A BASIX Certificate (Building Sustainability Index) is an approval document required for most residential building projects in New South Wales (NSW). It confirms that your design meets minimum standards for energy efficiency, water use and thermal comfort. Without a valid BASIX Certificate, councils and certifiers cannot approve your Development Application (DA) or Complying Development Certificate (CDC).

Put simply: BASIX aims to ensure homes across NSW are designed to be more comfortable to live in, less expensive to run and more considerate of the environment. For builders, architects and homeowners, it’s a mandatory step in the approval process, and one you want completed accurately the first time to avoid delays. BASIX is a NSW Government initiative designed to improve building sustainability.

What does BASIX assess?

BASIX looks at three key areas of performance:

1. Energy: Targets for heating and cooling loads, glazing, insulation, lighting and fixed appliances. The goal is to reduce overall energy demand and improve thermal performance alongside a NatHERS star rating when required.
2. Water: Measures to reduce potable water use, such as water‑efficient fixtures, rainwater tanks and landscaping choices.
3. Thermal Comfort: Ensures the building envelope (walls, roof, windows and shading) supports year‑round comfort. This is typically demonstrated through a NatHERS Assessment or through a Deemed‑to‑Satisfy pathway where applicable.

Who needs a BASIX Certificate?

You will generally need BASIX if your project is one of the following:

• New single dwellings and dual occupancies.
• Alterations and additions over the cost threshold.
• Secondary dwellings/granny flats.
• Multi‑unit residential developments (Class 2).
• Swimming pools and outdoor spas over 40,000 litres.

If you’re unsure, Evergreen Energy Consultants can confirm whether your scope triggers BASIX requirements and which assessment pathway is appropriate for your design.

When in the process do I get BASIX?

You should obtain your BASIX Certificate before lodging a DA or CDC. Many builders and designers in Sydney, Newcastle, the Central Coast, Hunter Valley and Byron Bay engage Evergreen EC as soon as plans are sufficiently detailed (floor plans, elevations and site plan) so we can assess the design, recommend any tweaks and issue the certificate quickly.

What information do I need to provide?

To complete your BASIX assessment efficiently, have the following ready:

• Architectural drawings: floor plans, elevations, sections and site plan.
• Window and glazing schedule if available.
• Insulation specifications and wall/roof construction details.
• Any proposed fixed systems (hot water, pool/spa heating, solar PV, etc.).

If something is not final, that’s okay – we can advise on practical options that help you meet BASIX targets without compromising the design intent.

How BASIX and NatHERS work together:

For most homes, thermal comfort is demonstrated using a NatHERS energy rating (0–10 stars). A higher NatHERS star rating often makes it easier to satisfy BASIX energy and thermal comfort targets. Evergreen EC provides both BASIX Certificates and NatHERS Assessments so you get a coordinated outcome and a smoother approval process.

Common BASIX misconceptions:

• “BASIX is just paperwork”. In reality, it drives real performance outcomes. Decisions around orientation, shading, glazing ratios and insulation all influence your comfort and bills for decades.
• “I can use one certificate for multiple dwellings.” For multi‑unit residential projects, each dwelling must demonstrate compliance.
• “Pool BASIX is optional.” Pools/spas over 40,000 L require BASIX.
• “I can ignore BASIX once construction starts.” Certifiers check that what’s built matches the certificate.

How Evergreen EC helps (across NSW)

Evergreen Energy Consultants serves clients across NSW, including Sydney, Newcastle, Lake Macquarie, the Central Coast, the Hunter Valley, Byron Bay and Port Macquarie. Our accredited team models your design, advises on simple improvements if needed, and issues a certificate that aligns with your DA or CDC requirements. Most certificates are delivered within three business days once we have the required plans.

The outcome you can expect:

With a well‑prepared BASIX Certificate, councils and certifiers can progress approvals confidently. You’ll also have a clear list of commitments (e.g., insulation levels, window specifications, rainwater volume) to pass on to your builder so construction stays aligned with the approved design.

Ready to get started?

Request A Quote Contact Us

Written by Evergreen Energy Consultants — accredited BASIX and NatHERS assessors providing residential energy assessments across NSW.