Improving Thermal Efficiency in Lightweight Construction: Subfloor Insulation

This research was undertaken to obtain new data to inform the challenges facing the construction of thermally efficient, light-weight, timber framed, small-scale buildings. The report focuses on the installation practices and measured thermal performance of reflective and bulk subfloor insulation systems for timber platform floored construction. 

The subfloor insulation tasks included the installation, detailed measurement and detailed simulation of three platform floor subfloor insulation methods, namely: 

  • Reflective subfloor insulation installed to contemporary industry practice,
  • Reflective subfloor insulation installed to the manufacturers specification, and
  • Bulk subfloor insulation installed to contemporary industry practice.

In each case there were significant differences between measured and simulated results with  differences occurring between subfloor zone temperatures, room zone temperatures, roof space temperatures and energy use for heating operation. The measured thermal performance involved four operational methods, namely Unconditioned and unoccupied, Continuously conditioned (heated), Intermittently heated, and Continuously conditioned (cooled). 

These operational modes allowed for the comparison of both the envelope module and the heating and cooling energy modules within the house energy rating software. The differences between simulated and measured temperature data were often greatest at times of daily maximum or minimum temperatures. 

The critical findings from this research are many but key elements include: 

  • The thermal performance for correctly installed reflective subfloor insulation was good and was well represented by the AccuRate building envelope simulation. However, the time taken to install the reflective subfloor insulation correctly was much longer than expected.
  • The reflective subfloor insulation research tasks identified a need for appropriate and consistent installation documentation to support marketed, (and often simulated), thermal resistance values. 
  • The quality of contemporary installation practice for reflective subfloor insulation was very inadequate and does not appear to follow manufacturers’ specified methods.
  • Contemporary installation practises for the bulk subfloor insulation was of a lessor quality than that shown in product installation literature. However, due to the nature of bulk insulation, this did not impact on the short-term thermal performance in this research task. 
  • Both subfloor insulation tasks highlighted practises of product installation that did not follow market expectations. Contractors, construction supervisors and inspectors need to be educated and informed of the correct methods for subfloor insulation installation.
  • In all the research tasks there was an unacceptable difference between the measured and simulated energy use for the reverse-cycle air-conditioner. This may not be caused by the AccuRate energy algorithms but by a significant difference between the Coefficient of Performance (COP) labelling and the actual installed energy efficiencies of the equipment. This requires further analysis and research to inform input variables for the National House Energy Rating Scheme.    

Findings Report:

Other Reports:
Improving Thermal Efficiency in Lightweight Construction: mass timber as thermal mass