To build a High-Performance home, Passive House has developed a science based proven path over the years, yet Certification is voluntary. The Passive House building science concepts and techniques are Open-Source so can be incorporated into any project which is why many building codes, throughout the world, are referencing it.  Certification with the Passive House Institute is a good way to provide added quality assurance as it can get tempting to stray from the goals. Nevertheless, certification does add upfront cost and can add execution time which can be limiting for some, despite the added values and long-term returns.  In such cases I say use Passive House as a data driven tool to obtain the results you desire for your project…“If you can sneak in the vegetables into the smoothie, why not”