Masterspec

UNDERLAYS - NZS 2295 AMENDED

29 Nov 2017

Standards have published NZS 2295:2006 Amendment 1 (2017) Pliable, Permeable Building Underlays, apparently driven by the need for a Standard that reflected up-to-date test methods and products that are already in used by the building industry.  Although NZS 2295:2006 was developed to allow the use of synthetic wall underlays, this new amendment has added synthetic roof underlays.

Amendment 1 incorporates the following changes to NZS 2295:2006:

  • Inclusion of performance requirements, related test methods, and limitations of use for synthetic roofing underlays
  • Minor changes to specifications and limitations for wall underlays, including deletion of W1 class due to non-use
  • Updating reference documents.

NZS 2295:2006 is cited in NZBC AS/1, but the Amendment 1 (2017) is not, at least not yet.  This means that synthetic roofing underlays are an Alternative Solution to NZBC AS/1, however the amendment would be a good tool to show compliance and support an Alternative Solution.

There are a few new details in the amended Standard that are worth mentioning here:

Classification of building underlay types 

LOCATION  TYPE GRADE 
WALL  W2 Wall underlay Kraft/bituminous based Heavy grade
 W3 Wall underlay Synthetic based non-absorbent
 W4 Wall underlay Synthetic based absorbent
ROOF  R1 Roof underlay Kraft/bituminous based Heavy grade
 R2 Roof underlay Kraft/bituminous based Self-supporting
 R3 Roof underlay Synthetic based Heavy grade
 R4 Roof underlay Synthetic based Self-supporting

Note: W1 deleted, R3 and R4 added.

Clause 3.3.2 Amended list
Roofing underlay clause "Mechanical strength" the new list reads

  • R1 and R3 – shall be fully supported and only used when the roof pitch is equal to or greater than 10 degrees
  • R2 and R4 – when the roof pitch is equal to or greater than 10 degrees underlay is self-supporting to a maximum span of 1200 mm. When the roof pitch is below 10 degrees, the roof underlay shall be fully supported

Appendix C - Underlay applications
Table C2 Pliable roof underlay applications, has been amended to:

SPAN  SUPPORT WIND LOAD ZONE
Low/Medium High/Very High
Less than 1200mm Fully Supported R1/R3 R1/R3
Less than 1200mm Unsupported R2/R4 R2/R4
Over 1200mm Fully Supported R2/R3/R4 R2/R4

Note: R3 with over 1200mm span can only be used in Low/Medium wind zones.

Masterspec
The Masterspec generic section 4161 UNDERLAYS, FOIL AND DPC (all Masterspec systems except Minor) has been generally updated with, amongst other things:

  • the addition of underlay types, including synthetic roofing underlays, to allow easier cross referencing to the Standard and NZBC E2/AS1
  • the deletion of type W1 wall underlay in line with the new amendment
  • although the section still used NZBC E2/AS1 and NZS 2295:2006 as the basis, guidance has been added on the requirements of Amendment 1 for projects using synthetic roofing underlays
  • the critical roof pitch of 10° has been corrected in few instances.

Some related Masterspec branded sections have been updated to a lesser extent, these may be updated more in the future depending on the manufacturer/supplier requirements.

It would be reasonable to assume that at some time the new amendment will be cited in the Acceptable Solution.  If and when that happens Masterspec will communicate the changes to all users.


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