What Licensed Builders Need to Check on Class 2, 3 and 9c Buildings

Common Building Defects in NSW: A Practical Guide for Licensed Builders

Building defects can be expensive, disruptive and difficult to rectify once a building is occupied.

For NSW licensed builders, identifying defects during construction is therefore much more effective than discovering them after completion. Early inspections, quality control and checking construction against the approved documentation can help prevent relatively simple construction issues from developing into significant compliance, safety, waterproofing or structural problems.

This is particularly important for Class 2, Class 3 and Class 9c buildings, where defects can affect multiple occupants and may involve critical building elements such as waterproofing, fire separation, structural components, the building enclosure and building services.

The NSW regulatory environment has also placed increasing emphasis on proactive compliance. The uploaded AMEC COLLEGE® compliance brief notes the establishment of Building Commission NSW on 1 December 2023, together with the regulatory changes associated with the Residential Apartment Buildings (Compliance and Enforcement Powers) Act 2020 and the Design and Building Practitioners Act 2020.

So, what are some of the common building defects NSW builders should be looking for?

1. Waterproofing Defects

Waterproofing is one of the most important areas of construction quality control.

Water ingress can result in damage to finishes and building elements, mould growth, deterioration and significant rectification costs. The document identifies waterproofing as a persistent source of building defects and a critical inspection priority.

Common waterproofing defects include:

• Waterproofing membranes incorrectly terminated at puddle flanges
• Membranes not properly terminated at overflows
• Ponding or inadequate falls on roofs and balconies
• Poor substrate preparation before membrane installation
• Incorrect membrane termination at sliding doors
• Inadequate falls in bathrooms
• Inadequate falls within shower areas
• Missing waterstops at wet-area doorways
• Incorrectly installed internal puddle flanges
• Incorrect fillets or bond breakers at wall-to-floor junctions

For example, a membrane that is not correctly connected to a puddle flange can create a concealed pathway for water to bypass the drainage system and enter the building structure.

What should NSW builders check?

Waterproofing inspections should not simply focus on whether a membrane is visible.

Builders should consider:

Substrate → membrane installation → falls → penetrations → drainage → terminations → interfaces → protection.

A defect at any one of these interfaces can compromise the overall waterproofing system.

The document references NCC Volume One and AS 4654.2 for external waterproofing, while wet-area requirements include AS 3740.

2. Bathroom and Wet Area Defects

Wet areas deserve particular attention because small construction errors can create long-term water damage.

One important issue identified in the document is inadequate bathroom falls. For certain Class 2 and 3 building applications, the document notes an NCC requirement for a continuous fall of 1:80 minimum and 1:50 maximum where a floor waste is installed in a bathroom or laundry above another unit.

Other wet-area defects include:

• Ponding in showers
• Poor falls to floor wastes
• Missing waterstops
• Incorrect puddle flange installation
• Inadequate membrane termination
• Incorrect bond breaker or fillet installation

These are not merely cosmetic issues. Poor wet-area detailing can allow moisture to enter concealed spaces and damage adjacent building elements.

3. Fire Safety Defects

Fire safety defects are among the most serious defects that can occur in a building.

The document identifies passive and active fire safety systems as non-negotiable life-safety elements and emphasises that fire safety should be verified throughout construction rather than treated solely as a final-stage inspection.

Examples of common fire safety defects include:

• Fire walls not extending to the required structure above
• Unprotected service penetrations through fire-rated elements
• Fire doors that do not self-close or latch
• Excessive gaps around fire doors
• Hollow or incorrectly filled fire door frames
• Non-compliant services within fire-isolated exits
• Steps at fire-isolated exit thresholds
• Insufficient head height in required exits
• Inconsistent stair risers and goings
• Incorrect fire hydrant outlet positioning
• Insufficient clearance in front of fire hydrants

For example, an unprotected service penetration through an FRL element can create a pathway for fire and smoke to move between compartments.

A required fire door that does not self-close and latch can similarly compromise the intended fire separation.

Builder takeaway

Fire-rated construction should be checked before walls and ceilings conceal critical components.

Once a penetration, fire-stopping system or fire-rated junction is concealed, identifying and rectifying the defect can become considerably more difficult.

4. Structural Building Defects

Structural defects require immediate attention because they can affect the stability, durability and load-carrying capacity of a building.

The document identifies several structural defects relevant to construction inspections, including:

• Unreinforced masonry without appropriate support over openings
• Inadequate concrete cover
• Exposed reinforcement
• Honeycombing
• Concrete placed during rain or inclement weather without appropriate protection
• Cut or damaged reinforcement
• Incorrect movement or expansion joints
• Missing slab joints where required by the approved design
• Debris or contaminants incorporated into concrete

For masonry openings, the document references AS 3700, including requirements for supporting unreinforced masonry over openings with appropriate arches, lintels or frames.

Concrete defects can also have long-term consequences. Inadequate cover, exposed reinforcement and honeycombing can allow moisture and chlorides to reach reinforcement, contributing to corrosion and concrete deterioration.

Never treat damaged reinforcement as a minor defect

Cutting or damaging reinforcement can directly affect the structural capacity of a concrete element.

The document specifically highlights the importance of scanning concrete before drilling or coring where reinforcement locations need to be established.

For builders, the practical lesson is straightforward:

Do not allow site modifications to structural elements without appropriate verification.

5. Building Enclosure Defects

The building enclosure is the building's first line of defence against weather and moisture.

Defects in the building enclosure can contribute to water ingress, poor thermal performance and premature deterioration of building materials.

Common defects identified include:

• Incorrect damp-proof course installation
• Missing or incorrectly spaced weepholes
• Poor window and door flashing
• Weepholes obstructed by ground or paving
• Combustible cladding where non-combustibility is required
• Flashings with insufficient projection or incorrect orientation

For example, the document identifies inadequate window and door flashings as a potential pathway for water to enter the wall cavity and building interior.

Weepholes deserve attention

Weepholes are sometimes overlooked during construction inspections.

However, their function is important: they allow moisture within a cavity wall to drain.

The document identifies both missing/incorrectly spaced weepholes and weepholes obstructed by adjoining ground or paving as defects.

6. Combustible Cladding and External Wall Compliance

Cladding is another area where builders need to pay close attention to the approved design and applicable NCC requirements.

The document identifies the use of combustible cladding on certain Type A or Type B buildings as a significant fire safety concern. It also notes NSW restrictions concerning aluminium composite panels containing more than 30% polyethylene by mass for external cladding on specified buildings.

Builders should therefore verify:

• The specified cladding product
• Product documentation
• Approved drawings
• Applicable NCC requirements
• Required fire performance
• Installation details
• Substitution of products or systems

A product substitution should never be treated as simply a commercial or procurement decision where compliance or performance characteristics may change.

7. Building Services Defects

Building services can have a direct effect on occupant health, safety, comfort and building performance.

The document identifies several defects involving ventilation and air-handling systems, including:

• Jet fans obstructing fire protection devices
• Rooms without required natural or mechanical ventilation
• Flexible duct connections that are not airtight
• Flexible ducts without appropriate compliance markings
• Incorrect rigid duct sealing
• Inadequately supported rigid ductwork

For example, inadequate ventilation can contribute to poor indoor air quality, moisture accumulation, condensation and mould growth.

Flexible ductwork also requires attention. The document references AS 4254.1 for airtightness and identification requirements, including labelling information such as manufacturer, compliance with the standard and R-value.

8. Why Early Defect Identification Matters for NSW Builders

One of the most important lessons from common building defects is that timing matters.

A defect identified while the work is accessible may be relatively straightforward to correct.

The same defect discovered after:

• wall linings have been installed,
• waterproofing has been concealed,
• ceilings have been closed,
• finishes have been completed, or
• the building has been occupied

can become significantly more complicated and expensive to investigate and rectify.

The AMEC COLLEGE® document explains that the defects selected are particularly relevant because of their recurrence, their ability to be visually verified without specialist equipment, and the potentially much higher cost of post-occupation rectification.

This makes quality control during construction one of the most effective tools available to a NSW licensed builder.

9. A Practical Defect Prevention Approach

For NSW builders, a useful approach is to divide inspections into the major building elements:

Waterproofing

Check membranes, falls, drainage, puddle flanges, overflows, waterstops, penetrations and terminations.

Fire safety

Check fire-rated walls, penetrations, fire doors, exits, fire hydrants and fire-stopping before concealment.

Structure

Check reinforcement, concrete placement, cover, joints, masonry support and compliance with approved structural documentation.

Building enclosure

Check DPCs, flashings, weepholes, windows, doors, cladding and external interfaces.

Building services

Check ventilation, ductwork, service installation, support, sealing and interaction with fire safety systems.

Most importantly, inspections should be undertaken at the appropriate construction stage, not simply when the building is nearly complete.

10. Common Building Defects: What Should Builders Remember?

There is no single inspection that will identify every building defect.

Good construction quality requires a systematic process of checking the work against the:

• Approved drawings
• Specifications
• National Construction Code
• Relevant Australian Standards
• Manufacturer requirements
• Design documentation
• Applicable regulatory requirements

The document references standards including AS 1379, AS 1668, AS 1905.1, AS 2047, AS 2419.1, AS 3600, AS 3700, AS 3740, AS 4254 and AS 4654.2.

Final Thoughts for NSW Licensed Builders

Common building defects are not simply a problem for certifiers or inspectors.

For NSW licensed builders, identifying defects early is an essential part of delivering compliant, durable and high-quality buildings.

Waterproofing failures, fire safety defects, structural problems, building enclosure failures and non-compliant building services can all become significantly more difficult and expensive to rectify when discovered late.

The practical objective should therefore be simple:

Find the defect early. Verify the requirement. Rectify the problem before it becomes concealed. Document the outcome.

For builders working on Class 2, Class 3 and Class 9c buildings, understanding these common defects can strengthen construction quality control and help reduce the risk of costly rectification work.

Continue Your NSW Builder CPD

AMEC COLLEGE® provides practical CPD education for the NSW building industry, with courses designed around real construction issues, compliance requirements and site-based knowledge.

If you are a NSW licensed builder looking to strengthen your knowledge of building defects, compliance and construction quality, explore the available NSW Builder CPD courses from AMEC COLLEGE®.

Important: This article is an educational overview based on the accompanying AMEC COLLEGE® compliance brief. Builders and other building professionals should refer to the current NCC, applicable Australian Standards, approved documentation, manufacturer requirements and relevant NSW regulatory requirements for project-specific compliance decisions.

FAQ 

What are the most common building defects in NSW?
Common defects include waterproofing failures, inadequate falls, fire-rated construction defects, structural defects, poor flashing and drainage details, combustible cladding issues and defects in building services.

What are common waterproofing defects in NSW buildings?
Examples include inadequate falls, ponding, incorrect membrane termination, missing waterstops, incorrect puddle flange installation and inadequate substrate preparation.

Why are Class 2 building defects important for NSW builders?
Class 2 buildings contain two or more separate dwelling units. Defects in these buildings can affect multiple occupants and may involve critical waterproofing, fire safety, structural and building enclosure elements.

What is a Class 3 building in NSW?
The document defines a Class 3 building as a residential building providing long-term or transient accommodation for a number of unrelated persons, such as a boarding house, guest house, hostel or certain residential parts of hotels and motels.

What is a Class 9c building?
A Class 9c building is a residential care building where 10% or more of residents require physical assistance to conduct daily activities and evacuate, excluding hospitals.

How can builders reduce building defects?
A systematic quality-control process, staged inspections, checking work against approved documentation and identifying defects before they are concealed can help reduce the risk and cost of rectification.