Code changes

, Build 126

Changes to key Building Code documents dealing with building structure (B1) and weathertightness (E2) came into effect on 1 August 2011.

Recent Building Code changes involve B1/AS1, the Acceptable Solution that references the standard for timber-framed buildings, NZS 3604, and E2/AS1, the Acceptable Solution for the building envelope of timber-framed houses.

There is also a new Acceptable Solution for weathertightness of concrete and concrete masonry houses and small non-residential buildings, E2/AS3, and the NASH design standard for light steel framing is referenced in B1/VM1.

Acceptable Solution B1/AS1

Acceptable Solution B1/AS1 now references NZS 3604:2011, rather than the 1999 version. NZS 3604 is used to design most homes and other low-rise timber-framed buildings in New Zealand and was updated to align with the wind, earthquake and snow loads in AS/NZS 1170 and to reflect current construction practices.

There are some crucial modifications in the reference to NZS 3604:

  • All floor slabs throughout New Zealand must be reinforced with ductile steel mesh which is tied to perimeter foundation reinforcement. Unreinforced floor slabs are no longer an option.
  • All reinforcing steel in slab foundations, including welded mesh, must be ductility Class E. This mesh is not currently available. For an interim solution, see www.dbh.govt.nz/earthquake-concrete-slabs-guidance.
  • ‘Good ground’ for the Canterbury earthquake region excludes ground where liquefaction or lateral spread could occur.

Verification Method B1/VM1

B1/VM1 now references two new documents:

  • The standard for restraining engineering systems in earthquakes NZS 4219:2009 Seismic performance of engineering systems in buildings, which covers tanks, piping systems, ducting and mechanical and electrical services.
  • The design standard for steel-framed low-rise buildings published by the National Association of Steel-framed Housing (NASH). This document, Residential and low-rise steel framing part 1: Design criteria: October 2010, can be obtained from the NASH website www.nashnz.org.nz.

E2/AS1 and E2/VM1

The update to E2/AS1, the Acceptable Solution for the building envelope of timber-framed houses and companion document to NZS 3604, reflects the trend towards wider use of drained cavities. Changes in E2/AS1 include:

  • a new extra-high wind zone
  • all monolithic claddings must be on a cavity, regardless of matrix score
  • in extra-high wind zones, rigid underlay is required with an extra layer of flexible underlay over, unless a proprietary system is used
  • new wall soffit details, sill details for doors and windows
  • increased minimum pitch for membrane roofs and decks
  • brick veneer information added
  • revised window sill, jamb and head details
  • changes to parapet and enclosed balustrade wall junctions
  • all parapets and enclosed balustrades now require a cavity
  • changes to many of the figures and tables.

Changes reflect the latest research and building practice. The extension of the wind range to 55 m/s brings a greater range of sites and number of buildings within the scope of the document. This change is reflected in the amendments to the Verification Method E2/VM1. Design details beyond the 55 m/s range of E2/AS1 can be tested using the updated E2/VM1 for individual buildings.

New Acceptable Solution E2/AS3

E2/AS3 references the Code of practice for weathertight concrete and concrete masonry construction, recently published by the Cement and Concrete Association of New Zealand (CCANZ). It covers the weathertightness of: concrete slabs on ground and footings; concrete walls; concrete low-slope roofs and decks; junctions between walls, roofs and floors; and concrete to timber junctions.

Systems for concrete masonry walls, in situ concrete walls and precast concrete walls are covered in the Acceptable Solution.

Weathertight details are provided for walls and roofs or decks with thermal insulation in different positions:

  • on the outside of the wall/roof
  • within the wall/roof structure
  • on the interior face of the wall/roof structure.

The Acceptable Solution also includes:

  • details for openings and penetrations through walls, such as windows and doors
  • footings and concrete slabs on ground
  • weathertight systems for concrete roofs and decks.

New barrier guidance document

The Department is soon to publish a new guidance document for timber, glass and metal barriers and will be withdrawing B1/AS2 for timber barriers.

The document incorporates loadings from AS/NZS 1170 and will cover the range of materials now being used for barriers. It has been developed by a working group of structural engineers and specialists from the design, manufacturing and construction industries.

Transition arrangements

The amendments to clause B1 Structure and E2 External moisture documents took effect on 1 August 2011.

Both old and new versions of these documents can be used until 31 January 2012. From 1 February 2012, only the revised documents can be used for consenting purposes.

For more

Building Code documents are available for free at the Department of Building and Housing website www.building.govt.nz/building-code-compliance/building-code-and-handbooks.

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