Building construction in bushfire prone areas



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MFPE 2014




CHAPTER 7
BUILDING CONSTRUCTION IN BUSHFIRE PRONE AREAS
Scope


  1. This chapter details the Defence design requirements for New Construction, alterations, additions or Change-in-Use to buildings that are located within or adjacent to designated bushfire prone areas.


Note

Existing buildings that are not the subject of new works are addressed in chapter 6.



Aim


  1. The aim of this chapter is to define the minimum standards for bushfire protection for Defence buildings. This includes minimising the risk of impact of bushfire on life safety and strategic Defence assets as well as the damage caused by secondary fires after the passage of the main fire front.


References


  1. Reference is necessary to the following documents:




  1. National Construction Code Volume One and Volume Two– Building Code of Australia (BCA);

  2. AS 3959—Construction of buildings in bushfire-prone areas;

  3. AS/NZS 4200.1—Pliable building membranes and underlays – Materials; and

  4. National Guidelines for Bushfire Management and Mitigation on the Defence Estate.


Objectives


  1. The objectives of protecting Defence buildings from bushfire are to:




  1. protect human life (including firefighters); and

  2. minimise the impact of bushfire on buildings, assets and functions.


Compliance requirements


  1. New class 1, 2, 3 and associated class 10 buildings in designated bushfire prone areas shall comply with BCA.




  1. All classes of buildings with a Contribution Factor of CF1 or CF2 – and CF3 elements identified as having an intolerable loss in a fire event – in designated bushfire prone areas shall comply with AS 3959 and the additional requirements specified herein.


Note

There are no specific requirements for Contribution Factor 4 or 5 buildings with BCA classifications of class 4 to 9.




  1. Specialist facilities such as fuel installations and explosive ordnance buildings must adopt a performance based approach using this chapter, the BCA and AS 3959 to determine requirements necessary to mitigate the identified hazards. The assessment shall include but not be limited to:




  1. Building hazard identification

  2. Bushfire attack level;

  3. potential exposure to radiant heat, wind and ember attack; and

  4. method to protect the facility and surrounding assets.




  1. Fire Protection Association Australia Bushfire Planning and Design (BPAD)-A or BPAD-D Certified Practitioners may undertake and / or review designs compliant with the BCA deemed to satisfy provisions and/or designs compliant with this chapter.




  1. Any Alternative Solution or Dispensation must be produced or verified by a BPAD-A Certified Practitioner.


Determining Bushfire Prone Areas


  1. All building works must have regard to the Bushfire Management Plan for the site established under chapter 6.




  1. Areas of the Defence Estate designated as bushfire prone are to be treated as ‘designated bushfire prone areas’ for the purposes of the BCA and AS 3959.




  1. All buildings within 145 metres of classifiable vegetation are to be assessed for bushfire risk using the process set out below.


Determination of Bushfire Attack Level


  1. The vegetation surrounding the building is to be classified based on AS 3959.




  1. Vegetation classifications used or relied on to assess bushfire risk must be confirmed by a Bushfire Certified Practitioner or Ecologist.




  1. The distance between the edge of the building and the edge of the closest classifiable vegetation must be calculated and recorded. The edge of the vegetation hazard is to include any branches above ground level.




  1. The dominant slope within 145 metres of the building is to be calculated through survey or the Digital Terrain Model of the site. Where slopes are complex (such as gullies) bushfire attack is to be calculated separately for each component of the landscape and the highest threat used.




  1. The Fire Danger Index (FDI) for the site must be determined by one of the following methods:




    1. the FDI value for the site as stated in the Bushfire Management Plan;

    2. FDI values specific to the site as calculated by a BPAD-A certified practitioner; or

    3. FDI values taken from AS 3959.




  1. Taking the vegetation type, distance to vegetation, slope and FDI for the site in to account, the Bushfire Attack Level (BAL) for the building shall be determined via the following methods:




    1. by consulting Tables 2.4.2 – 2.4.5 within AS 3959-2009, noting that a specific table is provided for each FDI value. Where a specific FDI has been calculated for the site that falls between two values, this value will be rounded up to the next highest FDI table (Method 1); or

    2. by direct calculation of BAL for the building by a BPAD-A certified practitioner.

Note

The process to determine the BAL is available in National Guidelines for Bushfire Management and Mitigation on the Defence Estate



  1. No reduction in the calculated BAL from shielding by walls of the building is permitted.


Building construction (General Provisions)


  1. The construction requirements in the remainder of this chapter apply to all buildings referred to in paragraphs 7.5. to 7.7..




  1. Unless higher levels are specified, all buildings within designated Bushfire Prone Areas shall meet the prescriptive requirements for BAL12.5 under AS 3959.




  1. For all buildings within a zone that is above BAL12.5 and below BAL 40 either the prescriptive requirements under AS 3959 or Alternative Solutions of the BCA may be used. Where requirements for buildings or facilities are not specified in the BCA, the performance requirements associated with class 1 to 3 buildings shall be met.




  1. Buildings should not to be sited within areas with a BAL rating of 40 and above unless there is no viable alternative. Where there are no viable alternative siting options, an Alternative Solution shall be undertaken by a BPAD-A accredited practitioner. Where requirements for buildings or facilities are not specified in the BCA, the performance requirements associated with class 1 to 3 buildings shall be met.




  1. Designs that incorporate exposed subfloors and/or re-entrant corners on the rooflines of buildings are to be avoided wherever possible.




  1. Consultation with the relevant State or Territory Fire Service shall be undertaken for all Defence projects that are to be constructed on designated bushfire prone land.


Building construction (Special Provisions)


  1. All roofs are to be fully sarked. Sarking material will comply with the following:

    1. non-combustible material; or

    2. breather-type sarking that complies with AS 4200.1 and with a flammability index of not more than 5, with sarking to be installed on the outside of the frame.




  1. All elevated floors and subfloors within zones with a BAL 12.5 – BAL 29 are to meet the following requirements:

    1. constructed entirely of non-combustible material;

    2. constructed of bushfire resistant timbers (as per AS 3959-2009 Appendix H); or

    3. a combination of the above.




  1. Where decking material is to be sealed to restrict entry of embers into subfloor areas, this is to be accomplished through either:

    1. ember mesh installed directly underneath the deck boards; or

    2. silicon sealing of all gaps in the decking, with holes with a maximum aperture of 2mm drilled in the sealant to allow for drainage.


Access


  1. Where a bushfire hazard exists on or adjacent to the site, the access design criteria applied to the development shall meet responding fire brigade requirements, particularly in terms of road design standards for emergency vehicles and potential for alternative access paths. Also refer to paragraph 1.29 of chapter 1.


Bushfire Sprinkler Systems


  1. Where sprinkler systems are installed to provide additional bushfire protection the following must apply:




  1. Sprinkler systems are not to substitute building design solutions under AS 3959 unless these are:

  1. sprinkler systems designed as a comprehensive solution with regard to building coverage, water output, hydraulic loading, pump pressure and water supply;

  2. pumps that are independently powered, appropriately shielded from bushfire attack and activated from within the building (ie no need to leave the shelter to activate); and

  3. sprinkler systems are to have a minimum water supply of four hours.




  1. In the case of heritage buildings or other assets that cannot be readily modified, the risk of these buildings and potential options to mitigate these risks should be assessed by a BPAD-A certified professional with regard to their function and intended use.




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