Part F1 Surface water management, rising damp and external waterproofing

F1O1(a) aims to minimise the risk of water leaking into or accumulating within a building and causing musty, damp and unhealthy conditions or damaging building elements by corrosion.

Examples

F1O1(a) aims to minimisethe risk of water leakinginto or accumulating within a buildingand causing musty,damp and unhealthy conditions or damaging building elements by corrosion.

• Damp conditions in houses can cause seriousdiseases. What appearto be less serious illnesses, such as colds, can have serious consequences, particularly for children and the elderly.
• Rotten floorboards can collapse, causinginjury.
• Electrical connections can corrode, causingfailure of safetydevices, or increasing the risk of electrocution.
• Penetration of moisture into building elementscan cause degradation to a buildinglong before the damage is detected.

F1O1(b) aims to minimise the risk of other property being damaged by surface water redirected from a building or any associated sitework. Property that is to be protected from redirected surface water includes buildings on the same allotment, buildings on adjoining allotments, adjoining allotments themselves and roads.

Examples

Construction on an allotment must not cause re-directed water damage to “other property”, including:

• any building on the same allotment;
• any buildingon an adjoining allotment;
• any adjoiningallotment (whether thereis a building on it or not); and
• any road.

People and other property are to be protected from any problems caused by surface water re-directed by a building and any sitework involved in its construction. Remedial works must be undertaken to dispose of any surface water which, because of any variation or addition to its flow caused by any buildingor sitework, causesharm to peopleor other property.

A building must resist:

• rainwater, coming throughthe roof or walls, due to poor waterproofing
• surface water, comingthrough openings which are too low; and
• ground water, which could rise up throughporous floors or walls.

Ground water could enter a building if there are inadequate damp-proof courses or vapour barriers installed, or if other ways of resisting the rising damp have not been provided.

Surface water resulting from a storm with a 5% annual exceedance probability (i.e. a 1 in 20 year storm) that is collected or concentrated by a building or sitework must be disposed of without damage to other property.

Construction should not cause stormwater problems on other properties, worse than those which existedpreviously.

Examples

As a generalrule, undeveloped land tends to absorb rainwater, usually resulting in comparatively slow run-off.

However, a building’s hard surfaces, such as roofsand pavements, causecomparatively quick run-off.Consequently, the design of the surface water disposal system must make provision for run-off stormwater from hard surfaces collected or concentrated by a building or sitework.

This is considered an appropriate limit, fair on the person responsible for the building and siteworks and the person responsible for properties affected by re-directed surface water.

Building and siteworksmust be arrangedso that surfacewater from a storm with an annual exceedance probability of 1% (i.e. a 1 in 100 year storm) does not enter into a building.

A storm with an annual exceedance probability of 5% (1 in 20 year storm) has a less intense flow of water than a storm with an annual exceedance probability of 1% (1 in 100 year storm), which is what the subject building must be protected from.

It is considered more important to prevent water entering a building than it is to prevent water entering a neighbouring allotment or property.

The limitations contain several exemptions to F1P2 These are based on the belief that the use and safety levels of the exempted buildings will not be significantly diminished by surface water entering them.

Limitation (a) 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 F1P2. 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. The structures like garages, tool sheds, and sanitary compartments forming part of a building used for other purposes are also exempted, provided they do not contribute to the weatherproofing of another part of a building that needs to be weatherproofed. Lastly, open spectator stands and open-deck carparks are not required to comply with this provisions.

Under F1P3(a) a drainagesystem for the disposal of surface waterfrom storm with an annual exceedance probability of 5% must:

• have an appropriate outfall; and
• avoid damage to the building.

An outfall includes a kerb and channel, a soakage system, and a natural watercourse, with the decision as to what is appropriate being made by the appropriate authority. Damage to the building could be caused by a building’s subsidence.

Under F1P3(b), a drainage systemfor the disposalof surface watermust avoid surfacewater from a storm with an annual exceedance probability of 1% from entering a building. This provision is intended to prevent surface water causing internal damage to a building, or causing injury or illness to occupants.

The F1P3(b) prohibition on surfacewater entering the building:

• does not prohibita drainage systemthat passes surfacewater through a building (probably by way of pipes) without causing damage; and

clearly does not prohibit water entering a building when it is required for various purposes.

Building elements must be protected from deterioration and occupants must be protected from unhealthy or dangerous conditions or a loss of amenity causedby moisture from the ground (causing such problems as rot, rising damp, rust, and so on). In essence, this requires that the materials and components which make up building elements must either be fit for this purpose or made fit by protection.

See commentary from F1P2 limitations as the same limitations apply to F1P4.

Examples

The followingmay be acceptable to achievecompliance with F1P4. They should not be regarded as absolute.

• damp-proof course in masonry walls above finished ground level;
• vapour barrier under a concrete slab;
• adequate subfloor ventilation;
• painted or other similar protective coatings on steel and timber on or near ground level;
• appropriate concrete cover on steel reinforcing;
• galvanised coatings on steel; and

specific concrete mixes to achieve required protection levels.

F1D2 clarifies that F1D4 and F1D5 are not applicable to roofs that comply with F3D2(a) to (d). Additionally, F1D3 to F1D5 do not apply to balconies, podiums, or similar horizontal surface part of a building if the flooring consists of timber decking or other perforated material, or if the structure is located directly above ground.

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

F1D4 sets standards for exposed joints in the drainage surface on roofs, balconies, and similar horizontal surfaces. For the purposes of F1D4, an exposed joint is a construction joint, control joint, expansion joint, contraction joint or movement joint and includes an exposed joint which is directly below a drainage surface.

These joints must be protected as per Section 2.9 of AS 4654.2 and must not be positioned beneath or run through planter boxes or water features. The provision aims to minimise water ingress, suggesting joints be located at structural high points when possible. If joints are subject to excessive movement (over 10 mm), additional measures like a hob or discontinuous membrane in accordance with Section 2.9 of AS 4654.2 are recommended.

F1D5 referencesthe standard for materials and the design and installation of waterproofing membranes for a roof, balcony, podium or similar horizontal surface part of a building.

Damp must be preventedfrom reaching:

• a building’s lowest floor timbers;
• suspended concrete floorsor 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.

F1D6(3) contains exemptions to F1D6(1) because the safety level of buildings will not be significantly diminished by moisture from the ground.

F1D6(3)(a) regarding Class 7 and Class8 buildings refers only to such buildings which, in a particular case, do not exhibit any need for compliance with F1D6. 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.

F1D7 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 F1D7 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 F3P1 for a listing of exempted buildings); and
• the base of a stairwayor lift or similar shaftis suitably drained.

Figure F1D7 illustrates a method of installing damp-proofing in subfloor structures.

Figure F1D7: Installation of DPC in subfloor structures

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 F1D8.

Table F1D8 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 F1D8. 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.

F1D8(5) 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.