Part J1 Building Fabric

See comments for Deemed-to-Satisfy Provisions of .

The Deemed-to-Satisfy Provisions of apply to building elements that form part of the envelope, where the envelope separates a conditioned space or habitable room from the exterior of the building or a non-conditioned space.

Some Class 6, 7, 8 and 9b buildings that are not a conditioned space by definition may be excluded from controls for building fabric. Class 6 and 9b buildings cover a wide range of uses and some could reasonably be expected to be air-conditioned at some time in the future while others may not. For example, it may be unlikely that a school gymnasium will be air-conditioned while classrooms may well be when funds are available. Some States are already retrofitting air-conditioning to schools. Note that the phrase "likely by the intended use of the space to be air-conditioned" is in the definition of a conditioned space.

The external elements of an atrium or solarium that is not a conditioned space may also be excluded. The atrium may be attached to a Class 5 building and would otherwise attract some of the requirements appropriate for a Class 5 building. Again, either there is no energy saving to be made by thermally treating the elements, or the saving is below the minimum threshold and so not cost-effective.

The Deemed-to-Satisfy Provisions of do not apply to Class 8 electricity network substations as these buildings are not required to be air-conditioned for the purposes of . See the definition for air-conditioning. The air-conditioning systems of these buildings are instead designed to maintain the efficient operation of sensitive electrical equipment.

requires that insulation must be tested in accordance with AS/NZS 4859.1.

Care should be taken when installing insulation to ensure a continuous envelope between a conditioned space and either the outside environment or a non-conditioned space.

Insulation is to be fitted tightly to each side of framing members but need not be continuous over the framing member. The Total R-Value requirements in , and are calculated for parts of the roof, walls or floor that are clear of any framing members.

The provisions also state that the installation of insulation should not interfere with the safety or performance of domestic services and fittings such as heating flues, recessed light fittings, transformers for low voltage lighting, 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. Low voltage lighting transformers should not be covered by insulation and be mounted above the insulation rather than on the ceiling. Expert advice may also be needed on how much bulk insulation can be placed over electrical wiring.

Note that the addition of insulation to other building elements may alter the fire properties of those elements. Re-testing or re-appraisal of these elements may be required.

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

Where the width of airspace is to be achieved in a wall cavity or the like, care should be taken to ensure compliance with all other applicable BCA provisions. For example, the provisions relating to weatherproofing masonry may require a greater width of cavity.

The R-Value of bulk insulation is reduced if it is compressed. The allocated space for bulk insulation is therefore to allow the insulation to be installed so that it maintains its correct thickness unless exempted such as at wall studs. 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.

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.

covers roofs, including their ceilings, and any ceiling that is part of an intermediate floor being part of the building's envelope, or where there is no ceiling.

and Table J1.3(a) detail the insulation properties required of a roof or ceiling. Table J1.3(a) provides the minimum Total R-Value to be achieved by the roof or ceiling.

Part or all of this may be provided by the roof construction itself and any inherent insulating property of the roof and airspaces reduces the amount of insulation needed.

Where the ceiling space below the roof is used as the return air plenum, it is considered part of the conditioned space. In this instance, the envelope boundary for the roof and ceiling construction is located at the roof.

A ceiling that is part of the envelope but is below a non-conditioned space such as a plant room is covered in .

The direction of heat flow stated should not be taken as the only direction in which any insulating properties operate but it is a statement of the prominent direction for that particular climate zone. It is assumed that materials, be they construction materials or insulating materials, will also have insulating properties in the other direction. For a residential building, the night time direction is important as the building is most likely to be occupied at that time and the outside temperature likely to be the lowest of the day.

The Total R-Value in Table J1.3(a) is dependant on the climate zone and also the colour of the roof. A light colour is beneficial in a hot climate. An industry recognised international standard for testing absorptance is ASTM E903. Typical thermal absorptance values using that standard are provided below.

Typical Absorptance Values

Because of the high thermal conductance of metal, a thermal break is required by where the ceiling lining of a building is fixed directly to the underside of the metal purlins or metal battens of a metal sheet roof, or where there is no ceiling. 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. This is only required where a metal roofing member has the roofing directly on one side of the member and the ceiling lining directly on the other side of the same member, or no ceiling at all. Once there are two members perpendicular to each other, such as battens and rafters, there is no requirement for a thermal break.

A thermal break may be provided by materials such as 20 mm thick timber or 12 mm thick expanded polystyrene strips, plywood or bulk insulation. The material used as a thermal break must separate the metal purlins or metal battens from the metal sheet roofing and achieve an R-Value of not less than 0.2. Reflective insulation alone is not suitable for use as a thermal break because it requires an adjoining airspace to achieve the specified R-Value.

The loss of ceiling insulation because of downlights, fans and other penetrations means that more energy is lost unless the amount of insulation on the remainder of the ceiling is proportionately increased. requires such compensation. contains a minimum "free" allowance.

When considering the loss of insulation because of exhaust fans and recessed downlights, 0.5% of the ceiling area for a 200 m² dwelling would permit 2 bathroom heater-light assemblies, a laundry exhaust fan, a kitchen exhaust fan and either approximately 20 recessed downlights 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. It should also be noted that uses 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. Note that the table is in R-Value and not Total R-Value.

It should be noted that does not require an increase in ceiling insulation for roof lights.

The weight of roof or ceiling insulation needs to be considered in the selection of plasterboard, plasterboard fixings and building framing.

Details of the Total R-Values of typical constructions are provided in .

has values for Total System SHGC and Total System U-Values, which are expressed in accordance with the Australian Fenestration Rating Council (AFRC) protocol.

The provisions of require roof lights that form part of the envelope, other than of a sole-occupancy unit of a Class 2 building or a Class 4 part of a building to comply with .

addresses the specific situation where a roof light is needed to meet the requirements of . The allowable area isrelaxed.

provides the requirements that satisfy .

contains Total System SHGC and Total System U-Values for roof lights with or without a ceiling diffuser. A roof light may achieve the required performance on its own or in conjunction with a ceiling diffuser.

The Total System SHGC and Total System U-Values for some simple types of roof light are shown in the tables below. Smaller numbers indicate better glazing element performance. The tables give worst case assessments, which can be improved by obtaining custom product assessments from suppliers, manufacturers, industry associations (including their online resources) and from competent assessors.

and provide options for walls, including both external walls and internal walls that, because they are part of the building's envelope, need to have insulating properties. The provision is structured with a required minimum Total R-Value for external walls in and which may be reduced in some climate zones for:

• Wall materials of 220 kg/m² surface density and different thermal conductivity values.
• Shading.
• Light coloured walls.
• Improved glazing performance.

A below ground, backfilled wall is exempted in most climate zones. Modelling has shown that only in climate zone 8 does a wall below ground need insulation. In all other instances it provides thermal stability and usually some free cooling.

Opaque curtain walls are considered as walls and so are to meet the Total R-Values for walls. Transparent or translucent elements are considered as glazing because of the solar energy they permit to enter the space.

For complying with the shading requirement, note that the shading projection for walls is measured from the wall face whereas for glazing the projection is measured from the glass face.

Gutters can only be considered as providing shading if attached to a building projection such as a verandah, fixed canopy, eaves, shading hood, balcony or the like. On their own they are likely to be well above the head of the window and so not likely to produce any significant shading.

Walls with a surface density of 220 kg/m² or more provide an enhanced level of thermal performance in certain climate zones. This is related to their ability to store heat and therefore slow its transfer through the building fabric. These walls are defined by surface density (kg/m²) to reduce the complexity when measuring mass walls with voids (surface density is the mass of one vertical square metre of wall).

As a result of thermal modelling, it has been found that because commercial buildings are more likely to be air-conditioned for long periods, the high mass option is not as beneficial as it is for houses. However, it still offers a benefit, particularly in the temperate climates. Thermal conductivity is the property of a material from which R-Value is derived by dividing the thickness of the material by the thermal conductivity. In some climate zones, a high mass wall may still require some insulation, but less than the insulated framed wall would require. Note also that the options in requiring a slab-on-ground, would only apply to the walls on the ground floor.

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

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

also contains an option for walls using furring channels, which consequently cannot accommodate the insulation required to achieve the Total R-Value. In this case, the furring channels can still be used provided the more stringent glazing energy index is used. This is effectively trading between the thermal performance of walls and glazing without using a Verification Method.

Because of the high thermal conductance of metal, a thermal break is required when a metal framed wall is clad with weatherboards, cement sheeting, or the like. This is only required where a metal framed wall member has the cladding directly on one side of the member and the lining directly on the other side of the same member, or where there is no wall lining. 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. The thermal break must separate the metal frame from the cladding and achieve an R-Value of not less than 0.2.

A thermal break may be provided by materials such as timber battens, plastic strips or polystyrene insulation sheeting. For the purposes of , 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. There is also some bridging occurring in brick veneer walls but it is not as severe as in lightweight framed walls.

Internal walls that are part of the building's envelope, i.e. that separate a conditioned space from a non-conditioned space, require less insulation than an external wall that is part of the envelope.

Envelope walls, other than external walls, are covered by J1.5(b) and Table J1.5b. The required thermal performance depends on the degree of uncontrolled heat gains and losses in the adjacent non-conditioned space. Note that glazing, other than roof lights, in the external fabric of the adjacent non-conditioned space must be assessed using energy index Option A separately from the glazing of the conditioned space.

For a floor that is part of the building envelope other than a sole-occupancy unit in a Class 2 building or Class 4 part of a building, the required Total R-Values are in . For the purposes of calculating the Total R-Value of a floor, the R-Value attributable to an in-slab or in-screed heating or cooling system is not included.

The Total R-Value required by will depend on whether the space above or below is enclosed and the amount of ventilation to that space. For example, even if a carpark is mainly enclosed except for an open ramp, the carpark will be ventilated by more than 1.5 air changes of outside air so being enclosed or unenclosed is, in this case, irrelevant.

An enclosed perimeter means that the lowest floor of a building has a space below which is enclosed by slab-to-slab cladding or walls. The ground-to-floor cladding can have the required subfloor vents and still be considered enclosed.

The values in can be reduced in climate zones 1 to 6 provided the Total R-Value achieved by the roof is increased to compensate (refer ).

For example, if a building was located in climate zone 6, a Total R-Value of 1.0 would be required from if the floor used is a solid suspended concrete slab, without an in slab or in-screed heating or cooling system. The floor would have an R-Value of 0.30 downwards, obtained from . Using the concession means R0.5 of the required Total R-Value could be compensated by adding R0.75 to the roof, so the added floor insulation R-Value only needs to be 0.2.

This could be achieved by installing a range of products including reflective insulation, bulk insulation boards or bulk insulation batts on a plasterboard or fibre cement ceiling. This concession is straightforward for a single storey building with one roof and one floor. For a multi-storey building with a series of envelopes around plant rooms at different levels, the concession only applies between the roof and the floor that makes up one envelope, i.e. the uppermost envelope.

and apply to all concrete slab on ground floors including those in sole-occupancy units in a Class 2 building, or Class 4 part of a building as described in .

requires all floors with an embedded in-slab or in-screed heating or cooling system to have additional insulation installed around the vertical edge of the perimeter. This provision aims to limit heat loss or gain through the perimeter of the slab.

Regarding the installation of slab edge insulation in , care should be taken to ensure that the insulation is compatible with the type of termite management system selected.

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