Proposed changes to BCA Volume 1

Reading the proposed changes to BCA Vol 1 2025, most of the changes appear appropriate and sensible.

Items I would note (maybe a concern to some);

  • J1V3 – Verification using a reference building, deletes or removes the ability to offset Greenhouse Gas emissions with PV.  It appears the intent is to stop trading between PV and the Building Fabric.
  • J4D4 (2) – Roof and ceiling construction, changes the method of limiting roof colour from Solar Absorptance to Solar Reflectance Index (SRI) there is some other options or calculations however most manufacturers are now quoting SRI figures, the colour range which is acceptable or compliant appears to be same as BCA 2022, just a change in metric (the intent is to reduce Urban Heat Island effect).
  • J4D6 (2) Walls and glazing, removing the word “display”, good idea, not sure why it was there in the first place, means no more aluminium frame and clear glass windows, there are many other frame or glazing options for single and double glazing.


  • J4D6 (5) Walls and glazing, solar admittance there is a stringency increase roughly from 0.13 to around 0.07 to 0.08, which means more shading or glass with a lower shgc (tinted glass or multiple layers of glass)???
    • It treats climate zone 1 (Darwin) the same as climate zone 7 (Hobart), how is this appropriate? Why would we want buildings such as group homes or aged care to have less natural light making it harder for occupants to see or stay warm? Would they not turn the lights on earlier or the heater on more?
    • The number of glass options on the market to do this is limited.

In total contradiction S45C3, table S45C3a shows annual heating & cooling hours, this demonstrates;

  1. Climate zones 1 to 3 with predominate cooling issues hence the proposed requirements make sense.
  2. Climate zone 4 is mixed more heating than cooling but some cooling issues, not really appropriate.
  3. Climate zones 5, 6 & 7, much larger heating loads than cooling loads but we are going to make it harder to get heat in by reducing the solar admittance??? makes no sense.
  4. Climate zone 8 is treated separately but still has a stringency increase despite have 416 times more heating requirement than cooling (go figure).

I can sort of understand the roof colour discussion but the solar admittance of glass when we spend more energy heating than cooling should not be accepted.

Even if the climate is warming up faster than expected, either the data in S45C3 need to be changed for future climates or the stringency increase is not justified.

How do we say to someone building in Tumut that we need to shade the glass more or have darker tinted windows? They will think we have gone mad.

Love to hear your thoughts!

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