Bondi Junction Alterations & Additions
Project Details
- Location: Bondi Junction, Sydney NSW
- Project Type: Alterations and additions (renovation and vertical extension)
- Building Form: Three-storey (existing levels plus new addition)
- Services: NatHERS Assessment + BASIX Certification (alterations and additions pathway)
Project Overview
This project in Bondi Junction involved alterations and additions to an existing dwelling, extended to a three-storey configuration. Vertical extensions like this — adding a new level above an existing home — bring together two separate challenges at once: the usual complexities of an alterations and additions energy rating, plus the added complication of a taller, multi-level building where the original design was never conceived as a three-storey home.
Why a Three-Storey Vertical Addition Adds Complexity
Renovations that add a new storey on top of an existing home involve more than just designing the new level well — the whole building’s thermal behaviour changes once it’s reconfigured:
The old roof becomes an internal floor: What used to be the ceiling and roof space of the original home often becomes an internal floor between the existing levels and the new addition, which needs to be correctly modelled as an internal element rather than assumed to still behave like an external roof.
Mismatched construction eras: The existing lower levels and the new upper level are typically built to very different standards — different insulation levels, different glazing performance — and the assessment has to accurately reflect both rather than applying one specification across the whole building.
Vertical airflow and stair voids: Stairwells and voids connecting three levels can create airflow pathways between zones that behave very differently thermally, particularly where a warmer new upper level sits above cooler, more established lower levels.
Existing structure constrains the new design: The new upper level’s footprint, window placement, and form are often constrained by what the existing structure below can support, which limits some of the passive design choices available on a from-scratch build.
Our Approach
The Ecomaxhomes team assessed the existing dwelling and the new upper-level addition as a single, integrated three-storey building, rather than treating the addition in isolation:
- Confirmed the correct BASIX and NatHERS pathway for the alterations and additions scope, including how the new upper level factored into the overall assessment
- Modelled the existing lower levels’ actual insulation and glazing performance as a realistic baseline, rather than assuming new-build-equivalent standards
- Correctly treated the former roof/ceiling line as an internal floor between levels, with insulation and construction detail reflecting its new role
- Specified insulation and glazing for the new upper level to help offset the more limited performance of the unaltered existing levels below
- Considered how stairwells and voids connecting the three levels would affect airflow and thermal zoning between the older and newer parts of the home
The Result
- Achieved a compliant energy rating across the full three-storey building, not just the new addition in isolation
- Correctly accounted for the former roofline now functioning as an internal floor
- Balanced the differing performance of existing and new construction without requiring unnecessary upgrades to the lower levels
- Delivered a compliance pathway suited to the specific complexity of a vertical alterations and additions project
Key Features
- Three-storey alterations and additions project
- Existing dwelling extended with a new upper level
- Former roofline reassessed as an internal floor between levels
- Mixed-era construction modelled accurately across all three storeys
- Stairwell and vertical airflow considerations addressed
- Compliant outcome without unnecessary upgrades to existing levels
Frequently Asked Questions
Does adding a third storey to an existing home need a full new energy assessment?
Do the existing lower levels need to be upgraded to match the new addition?
Not necessarily. Alterations and additions assessments generally work with the existing fabric’s actual performance rather than requiring it to be brought up to new-build standards, though the new works still need to meet compliance requirements and may need to help offset what can’t be economically upgraded.
Why does the old roofline matter once a new storey is added?
Because it changes function — from an external roof exposed to outdoor conditions, to an internal floor between two conditioned levels. It needs to be modelled and detailed correctly for its new role, not left as though it were still an external element.
Is a three-storey renovation more expensive to certify than a single-storey one?
It generally requires more assessment work, since more levels and more old-to-new junctions need to be modelled accurately, but that detailed approach is also what avoids unnecessary or misdirected upgrade costs elsewhere in the project.
Why Choose EcoMaxHomes?
- Deep expertise in both alterations-and-additions and multi-storey NatHERS/BASIX compliance across NSW
- Practical experience with vertical extensions and mixed-era construction
- Careful treatment of internal floor/former-roofline junctions, a detail that’s easy to get wrong
- Fast turnaround times for approvals
Ready to Start Your Project?
If you’re planning a renovation, extension, or vertical addition in Sydney or NSW and need an energy rating approach that accounts for your home’s full complexity, Ecomaxhomes can help.
Our team will help you meet compliance requirements while working within the realities of your existing home.