Building a deck on bush fire prone land in NSW
On land mapped as bush fire prone, a deck is part of the bush fire rules: the RFS says that in NSW the building code’s bush fire provisions apply to Class 1, 2 and 3 buildings, among others, and to associated Class 10a buildings and decks, and its Planning for Bush Fire Protection 2019 adds measures for verandas, decks, steps, ramps and landings. An exempt deck on bushfire prone land that is less than 5 metres from a house needs to be constructed of non-combustible material.
This guide describes the NSW rules in general terms; it isn’t a bush fire assessment of your property. The NSW Rural Fire Service and your council are the places to check.
From the map to the boards, in order
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First
Check whether your land is mapped
Bush fire prone land is land shown on a map certified by the Commissioner of the RFS. The RFS has an online tool for checking an address. It says the result is valid only for the day you search, that the maps are updated periodically, and that you can confirm whether a lot is bush fire prone on the Section 10.7 Planning Certificate from your council.
The RFS is also plain about what the tool is not: it “does not provide an assessment of the bush fire risk you may face on your property.”
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Then
Know the document that governs
Development on mapped land has a legal obligation to consider bush fire and meet the specifications and requirements of Planning for Bush Fire Protection 2019, known as PBP. The RFS describes PBP as a statutory document, adopted in the Environmental Planning and Assessment Regulations on 1 March 2020, and says a five-yearly review of it is underway.
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Then
Find the approval pathway
- Exempt. PBP names decks among the minor works that can be exempt development. On bushfire prone land, an exempt deck less than 5 metres from a house needs to be constructed of non-combustible material. The other exempt standards are in the approval guide.
- Complying development. Can be undertaken on lower risk bush fire prone land up to and including BAL-29, where the construction requirements and other development standards are met.
- A development application. Complying development is not permitted at BAL-40 or BAL-FZ, and a development application is required there.
PBP adds that in certain circumstances a BAL certificate must be obtained, from the local council or a person the RFS recognises as a suitably qualified consultant in bush fire assessment, stating that the development is not located in BAL-40 or BAL-FZ.
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Then
Learn the deck’s Bush Fire Attack Level
PBP defines the Bush Fire Attack Level, or BAL, as “a means of measuring the severity of a building’s potential exposure to ember attack, radiant heat and direct flame contact”, and says the building code uses it as the basis for construction requirements. Its table of levels is reproduced in full below.
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Last
Build to the standard, as varied in NSW
The construction requirements of AS 3959 and the NASH Standard are Deemed-to-Satisfy solutions in the National Construction Code, as varied in NSW, for buildings in designated bush fire prone areas. The details follow below.
The six Bush Fire Attack Levels
| AS 3959 construction level | Heat flux exposure | Description |
|---|---|---|
| BAL-LOW | N/A | “Minimal attack from radiant heat and flame due to the distance of the building from the vegetation, although some attack by burning debris is possible. There is insufficient threat to warrant specific construction requirements.” |
| BAL-12.5 | ≤12.5 | “Attack by burning debris is significant with radiant heat (not greater than 12.5kW/m²). Radiant heat is unlikely to threaten building elements (such as unscreened glass). Specific construction requirements for ember protection and accumulation of debris are warranted.” |
| BAL-19 | >12.5 ≤19 | “Attack by burning debris is significant with radiant heat flux (not greater than 19kW/m²) threatening some building elements (such as screened glass). Specific construction requirements for embers and radiant heat are warranted.” |
| BAL-29 | >19 ≤29 | “Attack by burning debris is significant and radiant heat flux (not greater than 29kW/m²) threatens building integrity. Specific construction requirements for ember and higher levels of radiant heat are warranted. Some flame contact is possible.” |
| BAL-40 | >29 ≤40 | “Radiant heat flux and potential flame contact could threaten building integrity.” |
| BAL-FZ | >40 | “Significant radiant heat and significantly higher likelihood of flame contact from the fire front will threaten building integrity and result in significant risk to residents.” |
PBP defines the flame zone as the area with significant potential for sustained flame contact, determined by the calculated distance at which the radiant heat of the design fire exceeds 40kW/m². The NSW variation to the building code excludes both AS 3959 and the NASH Standard as a Deemed-to-Satisfy solution for buildings required to be built to BAL-FZ; PBP says they should still be used as a basis for a performance based solution.
What the rules single out for decks
PBP adopts measures over and above AS 3959 and the NASH Standard, including construction measures for ember protection at BAL-12.5 and BAL-19. It says these address, in particular:
- sarking;
- subfloor screening;
- floors;
- verandas, decks, steps, ramps and landings;
- timber support posts and beams; and
- fascias and bargeboards.
Section 7.5.2 of PBP then lists, clause by clause, the variations to AS 3959 that apply in NSW, based on the findings of the Victorian Bush Fires Royal Commission and bush fire industry research. The clause wording lives in PBP and the standard, and a designer or certifier works from both.
Timber in a bush fire deck
WoodSolutions’ deck guide says that where bushfire is a risk in Australia, there are limits on using timber to build a deck, and they depend on how high the risk of bushfire attack is and which part of the deck it is. Its Appendix A lists common decking species and the maximum BAL each can be used for in a deck under AS 3959, and it notes that NSW and South Australia have some different requirements.
Materials that flame
PBP explains that the RFS does not support materials that allow flaming, because they increase the exposure of other parts of the building, and of the people in it, after the fire front has passed. For development that may face flame contact, BAL-40 and BAL-FZ, it considers systems tested to AS 1530.8.1 and AS 1530.8.2, with no flaming of the specimen, except that window frames which have passed those tests, and minor elements such as address numbers, may be approved or considered where they don’t compromise the building’s fire safety.
Around the deck
The RFS says the more you prepare your home, the more likely it is to survive a bush fire or ember attack, and that this holds even if you plan to leave early. Among its actions, several touch a deck directly:
- Remove material that can burn around your home, which the RFS lists as “door mats, wood piles, mulch, leaves, outdoor furniture”.
- Clean up fallen leaves, twigs and debris around the property.
- Cut back trees and shrubs overhanging buildings.
- Enclose the areas under the house, and block areas where embers can enter the house, which the RFS lists as external walls, windows, doors and under the house.
The full checklist is in the RFS’s Prepare your home fact sheet.