Part 3.12.1 Building fabric

1. For example, in a two storey house with the second storey set back, the insulation in the first storey wall, the second storey wall and the roof over the set-back must be continuous. Therefore if the roof over the set-back has insulation on a horizontal ceiling, then insulation is also needed on the vertical in any ceiling space in order to connect the ceiling insulation to the second storey wall.
2. To form a continuous barrier, insulation should be placed in gaps between window and door jambs, heads and sills, and the adjoining wall framing unless a gap is otherwise required. This may need to be compressible to allow for movement between members.

Care should be taken when installing insulation to ensure that it does not interfere with the safety or performance of domestic services and fittings such as heating flues, recessed light fittings, light transformers, gas appliances and general plumbing and electrical components. This includes providing appropriate clearance as detailed in relevant legislation and referenced standards such as for electrical, gas and fuel oil installations.

Airspace adjoining reflective insulation

For reflective insulation and the adjoining airspace to achieve its tested R-Value, the airspace needs to be a certain width. This width varies depending on the particular type of reflective insulation and the R-Value to be achieved.

Adjoining sheets of roll membrane

Where reflective insulation also acts as a vapour barrier or sarking, both the minimum overlap and taping may be necessary.

Compression of bulk insulation

The R-Value of bulk insulation is reduced if it is compressed. The allocated space for bulk insulation must therefore allow the insulation to be installed so that it maintains its correct thickness when using the product’s stated R-Value, otherwise the R-Value needs to be reduced to account for any compression. This is particularly relevant to wall and cathedral ceiling framing whose members can only accommodate a limited thickness of insulation. In some instances, larger framing members or thinner insulation material, such as polystyrene boards, may be necessary to ensure that the insulation achieves its required R-Value.

1. The R-Value of reflective insulation and its adjoining airspace is affected by the width of the airspace between a reflective side of the reflective insulation and the building lining or cladding. For further information on reflective insulation, refer to the explanatory information accompanying Figure 3.12.1.1.
2. Artificial cooling of buildings in some climates can cause condensation to form inside the layers of the building envelope . Such condensation can cause significant structural or cosmetic damage to the envelope before it is detected. Associated mould growth may also create health risks to the occupants. Effective control of condensation is a complex issue. In some locations a fully sealed vapour barrier may need to be installed on the more humid, or generally warmer, side of the insulation. Note that Part 3.8.7 contains specific provisions for condensation.

1. The term ‘as appropriate’ used in reference to Tables 3.12.1.1a to 3.12.1.1g, means the table used must be appropriate to the climate zone in which the building is to be located.
2. 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.
3. Care should be taken to ensure that the roof ventilation openings do not allow rain penetration and that they comply with appropriate bushfire provisions.
4. 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.
5. 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)(B).
6. 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

Colour	Value
Slate (dark grey)	0.90
Red, green	0.75
Yellow, buff	0.60
Zinc aluminium — dull	0.55
Galvanised steel — dull	0.55
Light grey	0.45
Off white	0.35
Light cream	0.30

The direction of heat flow in Tables 3.12.1.1a to 3.12.1.1g, as appropriate, 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. 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 Tables 3.12.1.1a to 3.12.1.1g. The inherent Total R-Value of the typical roof and ceiling has been determined by adding together the R-Values of the out door 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. Note that Part 3.8.7 contains specific provisions for condensation.

   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 relevant standards, taking 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 fill is the airspace, the Total R-Value should be reduced to take account of the loss of airspace.

R-Value added by reflective insulation—Flat skillion or pitched roof (≤10°) with horizontal ceiling

Notes:

1. The required direction of heat flow applicable in each of the climate zones specified in Tables 3.12.1.1a to 3.12.1.1g.
2. Ventilated roof space means ventilated in accordance with 3.12.1.2(b).

1. When considering the reduction of insulation because of exhaust fans, flues or recessed downlights,0.5% of the ceiling area for a 200m² 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 100mm clearance to insulation or only 3 recessed downlights with 200mm clearance to insulation.
2. Note that Table 3.12.1.1h refers to the R-Value of the insulation located on the ceiling and 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. Note that Part 3.8.7 contains specific provisions for condensation.

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(d)(ii), expanded polystyrene strips greater than or equal to 12 mm thickness and timber greater than or equal to 20 mm thickness are deemed to achieve an R-Value greater than or equal to 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 for 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 R-Value 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.

Explanatory information for R-Value added by reflective insulation

Wall construction	Reflective airspace details	R-Value added by reflective insulation
Concrete or masonry with internal plasterboard on battens	One 20 mm reflective airspace located between reflective insulation (of not more than 0.05 emittance inwards) and plasterboard	0.48
External wall cladding (70 mm timber frame with internal lining)	One 70 mm reflective airspace located between reflective insulation (of not more than 0.05 emittance inwards) and plasterboard	0.43
Masonry veneer (70 mm timber frame with internal lining)	One 70 mm reflective airspace located between reflective insulation and plasterboard; and One 25 mm anti-glare airspace located between reflective insulation (of not more than 0.2 emittance outwards) and masonry	0.95
Cavity masonry	No airspace between the reflective insulation and the inner leaf of masonry; and One 35 mm anti-glare airspace located between reflective insulation (of not more than 0.2 emittance outwards) and the outer leaf of masonry	0.50

For further information on reflective insulation, refer to the explanatory information following Figure 3.12.1.1. 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. Tables 3.12.1.5a and 3.12.1.5b provide 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 Tables 3.12.1.5a and 3.12.1.5b 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 Tables 3.12.1.5a and 3.12.1.5b. Reflective insulation will achieve a higher value which will need to be determined for each product in accordance with relevant standards. 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.
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.

3.12.1.5(e) 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.

The attachment of a Class 10a building, such as a garage, glasshouse, solarium, pool enclosure or the like should not compromise the thermal performance of the Class 1 building. In addition, the Class 10a building may be insulated and so assist the Class 1 building achieve the required thermal performance.

The following are examples of a Class 1 building with an attached Class 10a garage.

In (a), the thermal performance required for the Class 1 building may be achieved by including the walls and floor of the Class 1 building that adjoin the Class 10a garage.

In (b), the thermal performance required for the Class 1 building may be achieved by including the outside walls and floor of the Class 10a garage.

In (c),in climate zone 5, the thermal performance of the Class 1 building may be achieved by ensuring that the roof of the Class 10a building satisfies Tables 3.12.1.1a to 3.12.1.1g and the walls are of masonry construction.