NBR 15575, published by ABNT (Associação Brasileira de Normas Técnicas), is Brazil's national performance standard for residential buildings. It is one of the most comprehensive residential building performance standards in the Americas, addressing structural, thermal, acoustic, luminous, and functional performance in a single integrated framework. The current edition is NBR 15575:2021, which updated and replaced the original 2013 publication.
For acoustic performance, NBR 15575 sets mandatory minimum requirements and voluntary superior targets for airborne sound insulation of walls and floors, impact sound insulation of floors, and external noise insulation of facades. Unlike some European standards that apply only to specific building types or regulatory contexts, NBR 15575 applies to all multi-family residential construction in Brazil and is enforceable through the Consumer Protection Code. A developer who delivers a building that fails to meet the Minimum performance level faces legal liability for a construction defect, and the remediation obligation falls entirely on the developer.
This guide covers the acoustic requirements in Part 4 (NBR 15575-4: Floors) and Part 3 (NBR 15575-3: Walls) of the standard, explains the three-tier performance framework, and provides a complete reference for design and compliance verification.
The Three Performance Levels
NBR 15575 defines three performance levels for every parameter:
| Level | Code | Legal status | Market positioning |
|---|---|---|---|
| Minimum | M | Mandatory (legal minimum) | Standard residential construction |
| Intermediate | I | Voluntary | Mid-market and standard development |
| Superior | S | Voluntary | Premium residential, high-specification projects |
The Minimum level represents the floor below which buildings are legally non-compliant. Intermediate and Superior are marketing and differentiation tools — developers certifying Intermediate or Superior performance can demonstrate this to buyers and may command a price premium in segments of the Brazilian market where acoustic quality is valued.
In practice, a large proportion of Brazilian residential construction was built before 2013 and does not meet even the Minimum level. The standard's mandatory status applies to new construction; existing buildings are not retroactively required to comply.
NBR 15575-3: Acoustic Requirements for Walls
Airborne Sound Insulation of Separating Walls
Part 3 addresses walls that separate dwelling units (party walls) and walls within dwelling units. The primary metric is DnT,w measured in the field per ISO 16283-1.
Party Wall Requirements (Between Dwellings)
| Location | Level M (DnT,w) | Level I (DnT,w) | Level S (DnT,w) |
|---|---|---|---|
| Wall between bedrooms of different dwellings | ≥ 40 dB | ≥ 45 dB | ≥ 50 dB |
| Wall between living room and bedroom | ≥ 40 dB | ≥ 45 dB | ≥ 50 dB |
| Wall between kitchen/bathroom and bedroom | ≥ 40 dB | ≥ 45 dB | ≥ 50 dB |
Facade Requirements (External Noise)
The facade requirements depend on the outdoor noise level (Lden or LAeq), which must be assessed for the site. NBR 15575 defines four site noise classes:
| Site noise class | Outdoor LAeq, 24h (typical) | DnT,A required (M) |
|---|---|---|
| I (quiet) | ≤ 55 dB | ≥ 20 dB |
| II (moderate) | 56–60 dB | ≥ 25 dB |
| III (urban) | 61–65 dB | ≥ 30 dB |
| IV (noisy) | 66–70 dB | ≥ 35 dB |
Where outdoor LAeq exceeds 70 dB, the standard requires a specialist acoustic study and site-specific requirements. This situation is common in Brazilian cities where residential development has occurred adjacent to major arterial roads and airports without adequate noise impact assessment.
The metric used for facade evaluation is DnT,A (A-weighted single-number quantity), which differs from DnT,w in that it uses A-frequency weighting rather than the standard reference curve of ISO 717-1. DnT,A is more appropriate for traffic and environmental noise because A-weighting reflects the frequency content of those sources better than the ISO 717-1 reference curve optimized for pink noise.
NBR 15575-4: Acoustic Requirements for Floors
Airborne Sound Insulation of Floor-Ceiling Assemblies
| Location | Level M (DnT,w) | Level I (DnT,w) | Level S (DnT,w) |
|---|---|---|---|
| Floor between bedrooms of adjacent dwellings | ≥ 40 dB | ≥ 45 dB | ≥ 50 dB |
| Floor between living room above and bedroom below | ≥ 40 dB | ≥ 45 dB | ≥ 50 dB |
| Floor between kitchen/bathroom above and bedroom below | ≥ 40 dB | ≥ 45 dB | ≥ 50 dB |
Impact Sound Insulation of Floors
The impact sound metric in NBR 15575 is L'nT,w, the normalized impact sound pressure level measured in the field per ISO 16283-2. Lower values indicate better performance.
| Location | Level M (L'nT,w) | Level I (L'nT,w) | Level S (L'nT,w) |
|---|---|---|---|
| Floor between bedrooms of adjacent dwellings | ≤ 80 dB | ≤ 60 dB | ≤ 55 dB |
| Floor between living room above and bedroom below | ≤ 80 dB | ≤ 60 dB | ≤ 55 dB |
The Minimum level of L'nT,w ≤ 80 dB is notably less stringent than European requirements (DIN 4109 requires L'n,w ≤ 53 dB; Approved Document E requires L'nT,w ≤ 62 dB). This reflects both the lower baseline performance of typical Brazilian reinforced concrete slab construction without floating floors, and the lower baseline of acoustic expectations in the Brazilian residential market compared to northern Europe.
However, the Intermediate and Superior levels align more closely with international best practice. L'nT,w ≤ 55 dB (Superior level) is competitive with German DIN 4109 enhanced requirements and is achievable with floating floor systems or heavy concrete slabs with floating screeds.
Measurement Standards Referenced by NBR 15575
NBR 15575 references several ISO and NBR measurement standards:
| Parameter | Test standard | Brazilian equivalent |
|---|---|---|
| Airborne field (walls, floors) | ISO 16283-1 | NBR 15575-3, NBR 15575-4 |
| Impact field (floors) | ISO 16283-2 | NBR 15575-4 |
| Facade (external) | ISO 16283-3 | NBR 15575-3 |
| Single-number ratings | ISO 717-1, ISO 717-2 | Referenced directly |
Until the adoption of ISO 16283 in the 2021 revision, NBR 15575:2013 referenced the older ISO 140 series (Parts 4, 5, and 7). The 2021 revision updated the referenced measurement standards to align with current international practice.
NBR 10152: Background Noise Levels
NBR 15575 complements the acoustic insulation requirements with references to NBR 10152 (Acústica — Níveis de pressão sonora em ambientes internos a edificações), which specifies maximum background noise levels for occupied spaces. For residential bedrooms, NBR 10152 specifies:
| Condition | Maximum LAeq | Maximum L90 |
| Sleeping (night) | 35 dBA | 25 dBA |
| Daytime | 40 dBA | 30 dBA |
These background noise limits are the receiving room targets. Together with the facade DnT,A requirements and the outdoor noise level classification, they define the complete noise exposure management framework for Brazilian residential buildings.
Construction Methods and Typical Performance in Brazil
Reinforced Concrete Frame with Masonry Infill
This is the dominant construction system in Brazilian multi-family housing. A typical party wall consists of 14 cm hollow ceramic brick plastered on both sides (total thickness approximately 20 cm). This construction achieves Rw approximately 48–52 dB in the laboratory, and DnT,w 42–46 dB in the field — narrowly meeting the Minimum level requirement of DnT,w ≥ 40 dB in many but not all cases.
Common failure modes include:
- Brick/concrete column junctions left unplastered or inadequately sealed
- Service penetrations (electrical boxes, plumbing) that create acoustic short-circuits through the wall
- Structural frame columns that act as flanking paths because they are shared between adjacent dwellings
Solid Concrete Slab Construction
Brazilian apartment buildings almost universally use solid or ribbed reinforced concrete flat slabs as floor-ceiling assemblies. A 120–150 mm solid concrete slab achieves:
- L'n,w (laboratory) ≈ 72–78 dB
- L'nT,w (field) ≈ 75–82 dB
Drywall Partition Systems
The use of drywall (gypsum board on steel studs) as party walls is increasing in Brazilian residential construction. A double-stud drywall partition with resilient channel and acoustic infill can achieve DnT,w 50–55 dB, meeting the Superior level with proper detailing. However, the flanking paths through concrete slab and frame elements are the same regardless of partition type — the partition specification alone does not determine the field result.
Common Compliance Failures in Brazil
Facade Noise Classification Without Measurement
NBR 15575 requires the site to be classified by outdoor noise level, but many developers base this classification on visual inspection of the surroundings rather than actual noise measurements. A site classified as "Class I (quiet)" when the actual LAeq is 60–65 dB will lead to systematically under-specified facades and post-occupancy complaints.
Assuming Laboratory Data Predicts Field Results
The DnT,w in the field is consistently lower than the Rw predicted from laboratory data. For Brazilian hollow brick walls, the gap is typically 4–8 dB because the column junctions and service penetrations that are absent in a laboratory test are present in every apartment building. Acoustic consultants must design to field targets, not laboratory predictions.
Ignoring the Impact Noise Requirement
Brazilian developers and architects frequently focus on airborne DnT,w when designing for NBR 15575 and underspecify impact sound treatment. An apartment building that passes airborne insulation requirements but delivers L'nT,w = 78 dB (just meeting the Minimum level) will still generate neighbor complaints from walking noise, particularly in buildings with hard tile floor finishes throughout.
Comparison with Other National Standards
| Standard | Minimum airborne (party walls) | Minimum impact (floors) |
|---|---|---|
| NBR 15575:2021 Minimum | DnT,w ≥ 40 dB | L'nT,w ≤ 80 dB |
| UK Approved Doc. E | DnT,w ≥ 45 dB | L'nT,w ≤ 62 dB |
| DIN 4109:2018 | DnT,w ≥ 54 dB | L'nT,w ≤ 53 dB |
| NRA (France) | DnT,A ≥ 53 dB | L'nT,w ≤ 58 dB |
| NCC 2022 (Australia) | DnT,w ≥ 45 dB | L'nT,w ≤ 62 dB |
NBR 15575's Minimum level is lower than comparable European standards, reflecting the current baseline of Brazilian construction practice. The Superior level performance requirements are broadly competitive with UK Approved Document E, representing a significant improvement over typical Brazilian construction.
2021 Revision: Key Changes from 2013 Edition
The 2021 update to NBR 15575 included several significant changes to the acoustic requirements:
- Updated measurement references: Replaced ISO 140 Parts 4/5 with ISO 16283 Parts 1/2 for field measurement procedures
- Revised Intermediate level: The Intermediate DnT,w was raised from ≥ 40 dB to ≥ 45 dB, aligning the Intermediate level with what the 2013 edition called Superior
- New facade classification: The four-class outdoor noise level system was formalized and tied explicitly to measurement requirements
- Expanded scope: The 2021 revision extended acoustic performance requirements to cover townhouses and other non-apartment residential forms more explicitly
- Consumer information: New requirements for developers to document and disclose the acoustic performance level achieved, so buyers can make informed purchase decisions
Integration with AcousPlan
AcousPlan's Sound Insulation Calculator includes NBR 15575:2021 compliance checking across all three performance levels. Enter the wall or floor assembly type and the building context, and the calculator returns DnT,w predictions with NBR 15575 Minimum, Intermediate, and Superior thresholds displayed alongside the result. Brazilian facade noise classification (Classes I–IV) is included in the compliance view.
All calculations are advisory. NBR 15575 compliance requires field measurements by a qualified acoustic professional after construction is complete.