Part F1 Damp and weatherproofing (DtS)

The BCA does not contain any Deemed-to-Satisfy Provisions which can be followed as a means of complying with FP1.4 for water penetration through external walls. However, it is still compulsory to comply with this Performance Requirement.

This approach has not changed from the previous edition of the BCA.

Requires compliance with AS/NZS 3500.3 to achieve compliance with the Performance Requirements.

In BCA 90, this provision was performance-based. In subsequent editions of the BCA, the provision is covered by the Performance Requirements. F1.2 has been left blank rather than renumber subsequent clauses.

In BCA 90, this provision was performance-based. In subsequent editions of the BCA, the provision is covered by the Performance Requirements. F1.3 has been left blank rather than renumber subsequent clauses.

F1.4 references the Standard for waterproofing membranes for external above ground use.

F1.5 contains reference to Australian Standards and other reference documents for a range of roofing materials and fixing methods suitable for the prevention of water penetration.

F1.5(a) and (b), with regard to the use of concrete and terracotta roofing tiles, are not applicable to cyclonic areas, because the AS 2050 fixing details are inadequate for use in such areas. Accordingly, fixing in cyclonic areas must be approved by the appropriate authority.

F1.6 references the Standard for sarking materials where sarking is required for weatherproofing roofs and walls (eg under roof tiles or on walls before weatherboards are fixed).

F1.7 requires that certain areas designated as “wet areas” be made impervious to water. This applies to showers, floors and walls adjacent to baths, tubs or laundry troughs, basins, sinks and urinals. The aim is to protect adjacent areas from damage by water splashed from these fixtures.

Class 2 and 3 buildings and Class 4 parts of buildings must be impervious to water in accordance with the design and construction requirements of AS 3740 in the locations listed in Table F1.7.

Similar design and location requirements apply for a bathroom, shower room, slop hopper, sink compartment, laundry or sanitary compartment in a Class 5, 6, 7, 8 or 9 building. Table F1.7 determines when a building element is required to be waterproof or water resistant, while how to make the building element waterproof or water resistant is determined by AS 3740.

The defined terms for shower area, vessel, waterproof, water resistant and wet area are located under Schedule 3.

In BCA 90, this provision was performance-based. In subsequent editions of the BCA, the provision is covered by the Performance Requirements. F1.8 has been left blank rather than renumber subsequent clauses.

Damp must be prevented from reaching:

• a building's lowest floor timbers;
• suspended concrete floors or other suspended floors;
• supporting beams or girders; and
• walls above damp-proof courses.

AS/NZS 2904 and AS 3660.1 are referenced as alternative options for damp-proof course materials and installation details.

F1.9(c) contains exemptions to F1.9(a) because the safety level of buildings will not be significantly diminished by moisture from the ground.

F1.9(c)(i) regarding Class 7 and Class 8 buildings refers only to such buildings which, in a particular case, do not exhibit any need for compliance with F1.9. Such buildings must be considered on a case-by-case basis. However, it is the responsibility of a building proponent to satisfy the appropriate authority that the exemption should apply.

F1.10 covers floors resting on the ground. The aim is to prevent ground dampness causing:

• unhealthy and dangerous conditions or loss of amenity for occupants; or
• dampness and deterioration of building elements (which, in this case, includes surfaces and linings inside the building, such as floor tiles, wall paint and the like).

AS 2870 is referenced for acceptable materials and installation details for vapour barriers to stop ground moisture reaching the upper surface of floors and walls.

Exemptions apply to F1.10 where:

• weatherproofing is not required for Class 7 or Class 8 buildings where there is no necessity for compliance, sheds forming part of a building used for other purposes, and so on (see the Limitations to FP1.4 for a listing of exempted buildings); and
• the base of a stairway or lift or similar shaft is suitably drained.

Figure F1.10 illustrates a method of installing damp-proofing in subfloor structures.

Figure F1.10 Installation of DPC in subfloor structures

Floor wastes are to be installed in bathrooms and laundries in Class 2 and Class 3 buildings and Class 4 parts, where those bathrooms and laundries are above another sole-occupancy unit or public space.

The aims of this requirement are to minimise water overflows from fixtures in the specified rooms:

• causing costly and possibly dangerous water damage to other sole-occupancy units;
• creating unhealthy conditions in public spaces in buildings; and
• disrupting and intruding on neighbours in the unit below.

Subfloor ventilation is cross ventilation of the subfloor space between the underside of the floor and ground surface under the lowest suspended floor of a building.

Ground moisture rising into or entering the subfloor space can create a damp environment which encourages timber rot, fungus growth and the potential for termite activity. Subfloor ventilation increases air flow, reducing any damaging water vapour in the subfloor space.

Factors that can affect achieving satisfactory levels of subfloor ventilation include height above ground, prevailing breezes (air transfer), differential temperature and humidity between the subfloor and the external environment and good building practice.

The amount of subfloor ventilation required for a building is related to the relative humidity likely to be encountered in that location. For the purposes of the Deemed-to-Satisfy Provisions, Australia has been divided into three broad climatic zones based on the prevailing relative humidity.

The climatic zones were determined by analysis of the average relative humidity at 9 am and 3 pm in January and July. The season with the highest relative humidity is used. Generally this is July for southern Australia and January for northern Australia. The climatic zone limits are described in Figure F1.12.

Table F1.12 specifies the minimum amount of subfloor ventilation openings and height of subfloor framing members above ground level for the three climatic zones illustrated in Figure F1.12. The table allows subfloor ventilation rates to be halved if the ground within the subfloor space is sealed by an impervious membrane because humidity levels in the space will not be affected by moisture from the soil.

F1.12(e) specifies additional requirements for preventing deterioration of subfloor members where the ground or sub-floor space is excessively damp, as would occur in areas with high water tables, poor drainage or in areas frequently affected by flooding or water inundation.

F1.13 requires windows, etc to comply with the AS 2047 requirements for resistance to water penetration. The provision does not apply to:

• some Class 7 and 8 buildings;
• garages, tool sheds, sanitary compartments and the like forming part of a building used for other purposes; and
• open spectator stands and open-deck carparks.

The exemptions are consistent with limitations in FP1.4 (see FP1.4).