Welcome to the Bunnings Workshop community. Thank you for sharing your question about the D.I.Y. insulation for a healthy homes certificate.
Installing your own insulation in an existing roof requires that you have installation training and experience. There are many conditions and electrical hazards to be aware of when installing insulation. Because Healthy Homes is a government law, I recommend engaging the services of a professional insulation installer. This will guarantee that the work done in your home will pass the Healthy Homes standards.