Insulating timber floors (Nat)

The requirement to insulate a timber floor will depend on several factors including the orientation, design, fabric or external cladding and amount of glazing in the building. In some circumstances it may be worth considering insulating the sub–floor to achieve the required rating as more cost effective than other methods.

There are various systems and materials available to insulate timber floors. To ensure that the material or system used will be successful and not have a detrimental effect to the sub-floor, there are a few things should be considered.

One of the concerns when insulating sub–floors is that it will prevent air flow to sub-floor timbers and may be detrimental to building elements. This can be exacerbated if moisture is present when insulation is installed during construction, and retains moisture. It may also void manufacturers’ warranties in relation to flooring materials.

Infestation of pests and the longevity of the material or system used can also be an issue. There are various materials available to insulate floors. Foil laminate products are commonly used by either draping over floor bearers or joists or installing between floor joists; perforated foil can help to increase ventilation and reduce moisture build up.

The fixing of flooring must be taken into consideration when draping foils over floor joists. Bulk insulation can be installed between floor joists but will require adequate support. Rodent infestation and moisture retention are among the main concerns when using bulk insulation. There are some insulation products now available that claim not to retain moisture and are pest resistant.

Another method is the use of polystyrene as insulation, either as a composite of polystyrene sheet and foil laminate or polystyrene ‘pods’. Both generally rely on brackets to secure the material between the joists and can provide an air gap that can further enhance R ratings.

Recent developments in flooring materials have introduced systems with enhanced thermal properties over standard flooring. Lightweight autoclave concrete building materials have been adapted for use as a flooring material that will enhance the thermal quality and acoustic performance of the floor. Generally installed as panels over floor joists, this material can then be overlaid by the desired floor finish. The weight of the material would need to be considered as it may exceed the design weight limit of the floor structure.

A structural particleboard product is now available that incorporates a foil laminate veneer at the base of the sheet to improve thermal performance, which is designed to achieve a better rating over that of standard particleboard flooring.

When choosing an appropriate system, cost, ease of application and longevity of products should be considered. The Australian Government Forest and Wood Products Research and Development Corporation (FWPRDC) has produced a report “Insulation Solutions to Enhance the Thermal Resistance of Suspended Timber Floor Systems in Australia”, which provides generic information that may assist members and can be downloaded from www.fwpa.com.au.

For further information HIA members can contact HIA’s Building Services staff on 1300 650 620 or hia_technical@hia.com.au.

Ref No. NAT MAT 08-04

The above is intended to provide general information in summary form. The contents do not constitute specific advice and should not be relied upon as such. Formal specific advice should be sought by members with respect to particular matters before taking action.  ABN 99 004 631 752