Part one: the same floor over a ventilated subfloor
A suspended timber floor loses heat downwards. Your Home's first instruction is the simplest one: add bulk insulation between the joists and seal the gaps in the floorboards, or install a building membrane to the underside of the joists.
The page puts conditions on the material: insulation must be well supported and moisture tolerant.
The same page gives the sub-floor a rule of its own: an open sub-floor can be enclosed to reduce heat transfer, but it must still have adequate ventilation to prevent moisture and timber rot.
What holds the insulation up matters, and Your Home gives two options. The first suits a home where pests will never be a problem: bulk insulation added under the floor, supported by nylon cord or wire.
The second is for everywhere else: an impervious sheet below the joists, such as a thin fibre cement sheet, or rigid boards such as wood fibre, XPS or PIR.
There is a rolled option with its own cautions. A flexible foil-foam sheet can be installed from a roll, continuously under the joists.
Care is needed with it: manage condensation risks by consulting the manufacturer's technical information and installation guide, prevent pest entry, and ensure that all termite barriers remain fully visible.
The same page gives foil an electrical caution. Because foil insulation is electrically conductive, the risk of contact with electrical cables and equipment must be considered with all installations: avoid installing it under floors with electrical cables exposed under the joists, and check for stray wires, which are quite common in older homes. Reflective foil insulation should be installed by a certified installer, and foil insulation must be secured with nonconductive (non-metallic) staples.
The number under the boards
The insulation is not decorative: a standard stands behind it. The National Construction Code specifies that a suspended floor must achieve a certain R value for the downwards direction of heat flow for the relevant climate zone.
The code exempts one floor from that line. The requirement is set for a suspended floor other than an intermediate floor in a building with more than one storey.
Your Home supplies the figure that makes the point for timber: the total thermal resistance of typical timber floor construction must be appropriate for the climate zone and topographical location.
The same page gives the boards their own small number: the thermal resistance of 19 mm of timber is approximately R0.25, so insulation is required.
Read together, the two lines say something a sample board cannot: the boards themselves carry about R0.25, so Your Home says insulation is required.
Part two: the same floor over a slab
Over a slab-on-ground it is a different floor: the rules above name joists and suspended floors, so the way to insulate between joists does not apply to it.
For a slab, Your Home's insulation page gives one line: termite protection for slab-on-ground applications is critical in all states except Tasmania.
It adds a note about the exception: climate change may expose the island state to termites in the future.
The difference between the two floors, worked through: over a subfloor the work is what hangs below the boards, and over a slab the work starts with what the slab itself must be protected from.
Who installs what goes under the floor
Underfloor insulation is installed work, and Your Home's pages put two people around it. Insulation should always be installed by a qualified professional installer to ensure safe installation, especially in existing homes.
The risks named for those older homes are electrical, fire, moisture and access, and a householder who installs it should always follow the manufacturer's instructions.
Your Home advises that, in an existing home, a licensed electrician assess the wiring and electrical fittings before insulation is added, to confirm they will stay safe once it is in place.
The standard behind that is named: AS3999 requires a competent person to carry out an electrical safety assessment before insulation is installed.
It goes on to say who that person is: in Australia only a licensed electrician is qualified to give electrical advice, so the assessment should be carried out by a licensed electrician.
Certification can be required on top of that. Some government programs and regulations require insulation to be installed by a certified installer.
The national certifying body is named as well: the Energy Efficiency Council, through the Certified Insulation Installer certification. The page's own summary is to always use a certified insulation installer, in some cases as a mandatory requirement.
The air the floor brings inside
The weather inside a home is not only warmth. Your Home turns to the air as well: most cabinetry and flooring products, paints, sealants and adhesives release low levels of pollutants called volatile organic compounds.
The page's own words on what that costs: those compounds can impact indoor air quality and human health.
The advice that follows is about choice of product: use low VOC flooring products and sealers.
For timber and bamboo floating floors, Your Home asks for PEFC or FSC certification, and for bamboo flooring to be low VOC as well.
The timber itself has a source worth asking about: where timber products are used, they should come from sustainably managed sources with PEFC or FSC accreditation.
When upgrading flooring, cabinetry or furnishings, or using paints and sealants, Your Home's general line is to choose sustainable and eco-certified options, to reduce environmental impact and improve indoor air quality.
The floors above and below this one have their own guides: hard floors in a strata apartment takes the same boards into a flat, and who may lay a floor, state by state covers who may lay them.