Part 3.12.1 Building Fabric

1. The roof space ventilation option, in climate zones 1, 2, 3, 4 and 5, applies to a pitched roof with a flat ceiling to ensure that efficient cross ventilation is achieved in the roof space to remove hot air. Roof space ventilation is generally not suitable for most flat, skillion, cathedral ceiling and similar roof types because of the lack of space between the ceiling and roof.
2. Care should be taken to ensure that the roof ventilation openings do not allow rain penetration and that they comply with appropriate bushfire provisions.
3. Gaps between roof tiles with sarking (or reflective insulation at rafter level) and metal sheet roofing are not acceptable methods of providing roof space ventilation.
4. Compliance with the ventilation provisions in 3.12.1.2(b)(ii) may result in the ingress of wind driven rain, fine dust, corrosive aerosols, or stimulate the growth of mould or fungus in the roof enclosure. Consideration should therefore be given to the surrounding environmental features, including exposure to marine or industrial environments, prior to adopting this as an alternative to the roof insulation provisions in 3.12.1.2(b)(i).
5. A low solar absorptance roof reduces the flow of heat from solar radiation better than a high solar absorptance roof. A roof with a solar absorptance value of less than 0.4 typically corresponds to a roof of light colour such as white, off-white or cream. Typical absorptance values based on ASTM E903 are as follows.

Typical Absorptance Values

6. The direction of heat flow in Table 3.12.1.1a is considered to be the predominant direction of heat flow for the hours of occupation of the building. It takes into account the higher rate of occupancy of houses at night time rather than day time.
7. The weight of roof or ceiling insulation, particularly if additional ceiling insulation is used for compliance with the energy efficiency provisions, needs to be considered in the selection of plasterboard, plasterboard fixings and building framing.

1. Typical construction:

   Figure 3.12.1.1 provides examples of various roof and ceiling construction. The R-Value of the required insulation is calculated by subtracting the inherent Total R-Value of the roof and ceiling construction from the Total R-Value in Table 3.12.1.1. The inherent Total R-Value of the typical roof and ceiling has been determined by adding together the R-Values of the outdoor air film, roof cladding, roof airspace, ceiling sheet lining and internal film.

2. The Total R-Value of the roof and ceiling materials may need to be adjusted if other building elements such as sarking are also installed. For example, sarking or sheet insulation under tiles may change a roof space from “ventilated” to “unventilated”.
3. Thermal bridging:

   Irrespective of the framing material used, the minimum added R-Value specified in Figures 3.12.1.1 and 3.12.1.3 and Table 3.12.1.4 is deemed to include the effect of thermal bridging created by framing members in situations other than described in explanatory note 4.

4. Thermal break:

   Because of the high thermal conductance of metal, a thermal break is to be provided where the ceiling lining of a house is fixed directly to the underside of the metal purlins or metal battens of a metal deck roof or where there is no ceiling lining. The purpose of the thermal break is to ensure that the thermal performance of this form of roof construction is comparable to that of a similar roof with timber purlins or timber battens.

   A thermal break may be provided by materials such as timber, expanded polystyrene strips, plywood or compressed bulk insulation. The material used as a thermal break must separate the metal purlins or metal battens from the metal deck roofing and achieve the specified R-Value. Reflective insulation alone is not suitable for use as a thermal break because it requires an adjoining airspace to achieve the specified R-Value (see explanatory note 6).

   For the purposes of 3.12.1.2(c), expanded polystyrene strips of not less than 12 mm thickness, compressed bulk insulation, and timber of not less than 20 mm thickness are considered to achieve an R-Value of not less than 0.2.

5. Location of insulation:

   The thermal performance of the roof may vary depending on the position of the insulation, the climatic conditions, the design of the house and the way in which it is operated. For example, insulation installed under the roof, rather than on the ceiling, of a conditioned house with a large roof space is less effective because of the additional volume of roof airspace that would need to be heated or cooled. Conversely, for an unconditioned house, the use of reflective insulation is more effective when placed directly under the roof.

6. Choice of insulation:

   There are a number of different insulation products that may be used to achieve the minimum added R-Value. However, care should be taken to ensure that the choice made is appropriate for the construction and climatic conditions as the location and relationship between options in Figures 3.12.1.1 and 3.12.1.3 and Table 3.12.1.4 may not be suitable in all circumstances for both practical and technical reasons. For instance, in some climate zones, insulation should be installed with due consideration of condensation and associated interaction with adjoining building materials. As an example, reflective insulation or sarking installed on the cold side of the building envelope should be vapour permeable.

   Reflective insulation is considered to provide the following additional R-Values when used in conjunction with the Total R-Value of a pitched roof and flat ceiling construction described in Figure 3.12.1.1. To achieve these values, the reflective insulation must be laid directly under the roof cladding and have a minimum airspace of 15 mm between a reflective side of the reflective insulation and the adjoining lining or roof cladding (see 3.12.1.1(b)).

   The actual R-Value added by reflective insulation and its adjoining airspace should be determined for each product in accordance with the standard prescribed in 3.12.1.1(a), which takes into consideration factors such as the number of adjacent airspaces, dimensions of the adjacent airspace, whether the space is ventilated and the presence of an anti-glare coating. When reflective insulation has an anti-glare coating on one side, the emittance value of that side will be greater than the value of the uncoated side.

   Also, where another emittance value for reflective insulation is used (other than the value used in the table below), care should be taken to ensure that the number of airspaces allowed for is consistent with the form of construction and whether the airspace is reflective, partially reflective or non-reflective. Where bulk insulation fills the airspace, the Total R-Value should be reduced to take account of the loss of airspace.

1. When considering the reduction of insulation because of exhaust fans, flues or recessed downlights, 0.5% of the ceiling area for a 200 m² house would permit 2 bathroom heater-light assemblies, a laundry exhaust fan, a kitchen exhaust fan and either approximately 20 recessed down-lights with 50 mm clearance to insulation, 10 recessed downlights with 100 mm clearance to insulation or only 3 recessed downlights with 200 mm clearance to insulation.
2. Note that Table 3.12.1.1b refers to the R-Value of the insulation located on the ceiling and is not the Total R-Value required of the roof. The roof has an inherent R-Value and there may also be insulation at the roof line.
3. Note that 3.12.1.2(e) does not require an increase in ceiling insulation for roof lights.
4. Placing some of the required insulation at the roof level may result in a more practical outcome. Insulation at the roof level is effective in warm climates and significantly moderates the roof space extremes and condensation risk in cold climates.

1. The and Total System U-Values are expressed as Australian Fenestration Rating Council (AFRC) values.
2. The and Total System U-Values are for a roof light with or without a ceiling diffuser. A roof light may achieve the required performance on its own or in conjunction with a ceiling diffuser.
3. The and Total System U-Values for some simple types of roof lights are shown in the table below. Smaller numbers indicate better glazing element performance. The table gives worst case assessments, which can be improved by obtaining generic or custom product assessments from suppliers, manufacturers, industry associations (including their online resources) and from competent assessors.

Surface density is the mass of one vertical square metre of wall.

Guttering can be considered as providing shading if attached to a shading projection.

1. The thermal performance of metal and timber framed walls is affected by conductive thermal bridging by the framing members and convective thermal bridging at gaps between the framing and any added bulk insulation. Metal framed walls are more prone to conductive thermal bridging than timber framed walls.
2. Because of the high thermal conductance of metal, a thermal break is needed when a metal framing member directly connects the external cladding to the internal lining or the internal environment. The purpose of the thermal break is to ensure that the thermal performance of the metal framed wall is comparable to that of a similarly clad timber framed wall.

   A thermal break may be provided by materials such as timber battens, plastic strips or polystyrene insulation sheeting. The material used as a thermal break must separate the metal frame from the cladding and achieve the specified R-Value.

   For the purposes of 3.12.1.4(b)(ii), expanded polystyrene strips of not less than 12 mm thickness and timber of not less than 20 mm thickness are deemed to achieve an R-Value of not less than 0.2.

   The R-Value of the thermal break is not included when calculating the Total R-Value of the wall, if the thermal break is only applied to the metal frame, because this calculation is done for locations free of framing members.

1. Figure 3.12.1.3 provides examples of typical types of wall construction. The additional R-Value required can be calculated by subtracting the inherent Total R-Value of the typical wall construction in Figure 3.12.1.3 from the required Total R-Value. The inherent Total R-Value of the typical wall construction has been arrived at by adding together the R-Values for outdoor air film, wall cladding or veneer, wall cavity or airspace, internal lining and internal air film. Where a cavity or airspace is filled the Total R-Value should be reduced by 0.17 to take account of the loss of the cavity or airspace.
2. Reflective insulation with one reflective surface having an emittance and direction as indicated, is considered to achieve the following R-Values when used in conjunction with the Total R-Value of a wall construction, as described in Figure 3.12.1.3. The actual added by reflective insulation should be determined for each product in accordance with the standard prescribed in 3.12.1.1(a), which takes into consideration factors such as the number of adjacent airspaces, dimensions of the adjacent airspace, whether the airspace is ventilated and the presence of an anti-glare coating.

1. For further information on reflective insulation, refer to the explanatory information following Figure 3.12.1.1.
2. Walls with a surface density of 220 kg/m² or more are deemed to achieve acceptable levels of thermal performance in certain climate zones due to their ability to store heat and therefore slow the heat transfer through the building fabric. These walls are defined by surface density (kg/m²), which is the mass of one vertical square metre of wall, in order to reduce the complexity when measuring the mass of walls with voids.

   The following are examples of some typical wall constructions that achieve a surface density of 220 kg/m²:

   1. Two leaves each of 90 mm thick or greater clay or concrete masonry.
   2. 140 mm thick or greater dense-weight hollow concrete or clay blocks with—
      1. 10 mm plasterboard or render; and
      2. at least one concrete grouted horizontal bond beam; and
      3. vertical cores filled with concrete grout at centres not exceeding 1000 mm.
   3. 140 mm thick or greater concrete wall panels and dense-weight hollow concrete or clay blocks with all vertical cores filled with concrete grout.
   4. 190 mm thick or greater dense-weight hollow concrete or clay blocks with—
      1. at least one concrete grouted horizontal bond beam; and
      2. vertical cores filled with concrete grout at centres not exceeding 1800 mm.
   5. Earth-wall construction with a minimum wall thickness of 200 mm.

1. An enclosed perimeter treatment means that the airspace under the floor is enclosed between ground and floor level by walls which have only the required subfloor vents.
2. The barrier required by 3.12.1.5(a)(iii) could be an imperforate flashing.
3. Specific solutions for concrete slab and timber floors can be found in documents and online resources prepared by industry associations and product suppliers.

1. Table 3.12.1.5 provides examples of the inherent Total R-Values of enclosed and unenclosed suspended floors of two typical types of construction. Any added R-Value can be calculated by subtracting the inherent R-Value of the typical construction in Table 3.12.1.5 from the required Total R-Value in Table 3.12.1.4.
2. Any non-reflective building membrane fixed between or under floor joists is considered to add an R-Value of 0.2 to the Total R-Value of the base construction described in Table 3.12.1.5. Reflective insulation will achieve a higher value which will need to be determined for each product in accordance with AS/NZS 4859.1. Typically, a reflective building membrane attached beneath the floor joists of an unenclosed floor, with a single bright side facing upwards to a 90 mm airspace, can add an R-Value of 0.43 for heat flow upwards and 1.32 for heat flow downwards. Double sided reflective insulation with a 90 mm airspace installed under an enclosed floor can add an R-Value of 0.55 for heat flow upwards and 1.97 for heat flow downwards. Both examples allow for dust on the upper surface in accordance with AS/NZS 4859.1.
3. A reflective or non-reflective building membrane should be installed with due consideration of potentially damaging condensation in some climate zones and associated interaction with adjoining building materials.
4. For further information on reflective insulation, refer to the explanatory information accompanying Figure 3.12.1.1.

provides an exemption for an in-screed heating or cooling system used solely in bathrooms, amenity areas and the like, as these are typically small areas.

Care should be taken to ensure that the type of termite management system selected is compatible with the slab edge insulation.