Class 4 buildings are typically a single dwelling in a Class 5, 6, 7, 8, or 9 building such as the caretaker’s residence. For a more complete definition refer to Clause A3.2 of the Building Code of Australia.
The aim of improving energy efficiency in a building is to maximise thermal comfort of occupants whilst minimising the building’s energy consumption & running costs, thereby reducing greenhouse gas emissions.
Energy consumption in buildings is minimised by requiring buildings to contain the following features:
- Energy efficient building services, such as lighting, mechanical & hot water systems, and
- Treating the building envelope to reduce heat loss or gain in buildings or parts of buildings that are provided with air-conditioning or are likely to be provided with air-conditioning. Such areas are referred to by the BCA as conditioned space.
Building requirements
To achieve these objectives the building envelope must be constructed so as to satisfy the requirements of
• Section J of the Building Code of Australia (BCA)
• AS/NZS 4859.1 – Materials for the thermal insulation of buildings
• Manufacturer’s Specification to ensure that the product performs as tested
State Variations
In developing the design of your building, it is important to note that there are also state variations that alter, limit or increase the level of compliance required with the national energy efficiency provisions. These are identified in italics at the start of each section (eg: NSW Section J), part or clause within the national provisions of the BCA.
Alternative Solutions
If any of the above requirements cannot be met either because of innovative development or there is a particular construction issue, the building would not comply the Deemed-to Satisfy Requirements of the Building Code of Australia and consequently a Construction Certificate or an Occupation Certificate will not be able to be issued.
To overcome this situation the an Alternative Solution may be able to be prepared in accordance with Clause A0.8, A0.9, & A0.10 of the BCA, demonstrating that the method of construction will satisfy the Performance Requirements of Part J; by:
- Providing evidence that the form of construction satisfies the BCA;
- Using a Verification Method as set out in the BCA such as JV1 for a Class 4 building;
- Comparison with the Deemed-to-Satisfy provisions
- Expert judgement.
General Deemed-to-satisfy Requirements Insula tion
To satisfy the Deemed-to-Satisfy provisions of the BCA with respect to insulation, the first step is to refer to the Figure A1.1 of the BCA which establishes the climatic zone for the proposed building.
- Based on the climatic zone, Clause 1.3 of the BCA and Table J1.3 of the BCA sets out the minimum Total R-Value that needs to be achieved for that particular Class 4 Building in the particular location.
- Clauses J1.5 and Table J1.5 (a) of the BCA provides additional requirements for calculating the minimum Total R-Values the external wall of a Class 4 building.
- Clause 1.6 Table J1.6) provides additional requirements for calculating the minimum Total R-Values for floors.
The R-value is a measure of the insulation systems effectiveness, which must be determined in accordance with Part 4 of AS/NZS 4859.1, namely by testing; calculation and this information must be provided in the labelling by the manufacturer. Therefore when purchasing insulation it is critical that the product has been labelled in accordance with Clause 3.1 of AS/NZS 4859.1.
Insulation is only one element of construction when determining Total R-Values. Specification J 1.2 lists the thermal conductivity of some common construction materials as well as Typical R-Values for airspaces and air films. Specification J1.3, 1.5 & 1.6 provides Total R-Values for some typical, roof, ceiling, and wall and floor construction methods, upwards as well as downwards that is insulation must prevent the flow of heat from the warm side to the cold side.
Clause J1.2 of the BCA provides basic construction details that will need to be adhered to, such as:
- Insulation must abut or overlap adjoining insulation;
- Forms a continuous barrier with ceilings, walls and floors;
- Does not adversely affect services or fittings (for instance, electrical wiring may overheat etc)
- Reflective insulation is provided with requires airspace, is fitted close to openings (such as windows and doors) and is provided with adequate support;
- Bulk Insulation must maintain its position, thickness and to ensure that ceiling insulation overlaps uninsulated walls
DTS Requirement for Insulating Roof
Where a space under a roof or ceiling is a habitable room or conditioned space the roof or ceiling that is part of the envelope must achieve the Total R-Value specified in Table J1.3. Consideration must also be given as to whether insulation is to be used to prevent heat coming into the building (i.e. downwards such as in summer) or heat escaping from the building (i.e. upwards such as in winter).
Where a metal roof is fixed to metal purlins there must be a thermal break of at least R 0.2 between the metal roof and it’s supporting member. Typical roof & ceiling construction values are listed in Specification J1.3
For a Class 4 Building in climate zones 1, 2, 3, the Total R-Value specified in Table J1.3 can be reduced by R0.5, where the roof has a upper surface solar absorbance value of not more than 0.55.
DTS Requirement for Insulating Walls
Where an external wall forms part of the building envelope it must satisfy Table J1.5a. In a climate zone 1, 2, 3 south of latitude 200, a south facing part must satisfy Figure J2.3. A wall other than an external wall that is part of the envelope may have its Total R-Value reduced subject to the requirements detailed in J1.5 (c) & (d).
For climate zone 4, 6, 7, 8 where Total R-values cannot be achieved the deficit may be addressed by improving the performance of glazing.
Typical wall construction values are listed in Specification J1.5
It should be noted that wall linings fixed to metal framing must be separated from the metal framing by a thermal break having an R-Value not less than R0.2
DTS Requirement for Insulating Floors
Floors forming part of the building envelope must achieve the Total R-Values in Table J1.6.
In climate zones 1-6 the minimum R-Value for floors may be reduced by R 0.5 subject that R0.75 is added to the required Total R-Value for the roof & ceiling
Floor slab on the ground with in-slab heating or cooling or located in Climate Zone 8 must be provided with insulation around the vertical edge of its perimeter. Perimeter slab insulation must have:
- R-Value of at least 1.0
- Be water resistant
- Be continuous from a depth of 300 mm or the full depth of he slab
Typical floor construction values are listed in Specification J1.6
DTS Requirement for Building Sealing
To maintain comfortable conditions consideration must also be given to heat loss or gain via openings buildings.
For this reason the BCA requires seals to be fitted to windows and doors apart from:
- Window complying with AS 2047
- Louvre windows or doors
- Fire or smoke doors
- Roller shutter doors
Furthermore construction joints such as between wall and floor or wall and ceiling) to be tight fitting or sealed using caulking or joinery items such as architraves, skirtings and cornices.
Furthermore exhaust fans in a conditioned space or habitable room to be fitted with a self-closing damper or the like. An evaporative cooler must be provided with a self closing damper or like when serving a heated space of habitable room in a Climatic Zone 4, 6, 7, 8
Building Sealing applies to Class 4 building’s envelope, except:
- In climate zone 1, 2, 3 & 5 where the only means of air –conditioning is an evaporative cooler
- For ventilating a gas appliance;
- Where mechanical ventilation pursuant to part F4 provides adequate pressure to prevent air infiltration;
- For an atrium or solarium that is not a conditioned space and it is separated from the building envelope.
Roof lights serving a habitable room or conditioned space must be sealed such as by weatherproof seals if it is a roof window.
DTS Requirement for Air movement
To maintain occupant comfort air movement is required to be provided in accordance with Part J 4 of the BCA.
The aim of Part J4 is to ensure improve occupant comfort by providing evaporative coolers or ceiling fans.
Part J4 Deemed-to-Satisfy provisions of the BCA does not address roof ventilators, hence if roof ventilators are proposed they could be part of an alternative solution to the Deemed-to-Satisfy provisions Part 4 of the BCA.
Part J 4 – Air Movement applies to a habitable room in a sole occupancy unit in a Class 4 building. Air movement must be provided in accordance with Table J4.2.
DTS Requirement for Air-Conditioning and Ventilation Systems
To maintain occupant comfort air conditioning and ventilation systems are required to be provided in accordance with Part J5 of the BCA.
The Part J5 Deemed-to-Satisfy provisions of the BCA do not address roof ventilators, hence if roof ventilators are proposed to augment mechanical ventilation systems in accordance with J5.2 (b) they could be part of an alternative solution to the Deemed-to-Satisfy provisions Part 4 of the BCA.
In a Class 4 building, the air-conditioning system must be capable of controlling the temperature of a sole-occupancy unit at a different temperature during sleeping periods than during other periods;
The overall aim of Part J5 is to ensure maximum efficiency of system whilst minimising energy used, such as by ensuring ductwork is insulated J5.2 (a)(ii) of the BCA as well as Clause J5.4 (a) (i) which requires any piping, vessels, tanks containing heated or chilled fluids to be insulated. These are discussed in more detail below:
Insulating & Sealing of Ductwork
Specification J5.2 further details the requirements for sealing and insulating of supply and return ductwork used in a system that heats or cools a building.
Such ductwork (with the exception of air registers, diffusers, outlets, grilles & flexible fan connections) must be thermally insulated with insulation complying with AS/NZS 4859.1 and achieve a Total R-value specified in Tables 3a and 3b:
Flexible ductwork not more than 3m in length from an outlet need only achieve a Total R-Value of 1.0.
Ductwork insulation must be a continuous barrier, protected against the effects of weather and sunlight and must maintain it’s position and thickness, with the exception of flanges and supports only.
Insulation on ductwork conveying cold air must also have vapour barriers, and where such a barrier is a membrane it must be overlapped by at least 50mm with sheets bonded or taped together.
Insulating of Piping, Vessels, Heat Exchangers and Tanks
Specification J5.4 further details the requirements for insulating, piping, vessels, heat exchangers and tanks containing heated or chilled fluid.
Such insulation must:
- Be protected against the effects of weather and sun
- Be able to withstand the temperatures of the piping
- Piping must achieve the minimum Total R-Value in Table 2
- Vessels, heat exchangers and tanks must achieve a minimum Total R-Value of:
- 2.5 if the content is low temperature brine or glycol
- 1.8 if the content is chilled water
- 1.3 if the content is heated water
- 2.5 if the content is steam
- Piping that is encased within a concrete slab or panel which is part of the heating or cooling system, or piping where located within the conditioned space that it is serving need not be provided with an Total R-Value.
Learn more...
Definitions
Conditioned space means a space within a building where the environment is likely, by the intended use of the space, to be controlled by air-conditioning, but does not include—
(a) a non-habitable room of a Class 2 building or Class 4 part of a building in which a heater with a capacity of not more than 1.2 kW provides the air-conditioning; or
(b) a space in a Class 7, 8 or 9b building where the input power to an air-conditioning system is not more than 15 W/m2.
Envelope, for the purposes of Section J, means the parts of a building’s fabric that separate a conditioned space or habitable room from—
- the exterior of the building; or
- a non-conditioned space including—
- the floor of a rooftop plant room, lift-machine room or the like; and
- the floor above a carpark or warehouse; and
- the common wall with a carpark, warehouse or the like,
other than a non-conditioned space through which conditioned air is being exhausted or
relieved such as an internal corridor, cleaner’s room, chemical storage room or exhaust riser.
Habitable room means a room used for normal domestic activities, and—
- includes a bedroom, living room, lounge room, music room, television room, kitchen, dining room, sewing room, study, playroom, family room and sunroom; but
- excludes a bathroom, laundry, water closet, pantry, walk-in wardrobe, corridor, hallway, lobby, photographic darkroom, clothes-drying room, and other spaces of a specialised nature occupied neither frequently nor for extended periods
R-Value means the thermal resistance (m2.K/W) of a component calculated by dividing its thickness by its thermal conductivity
Total R-Value means the sum of the R-Values of the individual component layers in a composite element including any building material, insulating material, airspace and associated surface resistances.
Verification Method means a test, inspection, calculation or other method that determines whether a Building Solution complies with the relevant Performance Requirements.