Answer first: For NSW alterations and additions to an existing BASIX-affected dwelling costing $50,000 or more, a BASIX certificate is required regardless of the nature of the works. The online tool asks yes/no scope questions; if every answer is “no” and floor area is unchanged, you still get a certificate — sometimes with no commitments.
Author: Franz Phan, Senior Planning Consultant, giantA Pty Ltd · Updated 10 September 2026
Why does Planning Portal still insist on a BASIX certificate when nothing “energy-related” is changing?
Because planning regulations require a BASIX certificate for all alterations and additions to an existing BASIX building (such as residential premises) that cost $50,000 or more. The December 2025 BASIX Newsletter makes the policy intent explicit: this applies regardless of the nature of the alterations.
That is the trap many owners and builders miss. A veranda, covered outdoor area, or structural brickwork repair can sit well above the cost threshold without touching hot water, glazing or insulation — yet the lodgement package still needs a BASIX certificate. Completing the assessment for every alteration and addition at or above $50,000 ensures the development is classified correctly before DA or CDC proceeds.
Related giantA reading: BASIX for Alterations and Additions in NSW 2026 and BASIX Simulation for NSW Alterations 2026.
Sources: BASIX Newsletter December 2025 · Alterations and additions (BASIX).
What cost and scope thresholds actually trigger BASIX on alterations?
According to the NSW Planning Portal alterations and additions guidance:
- BASIX applies to all alterations and additions in NSW valued at $50,000 and over; and/or
- works that involve installation of a pool and/or spa with a total volume greater than 40,000 litres.
The alterations tool is also used to alter, enlarge or extend an existing BASIX-affected building, and for a swimming pool or spa (or combination) that serves only one dwelling.
Never rely on older informal figures you may have heard on site. The live Planning Portal threshold for alterations and additions is $50,000. Pool and spa volume is assessed on total volume greater than 40,000 litres.
If alterations valued at $50,000 and over are not for use as a dwelling (or capable of being used as a dwelling), check with your local council whether BASIX still applies.
Source: Alterations and additions.
How do the BASIX tool’s yes/no questions work for renovations?
The online BASIX tool creates the certificate. The first stage of an alterations assessment asks a series of yes / no questions about scope, then records existing and proposed floor area.
Typical scope questions include whether you are:
- installing a new hot water system;
- installing any new or altered lighting fixtures;
- installing or altering floors, walls, ceilings, windows or skylights.
You also enter the existing and proposed floor area.
What happens if every answer is “no” and floor area is unchanged?
You still generate a BASIX certificate — but it can carry no BASIX commitments. Planning Portal examples where this may apply include:
- verandas;
- covered unenclosed outdoor areas;
- brickwork repairs.
That zero-commitment certificate is still a required certificate for lodgement when the $50,000 threshold is met. It is not a waiver and it is not optional paperwork.
What happens when you answer “yes” to one or more questions?
In most jobs you will answer “yes” to at least one item. The tool then asks for further details, and the certificate includes BASIX commitments tied to those answers — for example efficiency expectations for new lighting, taps, hot water or fabric changes.
The alterations section differs from new single-dwelling and multi-dwelling paths: there are no set percentage reductions for energy or water. Instead the tool aims to reduce potential water use and emissions by encouraging efficiency improvements where the scope touches those systems.
Planning Portal notes that the alterations tool:
- reduces heating and cooling energy through improved glazing, insulation, design and materials where relevant;
- requires at least 40% of new or altered light fixtures to use high-efficiency globes;
- promotes solar, gas, heat pump or wood hot-water systems instead of high-emission electric systems;
- requires new taps, toilets and showerheads to meet a minimum 3 WELS stars;
- reduces pool and spa emissions by phasing out high-emission electric heating;
- reduces pool and spa water use through rainwater tanks and covers.
Sources: BASIX Newsletter December 2025 · Alterations and additions.
| Scope pattern | Typical yes/no outcome | Certificate result |
|---|---|---|
| Veranda / covered unenclosed outdoor area / brickwork repair, area unchanged | All “no” | Certificate with no commitments (still required ≥ $50k) |
| New windows, lighting, hot water, or fabric works | One or more “yes” | Certificate with commitments |
| Pool/spa total volume > 40,000 L | Pool pathway applies | Certificate with pool-related commitments as applicable |
| New granny flat or non-habitable → dwelling conversion | Not alterations | Assess as new single dwelling standards |
Do alterations need an embodied emissions calculation?
No — not for alterations and additions. The NSW Government amended the Sustainable Building State Environmental Planning Policy 2022 (Sustainable Building SEPP) to clarify that if you need a BASIX certificate for an alteration or addition, you do not have to calculate embodied emissions of the materials used. Embodied emissions assessment remains a new residential development requirement. The December 2025 newsletter states this was always the policy intent; the legislation was updated to make that clear.
For architects and owners this removes a common documentation scare: do not pad alteration packages with embodied-emissions worksheets that Planning Portal does not require for that pathway.
Source: BASIX Newsletter December 2025.
Is a granny flat or secondary dwelling assessed as “alterations”?
Usually no — and misclassification is expensive.
A secondary dwelling is a self-contained dwelling established in conjunction with a principal dwelling, on the same lot, whether within, attached to, or separate from the principal dwelling.
If there is an existing principal dwelling and you are:
- building a new granny flat, or
- converting non-habitable space (for example a garage or shed) into a new dwelling,
you must assess the work as a new single dwelling house. It is not alterations and additions to an existing BASIX building. New-dwelling BASIX standards apply.
Converting existing habitable space within the primary dwelling into a secondary dwelling can use a different path — the Portal notes the alterations tool can generate a certificate where the secondary dwelling is created by converting existing habitable space within the primary dwelling. Use the Secondary Dwelling (Granny Flat or Bedsitter) Help Note and confirm classification before modelling.
Sources: BASIX Newsletter December 2025 · Alterations and additions.
When do pools and spas force a BASIX certificate?
Separately from the $50,000 works threshold, BASIX applies where the project involves a swimming pool and/or spa with total volume greater than 40,000 litres. The alterations/additions tool can generate certificates for a pool or spa (or combination) serving only one dwelling. Efficiency settings for heating, covers and rainwater support may then appear as commitments.
If your renovation already sits over $50,000 and adds a large pool, expect both the general alterations assessment and pool-related commitments to be coordinated in one documentation set.
How should you answer the yes/no questions without over- or under-scoping?
Treat the questions as a scope audit, not a design wishlist. If the stamped drawings show new windows, altered ceilings, or a replacement hot-water unit, answer yes — even if those items are a small share of the $50,000+ budget. Under-scoping to chase a zero-commitment certificate creates a mismatch between plans and the BASIX certificate that certifiers and councils will query.
Conversely, do not invent fabric changes that are not on the drawings just to “look thorough”. The certificate must match the approved or lodged set. Where lighting is only partially upgraded, record the share of new or altered fixtures accurately so the high-efficiency globe commitment (at least 40% of new or altered fixtures) is achievable on site.
Floor area deserves special care. A covered outdoor room that does not increase habitable floor area may still sit over the cost threshold and still need a certificate. Record existing and proposed floor area honestly; an unchanged area plus all “no” answers is exactly the pattern Planning Portal cites for zero-commitment outcomes.
Coordinate early with your BASIX assessor or architect so the answer set, commitments (if any), and drawing notes speak the same language before lodgement.
What should architects and owners check before lodging?
- Confirm cost of works against the live $50,000 alterations threshold (and whether the building is BASIX-affected).
- Classify the building correctly — existing dwelling alteration vs new single dwelling (critical for granny flats and non-habitable conversions).
- List scope against the yes/no questions early: hot water, lighting, floors/walls/ceilings/windows/skylights, floor-area change.
- Expect a certificate even for zero-commitment scopes such as verandas, covered unenclosed outdoor areas, or brickwork repairs when cost ≥ $50,000.
- Do not invent embodied-emissions calcs for alterations — Sustainable Building SEPP clarification says they are not required.
- Flag pools/spas > 40,000 L as a separate trigger.
- Decide simulation vs tool defaults early where fabric changes are complex — see giantA’s guide to BASIX simulation / NatHERS modelling for alterations over $50k.
- Align drawings, BASIX certificate and commitments so the certifier/council can match stamped plans to certificate text.
- Re-check the Portal pages before lodgement — BASIX News and dwelling-type pages are updated periodically.
How does giantA help with BASIX alterations documentation?
giantA Pty Ltd supports homeowners, builders and design teams across Greater Sydney with residential alterations packages that treat BASIX as part of early design — not a last-minute lodgement scramble. We help clarify whether your project is alterations or a new dwelling pathway, prepare coordinated drawings, and organise BASIX-ready documentation for DA or CDC.
We do not publish fixed fee schedules in blog posts. Scope, pathway and documentation extent drive fees — contact us for a project-specific quote.
Need a BASIX-ready alterations package? Contact giantA.
FAQ: BASIX certificates for NSW alterations over $50,000
Do I still need a BASIX certificate if my renovation does not change energy systems?
Yes, if the works are alterations or additions to an existing BASIX building costing $50,000 or more. The December 2025 explainer confirms a certificate is required regardless of the nature of the alterations. Some scopes produce a certificate with no commitments.
What are examples of a BASIX certificate with no commitments?
Planning Portal examples include verandas, covered unenclosed outdoor areas, and brickwork repairs — where you answer “no” to all scope questions and floor area is unchanged.
Is the BASIX alterations threshold still $50,000 in 2026?
Yes. The Planning Portal alterations and additions page and the December 2025 BASIX Newsletter both state the $50,000 threshold. Do not use outdated informal figures.
Do I need to calculate embodied emissions for an alteration?
No. Sustainable Building SEPP amendments clarify that alterations and additions requiring a BASIX certificate do not need embodied emissions calculations; those apply to new residential development.
Does a new granny flat use the alterations BASIX pathway?
Not when you build a new secondary dwelling or convert non-habitable space (garage/shed) into a dwelling. Those are assessed as a new single dwelling. Converting existing habitable space within the primary dwelling can follow a different secondary-dwelling path — confirm with the Portal help notes.
When does a pool or spa require BASIX?
When the swimming pool and/or spa has a total volume greater than 40,000 litres, and/or when alterations otherwise meet the $50,000 threshold.
Can NatHERS simulation be used for alterations over $50k?
In some circumstances simulation may be used to model alterations and additions. See giantA’s dedicated article on BASIX simulation for NSW alterations 2026.
Where do I start if I only know my renovation cost?
Start with dwelling classification and the Planning Portal alterations pages, then map scope to the yes/no questions. giantA’s overview of when renovations trigger a BASIX certificate pairs with this explainer.
This article is general information for NSW homeowners, builders and designers. It is not legal advice or a site-specific BASIX assessment. Confirm the current Planning Portal BASIX pages, Sustainable Building SEPP, and advice from a suitably qualified practitioner before acting. Cited NSW Planning Portal sources researched 10 September 2026.