Pictured above: a mezzanine deck from our project archive (V5-8) carrying its own racking bays, wire cages of stock and a pallet truck, with the black edge railing on the right. A deck that holds racking is designed for that load whichever way the platform itself is supported, and how the platform is supported is what this article is about.

When you ask for a mezzanine in a warehouse that already has, or is about to get, pallet racking, there is a question that comes up early and gets answered too quickly: does the racking hold the deck up, or does the deck stand on its own columns? The first is a rack-supported mezzanine, sometimes called a rack-supported platform. The second is a freestanding mezzanine. On a drawing they can look almost identical. On the warehouse floor, five years later, they behave very differently.

This is what each one is, what changes when the racks are part of the structure, and the questions worth settling before you sign for either.

What each one is

A rack-supported mezzanine uses the pallet racking uprights as the supporting columns of the platform above. Our services page gives the advantages in one line: it saves floor space, integrates storage with workspace, and is more cost-effective than a freestanding mezzanine. The catch is in the same sentence. The racks carry the pallet load and the platform load at the same time, so the racks and the platform have to be designed as one structure.

A freestanding mezzanine has its own column grid, independent of the racking. Column spacing typically runs 4 to 6 metres on-centre, set by the beam span limits and the aisle layout underneath. Racking below is installed separately and can be moved or swapped, selective to drive-in for example, without touching the mezzanine structure. It costs more up front, and what you are paying for is that freedom.

Neither is the better product. They are two answers to a question about your own warehouse, and the question is the next heading.

The question that decides it: will the ground floor stay as it is?

A rack-supported platform limits future layout changes. If you reconfigure the ground-floor racking, you disturb the platform. A freestanding platform lets you change the racking underneath without re-engineering the deck, which is why we recommend it when you expect layout changes or seasonal shifts in your SKUs.

So the practical test is to list what could change the racking layout below in the next few years, and be honest about how likely each one is:

• A different truck. A reach truck or a narrower-aisle truck changes the aisle width the racking is laid out for. See checking a new truck against your racking.
• A change of racking type. Moving from selective to double-deep or drive-in is a layout change, not an add-on. See drive-in or double-deep.
• A new pallet format. When your suppliers change what they deliver on, beam lengths and levels can change with it. See non-standard pallet sizes.
• Extra beam levels. Even adding a level to existing racking is a load change. See adding a beam level. Under a rack-supported deck, that is a question for the engineer who designed the platform before anyone touches it.
• Handing space back. Giving up floor area, or leaving the unit, means taking racking away. See downsizing a warehouse.

If the honest answer is "the layout is fixed, the loads are predictable, and the pallets and trucks are not going to change", a rack-supported platform is a sound and economical choice. If the honest answer is "I cannot say what this floor will look like in three years", pay for the freestanding grid.

What "one structure" means in practice

Because the racks and the platform are designed together, four things follow. These are consequences of the design as we describe it, not extra promises.

• One party has to own the whole design. We design the racks and the platform as one system, so the quotation covers both. Be careful of racks from one supplier asked to carry a deck from another: the interface between them is exactly the part nobody is then responsible for.
• The uprights are doing two jobs. A forklift that strikes an upright is hitting something that also carries a platform. That is our reading of the design, not a published rule, but it is why we would ask any supplier how the uprights that carry the deck are inspected and recorded. How a periodic inspection works is on the rack inspection page, and what to do about a damaged upright is in repair, replace or de-rate.
• The slab takes the load at the baseplates. Mezzanine columns concentrate load into small footing areas, and racking does the same at the upright baseplates. We assess the slab at survey from the building's original structural drawings, which are typically obtainable from the landlord or BCA records. Most modern industrial slabs, built after 1995, handle typical point loads. Older slabs sometimes need larger base plates to spread the load. Racking on a deck is the same point-load question one level up, which is covered in mezzanine deflection limits.
• Column spacing and rack layout are one drawing. Even on a freestanding platform, the columns have to line up with whatever racking sits below, which is why we design the two together rather than as separate jobs. On a rack-supported one, the rack grid is the column grid.

What is the same either way

Several things do not depend on which type you choose, and they are where most mezzanine projects actually go wrong.

• The load rating comes from the use. Office or light gauge work is around 200 kg/m², carton picking and light assembly 250 to 350 kg/m², pallet storage on the deck 500 kg/m² as the minimum, and forklift drive-on access 1,000 kg/m² or more with thickened slab connections. A standard pallet-storage mezzanine is designed for hand pallet trolley loads only. Decide it at the start: raising a finished deck's rating is an engineering job, not an adjustment.
• Clear height is measured to the lowest obstruction. A mezzanine that is useful on both levels needs a minimum of 4.5 m, which leaves about 2.1 m of headroom on each side of a deck of around 300 mm. One client measured 5.4 m of clear height and the sprinkler heads turned out to be at 4.8 m, so the BCA plan had to be redrawn. The full reasoning is in mezzanine or taller racking.
• Sprinklers. If the unit is sprinklered and the mezzanine obstructs the existing heads, extra heads must go in below the deck. It adds cost and time, and it is either coordinated with your sprinkler contractor or included in the quotation, so ask which.
• Submission. The triggers we work to for BCA are a mezzanine above approximately 300 m² gross floor area, one carrying assembly use, one used for any public-facing function, and any that changes the building's GFA balance. SCDF comes in when a mezzanine affects fire compartmentation, needs sprinkler tap-offs, changes escape paths or is above 300 m² gross. A small storage mezzanine often needs none, and we still check the URA plot record before saying so. An office does not inherit that answer, as set out in a warehouse office on a mezzanine.
• PE-stamped calculations. Structural design is PE-stamped whichever type you pick.

What it costs

The published range for a mezzanine is S$280 to S$520 per square metre, including stair, handrail, gate and BCA submission coordination, and it moves with load rating, clear span, deck finish and submission complexity. We do not publish a separate figure for rack-supported against freestanding, and we are not going to invent one here. What we can say from our own services page is the direction: rack-supported is the more cost-effective of the two, and the saving depends on your unit, so it is quoted after a site survey. How to compare two mezzanine quotations fairly is in mezzanine floor cost per square metre.

Five questions to settle before you ask for a quote

1. What could change the ground-floor racking in the next few years? Trucks, pallets, racking type, a move. If more than one is plausible, lean freestanding.
2. What will the deck carry, weighed? The heaviest load, and whether anything with wheels or forks will ever go on it.
3. Who will be allowed to move racking, and will they ask first? On a rack-supported deck, beams and uprights are not just storage equipment, so the answer has to be written down.
4. How much clear height do you really have, measured to the lowest sprinkler head, duct or light?
5. Is the unit leased? Get the landlord's agreement in writing before anyone draws a column grid, and think about what you will have to take out when the lease ends.

The short version

• Rack-supported: the racking uprights are the deck's columns. Saves floor space and costs less, but racks and platform are one structure, and changing the racking disturbs the platform.
• Freestanding: its own column grid, typically 4 to 6 m apart. Costs more up front and leaves the racking below free to change.
• The deciding question is how likely the ground-floor layout is to change, not which type sounds more solid.
• Load rating, clear height to the lowest obstruction, sprinklers and the submission triggers apply to both.
• No separate published price for either type. The range is S$280 to S$520 per square metre, quoted after survey.

Planning a deck over racking, or racking under a deck? WhatsApp us on 9107 2601 with the clear height, the deck area and what the deck is for, and we will tell you which one the unit points to. The mezzanine page has the load ratings and regulatory triggers, and the services page sets out how a job runs and how we bill.

Related reading: mezzanine racking systems in Singapore · mezzanine or taller racking · a warehouse office on a mezzanine · mezzanine BCA submission conditions