Target design life

Target design life is the anticipated, satisfactory service life of a building component if assembled and maintained in accordance with good building practice and the requirements specified in this guide. Three categories of target design life are 5, 15 and 50 years’ service.

Within a single dwelling, there is usually a range of design life expectancies for different components. This means that at the time of design and construction it is anticipated that some timber components will have a shorter service life than others.

Factors that affect the performance of building applications include: ease-of-access for maintenance, relative cost of materials and labour for assembly, and propensity for refitting due to changes in fashion or the introduction of new materials.

This means that different components of structures may only be expected to provide satisfactory performance for 5 years (e.g. battens or fence palings), while other components are required to provide a service life of 50 years (e.g. roof trusses and house stumps).

Definitions:

TDL: Target design life

C and H codes: conditions for using otherwise ‘approved’ timbers for the application (and nominated TDL). Conditions and H level treatments determined in Schedules A, B and C.

Applications: building applications (with associated TDL and environment).

Durability hazard zones (allocated to regional areas):

  • Ag: above-ground decay hazard zones Ag:A, Ag:B, Ag:C or Ag:D.
  • Ig: In-ground decay hazard zones Ig:A, Ig:B, Ig:C or Ig:D.

Natural durability classes and expected service life (years):

  • Above-ground class 1 (>40), 2 (15-40), 3 (7-15) or 4 (0-7)
  • In-ground class 1 (>25), 2 (15-25), 3 (5-15), or 4 (0-5)

Target design life categories:

 


 

Five-year target design life applications - all

Target design life: 5 years
Environment: Protected from and/or exposed to the weather.                                                                                     
Application examples: Battens, fences, gates, lattice panels.

Environment

  • Fully protected from and/or exposed to the weather or other dampness.
  • Clear of the ground, well drained and/or ventilated and with free air circulation.
  • Non-structural (not load-bearing or not supporting in function).

Conditions of use

  • C and H codes—none are applicable for 5-year-TDL applications.
  • Unless otherwise specified for appearance reasons, sawn timber may contain untreated non-lyctine-susceptible sapwood, provided that the combination of such sapwood and any associated wane does not exceed the wane limits permitted by the relevant Australian Standard.

Treatment (other than for termites)

  • Any lyctine-susceptible sapwood must be treated to minimum H1 level in accordance with the provisions of AS 1604.

Termite protection

  • Where termite-resistant timber is required in accordance with the BCA, it may be either:
    • timber classified as naturally termite resistant (R) or
    • timber classified as not resistant (NR) but that has been treated to minimum H2 level in accordance with the provisions of AS 1604.

Examples

Building members with a 5-year-TDL are listed in the Building members and applications selector.


 

Fifteen-year target design applications

Skip to 15 years: Protected; Exposed; In-ground


Fifteen-year target design applications - protected

Target design life: 15 years
Environment: Protected                                                                                    
Application examples: Architraves, brackets, eaves, flooring, reveals, skirting.

Environment

  • Fully protected from the weather or other sources of dampness.
  • Clear of the ground, well ventilated and with free air circulation.
  • Structural and non-structural.

Conditions of use

  • As indicated by C and H codes for high-shrinkage timber species and species groups.

Treatment (other than for termites)

  • Any lyctine-susceptible sapwood must be treated to minimum H1 level in accordance with the provisions of AS 1604.

Termite protection

  • Where termite-resistant timber is required in accordance with the BCA, it may be either:
    • timber classified as naturally termite resistant (R) or
    • timber classified as not resistant (NR) that has been treated to minimum H2 level in accordance with the provisions of AS 1604.

Examples

Protected building members with a 15-year-TDL are listed in the Building members and applications selector.


Fifteen-year target design applications - weather-exposed

Target design life: 15 years
Environment: Weather-exposed                                                                                  
Application examples:           Boards (non-structural), capping, cladding, doors, end-stops, fascias, jambs, joinery, linings, mouldings, pergolas, weatherboards, window boards.

Environment

  • Exposed to, or not fully protected from, the weather or other sources of dampness.
  • Clear of the ground, well drained and ventilated and with free air circulation.
  • Structural and non-structural, relatively accessible for maintenance or replacement.

Conditions of use

  • As indicated by C and H codes for each timber species to be used in each of the four above-ground decay hazard zones (Ag:A, Ag:B, Ag:C and Ag:D).
  • Unless otherwise required by the relevant Australian Standard or by explicit specification, timber for sawn weatherboards, fascias and barge boards may be unseasoned except when subject to the requirements of any C codes in the schedules.
  • Unless otherwise specified for appearance reasons, timber may contain untreated, non-lyctine-susceptible sapwood provided that the combination of such sapwood and any associated wane does not exceed the wane limits permitted by the relevant Australian Standard.

Treatment (other than for termites)

  • Timbers classed as Above-ground durability class 2, 3 and 4 and that are deemed suitable for these uses (TDL 15 years, weather-exposed) must meet the minimum requirements of H3 level in accordance with AS 1604 and may contain limited amounts of unpenetrated or inadequately treated heartwood comprising no more than 20% of the cross-section of the piece at any point.
  • Any sapwood, except as allowed above, must be treated to minimum H3 level in accordance with the provisions of AS 1604.

Termite protection

  • Where termite protection is required in accordance with the BCA it may be either:
    • timber classified as naturally termite resistant (R) may be used provided any sapwood is treated to minimum H3 level or
    • timber classified as not resistant (NR) that has been treated to minimum H3 level in accordance with the provisions of AS 1604.

Examples

Weather-exposed building members with a 15-year-TDL are listed inthe  Building members and applications selector.


Fifteen-year target design life applications - in-ground

Target design life: 15 years
Environment: In-ground                                                                               
Application examples:           Posts, greenhouse frames, posts in-ground, retaining walls

Environment

  • In-ground or in contact with the ground or in poorly ventilated, persistently damp conditions.
  • Structural (load-bearing or supporting in function).
  • Relatively accessible for maintenance or replacement.

Conditions of use

  • As indicated by C and H codes for each timber species to be used in each of the four in-ground decay hazard zones (Ig:A, Ig:B, Ig:C and Ig:D).
  • Unless otherwise specified for appearance reasons, sawn timber may contain untreated non-lyctine-susceptible sapwood, provided that the combination of such sapwood and any associated wane does not exceed the wane limits permitted by the relevant Australian Standard.

Treatment and termite protection

  • Timber classed as In-ground durability class 3 and 4 that are suitable for these uses (TDL 15 years, in-ground) must meet the minimum requirements of H4 level in accordance with AS 1604 and may contain limited amounts of unpenetrated or inadequately treated heartwood provided that:
    • in sawn timber, not exceeding the want and wane limits permitted by the relevant Australian Standard (where no such standard exists, this unpenetrated heartwood must not exceed 20% of the cross-sectional area of the piece and not extend face to face or edge to edge through the piece);
    • in round timber, not extending beyond half the radius from the central axis of the piece, as determined at end sections;
    • any sapwood, except as allowed above, must be treated to H4 level in accordance with the provisions of AS 1604;
    • timber classified as not resistant (NR) used as members forming, or directly supported on primary foundations, are to be protected against subterranean termite access by soil treatment and/or physical barriers in accordance with AS 3660.1-2000 Termite management part 1—new building work.

Examples

Building members in ground contact or in persistently damp conditions with a 15-year-TDL are listed in the Building members and applications selector.


Fifty-year target design life applications

Skip to: 50 years: Protected, Exposed, In-ground

Fifty-year target design life applications - protected

Target design life: 50 years
Environment: Protected                                                                              
Application examples:           Binders, braces, lintels, purlins

Environment

  • Fully protected from the weather or other dampness.
  • Clear of the ground, well ventilated and with free air circulation.
  • Structural and/or non-structural.

Conditions of use

  • As indicated by C and H codes for each timber.
  • For applications involving feature flooring, refer to the advisory notes about the implications of moisture content, density and hardness in the guide: Advisory information.

Treatment (other than for termites)

  • Any lyctine-susceptible sapwood must be treated to minimum H1 level in accordance with the provisions of AS 1604.

Termite protection

  • Where termite-resistant timber is required in accordance with the BCA, it may be either:
    • timber classified as naturally termite resistant (R) or
    • timber classified as not resistant (NR) that has been treated to minimum H2 level in accordance with the provisions of AS 1604.

Examples

Protected building members suitable for a 50-year-TDL are listed in Building members and applications selector.


Fifty-year target design life applications - weather-exposed

Target design life: 50 years
Environment: Weather-exposed                                                                   
Application examples:           Decking, engineered products, framing, handrails, joists, mullions, rafters, ridges, railings, stair treads, step stringers, studs.

Environment

  • Exposed to or not fully protected from the weather or other sources of dampness.
  • Clear of the ground, well drained and ventilated and with free air circulation.
  • Structural and non-structural.

Conditions of use

  • As indicated by C and H codes for each timber species to be used in each of the four above-ground decay hazard zones (Ag:A, Ag:B, Ag:C and Ag:D).
  • All timbers for use as prefabricated structural frames to external door and window openings to be seasoned, irrespective of other, general codes.
  • Unless otherwise specified for appearance reasons, sawn timber may contain untreated non-lyctine-susceptible sapwood, provided that the combination of such sapwood and associated wane does not exceed wane limits required by the relevant Australian Standard.

Treatment (other than for termites)

  • Timbers classed as Above-ground durability class 2, 3 and 4 and that are coded H3 in Part 2 –applications and conditions -are suitable for these uses (TDL 50 years, weather exposed) if the timber achieves the minimum requirements of H3 level as defined in AS 1604 and may contain limited amounts of non-penetrated or inadequately treated heartwood provided:
    • in sawn timber, not exceeding the want and wane limits permitted by the relevant Australian Standard (where no such standard exists, non-penetrated heartwood must not exceed 20% of the cross-sectional area of the piece and not extend face to face or edge to edge through the piece)
    • in round timbers, not extending beyond half the radius from the central axis of the piece, as determined at end sections
    • any sapwood, except as allowed above, must be treated to minimum H3 level
    • treatment must be in accordance with the provisions of AS 1604

Termite protection

  • Where termite-resistant timber is required in accordance with the BCA it may be either:
    • timber classified as naturally termite resistant (R) or
    • timber classified as not resistant (NR) that has been treated to minimum H3 level in accordance with the provisions of AS 1604
  • Structural members, such as poles and posts held clear of the ground by stirrups in pole frame and similar applications, are to be protected against subterranean termite access by soil treatment and/or physical barriers in accordance with AS 3660.1-2000 Termite management part 1—new building work (Standards Australia 2000b)

Examples

Weather-exposed building members with a 50-year target design life are listed in Building members and applications selector.


Fifty-year target design life applications - in-ground

Target design life: 50 years
Environment: In-ground                                                                  
Application examples:           Foundation timbers, sills, stumps

Environment

  • In-ground or in contact with the ground or poorly ventilated, persistently damp conditions
  • Structural (load-bearing, structural or supporting in function)
  • Difficult to access for maintenance or replacement

Conditions of use

  • As indicated by C and H codes for each timber species to be used in each of the four in-ground decay hazard zones (Ig:A, Ig:B, Ig:C and Ig:D)
  • Unless otherwise specified for appearance reasons, sawn timber may contain untreated non-lyctine-susceptible sapwood provided that the combination of such sapwood and any associated wane does not exceed the wane limits permitted by the relevant Australian Standard
  • Timber is to be free from untreated lyctine-susceptible sapwood
  • Timbers classed as In-ground durability class 3 and 4 and that are coded H5 are suitable for these uses (TDL 50 years, in-ground), if preservative treated to H5 level in accordance with AS 1604, and may contain limited amounts of unpenetrated or inadequately treated heartwood not comprising more than 20% of the cross-section of the piece at any point:
    • in sawn timber, not exceeding the want and wane limits permitted by the relevant Australian Standard (where no such standard exists, this heartwood must not exceed 20% of the cross-sectional area of the piece and not extend face to face or edge to edge through the piece)
    • in round timbers, not extending beyond half the radius from the central axis of the piece, as determined at end sections

Treatment and termite protection

  • Timbers classed as In-ground durability class 2, 3 and 4 and suitable for these uses (TDL 50 years, in-ground) must meet the minimum requirements of H5 level in accordance with AS 1604 and may contain limited amounts of unpenetrated or inadequately treated heartwood not comprising more than 20% of the cross-section of the piece at any point
  • Any sapwood, except as allowed above, must be treated to minimum H5 level in accordance with the provisions of AS 1604
  • Timber classified as not resistant (NR) used as members forming or directly supported on primary foundations are to be protected against subterranean termite access by soil treatment and/or physical barriers in accordance with AS 3660.1-2000 Termite management part 1—new building work (Standards Australia 2000b)

Examples

Building members in ground contact or in persistently damp conditions with a 50-year target design life are listed in the Building members and applications selector.

Last modified
10/24/2017 - 00:35