applied at the one moment in the programme when it is hardest to reach the steel.

This is not a guide to what the requirement is on your project — that is settled by your QP's design and the approved submission, and it varies with what the space is used for, where the steel sits and what it holds up. This is a guide to what fire protection does to the rest of your job once the requirement exists, which is the part nobody warns you about.

Get the answer in writing, in both directions

The first useful step costs nothing: ask your QP, in writing, whether the steel requires fire protection, and to what standard, and get the answer before the steel is fabricated.

Ask for the answer even when it is "no". An unwritten "we didn't think it needed any" is the version that becomes an argument at handover, and it is also the version that leaves a builder pricing a job without knowing whether a substantial trade is in it. On a leased industrial unit there is a second reader too, because the landlord and the building management have their own requirements — the wider approvals picture is in altering a leased industrial unit.

The reason to ask early rather than at the end is that the answer changes four things, and three of them are decided long before anyone would think to raise it.

1. It changes the steel itself

Protection is not a coat of something applied to a finished frame. It has to be designed with the frame.

An intumescent coating is a paint system with a specified dry film thickness, and the thickness depends on the shape and mass of each section. A heavier section heats more slowly and needs less; a light section needs more. That means the protection specification and the section sizes are one decision, not two, and a beam substituted for a lighter one after the coating was specified is a beam whose protection no longer matches it.

Encasement in fire-rated board is a different problem: the steel disappears inside a box, so the box needs room. A column that sits neatly against a wall in the drawings needs the board thickness added on every exposed face, and suddenly it does not. Connections, base plates and the junctions where a beam meets a column all have to be detailed so they can actually be wrapped, because a joint that cannot be covered is a gap in the protection.

2. It changes the sequence, and this is where money is lost

Fire protection goes on after the steel is erected and before anything covers it. That window is narrow, and it sits exactly where every other trade wants to start.

The failure is always the same. Services get run tight against the steel. The decking goes down. The ceiling closes. Then someone asks about fire protection and the answer is that the steel is now behind a ceiling, above a duct and under a floor. Getting to it means opening work that was already finished and paid for, and applying a coating in conditions where it cannot be done properly anyway.

There is a second reason the window matters: coatings have application conditions. Surface preparation, ambient conditions and the time between coats are part of the specification, not a preference. A coating rushed onto dusty or damp steel at the end of a programme is a coating whose paperwork will say one thing and whose performance will say another.

So the protection has to be a named step in the programme, positioned after erection and before first fix, with the steel accessible. On a mezzanine job this is the single most useful thing to fix on the programme early — the same discipline that makes the floor loading and submission side work, which we set out in steel mezzanines, floor loading and BCA submission.

3. It changes what the steel can look like

A lot of people choose steel because they want to see it. Exposed black steel, a slim staircase stringer, a beam left visible over an open space — this is a real reason to build in steel and we would not talk anyone out of it.

But the finish and the protection are the same coat. An intumescent system is applied to a thickness that is measured, and a decorative top coat goes over it; done well it looks like painted steel, done as an afterthought it looks like painted steel that somebody sprayed thickly in a hurry. If the look matters, it has to be specified as a finish and as protection at the same time, and the applicator has to know both are being judged.

Board encasement removes the option entirely. The steel is inside a box and what you see is a plastered column. That is a perfectly good answer where the steel was never meant to be seen, and a bad surprise where it was. If exposed steel is part of the design intent, say so at the point the protection method is chosen, not after. The same logic applies to the staircases and railings we make in-house, which is part of why we do not farm that work out — see why we don't outsource metalwork.

4. It changes the handover paperwork

Fire protection is one of the few parts of a build whose correctness cannot be seen once it is finished. A coating at the right thickness and a coating at half the thickness look identical.

Which means the record is the work. What should reach you at the end: the product data for the system actually used, the applicator's records, the thickness readings taken across the frame, and confirmation that what was applied matches what the QP specified. If any part of the steel was encased rather than coated, the detail of how junctions and penetrations were treated belongs in there too.

Ask for that list at the start. A specification that names the deliverables at tender time is a specification that gets them; asked for at handover, it becomes a hunt through a subcontractor's phone.

The retrofit trap

The most expensive version of this is not a new build. It is an existing mezzanine or loft — inherited with a unit, or built years ago by somebody else — where the steel is already boxed in, already loaded, already in use, and the question of fire protection surfaces during a change of use, a sale, or a landlord's inspection.

At that point nothing is cheap. The steel has to be exposed to be assessed, the space has to be emptied to be worked in, and the work has to happen around a business that is trying to operate. If you are taking over a unit with existing steel in it, put fire protection on the list of things you establish before you sign, alongside the loading and the approvals. It is the item most likely to be undocumented and most expensive to resolve later.

Five questions worth asking

Does the steel require fire protection, and to what standard? In writing, from the QP, before fabrication — including a written "no" if that is the answer.
Which method is specified, and who is applying it? Coating and encasement are different trades with different consequences for the look and the space.
Where does it sit in the programme, and who is holding that window open? If it is not a named step between erection and first fix, it is not planned.
Is the steel meant to be seen? Answer it before the method is chosen, not after.
What documents do I receive at handover? Product data, applicator records, thickness readings, and confirmation against the specification.

The short version

Whether your steel needs fire protection is your QP's call and belongs in writing before anything is fabricated. Once the answer is yes, it stops being a finishing item: it sizes the sections, it needs room around columns and detailing at every connection, it occupies a narrow window between erection and first fix that every other trade wants, it decides whether you can see the steel at all, and it can only be proved by paperwork. Get it into the programme as a named step and into the specification as a named deliverable. Both are free at the start and expensive at the end.

Planning a mezzanine, a loft or a steel frame and want the fire protection question settled at the right stage? WhatsApp us on 9107 2601 — tell us what the steel is for and what stage you are at, and we will tell you what has to be decided before fabrication and what can wait. Wong Lye Pte Ltd holds a BCA General Builder Class 2 (GB2) licence; see our metal works page and our A&A works page for how the two sides fit together.

Common questions

Does structural steel need fire protection?

That is settled by your QP's design and the approved submission, and it varies with what the space is used for, where the steel sits and what it holds up - so ask the question in writing and get the answer before the steel is fabricated. Ask for it even when the answer is no, because an unwritten assumption that none was needed is the version that becomes an argument at handover, and it also leaves a builder pricing the job without knowing whether a substantial trade is inside it. On a leased unit the landlord and building management are a second reader with requirements of their own.

Why does fire protection change the size of the steel?

Because an intumescent coating is a paint system applied to a specified dry film thickness, and the thickness required depends on the shape and mass of each section - a heavier section heats more slowly and needs less, a lighter section needs more. That makes the protection specification and the section sizes one decision rather than two. It also means a beam substituted for a lighter one after the coating was specified is a beam whose protection no longer matches it.

When in the programme should fire protection be applied?

After the steel is erected and before anything covers it, which is a narrow window sitting exactly where every other trade wants to start. The common failure is that services get run tight against the steel, the decking goes down and the ceiling closes, and only then does the question come up - at which point reaching the steel means opening finished, paid-for work, and applying a coating in conditions where it cannot be done properly anyway. Coatings have real application conditions covering surface preparation, ambient conditions and the interval between coats, so it needs to be a named step on the programme rather than an assumption.

Can steel still be left exposed if it needs fire protection?

With a coating, usually yes - but the finish and the protection are the same coat, so it has to be specified as both at once and the applicator has to know both are being judged. Done well an intumescent system with a decorative top coat looks like painted steel; done as an afterthought it looks like steel sprayed thickly in a hurry. Board encasement removes the option entirely, because the steel ends up inside a box and what you see is a plastered column. If exposed steel is part of the design intent, say so at the point the protection method is chosen rather than after.

How do I know the fire protection was done correctly?

By the records, because it is one of the few parts of a build whose correctness cannot be seen once finished - a coating at the right thickness and one at half the thickness look identical. What should reach you at handover is the product data for the system actually used, the applicator's records, the thickness readings taken across the frame, and confirmation that what was applied matches what the QP specified. Where steel was encased rather than coated, the detail of how junctions and penetrations were treated belongs in there too. Ask for that list at tender stage, not at handover.

What about an existing mezzanine that is already boxed in?

That is the most expensive version of the problem. Where a mezzanine or loft was inherited with a unit or built years ago by someone else, the steel is already enclosed, already loaded and already in use, and the question usually surfaces during a change of use, a sale or a landlord's inspection. By then the steel has to be exposed to be assessed, the space emptied to be worked in, and the work carried out around a business trying to operate. If you are taking over a unit with existing steel, establish the fire protection position before you sign, alongside the floor loading and the approvals.