Underlay Standards
Permeable underlays must comply with NZS 2295, Amendment 1:2017, as shown in Properties of Roofing Underlay, or have an appropriate product certification such as a Codemark certificate.
Reflective foil underlays must comply with AS/NZS 4200.1:2017
Minimum Requirements for Underlays for Metal Roof Cladding
| Classification | R1 | R3 | R2 | R4 | |
|---|---|---|---|---|---|
| Grade | Heavyweight | Heavyweight | Self-support | Self-support | |
| Type | Kraft | Synthetic | Kraft | Synthetic | |
| Application | Residential or light commercial buildings | ||||
| Property | Unit | ||||
| Absorbency | g/m² | ≥ 150 | ≥ 150 | ≥ 150 | ≥ 150 |
| Water Vapour Resistance | MN s/g | ≤ 7 | ≤ 0.5 | ≤ 7 | ≤ 0.5 |
| Water resistance | mm head | ≥ 100 | ≥ 100 | ≥ 100 | ≥ 100 |
| Tensile Strength MD | KN/m | ≥ 9 | ≥ 3 | ≥ 11 | ≥ 3 |
| Tensile Strength CD | KN/m | ≥ 4.5 | ≥ 2 | ≥ 6 | ≥ 2.5 |
| Edge Tear Resistance MD | N | ≥ 40 | ≥ 100 | ≥ 70 | ≥ 150 |
| Edge Tear Resistance CD | N | ≥ 35 | ≥ 80 | ≥ 55 ≥ 130 |
Based on Table B1 of NZS 2295 Amendment 1:2017.
- Self-supporting (S/S) is defined as strong enough to support its own weight up to a 1200 mm span.
- pH between 5.5 and 80.
- Kraft based underlays shall have shrinkage less than 0.5% and maximum run-length of 10 m.
- Synthetic underlays may have any run length.
- Any underlay is regarded as fire-retardant if it has a Flammability Index (FI) of 5 or less when tested to AS/NZS 1530 Part 2.
Clause:
010_011_001_000_000_000_000_000_000
Clause Number:
10.11.1
/cop/internal-moisture/underlay#underlay-standards
Revision Category:
2 - Editing and rearrangement
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