Industrial concrete slabs: the type under your feet decides what goes on top
Most warehouse floors are a slab-on-ground, poured once and rarely thought about again. Some are suspended, and a growing number are post-tensioned — and that last category changes something as basic as where you are allowed to drill.
Last updated 2026-08-24
Slab-on-ground or suspended
A slab-on-ground bears directly on the prepared ground beneath it. It is the default floor type for a single-storey warehouse because it is the simplest and most cost-effective way to get a working floor over a large footprint, and it is what most Australian sheds are actually built on.
A suspended slab is different: it spans between structural supports — beams, columns or walls — rather than resting on the ground, which is how you get usable space underneath it. You find suspended slabs over basements, on structural steel or precast frames, and on upper storeys. In a typical single-level distribution shed you are standing on a slab-on-ground; in a multi-level facility, you may not be. Which one you have is worth confirming before you plan a layout around what the floor slab will and will not take.
What post-tensioning actually does
Post-tensioning stresses steel tendons inside the slab after the concrete has cured, putting the whole slab into permanent compression. It is used on both slab types. On a slab-on-ground it improves crack control, adds stiffness and reduces how much the slab deflects under heavy or uneven loading, which can allow a thinner slab and wider joint spacing for the same performance. On a suspended slab it is often the preferred approach for the same reason: more strength for less material.
None of that changes how the finished floor looks. A post-tensioned slab is not visually different from a conventionally reinforced one, which is exactly the problem for anyone about to drill into it.
The important case: drilling into a post-tensioned slab
A post-tensioned slab has live steel tendons running through it under permanent stress. Drilling, cutting or coring into it without first locating those tendons risks severing one — and that is a structural and safety event, not a cosmetic one. A severed tendon does not just leave a hole; it releases stored tension in a way that can damage the surrounding concrete, and the loss of that tendon's contribution to the slab's design then has to be assessed and, usually, remedied.
That is why anchor location on a post-tensioned slab is not a decision made on site with a hammer drill. Tendon layouts are checked first, against structural drawings where they exist or by scanning the slab where they do not, before a single hole goes in. Choosing the anchor and where it sits is already an engineering decision on any slab; a post-tensioned one adds a location constraint on top of it that has to be resolved before the load question is.
What this means once racking goes in
An installer arriving to bolt a run of racking to the floor does not automatically know which slab type they are standing on unless someone has documented it, at design stage, in a handover pack, or in a structural assessment commissioned specifically to find out. The point load a racking footplate puts through the slab is a separate question that applies regardless of slab type, but a post-tensioned floor narrows where that load can be transferred, because some anchor positions are off-limits once tendons are mapped.
AS 4084, the standard behind Australian pallet racking installations, treats floor condition as part of what a compliant installation actually checks, not a detail to assume away. What the standard covers and the racking inspection process both start from the same premise: the floor is part of the racking system, not scenery underneath it.
What a page like this will not tell you
This page will not give you a slab thickness, a post-tensioning force or a tendon spacing, because none of those numbers exist in general — they are specific to the building, the pour and the design load, and they belong to whoever engineered the slab. What you can take from it is the question to ask before any racking, anchor or footing decision: what type of slab is this, is it post-tensioned, and where are the drawings that show it.
From there, the practical follow-ups are covered in why concrete floors crack and curl, the flatness question, and what floor repair actually involves once something in the slab has already gone wrong.
Common questions
- How do I find out if my warehouse floor is post-tensioned?
- Check the original structural drawings or building documentation. If they are not available, ask a structural engineer to confirm before any anchor or coring work — it is not something to guess from the surface.
- Can racking still be bolted to a post-tensioned slab?
- Yes, routinely. Post-tensioned floors carry racking throughout Australia. What changes is that anchor positions are checked against the tendon layout first, not that post-tensioning rules racking out.
- Is a suspended slab less suitable for racking than slab-on-ground?
- Not inherently. Suspended slabs are engineered for whatever loads their design specifies, including racking, but as with any slab that specific loading has to be checked against the specific design rather than assumed.
- Who decides whether my slab can take an anchor bolt at all?
- A structural or civil engineer, or the racking supplier's design engineer, working from the slab's actual documentation and condition — not a rule of thumb applied on the day.
Part of our guide to the floor and what is bolted to it.