Farm Forestry New Zealand

 NZS 3604 Timber Framed Buildings

Introduction

On 1 August 2011, the Department of Building and Housing announced changes to the B1 Structure and E2 External Moisture Building Code documents. This announcement was made in the Building Controls Update Bulletin No. 116. The changes to the Structure documents include the referencing of NZS 3604:2011 Timber-framed buildings, which was published in February 2011.

These changes took effect immediately with a transition period through to 31 January 2012. During the transition period, both NZS 3604:1999 and NZS 3604:2011 will be Acceptable Solutions. From 1 February 2012, only NZS 3604:2011 will apply.

NZS 3604:2011 Timber Framed Buildings sets a minimum standard for the design and construction of timber-framed buildings. NZS 3604 provides methods and details for the design and construction of timber-framed structures not requiring specific engineering design. NZS 3604 is a core resource for builders and building consent authorities determining compliance with the New Zealand Building Code.

Although NZS 3604 applies to only radiata pine and Douglas fir, the standards provisions may be applicable to other timbers, provided adequate structural performance and durability can be demonstrated.

This Standard applies to Radiata pine and Douglas fir.*2.3.4 Green and Dry Timber
However, The Standard's provisions may be applicable to timbers other than Radiata pine and Douglas fir such as other softwood species. Such use however, needs to be subject to demonstration of adequate structural performanceNZS 3603 Timber Structures Standard allows for determining Characteristic Stresses for structural timber. and durability2.3.1: The timber species, preservative treatment, in-service moisture range and their end use environment shall comply with NZS 3602 Timber and wood-based products for use in building..*C 2.3.4
 

Structural grades

Only verified timber grades can be used with NZS 3604:2011. All structural timber will now be known as structural grades SG6, SG8 and SG10 - for example, SG8 now collectively refers to both machine stress grade 8 (MSG8) and visual stress grade 8 (VSG8).

All structural grades for house framing are now verified grades in accordance with NZS 3622 and have been renamed SG 6, SG 8, SG 10, SG 6 (Wet) with properties meeting those currently specified in NZS 3603. The renaming simplifies structural grading for the market because there will be no distinction between framing timber which is machine graded and verified, MSG, or visually graded and verified, VSG. The renaming replaces No. 1 Framing with SG 6.*C2.3.2

The grade of timber identified by the modulus of elasticity parameter, E, which has been verified as either machine or visual stress graded timber in accordance with NZS 3622. The grades covered by this Standard are:
(a)    Dry timber

(b)   Wet timber

Timber sizes and moisture

The design solutions are for timber which is dry (maximum moisture content 18%) throughout its design life. *2.3.4
(Exceptions are provided in 2.3.4).
NZS 3604 does not provide design solutions for timber loaded in situations where prolonged high moisture contents can be expected, except for members specifically noted in 2.3.4. However, timber that is graded and installed green, namely SG 6 (Wet) framing, or timber that has been installed dry and become wet during the building process, may still be used with the Standard, provided it is propped and dried in place before being loaded and remains dry in service from that point on. *C2.3.4

The cross section dimensions of timber given in the Standard are the actual minimum dried sizes that shall be used. Where green timber is used its dimensions shall be no less than the green guaged equivalent size given below:

(C2.3.4 Green and dry timber)

Where the standard specifies members by call sizeFrom 1.3 Definitions: CALL SIZE. The dimensions as given by NZS 3601 and by which timber is referred to in commercial transactions those sizes shall be read as the actual minimum dried sizes given below:

(2.3.5 Call Sizes)
(Call size is also referred to as "nominal" size).
Note: 125 mm and 225 mm sizes were removed from the standard with Amendment 2 because of advice that they were no longer commercially available in significant quantities.

Flooring Timber

Wood-based components used for flooring shall be in accordance with AS/NZS 1860.*2.3.7

Engineered wood products

Engineered wood products shall be either laminated veneer lumber (LVL), or glue laminated timber manufactured using Radiata pine or Douglas fir.*2.3.9.1

The preservative treatment for engineered wood products shall comply with NZS 3602 provided however that where engineered wood products are not already specified, the level of treatment shall be the same as that required for kiln-dried Radiata pine structural grades to comply with NZS 3602.*2.3.9.4

Glue laminated timber shall be manufactured in accordance with AS/NZS 1328*2.3.9.3

LVL shall be manufactured in accordance with AS/NZS 4357 (Parts 0 to 4).*2.3.9.2


Engineered wood products may be used as a direct substitute for SG 6, 8 or 10 provided that they are of the same finished size as the member to be substituted and that the strength and stiffness properties have been verified and marked in accordance with NZS 3622 and are no less than the strength and stiffness properties of the grade to be substituted.*2.3.9.5

Disclaimer: While every effort is made to ensure the accuracy of the information provided on this site, Farm Forestry Timbers Society do not accept liability for any consequences arising from reliance on the information published. If readers have any doubts about acting on any articles they should seek confirming, professional advice.