How long does a NatHERS assessment take from booking to certificate?

Most existing-home NatHERS assessments take 5–10 business days end to end: 1–3 days to book an assessor, 1 day for the on-site inspection (1–3 hours), 2–5 days for thermal modelling and report writing, and 1–2 days for AAO certificate registration. New builds from plans take 3–7 business days because there's no on-site visit.

How long does the on-site inspection take?

The on-site inspection for an existing home takes 1–3 hours depending on size and complexity. A 3-bedroom single-storey home is typically 60–90 minutes. A two-storey 4–5 bedroom home is 2–3 hours. The assessor measures rooms, photographs construction, checks insulation, glazing, draught-proofing and HVAC.

How long does a NatHERS assessment take for a new build?

A new-build NatHERS assessment from architectural plans usually takes 3–7 business days. There's no on-site visit — the assessor models from CAD or PDF drawings and the BASIX or building specification. Add 2–5 days per re-rating iteration if you change the design after the first model.

Can I get a rush NatHERS assessment?

Yes — most assessors offer 48–72 hour rush turnarounds for a 30–50% surcharge on top of the standard fee. Rush jobs typically skip the design-tweak loop, so book a rush only when your plans are final. In peak season (March–June and Sept–Nov) rush availability is limited.

Why does the certificate take so long after the inspection?

After the inspection the assessor builds a 3D thermal model of your home in AccuRate, FirstRate5 or BERS Pro, runs simulations for your climate zone, writes the report, and lodges the certificate with their Assessor Accrediting Organisation (Design Matters, ABSA or HIA). Modelling alone is 2–4 hours of expert work; registration adds another 1–2 business days.

When is the best time to book a NatHERS assessment?

Demand peaks March–June (settlement and pre-winter retrofits) and September–November (spring selling season). Booking in July, August, December or January typically gets you a faster turnaround — often inside 5 business days. For new builds, book the NatHERS at the design-development stage, not after permit lodgement.

How long does it take to re-rate after changing the design?

Each re-rating iteration typically adds 2–5 business days. Most assessors include 1–2 re-rates in the base fee and charge $100–$250 per iteration after that. Send all design changes in a single batch — multiple rounds of small tweaks add the most time.

What can I do to speed up my NatHERS assessment?

Five things make the biggest difference: (1) book early and provide CAD-ready plans (DWG or vector PDF), not scanned drawings; (2) photograph your ceiling cavity, sub-floor and wall cavities ahead of the inspection; (3) have insulation R-values, glazing specs and HVAC model numbers ready; (4) book first or last appointment of the day so the assessor isn't time-pressured; (5) confirm whether you need a BASIX certificate so it's modelled in the same pass.

How Long Does a NatHERS Assessment Take? 2026 Timeline Guide

The short answer

• Existing home (on-site inspection): 5–10 business days end to end.
• New build (from plans): 3–7 business days.
• Rush turnaround: 48–72 hours, 30–50% surcharge.
• Peak season (Mar–Jun, Sep–Nov): add 3–5 days for assessor availability.

Stage-by-stage timeline

Stage	Existing home	New build
1. Quote & book assessor	1–3 business days	1–3 business days
2. On-site inspection	1–3 hours (same day)	N/A — plans-based
3. Thermal modelling	2–4 days	1–3 days
4. Report writing	1 day	1 day
5. AAO certificate registration	1–2 days	1–2 days

Typical total: 5–10 business days for existing homes, 3–7 for new builds — assuming a single design iteration and standard turnaround.

Find a Pro

Ready for an official assessment? Find certified NatHERS assessors in your area.

Find Local Assessors

What happens during the on-site inspection

For existing homes, your accredited assessor visits to capture the data their modelling software needs. A typical 3-bedroom single-storey takes 60–90 minutes; a 4–5 bedroom two-storey runs 2–3 hours. They'll:

• Measure every room, ceiling height, window and external door
• Photograph wall construction, ceiling cavity, sub-floor and roof space
• Record insulation R-values (or note where it's missing)
• Catalogue glazing types, frames and shading devices
• Check draught-proofing on doors, windows, exhaust fans and downlights
• Note HVAC system type, age and efficiency ratings
• Capture orientation, eaves and adjoining shading

Why the modelling stage takes 2–4 days

After the inspection, your assessor rebuilds your home as a 3D thermal model in NatHERS-accredited software (AccuRate Sustainability, FirstRate5, or BERS Pro). The simulation runs your home against the standard 8,760-hour weather file for your climate zone (one of 69 Australian zones) and calculates heating and cooling energy demand to land your star rating.

Modelling alone is typically 2–4 hours of expert work, but it's slotted in around other jobs — most assessors batch modelling sessions, which is why the calendar time runs 2–4 days even when the active work is shorter.

Free Tool

Get a personalised price range for your home in seconds — based on your state, dwelling type and size.

Estimate My Cost

5 ways to get your certificate faster

Send CAD-ready plans (DWG or vector PDF). Scanned hand-drawings add a "plans markup" step that costs $150–$400 and 1–2 days.
Photograph the cavities yourself — ceiling, sub-floor, wall — and email them with the brief. Assessors can pre-model before the inspection.
Have specs on hand: insulation R-values, glazing U-values/SHGC, HVAC model numbers, hot water type.
Book the first or last slot of the assessor's day so they're not racing the clock.
Batch your design changes. One round of revisions adds 2–5 days; three rounds can add a fortnight.

Common reasons assessments run late

• Missing plans or specs — assessor has to chase you or the builder
• Inaccessible ceiling or sub-floor — reschedule for a second visit
• Multiple design revisions — each re-rate is 2–5 extra days
• Peak season backlog (March–June, September–November)
• BASIX add-on in NSW — modelled separately, adds 1–2 days
• Strata or shared-wall homes — extra coordination with neighbours

Take the Next Step

Whether you're curious about your home's efficiency or ready to get a professional assessment, we have tools to help.

Ready to get started? Request free quotes from certified assessors.

Request Free Quotes

Ready to find out your home's energy rating? Find a certified NatHERS assessor near you

Need help choosing an assessor or got a tight settlement deadline? Get in touch and we'll match you to an assessor with current capacity.

How Long Does a NatHERS Assessment Take?