BlueFactor Calculator Explained: What Replaced STORM in Victoria
The aim didn't move, the tool did
For years, a Victorian planning permit that mentioned stormwater meant a STORM rating. That tool was retired on 14 October 2025. DEECA replaced it with the BlueFactor calculator, and the goal behind it is the same one STORM chased: less impervious area on the site, less fast runoff leaving it.
A permit condition written against the old STORM rating is now assessed against BlueFactor.
When BlueFactor applies, and when MUSIC still does
The BlueFactor calculator is now the standard stormwater assessment tool for sites under one hectare: single dwellings, townhouse and unit sites, most small commercial jobs. That's what a council officer or certifier will expect for a site that size. Push past one hectare, or into a larger and more complex development, and MUSIC modelling still applies; BlueFactor hasn't replaced it there. A job sitting near that line is worth a call to a town planner or the council's duty planner before the design goes further, because the choice of tool changes what your engineer has to produce.
What a permeable driveway or car park does to the number
Sealed concrete sheds rain straight into a pit. Permcon doesn't. Water passes through a slab holding 20 to 25 per cent void content into a base of clean screenings, which stores it, lets it soak into the subsoil, or releases it at a controlled rate. Treated as pervious in a passive design, that area comes off the impervious side of the ledger, and the tank or rain garden the tool calls for can shrink with it, sometimes enough to drop a detention structure from the design altogether.
We won't call a BlueFactor score before we've seen the site. It moves with total impervious area, soil, how the base is built and what else sits on the block. Get the permeable area modelled into the assessment before the design is locked in; that's the only figure worth trusting. Where a job needs MUSIC instead, Permcon is MUSIC certified, and we can supply the parameters.
The jobs we're building this into
In Victoria that means car park pours and driveway packages for sites under one hectare, the bracket BlueFactor sits over. Both give the stormwater engineer more room once sealed pavement comes out of the plan. Our commercial properties page covers how we work alongside developers and builders on jobs like these.
One thing no calculator checks
Neither BlueFactor nor MUSIC accounts for upkeep. A Permcon surface keeps its rated drainage only while the voids stay open. That means a look once a month. Keep leaves and garden soil off the slab, and give it a proper sweep once a year. Slow drainage after neglect recovers with a wash; the number your engineer modelled with assumes the surface keeps draining as designed.
Ring 1300 010 499 and we'll talk through where permeable concrete fits your BlueFactor or MUSIC job.