Important modifications made for the Canterbury Earthquake Region on 19 May 2011 required all slabs-on-ground to have reinforcing mesh which is tied to perimeter foundation reinforcing. This now applies to all parts of the country. Unreinforced concrete slabs-on-ground are no longer an option anywhere.
Mesh for reinforcement of concrete slabs-on-ground includes more on this.
However, the amended definition of good ground for the Canterbury Earthquake Region, excluding ground subject to liquefaction or lateral spread, still only applies to that region.
Building officials and designers need to be familiar with the changes made to NZS 3604:2011 and Acceptable Solution B1/AS1. Some key changes were:
- Only verified timber grades can be used with NZS 3604:2011. All structural timber is now known as structural grades SG6, SG8 and SG10 - for example, SG8 collectively refers to both machine stress grade 8 (MSG8) and visual stress grade 8 (VSG8).
- Section 11 content (which related to the Building Envelope) was removed and is now covered by E2/AS1. Section 11 references E2/AS1. NZS 3604 provides a structural solution while E2/AS1 provides a weathertightness solution for that structure.
- An “Extra High” wind zone with 55 m/s wind speed was added. Previously, the highest wind zone was “Very High” at 50 m/s. The inclusion of the “Extra High” wind zone resulted in changes to the sections dealing with bracing, and wall and roof framing.
- In the scope and interpretation, the classification of buildings was expanded to interpret and conform to the importance level classification in the loadings standard AS/NZS 1170.
- Engineered wood products laminated veneer lumber (LVL) and glued laminated timber (glulam) were introduced to the Standard.
- The Scala penetrometer test method for determining good ground was revised to reflect the dimensions of the penetrometer equipment used in New Zealand.
- Exposure zones were revised. Also, a clause on microclimatic considerations requires Specific Engineering Design (SED) for industrial and agricultural contamination and geothermal exposure.
- Fixings and fasteners of exposed framing in Zone D (the zone for coastal and sea spray areas) are required to be stainless steel.
- Steel fixings and fastenings in exposed or sheltered locations, in contact with timber treated with high copper-based preservatives, need to be a minimum of stainless steel.
- Durability information relating to flashings, underlays and associated materials, was removed and is now covered by E2/AS1.
- For wind bracing, the previous tables for all wind zones were simplified by a single table for the “High” wind zone, with factors for designers to calculate the requirements for other wind zones. Similarly, single tables based on Earthquake Zone 3 and Soil Type D/E are provided and can be used to calculate bracing requirements for other earthquake zones and soil types.
- Earthquake zones were renamed and reflect the new seismic hazard profile of the country.
- For bracing, the bracing capacity of proprietary bracing systems used in accordance with NZS 3604 was limited to:
- - 120 BU/m on timber-framed floor
- - 150 BU/m on concrete slab or concrete perimeter wall.
- For concrete slab-on-ground floors, provisions for fixings of bottom plates to the floor were revised.
- For wall framing, stud spacing is now at 300, 400 and 600mm centres.
- For roof framing, roof trusses require Specific Engineering Design (SED), but roof trusses meeting the requirements specified in the normative part of the Standard and manufactured by an accredited manufacturer are now part of the Acceptable Solution.
- Snow zones have been revised. All tables for wall and roof framing now incorporate a 1kPa snow loading. Additional tables are provided in the Appendix for 1.5kPa and 2kPa snow loading.
Snow loads now include increased loads from snow drifts formed against upper walls on lower roofs.