Don’t overlook the vapour barrier: a small step that prevents big problems

When constructing a slab-on-ground, one detail that’s often underestimated is the correct installation of the vapour barrier. According to AS 2870 – Residential slabs and footings and NCC Volume 2 Part 4.2.8, the vapour barrier must not only be placed beneath the slab but also returned up the side of the slab edge. 

This simple but critical step prevents moisture from migrating through the slab edge, which can cause: 

• Rising damp in internal finishes 

• Damage to floor coverings such as timber and vinyl 

• Efflorescence and staining of slab edges 

• Long-term structural deterioration 

• Voidance of product warranties (e.g. steel frames) 

NCC Volume 2 Part 4.2.8 Footings, Slabs and Associated Elements 2022 

Bluescope TB – 34 Steel Building Frames 

By ensuring the vapour barrier is turned up the slab edge and adequately protected during construction, builders significantly reduce the risk of moisture transfer and safeguard the durability and warranty of the structure. 

It’s a small detail that carries a big impact, getting it right the first time saves costly rectifications and ensures compliance with Australian Standards. 

If you have any questions or need further guidance, please don’t hesitate to contact our Workplace Relations team: 

📞 (02) 6175 5900
📧 workplace@mba.org.au