SURFACE FIRE PERFORMANCE OF INSULATION IN PLENUMS AND DUCTS
As a result of the amendments to NZBC C/AS2-AS7, in particular Table 4.1 Surface Finishes there have been some changes to Masterspec insulation sections.
The requirement for acoustic insulation or pipe insulation within an air handling plenum to have a group number has been removed from Table 4.1 in most Acceptable Solutions except for NZBC C/AS2 and AS3. In this case under NZBC C/AS2 or AS3 only, a Group Number of 3 is still required. This means that under the Acceptable Solutions a plenum, such as a ceiling space acting as an air plenum, does not require the insulation to have a group number, except for those under NZBC C/AS2 and AS3.
Unlike air plenums, ducts for HVAC systems are still included in Table 4.1 of NZBC C/AS2 to AS7, which states the internal and external duct surface maximum permitted Group Numbers allowed. For ducts in protected shafts (excluding lift shafts) only the duct internal surface requires a Group Number, to NZBC C/AS2-AS7, 4.17.11 Air Ducts. Under NZBC C/VM2, Appendix A, A1.4, a duct complying with the fire hazard properties of AS 4254, is deemed to have a Group Number of 1S.
Please note there is a difference between the Acceptable Solutions and the Verification Method VM2. Using NZBC C/VM2 under Design Scenario (IS), non-combustible materials like some insulation (when tested to AS 1530.1 or ISO 1182) are deemed to have a Group Number 1 or 1S, without the further evaluations of Appendix A. This means that for designs using VM2, tested, non-combustible insulation can always be considered as Group Number 1 or 1S. However in the Acceptable Solutions there is no mention of the status of non-combustible insulation, so it would seem that a Group Number test will be required to prove the Group Number, when necessary in the Acceptable Solutions. A complicated Alternative Solution may be able to combine the two aspects and overcome the issue, if no Group Number testing has been done.
- NZBC C/AS1 is not included in the above as it does not have a Table 4.1.
- Foamed plastics or combustible insulation have other requirements and in most exposed situations must be tested and have a Group Number.
The Masterspec acoustic insulation sections and mechanical duct and pipe insulation sections have now been updated.
NZBC C/AS2 (1 July 2014) Click the image for a larger file
NZBC C/AS3 (1 July 2014) Click the image for a larger file