Boundary Noise Limits and Where a Condenser Sits in Them

Noise from plant is regulated at the edge of the premises it stands on. It is not measured at the machine, and not in the room where it is a problem. That choice of measuring point separates a noise complaint from a compliance question. It is the fact most operators miss before pricing a fix.

NEA's technical guideline for air-conditioning and mechanical ventilation states the measuring points plainly. Equipment at ground level is read at the site boundary; equipment above ground, on a roof for instance, is read close to the source at the same height, then computed for a point on the boundary at that height. Where a barrier has been built, the reading is taken behind it, at its mid-height.

Distance, screening and height therefore sit between the machine and the number that counts. A loud machine deep inside a large site can read lower at the line than a quiet one bolted to the edge of a small one. Sound figures printed in a brochure describe the machine under test conditions, and nothing about your line.

Two adjustments push the assessment further from raw loudness. The guideline sets a background noise correction, comparing the permitted level against the background and adding a correction where the two sit close together. It also sets modifying-factor penalties for sound with a particular character: a clear tone, heavy low-frequency content, impulsive knocks, or a level that keeps falling back to background and rising again, each subject to a stated cap.

The character rule is the one operators find backwards: a machine that hums on a single note can be assessed more harshly than a louder machine producing even, broadband sound.

There is no single figure to comply with. Limits are written against the type of premises being affected, not the type of machine making the noise. NEA's guideline sorts affected premises into noise-sensitive uses, residential uses, and everything else, with the tightest figures on the noise-sensitive group.

Each group then carries separate figures for a daytime band, an evening band and a night band. The night figures are the tightest. Nothing about the machine changes between bands. The same condenser can sit inside the limit through a working afternoon and fall outside it once the block has gone to bed.

Mixed-use neighbours default to the stricter treatment, and a tower with shops below and flats above is read as flats.

Land next door counts even when nothing has been built on it yet. The guideline sends qualified persons to the URA master plan to check the intended use of adjacent premises, and to apply the stricter limit where current and intended uses differ. An empty plot zoned for housing is treated as the neighbour it will become, which matters before siting plant along a line that today faces a car park.

The figures themselves are deliberately absent from this page. They vary between instruments, are set out per premises type and period, and are amended from time to time. Take them from NEA for the premises you actually occupy, rather than from any article, this one included.

Three separate instruments carry the phrase boundary noise, and they do not reach the same premises. Picking the wrong one is how an operator ends up arguing against a limit that was never aimed at them.

Construction sites sit under their own regulations, written for work that is temporary and loud by nature. Factory premises sit under the boundary noise limits regulations made for them: the definition NEA uses covers premises used for industrial or manufacturing purposes, taking in repair and processing workshops and warehouses while excluding construction sites. A workshop or warehouse falls inside it; a shop, office or restaurant does not.

Cooling and ventilation plant in non-industrial buildings is addressed by a technical guideline, not those regulations. The guideline defines a non-industrial building as one used for trade, business or commerce. It names shopping complexes, office towers, hotels, schools and hospitals, while leaving out factory and residential premises. Qualified persons apply the guideline at specification, design and installation stage; NEA lists it among the pollution control requirements a new development should be designed to meet.

Read together, the practical shape appears. For most commercial premises the boundary figure was a design target, meant to be hit at building-plan stage. It does get tested once by measurement, near the end of construction, when a noise assessment report goes to NEA with the occupation permit application. What does not follow is a standing test an occupier gets put through later. Once a complaint arrives, two questions matter: whether the plant has drifted from what the design assumed, and whether anything about the neighbour has changed.

Most complaints trace back to siting, mounting or the hour of operation. Very few trace back to somebody buying a loud model.

Plant hemmed in by hard surfaces reads higher than the same plant in the open. A recess, a narrow gap between two blocks, or a wall sitting directly behind the discharge sends sound back out rather than letting it spread and fall away. The machine has not changed; the path to the property line has. Two identical installations on one estate can draw a complaint at one address and silence at the other, purely on that.

Mounting is the case where a quieter machine changes nothing. Where feet sit hard on a slab, or a bracket is bolted through a shared wall, part of the vibration travels through the structure rather than the air, surfacing as a hum inside a room with no view of the plant. Anti-vibration mounts, and the state they are in, decide how much crosses over. A neighbour describing a hum in the wall rather than noise outside the window is describing that path.

Night turns a tolerable machine into a complaint for two reasons at once. The permitted level drops after the evening band, and the background level around the plant drops with it. The machine holds its output while everything around it goes quiet, so it stands further above background exactly where less is allowed. The guideline also applies its intermittent-noise penalty at night only.

A fourth cause is drift rather than design. Fouled coils make the fan and compressor work harder, bearings develop play, guards and brackets work loose, and rubber mounts harden with heat and age. Each raises output, or adds a character the machine did not have at commissioning. That is the case where a service visit genuinely is the answer, which is reason enough to rule it in or out before anyone re-sites anything.

Four things decide whether a quote is worth reading. Where the property line runs and what sits across it. Which instrument, if any, reaches your premises. What the level reads at that line during the hours the complaint names, with the background recorded alongside it. And whether the sound carries a character that attracts a penalty.

The measurement only counts if the instrument does. The guideline calls for a calibrated integrating sound level meter meeting the international standards for the top instrument class. A phone app is a useful private hint about whether the noise gets worse once the estate quietens, but it is not evidence, and nobody assessing the complaint will treat a phone reading as proof.

If a contractor proposes a replacement condenser on the strength of a quieter number in a brochure, push back. That number comes from a test chamber at a fixed distance, and says nothing about reflections off the wall behind your unit, vibration entering the bracket, or where your line sits. Ask what the proposed machine is expected to read at the boundary, and on what basis.

The order of fixes follows the diagnosis, not the price list. Structure-borne transfer calls for isolation and mounting work, and a new machine is beside the point. An airborne path out of a boxed-in position calls for screening or a change of position. A level that has drifted upward from a healthy baseline calls for the machine to be serviced back to it. Choosing before measuring is how an operator pays twice.

Related ground sits on separate pages: placement limits, post-installation noise, and what a particular sound says about the machine.

The figures behind all of this belong to NEA, and its published version is the only one worth quoting. This page sets out the shape of the framework so the right question gets asked first. Treat it as orientation, not legal advice, and read the current text of whichever instrument covers the premises you occupy. Where a lease, a licence condition or a set of by-laws sets something stricter, the stricter one has to be met.