Is it true that construction projects under about 30 floors don't need a repeater?

No. The 30-floor figure is a sales rule of thumb, not an engineering threshold, and the figures circulating beside it do not agree with each other. The same search will tell you that radios struggle past 15 floors, that they cover 1 to 25 floors, that sites below 30 floors do not need a repeater, and that buildings under 40 floors and 400,000 sq ft are fine on a 4 W handheld. Those are four incompatible answers to one question, and the reason they conflict is that floor count is the wrong variable. What decides whether a site needs a repeater is whether a continuous vertical leakage path still exists between the two radios — and on a Singapore high-rise that path closes months before the structure tops out.

Where does the 30-floor number come from?

It comes from manufacturer coverage ratings, repeated by resellers and then rounded. Those ratings are derived under conditions the datasheet rarely states: a single building, light commercial construction, no basement, and usually a horizontal measurement converted into floors by assumption rather than by test. None of the published figures tell you the slab construction, whether the radios were talking direct to each other or through a repeater, or where in the building the weak end was standing. A number produced that way cannot survive contact with a reinforced-concrete core, which is why the same 30-storey job can pass in March and fail in September.

What the arithmetic actually says

Work the vertical budget for two 4 W portables talking directly to each other, which is the honest test of whether a site can go without a repeater:

• Design threshold for reliable DMR voice: −95 dBm at the portable

• Standard commercial fade margin: 10 dB (15 dB where the traffic is safety-critical)

• Portable transmit power: +36 dBm (4 W), less 3 dB body loss at each end

• Free-space loss at 450 MHz over 96 m — about 30 storeys of vertical separation: ≈65 dB

• Reinforced-concrete floor slab: 15–25 dB per slab; RC core or lift shaft wall: 25–35 dB

That gives a total allowable path loss of about 115 dB. Vertical distance over 30 storeys only spends 65 dB of it, which leaves roughly 50 dB — two and a half concrete slabs at 20 dB each. The budget is exhausted by the third floor, not the thirtieth.

This is the point the floor-count rules miss. Any radio that genuinely works across 20 or 30 floors is not penetrating 20 or 30 slabs; it is finding a leakage path — an open lift shaft, an uncast stairwell, an open façade, a reflection off the building opposite. The floor count tells you nothing about whether that path exists. The construction stage does.

Why the same site passes early and fails later

On a Singapore tower under construction, the radio environment gets progressively worse as the job progresses, and the sequence is predictable. Basements are cast first, so the deepest levels are already 25 to 35 dB down through the core while the superstructure above is still an open slab-and-column frame that radio crosses easily. As blockwork, risers, lift shafts, M&E plant and finally the façade go in, the leakage paths close one by one. A site that tested clean at structural topping-out can lose the basement-to-crane link entirely once the curtain wall is glazed — the same building, the same radios, a different answer.

Two more things break the rule of thumb regardless of height. If the site has two or more towers rising at once, or the site office sits several hundred metres from the works, you are no longer asking a vertical question at all. And deep basements — three to five levels is now routine on Singapore plots — fail on almost every site regardless of how many storeys sit above them.

Does the 30-floor rule work any better in Singapore?

Less well, for two reasons. Singapore's residential high-rise stock runs well past the range these figures were written for: Pinnacle@Duxton stands at 50 storeys, HDB projects above 40 storeys are increasingly common as land gets scarce, and a Build-To-Order development at Pearl's Hill is planned to exceed 60. A rule of thumb that tops out at 30 or 40 floors simply does not address the buildings being built.

The second reason is power. The overseas figures assume a 4 W portable. Under IMDA's Localised Private Network (Multi-Channel Radio-Communication) Licence, effective radiated power is capped at 1.0 W, and exceeding that — or needing an exclusively assigned frequency, or installing a fixed repeater or base station — moves the site up to a Localised Radio-Communication Station Licence, charged per station and per frequency. Verify your own case with IMDA, since fees and conditions change. But note what the arithmetic makes of the difference: 1 W against 4 W is 6 dB, and 6 dB is less than a third of one concrete slab. Power is not the lever here.

Related questions

Does a 12-storey site ever need a repeater when a 30-storey one doesn't?

Frequently. A 12-storey building with three basement levels, a central RC core and cast stairwells is a harder RF problem than a 30-storey frame still open to the sky. Depth below grade and core construction beat height almost every time.

Can we just test it instead of guessing?

Yes, and it is a half-day job. Run a talk-around survey at the current construction stage, measure in both directions rather than downlink only, and re-test at façade completion. Two surveys cost far less than discovering the gap during an incident.

Does going digital change the threshold?

No. DMR buys roughly 5 to 7 dB of usable sensitivity over analogue, which is a useful fraction of one slab and nothing like a floor-count reprieve. It also fails abruptly rather than degrading audibly, so the last working floor gives less warning.

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Suneast designs, licenses and installs two-way radio coverage for Singapore buildings and construction sites, and we do not quote floor counts. We survey the site at its current stage, work the uplink and downlink budgets against the −95 dBm threshold with a stated fade margin, and specify whatever the arithmetic requires — a single repeater with a well-sited antenna, a distributed antenna system down the ELV risers, or nothing at all if the site genuinely does not need one. We handle the IMDA licence application with the design. For related reading, see our article on how much signal a radio loses through each concrete floor slab and basement wall and on why advertised square-footage coverage ratings do not translate into floors covered.