BASIX for New Homes vs Alterations and Additions

Building Sustainability Index (BASIX) requirements can vary significantly depending on whether a project is a new home, renovation or extension.

While both project types may require BASIX assessments in NSW, the compliance pathway, documentation requirements and thermal performance expectations can differ considerably between developments.

Understanding these differences early in the design process can help reduce approval delays, redesigns and unexpected compliance issues later in the project.

BASIX for New Homes

New residential dwellings in NSW generally require a full BASIX assessment covering:

water efficiency
energy efficiency
thermal comfort

New homes are typically assessed as complete building systems. This means the orientation, glazing, insulation, construction materials, ventilation and hot water systems all contribute to the final BASIX outcome.

Thermal comfort requirements for new homes are often more comprehensive, requiring detailed assessment of:

glazing performance
SHGC and U-values
insulation levels
shading
building orientation
roof and wall construction
ventilation strategies

Because the entire dwelling is being assessed, early passive design decisions can significantly influence compliance outcomes.

Common BASIX considerations for new homes

north-facing glazing and solar access
external shading design
insulation selection
glazing performance
hot water systems
rainwater harvesting
cross ventilation
roof colour and construction

Explore:

BASIX for New Homes
Thermal Comfort and BASIX
SHGC and U-Values
Passive Design Principles

BASIX for Alterations and Additions

Alterations and additions are assessed differently from new homes because only the proposed works are generally considered within the BASIX assessment scope.

Depending on the project size and approval pathway, BASIX requirements may focus more specifically on the new or modified areas of the dwelling rather than the entire house.

This can include areas such as:

new glazing
extensions
upper-storey additions
modified living areas
new insulation requirements
updated hot water systems

In many renovation projects, achieving thermal comfort compliance can become more complex due to existing building limitations, orientation constraints or existing glazing conditions.

Older homes may also require design adjustments to improve compliance performance without significantly impacting the existing structure.

Common BASIX considerations for renovations and additions

retaining existing glazing
matching insulation to existing construction
shading limitations
extension orientation
roof upgrades
balancing old and new construction materials

Explore:

BASIX for Alterations and Additions
Common BASIX Issues
BASIX Consultants
Windows, Glazing and Thermal Performance

Why Early Planning Matters

Whether the project is a new home or renovation, early-stage BASIX planning can often help reduce redesigns and streamline the approval process.

Working through thermal comfort, glazing performance and energy efficiency considerations early in the design phase can help improve compliance outcomes while supporting long-term residential comfort and efficiency.

Projects that leave BASIX considerations until late in the approval process may require additional glazing upgrades, insulation changes or redesigns to achieve compliance targets.