Why Get an Energy Assessment for an Existing Home?
Most energy rating discussions focus on new builds, but the vast majority of Australian homes are existing dwellings — many built decades before modern energy efficiency standards existed. These homes often have minimal insulation, single-glazed windows, and building envelopes that allow significant heat transfer, resulting in high energy bills and poor comfort.
An energy assessment for an existing home provides a clear picture of your property’s thermal performance and identifies the most impactful improvements. The reasons homeowners seek these assessments include:
- Pre-sale disclosure — In the ACT, an Energy Efficiency Report (EER) is mandatory for all property sales. Other states are moving towards similar requirements.
- Understanding energy performance — Knowing your home’s star rating helps you make informed decisions about which upgrades deliver the best return on investment.
- Planning renovations — If you are planning a renovation, an assessment helps you incorporate energy improvements into the project scope.
- Accessing rebates and programs — Programs like the Victorian Energy Upgrades program may require or recommend a baseline energy assessment.
- Reducing energy costs — With rising electricity and gas prices, understanding and improving energy efficiency translates directly to lower bills.
NatHERS for Existing Dwellings
A NatHERS assessment can be performed on existing homes using the same accredited software tools and methodology as for new builds. The key difference is that the assessor needs to determine the actual construction details of the home rather than reading them from architectural specifications.
For existing homes, the assessment process typically involves:
- Plan review or site measurement — If original building plans are available, the assessor uses these as a starting point. Otherwise, the assessor visits the property to measure room dimensions, ceiling heights, window sizes, and other key dimensions.
- Construction identification — The assessor identifies wall construction type (brick veneer, weatherboard, double brick, etc.), roofing material, insulation presence and type, window framing, and glazing type.
- Thermal modelling — The home is modelled in NatHERS-approved software using the identified construction details and the property’s specific climate zone.
- Rating and recommendations — The assessment produces a star rating and the assessor provides recommendations for improvements that would increase the rating.
Typical Star Ratings for Existing Homes
The star rating of an existing home depends heavily on when it was built and what construction practices were common at the time:
- Pre-1990 homes: Typically 1.0–2.5 stars. Often uninsulated or minimally insulated with single glazing.
- 1990–2005 homes: Typically 2.5–4.0 stars. Some insulation, but often below current standards.
- 2005–2010 homes (5-star era): Typically 4.0–5.5 stars. Built to the first mandatory energy standards.
- 2010–2022 homes (6-star era): Typically 5.5–6.5 stars. Reasonable insulation and glazing but below current 7-star requirements.
Cost-Effective Upgrades for Existing Homes
The accredited consultants in our network regularly recommend practical, cost-effective upgrades that deliver measurable improvements in both star rating and energy savings:
- Ceiling insulation (R4.0–R6.0) — The most impactful single upgrade for most homes. Can improve the rating by 0.5–1.5 stars. Cost: $1,500–$3,000 for an average home.
- Draught sealing — Sealing gaps around doors, windows, and service penetrations. Cost: $200–$800. Rating improvement: 0.2–0.5 stars.
- Window upgrades — Adding secondary glazing, window film, or replacing with double glazing. Cost: $2,000–$15,000. Rating improvement: 0.5–1.5 stars.
- Wall insulation (retrofit) — Possible for some construction types. Cost: $2,000–$5,000. Rating improvement: 0.3–1.0 stars.
- External shading — Adding awnings, pergolas, or shade sails to west and north-facing windows. Cost: $500–$3,000.
Getting Started
Ready to find out how your existing home performs? Use our Energy Rating Calculator for a quick preliminary estimate, or request a free quote to be connected with an accredited assessor who can provide a formal assessment. You can also find a consultant in your area directly. For homes where you want a broader assessment beyond just the star rating, consider a home energy audit.
Frequently Asked Questions
Can I get a NatHERS rating for my existing home?
Yes. An accredited assessor can perform a NatHERS assessment on an existing home using the same methodology as for new builds. If original building plans are not available, a site inspection is conducted to measure the property and identify construction details.
Do I need an energy rating to sell my existing home?
Currently, only the ACT requires mandatory energy disclosure (via an Energy Efficiency Report) for residential property sales. However, other states are considering similar requirements. In all states, having an energy rating can be a marketing advantage.
How accurate is a NatHERS rating for an older home?
NatHERS ratings for existing homes are reliable when performed by an experienced assessor. The accuracy depends on the quality of information about construction materials and insulation. A site inspection helps the assessor identify actual construction details rather than making assumptions.
What star rating do most existing homes achieve?
Most existing homes built before 2005 typically rate between 1.5 and 3.5 stars. Homes built between 2005 and 2010 (under 5-star requirements) typically rate 4 to 5.5 stars. Post-2010 homes built to 6-star standards usually rate 5.5 to 6.5 stars.
Can I improve my existing home's energy rating?
Absolutely. Common upgrades like adding ceiling insulation, sealing draughts, upgrading windows, and adding wall insulation can improve a home's rating by 1 to 3 stars. An assessor can model specific upgrades and show the expected rating improvement for each.