Section 4.55 of the Environmental Planning and Assessment Act 1979 lets you change an approved development consent without lodging a new DA, as long as the modified development is substantially the same as the one council approved. There are three pathways: 4.55(1) for correcting minor errors and misdescriptions, 4.55(1A) for changes with minimal environmental impact, and 4.55(2) for everything else that still passes the substantially the same test. The right pathway sets the fee, the notification and the time it takes. If the change fails the substantially the same test, for example adding a dwelling, the only option is a fresh DA.
Key takeaways
- Every 4.55 modification must leave the development substantially the same as originally approved, judged qualitatively and quantitatively against the whole consent.
- 4.55(1A) is the workhorse for house and duplex changes: window moves, internal layout, small footprint shifts and material changes with minimal environmental impact.
- 4.55(2) covers bigger changes such as an extra 40 square metres of floor area or a taller roof, is notified like a DA, and needs a fuller Statement of Environmental Effects.
- Council must consider the reasons for the original conditions and any submissions, and can only alter conditions that relate to the modification.
- A consent can be modified after works have started or finished, but not after it has lapsed, and modifications cannot be used to revive an expired consent.
The test that sits over all three pathways
Before council looks at the merits, it has to be satisfied that the development as modified is substantially the same development as the one for which consent was granted. The Land and Environment Court has read that phrase as “essentially or materially the same”, comparing the modified proposal with the original in both qualitative and quantitative terms. In practice, on residential consents:
- Moving a garage, enlarging a bedroom, adding a rumpus room or altering a roof form usually passes.
- Adding a storey to a single storey consent, or converting an approved house into a dual occupancy, usually fails.
- Changing the number of dwellings or lots fails almost every time.
- A series of small modifications that together turn the project into something else can fail, because the comparison is with the original consent, not the last modification.
If the change fails, a new DA is the answer. Council cannot approve a modification that doesn’t pass the test, no matter how sensible the change is. The Department’s guide to DA determination makes the same point: modifications are available where the development remains substantially the same.
The three pathways compared
| Pathway | What it is for | Notification | Typical examples on a house or duplex |
|---|---|---|---|
| Section 4.55(1) | Correcting a minor error, misdescription or miscalculation in the consent | None | Wrong lot number in a condition; a condition referencing the wrong plan revision; a miscalculated contribution figure |
| Section 4.55(1A) | Modifications of minimal environmental impact | Only if the council’s community participation plan requires it; often not for small changes | Relocating windows; internal layout; deleting a pergola; changing external materials; shifting a wall 300 mm within setbacks |
| Section 4.55(2) | Other modifications that still pass the substantially the same test | Notified in the same way as the original DA | Adding a first floor room; extending the footprint into the rear yard; changing the roof to a higher pitch; altering the driveway and parking layout |
Blacktown’s modification of a consent page is a clear council statement of the same three categories and of the rule that changes making the development substantially different need a new DA. The fourth pathway, section 4.56, applies where the Land and Environment Court granted the consent, and the modification goes to the council with the same tests.
What council assesses on a modification
Section 4.55(3) requires the council to take into account the matters in section 4.15 that are relevant to the modification, the reasons the original consent was granted, and any submissions. That has three consequences we see on knock-down rebuilds in Penrith and the Hills:
- The original conditions are read for their purpose. If the consent limited the rear setback because of a neighbour’s solar access, a modification that pushes the rear wall out will be measured against that reason, not just against the DCP number.
- Only the relevant section 4.15 matters are opened. A modification to change a window does not reopen the whole DA. A modification to add floor area reopens overshadowing, privacy, bulk and, if an LEP standard is involved, clause 4.6.
- Council can only vary conditions that relate to the modification. It cannot use a 4.55(1A) for a window change to rewrite the landscaping condition, and the applicant cannot use it to have an unwanted condition deleted unless the deletion is the modification.
Where the modification breaches a development standard, a clause 4.6 request is required in the same way as on a DA, and a variation over 10% sends the modification to the local planning panel in Sydney and Wollongong councils.
Timing and lapsing
A consent generally lapses five years after it operates unless works have physically commenced. A modification does not extend that period, and a lapsed consent cannot be modified or revived; a new DA is needed. On the other side, a consent can be modified after work has begun and even after the building is occupied, which is how as-built discrepancies are regularised. That route is legitimate, but it’s cheaper to lodge the modification before the certifier issues the construction certificate than after the frames are up and the neighbour has noticed.
Reforms passed by the NSW Parliament in late 2025 are due to commence later in March 2026 and will widen section 4.55(1) to cover modifications with no environmental impact and introduce a short determination period for them. We’ll update this post once the provisions are in force; until then, the three pathways above are the ones that apply.
What a modification application contains
- The completed modification application on the NSW Planning Portal, referencing the consent number.
- Amended plans with the changes clouded and a revision note, plus a copy of the approved plans for comparison.
- A short Statement of Environmental Effects for the modification: what is changing, why, an assessment against the substantially the same test, the relevant section 4.15 matters and the reasons for the original conditions.
- Updated BASIX certificate if the change affects any commitment, and updated engineering if the footprint or drainage changes.
- A list of the conditions to be amended and the proposed wording.
The comparison table is the document officers value most. Approved figure, proposed figure, control, compliance, one row per change. It lets the officer see that a 4.55(1A) really is minimal, or that a 4.55(2) has been properly considered.
Where modifications go wrong
- Choosing 4.55(1A) for a change that isn’t minimal. Council reclassifies it as 4.55(2), charges the higher fee and notifies, and the time saved is lost.
- Drip-feeding changes. Three modifications in a year on one duplex consent invite a comparison of the current building with the original approval, and the cumulative change can fail the test.
- Using a modification to fix an unlawful building. It can be done, but the assessment is against the controls, not against the fact that the wall already exists.
- Forgetting the certifier. A construction certificate issued against the original plans has to be amended to match the modified consent before work proceeds.
Frequently asked questions
What is the difference between a section 4.55(1A) and 4.55(2) modification?
4.55(1A) is for modifications of minimal environmental impact and is usually not notified and is cheaper and quicker. 4.55(2) is for larger changes that still leave the development substantially the same, is notified in the same way as the original DA, and needs a fuller assessment.
Can I add a bedroom to my approved house with a section 4.55?
Usually yes, under 4.55(1A) if it fits within the approved envelope with minimal impact, or under 4.55(2) if it adds floor area or height. The house remains substantially the same. Adding a whole storey or a second dwelling is generally a new DA.
Can a development consent be modified after the building is finished?
Yes, provided the consent has not lapsed. Post-completion modifications are commonly used to regularise minor differences between the approved and built design, but they are assessed on merit against the controls like any other modification.
Does a section 4.55 modification extend the life of the consent?
No. The lapse date is fixed by the original consent. A modification to a lapsed consent cannot be lodged, and a modification cannot be used to extend or revive one.
Our planners prepare section 4.55 modification applications with the comparison table and the modification SEE that officers expect, and where a change breaches an LEP standard we prepare the clause 4.6 request alongside it. If you need to change an approved house, duplex or granny flat consent in Penrith or anywhere in NSW, our Penrith planning team can advise on the pathway, or you can request a fee proposal.