What percentage of a building's floor area must have working radio coverage?

The 90% general and 99% critical-area figures are real, but they are American. They come from the International Fire Code Section 510 and NFPA 1225 (which since 2022 has absorbed the radio coverage requirements previously carried in NFPA 1221 and NFPA 72), and they apply where a jurisdiction has adopted that code. Singapore has adopted no equivalent. Neither the SCDF Fire Code nor IMDA's COPIF prescribes a floor-area coverage percentage for two-way radio, so in a Singapore building the number is whatever the tender or the specification says it is — and if nobody writes one down, the system has no pass criterion at all. In practice I design to 95% area coverage as the working default, with every test point in critical areas required to pass.

Where the 90% and 99% figures actually come from

Under IFC 510 and NFPA 1225, general building areas must achieve 90% floor area radio coverage and critical areas 99%. Critical areas are typically listed as exit stairs and passageways, lift lobbies, fire pump rooms, standpipe cabinets, the fire command centre, and anything else the authority having jurisdiction adds. The percentage is measured, not modelled: each floor is divided into a grid of 20 approximately equal test areas, a point near the centre of each is measured, and a failure at that point fails the whole cell. I have set out the survey method itself in more detail in how in-building two-way radio coverage is measured and passed. Ninety percent therefore means 18 of 20 cells pass — two failures allowed per floor.

That grid arithmetic is where the 99% figure gets interesting. On a 20-cell grid, one failure is 95%, which is already below 99%. So 99% is not a number you can express on a 20-cell survey at all. Read literally, it means every test point in a critical area must pass, and the practical effect is a zero-failure requirement in stairwells and lift lobbies rather than a slightly stricter percentage. That is my reading of the code text rather than something the code states in those words, but it is the only reading that survives the arithmetic, and it is how I would write it into a specification.

The figures are also not as universal as they are quoted. New York City's FDNY technology bulletin specifies 97% for both general and critical areas rather than 90/99. Anyone quoting "90% and 99%" as the global standard is quoting one code family and calling it the industry.

The numbers that actually go in a specification

• General area coverage: 90% of floor area (18 of 20 grid cells) — IFC 510 / NFPA 1225 baseline

• Critical areas: 99%, which on a 20-cell grid means zero failed cells

• Suneast design default in Singapore: 95% area coverage, zero failures in critical areas

• Signal level at the portable: −95 dBm minimum, downlink and uplink both

• Fade margin above threshold: 10 dB commercial, 15 dB mission-critical

• Audio quality: DAQ 3.0 general, DAQ 3.4 in critical areas

• Grid: 20 cells per floor, measured with a calibrated portable, not a spectrum analyser on a tripod

Why a percentage on its own is a weak acceptance criterion

A coverage percentage says how much of the floor works. It says nothing about how well, in which direction, or where the failures sit. Three gaps matter.

First, a percentage without a level is unenforceable. Ninety percent of the floor above what? A system reading −93 dBm everywhere passes a bare percentage clause and still falls off the digital cliff the moment a lift motor or an LED driver raises the noise floor by 10 dB. Percentage and level have to be specified together, which is why every serious criterion pairs 90% with −95 dBm.

Second, a percentage without a direction is a downlink test. The portable transmits 4 W (+36 dBm) less about 3 dB body loss; a rooftop repeater transmits 40 W (+46 dBm). That 13 dB asymmetry means the uplink fails several floors before the downlink does, and a survey that only measures received signal will certify a building whose fire command centre cannot hear anyone in the basement.

Third, a percentage without an adjacency rule allows the two permitted failures to sit side by side. Two failed cells in opposite corners of a floor plate is patchy coverage. Two failed cells adjacent to each other is one contiguous dead area roughly a tenth of the floor, and if that area happens to be the stair core, the floor has passed on paper while failing at the only place a responder will be standing. I specify that failed cells must be non-adjacent, and I would not accept a floor where they are.

What a Singapore tender should say instead

Because no Singapore code supplies the number, the specification has to. The wider regulatory picture — why Singapore sits on COPIF plus the Fire Code rather than an IFC 510-style statutory code — is covered in is Singapore adopting a US-style emergency responder radio coverage code. A workable clause names four things together: the percentage and grid size, the minimum signal level in both directions, the audio quality target, and the list of areas treated as critical. Without the fourth, "critical areas" is argued at handover instead of agreed at tender. I would name the stair cores, lift lobbies and lift cars, the fire command centre, basement carpark levels, the pump and generator rooms, and any plant space a technician works in alone.

Related questions

Does Singapore legally require any radio coverage percentage in buildings?

No. Neither the SCDF Fire Code nor IMDA's COPIF sets a floor-area coverage percentage for two-way radio. The figures used here are contractual, drawn from US practice, and only binding because a tender writes them in.

Is 95% or 90% the right target for a commercial building?

Ninety percent is the US code floor for general areas. I design to 95% because the two failed cells that 90% permits are usually the two cells a client complains about, and the incremental cost of closing them at design stage is far lower than retro-fitting an antenna after handover.

Can a building pass a 90% coverage test and still have an unusable stairwell?

Yes, and this is the single most common failure of a bare percentage clause. The stair core is one or two cells on a 20-cell grid, so it can fail entirely while the floor passes. Treating stairwells as critical areas with a zero-failure requirement is what prevents it.

Suneast designs and builds in-building radio coverage systems in Singapore against a written, measurable criterion rather than a vendor's assurance. We set the percentage, the grid, the −95 dBm level in both directions and the critical-area list into the specification before design starts, run the acceptance survey with a calibrated portable on the client's own frequencies, and hand over the cell-by-cell results as the compliance record for annual re-testing. Where a building is being tendered, we will write the coverage clause so it cannot be answered with a manufacturer's advertised square-footage rating.