Insulation R-Value of Suspended Concrete

Published : 04 August 2009 / BCA 2009

In the sketch opposite, Details A and B illustrate typical areas where the suspended concrete slab projects beyond the upper storey floor area to form the “Roof” of a lower storey.

Whilst BCA 2009 Volume Two Part 3.12.1.2 Roofs only provides a limited number of typical details for roof and ceiling construction the “Specification” sections in BCA Volume One provide information that can be used to calculate the Total R-Value of non-standard construction details.

Refer to BCA 2009 Volume One (Class 2-9 Buildings) Specifications J1.2 Material properties, J1.3 Roof and ceiling construction, and J1.5 Wall construction.

The calculations for Detail A in the Table opposite show that R3.0 insulation is required. For the construction shown in Detail A this can be added using standard bulk insulation.

 

 

 

 

 

 

 

 

 

 

The calculations for Detail B in the Table opposite also show that R3.0 insulation is also required. But Detail B construction requires the insulation to be located under the slab.

Standard bulk insulation will require the plasterboard ceiling to be dropped approximately 160mm (varies by product) below the underside of the concrete.

If polyurethane panel insulation is used an equivalent R-Value can be achieved in approximately 60mm:

R-Value = 0.06m ÷ 0.02W/m.K = 3.0 

Note 1: Verify the W/m.K value from a product specific datasheet.

Note 2: The thermal performance of the air gap that is included in BCA typical ceiling and roof construction Total R-Values must be deleted when the space is filled with bulk insulation – refer to Explanatory Information Note No. 1 at the foot of BCA 2009 Volume Two Figure 3.12.1.1 (Roof) and Figure 3.12.1.3 (Wall).