Randwick Alterations & Additions
An alterations and additions project in Randwick, Sydney, achieving a compliant NatHERS and BASIX energy rating by working with the constraints of an existing dwelling rather than a clean-slate new build.
Project Details
- Location: Randwick, Sydney NSW
- Project Type: Alterations and additions (renovation and extension)
- Services: NatHERS Assessment + BASIX Certification (alterations and additions pathway)
- Site Condition: Existing dwelling with new extension works
Project Overview
This project in Randwick involved alterations and additions to an existing home — a renovation and extension rather than a new build. Energy rating an alterations and additions project is a genuinely different exercise to a new home: much of the existing building fabric is already fixed, can’t always be economically upgraded, and has to be worked with rather than redesigned from scratch
Why Alterations & Additions Projects Are Assessed Differently
New builds get a clean slate — every wall, window, and insulation specification can be chosen to hit a target rating. Renovations and extensions don’t have that luxury, which changes both the compliance pathway and the design strategy:
BASIX threshold applies differently: In NSW, alterations and additions typically only require a BASIX certificate once the works exceed a set cost threshold, unlike new dwellings, which always require one. Confirming which pathway applies is one of the first steps on a project like this.
Existing fabric can’t always be upgraded: Walls, roof, and flooring already in place may not be practical or cost-effective to bring up to current standards, so the new works often have to do proportionally more of the thermal performance “work” to offset what can’t be changed.
Junctions between old and new are a common weak point: Where a new extension meets the existing structure, thermal bridging and gaps in continuity of insulation are a real risk if the junction isn’t specifically detailed and modelled, not just assumed to match the new work’s performance.
Existing orientation and layout are fixed: Unlike a new build, the existing home’s orientation, room layout, and window positions on the unaltered portions of the house can’t be changed, so the extension has to work around constraints a new-build project wouldn’t face.
Our Approach
The Ecomaxhomes team assessed the project against the correct compliance pathway for an alterations and additions project, then worked through the specific detail required to make the existing home and new works perform together:
- Confirmed which BASIX and NatHERS requirements applied to the scope of works, based on the project’s classification as alterations and additions rather than a new dwelling
- Assessed the existing building fabric to establish a realistic baseline, rather than assuming new-build-equivalent performance from the outset
- Specified insulation and glazing for the new extension to help offset the thermal performance of the parts of the home that weren’t being altered
- Paid particular attention to the junctions between old and new construction, where thermal bridging is most likely to undermine an otherwise well-performing extension
- Coordinated with the design team to keep the compliance strategy aligned with the renovation’s architectural and budget constraints
The Result
- Achieved a compliant energy rating for the alterations and additions works
- Avoided unnecessary and costly upgrades to existing fabric that didn’t need to change
- Addressed the old-to-new junction risk that often gets missed in renovation projects
- Delivered a compliance pathway matched to the actual scope of works, not a blanket new-build approach
Key Features
- Alterations and additions to an existing Randwick home
- Correct BASIX/NatHERS pathway identified for the scope of works
- Existing building fabric assessed as a realistic baseline
- New extension insulation and glazing calibrated to offset unchanged existing areas
- Old-to-new junction detailing addressed
- Compliant outcome without unnecessary upgrade costs
Frequently Asked Questions
Do all home renovations in NSW need a BASIX certificate?
Not always. BASIX for alterations and additions generally applies once the cost of works exceeds a set threshold — smaller renovations may fall outside that requirement. It’s worth confirming which pathway applies early, since it affects both the assessment process and the design brief.
Does the whole house need to meet the same energy rating as a new home?
No. Alterations and additions projects are typically assessed differently to a full new build — the existing, unaltered parts of the home aren’t usually required to be brought up to new-build standards, but the new works still need to meet compliance requirements.
Why does the junction between old and new construction matter for energy rating?
Because gaps or breaks in insulation continuity at that junction — thermal bridging — can undermine the performance of an otherwise well-designed extension. It needs to be specifically detailed and modelled rather than assumed to match the new work’s performance.
Can I upgrade only part of my home and still be compliant?
Generally yes, provided the works are correctly classified and assessed under the alterations and additions pathway rather than treated as a full new dwelling. The specific requirements depend on the scope and cost of the works.
Why Choose EcoMaxHomes?
- Deep expertise in both new-build and alterations-and-additions BASIX/NatHERS compliance across NSW
- Practical experience working with existing building fabric rather than assuming a clean-slate design
- Careful attention to old-to-new construction junctions, a common weak point in renovation projects
- Fast turnaround times for approvals
Ready to Start Your Project?
If you’re planning a renovation, extension, or alterations and additions project in Sydney or NSW and need the right energy rating pathway for your scope of works, Ecomaxhomes can help.
Our team will help you meet compliance requirements while working within the realities of your existing home.