AS 3740:2021 Waterproofing Standard - Everything you need to know

Waterproofing buildings is essential to maintaining their integrity. Water can cause significant damage if it infiltrates building structures, causing leakage, moisture and mould, cracking, and building collapse. 

The guidelines introduced significant revisions from the old 2010 guidelines and categorised domestic wet areas into three levels based on the potential risk of water or moisture causing damage to the building structure.

This blog will cover the Standard's key requirements, relevance, and practical applications for construction and renovation projects.

What is AS 3740:2021 and Why is it Important?

The Waterproofing Standards AS3740 2021 edition sets out the criteria for waterproofing residential buildings. It consists of four sections:

• Section 1: Scope, definitions, reference documents.
• Section 2: Design principles that apply to the Standard.
• Section 3: Requirements for acceptable materials that can be used in waterproofing.
• Section 4: Details for installing waterproof and water-resistant materials in domestic areas.

The Standards are essential as they ensure that all building projects have effective waterproofing in the wet areas to protect them from water damage, which can lead to catastrophic financial and even health consequences for homeowners. 

The 2021 updates the 2010 version of the Standards with the old Standards plagued with misunderstandings and misinterpretations that necessitated the revised 2021 Standards. The new 2021 Standards are comprehensive and broad, and the main changes include:

• Broader scope for waterproofing
• Imposing extra responsibilities on the waterproofer
• Greater emphasis on diligence in applying waterproofing
• Greater scrutiny of materials used
• Basic construction and layout
• New requirements for different areas
• Better defined roles and responsibilities of all concerned parties

Compliance with AS3740 is essential not only to preserve building structure and integrity but also to protect the health of the home occupants. The need for compliance with waterproofing Standards arose from severe building defects found by research to be related to waterproofing. According to NSW Government research, of the buildings surveyed in 2021, 24% had waterproofing defects, making it one of the most prevalent defects.

Benefits of proper waterproofing include:

• Protection from structural damage
• Prevent mould and mildew and ensure the health of the occupants
• Enhance building longevity and property value

Key Requirements of AS 3740:2021

The key requirements of the AS 3740 Waterproofing Standards are:

1. Shower area 

• Introduce a vertical water stop – when the shower is located within 200mm of a wet area exit to prevent water from escaping the shower area and causing damage to adjacent structures or areas.
• The entire wall lining of a shower area must be waterproofed to a minimum height of 1800 mm above the finished floor level or 50 mm above the shower rose, whichever is higher.
• Floor waste needs to fall a minimum of 1:80 (12.5mm over 1m) and a maximum of 1:50 (20mm over 1m).

2. Material and installation

• Greater emphasis on using suitable water-resistant materials and detailed installation processes to ensure compatibility and durability.
• Particleboard sheeting can no longer be used as a substrate for waterproofing layers.

3. Visual inspection of the membrane is required before installation of any overlaying finish.
4. Expansion of permitted materials, categories of wet areas and surface preparation requirements.

• For example, a membrane must be installed above or below the tile bed to ensure maximum protection.
• Surface must be prepared so that it is smooth, with no protrusions, voids, or distortions, clean, dry and free from dust and contamination.
• Permitted materials include fibre cement sheeting and structural plywood that comply with Australian Standards.

5. Other updated details, such as bond breaker applications and specific measurements for areas such as the shower recess, to reflect modern construction practices.

To ensure these requirements are met, and wet areas comply with the Standards, it is important to seek guidance and advice from waterproofing and drainage experts and conduct regular inspections and acceptance testing throughout the project. 

Areas Covered by the AS 3740:2021 Standard 

Waterproofing is critical to all wet areas in a residential building, such as:

• Bathrooms
• Laundries
• Kitchens
• Balconies

The AS3740 Waterproofing Standards categorise domestic wet areas according to the level of risk of potential water or moisture damage:

• Category 1 – high risk: wet areas that have enclosed and unenclosed shower areas, baths with unenclosed showers over them, any area within reach of a hand-held shower fitting, water closets with a hand-held douche spray, and douche rooms.
• Category 2 – moderate risk: wet areas such as a bathroom area outside an unenclosed shower area and the bathroom area outside the unenclosed shower over the bath.
• Category 3 – low risk: any wet area without a shower.

Meeting minimum waterproofing requirements is not enough, as this can still cause deterioration and future damage to buildings. Standards must be exceeded to avoid long-term moisture issues such as mould growth and decay.

Who Needs to Comply with AS 3740:2021?

Everyone involved in the conception, planning, selection, and installation of waterproofing systems is required to comply with the AS3740 Standards; these include:

• Architects and specifiers
• Interior designers
• Builders
• Site supervisors
• Building inspectors
• Compliance certifiers
• Waterproofing contractors
• Manufacturers
• Kitchen and bathroom installers
• Carpenters

Hiring a licensed waterproofer is essential to ensure a home has been adequately waterproofed. A licensed waterproofer will issue a waterproofing certificate to confirm that the construction complies with AS3740. The waterproofing certificate provides proof and assurance to homeowners, building contractors, and the local council that the waterproofing system in a building is compliant and has been installed correctly.

Non-compliance with waterproofing Standards can cause significant legal and financial implications. Aside from devastating damage such as corrosion, fungal growth, and deterioration that can cause catastrophic building damage, non-compliance can lead to:

• Costly repairs and rework
• Significant regulatory penalties for non-compliance
• Legal liability
• Decreased property value
• Increased insurance costs

How to Ensure Compliance with AS 3740:2021

The following steps are necessary to ensure compliance with the AS3740.

1.     Use qualified waterproofing systems.

A comprehensive waterproofing system includes selecting the correct product, membrane detail, drainage design, substrate preparation, design, installation, quality assurance, and maintenance. A team of suitably qualified contractors is essential to design, install, and maintain the waterproofing system correctly.

2.     Consult experienced professionals for installations.

Waterproofers must carry a licence to carry out residential waterproofing work. There are different licence types depending on the type of work:

• A contractor licence for those who carry out waterproofing work.
• A qualified supervisor certificate for those who supervise a contractor's work but are not licensed to carry out the contractor work.
• Endorsed contractor licence for those contractors who have the additional experience needed to be a qualified supervisor.

3.     Follow certification procedures to verify compliance.

Waterproofers are required to test the waterproofing system and issue a compliance certificate after completing the job. Only a licensed waterproofer registered with a professional board can issue a compliance certificate. A compliance certificate is a homeowner’s assurance that the system is compliant with the Standards, and many local councils and banks require the certificate as proof of compliance.

Conclusion

Complying with the AS3740 Waterproofing Standards is essential to all construction projects. This ensures the structural integrity of a building and protects homeowners' health and safety from damage caused by water and moisture. Failure to comply with the Standards can lead to significant legal and financial consequences and health and safety risks.

When embarking on your next construction project, ensure it meets the waterproofing requirements outlined in AS 3740.

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