The standard that defines minimum acoustic quality in Chilean homes
NCh 352 is the Chilean National Standard (Norma Chilena) that establishes the minimum acoustic performance requirements for residential buildings. It is part of the regulatory framework that governs construction quality in Chile and applies to multi-family residential buildings — apartment buildings — of the type being built across Chilean cities today.
The standard defines minimum thresholds for two key acoustic measurements: airborne sound insulation between dwellings, and impact sound insulation through floors. Buildings must meet these thresholds to comply with the standard.
Importantly, NCh 352 sets minimum requirements. A building can comply with NCh 352 and still have acoustic performance that some residents find less than ideal. A building that fails to meet NCh 352 has measurably inadequate acoustic insulation.
The Two Key Measurements
NCh 352 compliance is assessed through two standardized measurements. Both are performed in the field using calibrated equipment following ISO 16283 methodology.
DnT,w — Airborne Sound Insulation
The weighted standardized level difference. This value measures how much a wall or floor reduces airborne sound — voices, music, television — between two spaces. It is measured in decibels (dB). Higher values indicate better insulation. NCh 352 specifies a minimum DnT,w value that walls between adjacent dwellings must achieve.
L'nT,w — Impact Sound Insulation
The weighted standardized impact sound pressure level. This value measures how much impact noise — footsteps, dropped objects, chair movements — transmits through a floor from the unit above. It is measured in decibels (dB). Lower values indicate better isolation. NCh 352 specifies a maximum L'nT,w value that floors between dwellings must not exceed.
What "Standardized" Means
Both measurements are "standardized" — meaning the raw measurements are adjusted to account for the reverberation characteristics of the receiving room. This allows results to be compared consistently across different rooms and buildings.
In-Situ vs. Laboratory Values
NCh 352 compliance is assessed through in-situ measurements — measurements performed in the actual building, not in a laboratory. Laboratory values for materials are typically higher than in-situ values because real-world construction introduces flanking paths and installation variations.
What the Values Mean in Practice
Understanding the numbers in terms of everyday experience helps put the measurements in context.
| DnT,w Value (dB) | Practical Meaning | NCh 352 Status |
|---|---|---|
| Below minimum threshold | Normal speech audible and intelligible through the wall | Does not comply |
| At minimum threshold | Loud speech audible but not necessarily intelligible | Marginal compliance |
| Above minimum threshold | Loud speech may be heard as a murmur; normal speech not audible | Complies |
| Well above minimum | Very loud sounds barely perceptible; normal speech not audible | Complies with margin |
Note: Specific threshold values are defined in the NCh 352 standard and vary by building element type. The table above describes the general relationship between insulation levels and perceptible noise.
Why Independent Verification Matters
NCh 352 compliance is a regulatory requirement, but independent verification of compliance before handover is not always performed. The building permit and construction inspection process in Chile does not always include acoustic measurement by an independent party.
Design vs. As-Built Performance
A building may be designed to meet NCh 352 using specified materials, but actual performance depends on how those materials were installed. Flanking paths, construction joints, and installation quality all affect the final in-situ result.
Material Substitutions
During construction, materials are sometimes substituted. If a substituted material has different acoustic properties from the specified material, the as-built performance may differ from the design intent.
The Value of Measurement
Only an in-situ measurement with calibrated equipment can confirm actual performance. No amount of reviewing specifications or material datasheets can substitute for measuring the finished building.
Timing
Measurements performed before the final deed give the buyer information they can act on. Measurements performed after the deed provide documentation but do not change the buyer's initial position.