Insulation, Section J, and You

By July 2, 2018Uncategorised

As an Australian builder, project engineer, or architect, you will be aware of the Section J provisions under the BCA, and the need to make buildings energy efficient. Part of this assessment, in fact the most important part, is the thermal efficiency of the building.

Insulation, naturally, is a primary factor in thermal efficiency. It’s not the only factor. The Australian Government depends heavily on R-values to determine thermal efficiency, which is an outcome very good for the insulation industry and not very good for builders.

Section J: the costliness of R-values

R-values are a poor indicator of the thermal efficiency of a building, but the government insists on using these values. That means concrete, one of the least expensive and most thermally efficient construction materials available, rates poorly because its R-value is almost non-existent.

This is because concrete doesn’t significantly resist heat, and heat resistance is the only factor R-values take into account. The high thermal mass of concrete does delay the transfer of heat sufficiently to make it an excellent insulator, however.

Due to the unrealistic bias that dependence on R-values creates, the provisions must eventually be replaced with more practical values. Until then, R-values are the main factor taken into consideration, and that means you need to choose insulation that gives you the highest R-value for its cost per m² if you want all the advantages that come from using lower cost cladding materials.

Types of insulation

The two main types of insulation used in construction are reflective insulation and bulk insulation. The first type is the most simple, and is simply a surface that reflects most of the heat energy, allowing only a fraction of it to be absorbed and subsequently transferred. The heat energy is then absorbed by the air opposite the reflective surface, and transferred to colder air beyond.

Bulk insulation is quite different. This insulation resists heat transfer but does not avoid heat absorption. It can be made from many different types of materials, including:

  • Cellulose
  • Fibreglass
  • Glass wool
  • Rock wool
  • Foam
  • Polystyrene
  • Straw bales

There are various other materials that could be used for insulation as well. Cellulose may be the best for most applications because it is environmentally friendly, has a low cost, and has a high R-value. It can be used for insulation in walls, ceilings, and floors.

For projects where quick completion time is a primary factor, fibreglass batts are the most popular choice, as they can be installed more quickly than most other options, have acceptable R-value, and moderate cost. Fibreglass is certainly not as safe or as eco-friendly as cellulose, however.

Acceptable installation methods

In addition to selecting the right materials, to be fully Section J compliant, you will need to ensure the insulation material is installed properly.

The reflective insulation must be installed in a way that the correct airspace is provided so that the highest R-value of the material can be achieved. The material also needs to overlap, not just be fixed flush to panels, and the overlapping segments should be fixed together.

Bulk insulation needs to be installed so that it entirely fills the space available for it, with compression only allowed where it is necessary to allow pipes, cabling, and similar things.

Section J compliant insulation is easy to achieve

Of all the Section J compliance criteria, insulation is the easiest to get right. After all, the R-values are usually known in advance for each of the materials, so really all you need to do is ensure you make an economically viable choice and then make sure it is installed correctly.

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