Section 4.55 Modifications And The Engineering Behind Them

When an approved development has to change in a way its consent does not cover, the developer applies to modify the consent under section 4.55 of the Environmental Planning and Assessment Act 1979. Many of those changes start in the engineering. So the structural, civil and geotechnical effects need to be worked out before the application goes in, not after the council asks.

A modification that is lodged with the engineering already resolved is a short conversation. One that is lodged first and engineered later tends to be lodged twice.

The three paths

Section 4.55 sets out three kinds of modification.

Section 4.55(1) covers correcting a minor error, misdescription or miscalculation in the consent.

Section 4.55(1A) covers modifications with minimal environmental impact.

Section 4.55(2) covers other modifications.

All three rest on the same test. The consent authority has to be satisfied that the development as modified is substantially the same development as the one approved. A change that fails that test needs a new development application.

The construction certificate test

The certifier has to be satisfied that the construction certificate plans are not inconsistent with the development consent. That is where most engineering changes come to light.

A change that stays inside the approved building is ordinary design development. A different slab system, a revised column size inside the walls or a changed reinforcement layout does not touch the consent. A change that alters what the approved plans show, such as the height, the basement footprint, the setbacks or the external appearance, does.

Engineering changes that trigger a modification

A deeper or larger basement. An extra basement level, or a basement pushed closer to a boundary, changes the excavation, the shoring, the groundwater and the effect on neighbours.

A transfer structure that needs depth. Where a transfer level needs a deeper zone than planned, the floor levels above it rise, and so does the building.

Structure that appears on the outside. A column or wall that lands on the facade, in a ground floor opening or in the deep soil zone changes what the approved plans show.

Stormwater changes. A relocated or resized detention tank, or a changed discharge point.

Driveway and level changes. A moved crossing, a regraded ramp or higher retaining walls on a boundary.

What the engineer has to update

The modification package carries the engineering that supports it.

That usually means an updated stormwater plan and detention calculations, a revised geotechnical report where the excavation has changed, and an updated structural statement of the kind described in [structural adequacy reports for a council DA](/blog/structural-adequacy-reports-council-da). If the original consent carried conditions from Sydney Water or Transport for NSW and the change touches them, those agencies see it again.

What a late change costs

A modification takes time to assess, and while it sits with the council the construction certificate for the affected work waits with it.

That is why we push for engineering at the DA stage. Column grids, transfer depths, basement levels and detention tank positions settled before the DA is lodged are changes that never need a modification. The commercial case is set out in [why early engineering involvement saves money](/blog/why-early-engineering-involvement-saves-money), and the working relationship that makes it possible in [how engineers and architects work together](/blog/how-engineers-architects-work-together).

How we approach it

Before a modification is lodged, we go through the proposed change across structure, civil and geotechnical and list what it touches: drawings, reports and authority conditions. Sometimes the engineering can stay inside the consent with a different detail, and when it can, we say so, because a modification avoided is time the programme keeps.

Changes after construction starts follow a separate path, covered in [who is responsible when a design changes on site](/blog/who-is-responsible-when-a-design-changes-on-site). The consent describes a building, and when the engineering changes that building, the paperwork has to change with it.

ACSES provides structural, civil and geotechnical engineering from DA stage through construction across Sydney. Talk to us about a project.

Building Relationships Beyond Structures