Subfloor clearances for termite management systems

NCC Volume Two

The NCC contains references to reduced subfloor height and termite management under subfloor ventilation Table 6.2.1b through a reference in the notes (see Table Note 1).

Table notes:

1. 400mm clearance required only where termite management systems are installed that need to be inspected (see Part 2.2.4).  
2. On sloping sites, the 400 mm clearance required by (1) may be reduced to 150 mm within 2 m of external walls in accordance with Figure 6.2.1b.

The obligation for a termite management system is contained in H1D3 Site Preparation and Subclause (3) refers the reader to Part 3.4 of the Housing Provisions.

(3) Compliance with Part 3.4 of the ABCB Housing Provisions satisfies Performance Requirement H1P1 for termite risk management.

Part 3.4.2 Termite management systems states where a termite management system is required it must comply with AS 3660.1 Termite Management or be tested and passed the test required by section 5 of AS 3660.3.

Reduced clearances

The Standard AS 3660.1 is a Deemed-to-Satisfy solution for physical and chemical barriers to deter termites, which references the following relevant subfloor height requirements under Clause 2.4 of the standard:

• where a suspended floor has less than 400 mm clearance, an underfloor termite management system shall be installed to the whole of the subfloor area of reduced clearance except as permitted by clause 3.3.2(b)

Clearances are detailed in 3.3.2 Access for visual inspection which states the following shall apply:

• A minimum clearance of 400 mm between the finished ground level and any structural components or other obstructions (bearers, joists, plumbing fixtures or ducting systems). 
• The minimum clearance in (a) may be reduced to 150 mm at the inside face of an external wall, provided clearance from the finished ground level slopes to 400 mm within a horizontal distance not more than 2 m from the reduced clearance. Where the reduced clearance is applied, it shall be ensured that access for visual maintenance is maintained throughout the entire suspended floor.

Therefore, if a height which does does not meet subclause (a) and (b) and access for visual maintenance can’t be achieved, the only option the standard provides is a chemical barrier. Clause 7.7.3 of the standard states that where compliance with 3.3.2 can’t be achieved (400 mm clearance) all areas of the subfloor, soil shall be treated.

A chemical termite management system throughout the subfloor area and horizontal elements would therefore allow the overall height of the subfloor to reach 150 mm, providing other considerations relating to subfloor ventilation can be achieved.