What is BASIX? Your complete guide to BASIX & their requirements

If you’re planning to build a new home in Newcastle, the Hunter, Central Coast or elsewhere across NSW, you’ve probably heard the term BASIX — usually alongside building approvals, energy ratings and sustainability requirements.

For many buyers, BASIX sounds complicated. In reality, it’s designed to help create homes that are more comfortable to live in, cheaper to run and better suited to Australia’s changing climate.

Here’s what you need to know before building in 2026.

BASIX (Building Sustainability Index) is a NSW Government sustainability assessment required for most new homes and certain renovations.

Introduced in 2004, BASIX aims to reduce:

• Household energy consumption

• Greenhouse gas emissions

• Drinking water use

A BASIX Certificate is generally required before lodging a Development Application (DA) or obtaining approval through a Complying Development Certificate (CDC).

BASIX commonly applies to:

• New homes

• Knockdown rebuilds

• Dual occupancies

• Granny flats

• Major renovations valued above certain thresholds

• Large swimming pools or spas

If you’re building a new home in NSW, chances are BASIX will form part of your approval process.

BASIX evaluates three major areas:

Energy efficiency — Your home may need features including:

• Improved insulation

• Efficient hot water systems

• Solar compatibility

• Better-performing glazing

• Energy-efficient appliances

Water efficiency — Requirements may include:

• Rainwater tanks

• Water-efficient fixtures

• Reduced potable water use

Thermal comfort — Thermal performance has become increasingly important. Modern homes are expected to perform better year-round through:

• Orientation

• Window placement

• Insulation

• Shading

• Ventilation

• Glazing selection

• Orientation

• Window placement

• Insulation

• Ventilation

• Glazing selection

The goal is a home that stays cooler in summer and warmer in winter while reducing reliance on heating and cooling.

A common question is: “How much does BASIX add to my build cost?”

The answer depends on:

• Home size

• Orientation

• Block conditions

• Window design

• Climate zone

• Inclusions selected

Compliance may influence selections such as:

• Double glazing

• Insulation upgrades

• Hot water systems

• Rainwater tanks

• Solar readiness

However, good design decisions early can minimise additional costs and improve long-term running costs.

Many buyers don’t realise land selection can affect BASIX outcomes. Important factors include:

Block orientation — North-facing living areas often improve thermal performance.

Sloping sites — Slope may influence design efficiency and construction methods.

Overshadowing —Nearby homes and vegetation can affect solar access.

Estate requirements — Some estates include design guidelines impacting sustainability outcomes.

Building on a sloping block? Here’s why it matters

At Montgomery Homes, many clients build on challenging sites. Sloping blocks can influence:

• Orientation opportunities

• Retaining requirements

• Window placement

• Passive heating/cooling performance

With thoughtful design, difficult sites can still achieve strong BASIX outcomes.

Building regulations continue to evolve, but navigating BASIX shouldn’t feel overwhelming.

At Montgomery Homes, BASIX considerations are integrated early into the design process — helping clients understand how block choice, home design and inclusions can influence sustainability requirements before construction begins.

Whether you’re building your first home, upgrading for a growing family or planning a knockdown rebuild, early planning can make compliance simpler and help avoid costly changes later.

Whether you’re purchasing land, planning a knockdown rebuild or comparing home designs, understanding BASIX early can help avoid surprises later.

Talk to the Montgomery Homes team about your block, sustainability requirements and the best design approach for your site — or book a complimentary site assessment to get started.