SN4 vs SN8 Pipe: What’s the Difference?
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When choosing underground drainage pipe, you may come across different stiffness classifications, including SN4 and SN8.
Both are commonly used for underground drainage and sewer systems, but the main difference is their ring stiffness and the level of external loading they are designed to withstand.
What does SN4 mean?
SN4 refers to a pipe with a ring stiffness of 4 kN/m².
It is commonly used for standard underground drainage applications where the pipe is not expected to experience particularly high external loads.
Typical applications include:
- Domestic foul drainage
- Surface water drainage
- Gravity drainage systems
As with all underground drainage pipes, the performance of an SN4 pipe depends heavily on correct installation, including suitable bedding, side support and backfill.
What does SN8 mean?
SN8 refers to a pipe with a ring stiffness of 8 kN/m².
This makes SN8 pipe approximately twice as stiff as SN4 pipe in terms of its ring stiffness classification.
SN8 is often selected for installations where the pipe may be subject to greater external loading or more demanding ground conditions.
Typical applications can include:
- Roads and trafficked areas
- Commercial and industrial developments
- Greater depths of cover
- Areas subject to heavier surface loading
- Installations with more demanding ground conditions
The exact suitability of SN8 pipe will depend on the full pipework design and the installation.
SN4 vs SN8: the key difference
The main difference is the pipe's nominal ring stiffness:
Pipe classification | Nominal ring stiffness |
SN4 | 4 kN/m² |
SN8 | 8 kN/m² |
In simple terms, SN8 pipe is stiffer than SN4 pipe and is generally better suited to applications where the pipe is exposed to higher external loads.
However, this does not mean that SN8 is always the better choice. The pipe classification should be selected based on the requirements of the installation.
Is SN8 pipe stronger than SN4?
Yes, in terms of ring stiffness.
An SN8 pipe has a higher ring stiffness than an SN4 pipe, meaning it offers greater resistance to deformation from external loads.
However, the overall performance of an underground pipe system is affected by more than just the pipe stiffness. Factors such as the following are also important:
- Trench width
- Bedding material
- Side support
- Backfill material
- Depth of cover
- Ground conditions
- Traffic loading
- Installation quality
A correctly installed SN4 pipe may be suitable for an application where SN8 is not required, while more demanding installations may require the additional stiffness provided by SN8.
Which should you choose: SN4 or SN8?
The right pipe depends on the installation conditions.
SN4 may be suitable for standard underground drainage applications with normal loading conditions and appropriate installation.
SN8 may be more suitable where there are higher external loads, greater depths of cover or more demanding ground conditions.
Before choosing a pipe, always check the project specification and the manufacturer's technical information. The required pipe stiffness should be suitable for the depth, loading and ground conditions of the installation.
Choosing the right pipe classification helps ensure that an underground drainage system performs reliably throughout its service life.