Understanding Different Pipe Strengths in Plumbing and Drainage

Ryan Hofman
Sep 9
2 min read

When it comes to plumbing and drainage, choosing the right pipe isn’t just about size or material—it’s also about pipe strength. Pipe strength determines whether a system can withstand soil pressure, traffic loads, and water pressure without failure. Using the wrong pipe class can lead to cracks, blockages, or costly replacements down the line.

This article explains the different strengths of pipes used in plumbing and drainage, why they matter, and examples of where each type is most suitable.

Example of Twinwall HDPE ribbed stormwater pipe

What Does Pipe Strength Mean?

Pipe strength refers to a pipe’s ability to resist:

External loads – soil weight, heavy vehicle traffic, and construction activity.
Internal loads – water pressure, pump surges, and airlocks.
Environmental factors – soil movement, ground water pressure, or tree root intrusion.

In Australia, pipe strength is usually defined by classifications such as:

Concrete pipes – Class 2, 3, 4, or 6 depending on load capacity.
PVC and HDPE pipes – stiffness ratings such as SN4, SN8, or SN16.
Pressure pipes – nominal pressure ratings such as PN12.5, PN16, or PN25.

Selecting the correct strength depends on pipe depth, traffic conditions, and whether the pipe carries water under pressure or flows by gravity.

Types of Pipe Strength and Applications

1. Light Duty Pipes

Examples: PVC-U stormwater pipes, Class 2 concrete, SN4 PVC.
Best for: Shallow installations in gardens, landscaped areas, or backyards.
Application: A stormwater pipe from roof downpipes to a kerb outlet with minimal ground cover and no vehicle traffic.

2. Medium Duty Pipes

Examples: Class 4 concrete pipes, PVC SN8, HDPE SN8.
Best for: General sewer and drainage under footpaths or residential driveways.
Application: A sewer pipe crossing beneath a suburban driveway where occasional car traffic is expected.

3. Heavy Duty Pipes

Examples: Class 6 concrete pipes, ductile iron, HDPE SN10–SN16.
Best for: Roads, industrial estates, or deep sewer mains.
Application: A stormwater culvert beneath a council road carrying heavy trucks and buses.

4. Pressure-Rated Pipes

Examples: PVC-M, PVC-O, copper, steel, HDPE PE100 PN16–PN25.
Best for: Water supply networks, fire services, and pumped sewer mains.
Application: A rising main transferring wastewater uphill to a treatment facility.

Why Pipe Strength Matters

Correct pipe selection ensures:

Durability: Pipes resist deformation, cracking, and long-term settlement.
Compliance: Installations meet requirements under the National Construction Code (NCC) and relevant Australian Standards (such as AS/NZS 1260 for PVC-U and AS/NZS 4058 for concrete pipes).
Performance: Systems maintain full hydraulic capacity without failures caused by collapse or misalignment.

Understanding pipe strength is essential for reliable plumbing and drainage design. Whether it’s a light-duty PVC line in a backyard or a heavy-duty concrete culvert beneath a road, the correct choice ensures long service life and compliance with regulations.