AS 3700 Masonry Structures Explained
If you’re building or buying a brick or block masonry home in Australia, understanding the requirements of AS 3700 – Masonry Structures is essential. This national standard outlines how masonry walls, piers, and other components must be designed and built to ensure strength, stability, fire resistance, and durability.
Whether you're a builder, property buyer, architect, or homeowner, this page will give you a full understanding of what’s in AS 3700—without needing to read the full PDF.
Table of Content
What Is AS 3700?
AS 3700 – Masonry Structures is the Australian Standard that sets the minimum requirements for the design and construction of masonry used in residential and commercial buildings. It provides rules and performance requirements for:
Load-bearing and non-load-bearing masonry walls
Clay brick, concrete block, AAC, and natural stone units
Mortar types and jointing methods
Reinforced and unreinforced masonry
Prestressed masonry (less common in homes)
When Does It Apply?
AS 3700 applies to:
New homes, extensions, and renovations using masonry
Boundary walls, fences, garages, and retaining walls
Buildings with brick veneer, double brick, or blockwork construction
It is used by engineers, architects, and builders during structural design and construction phases and by inspectors to assess workmanship and durability.
Key Goals of AS 3700
Ensure structural strength and stability under loads (wind, gravity, seismic)
Promote durability across Australia’s varied climates
Provide fire and acoustic protection
Support cost-effective design for common wall systems
Types of Masonry Covered
Clay bricks and concrete masonry units
Autoclaved aerated concrete (AAC) blocks
Natural stone (dressed units)
Reinforced and prestressed masonry systems
Cavity and veneer wall systems
Overview of Structural Design Requirements
Unreinforced and reinforced masonry have different design formulas for strength and stiffness
Load-bearing walls must be designed to resist vertical and lateral loads
Use of control joints is recommended to accommodate thermal expansion and prevent cracking
Wall tie spacing, reinforcement placement, and construction detailing are defined for safety and compliance
Materials and Construction Practices
Mortar must be mixed to specific mortar classes (M2–M4) depending on exposure
Grout must meet compressive strength requirements and be properly placed in reinforced cells
Reinforcement must comply with AS/NZS 4671, with a minimum cover for corrosion protection
Ties, damp-proof courses, and weep holes must be used to manage moisture
Fire Resistance & Acoustic Provisions
AS 3700 supports compliance with NCC fire separation requirements
Provides minimum wall thicknesses for specified fire resistance levels (FRLs)
Includes wall designs that provide sound insulation, especially in boundary walls and multi-unit dwellings
Durability & Weather Exposure Ratings
Masonry must be selected based on exposure zones: mild, moderate, marine, and severe
Durability is achieved through:
Correct mortar class
Cover to reinforcement
Suitable surface finishes or water-resistant coatings
Stainless steel ties may be required in coastal areas
Workmanship and Construction Tolerances
Tolerances include:
Plumb: ±10 mm per 3 m
Alignment: ±15 mm in horizontal plane
Level: ±10 mm per 10 m run
Laying techniques, joint width (typically 10 mm), and surface finish must follow best practices
Control joints every 6–8 m are recommended for large unreinforced walls
Common Issues AS 3700 Helps Prevent
Diagonal cracking in walls from poor jointing or inadequate reinforcement
Structural instability in load-bearing walls
Moisture ingress due to incorrect flashing or wall ties
Efflorescence and long-term water damage
Wall bulging or leaning due to incorrect tie spacing or poor construction
Book an Inspection in Perth
At Descom Consultant, our inspectors are trained in AS 3700 compliance. Whether you're building, buying, or concerned about cracks, we provide detailed masonry reports backed by industry standards.
FAQ
Q1. Is AS 3700 mandatory in residential construction?
Yes. It's referenced in the National Construction Code (NCC) and is used to prove compliance for masonry components.
Q2. Can brick veneer walls fall under AS 3700?
Yes. Both veneer and cavity brick walls are included, with detailed provisions for structural stability and tie spacing.
Q3. What kind of mortar is required for coastal homes?
Homes in marine or severe exposure zones need a higher durability mortar class, often M3 or M4, and stainless steel components.
Q4. Are minor cracks in mortar joints a defect?
Small hairline cracks (<0.3 mm) are common. Larger cracks, separation, or movement may indicate design or workmanship issues.
Q5. How is fire resistance ensured in masonry walls?
By using the correct wall thickness, unit density, and ensuring full mortar bedding as per the FRL tables in AS 3700.
Q6. Does AS 3700 cover retaining walls?
Yes. Structural design and reinforcement requirements for masonry retaining walls are included, especially for load-bearing cases.
Q7. Who checks if a wall complies with AS 3700?
Your builder, structural engineer, and building inspector should all ensure compliance before handover.
Q8. Are reinforced block walls covered in this standard?
Yes. AS 3700 includes guidance for reinforced and grouted masonry, including reinforcement size, spacing, and grout strength.
Q9. Can I build masonry in a bushfire zone?
Yes, and it’s often preferred. Masonry walls offer high resistance to bushfire attack, especially when paired with non-combustible roofing and eaves.
Q10. Does AS 3700 apply to fences or boundary walls?
Yes, especially for load-bearing or structural masonry fences. Non-load-bearing decorative walls may still benefit from its guidance.