Insights / Stormwater
What is a Blue Factor score?
It tells council how much of a site’s stormwater nitrogen load the design treats. 100% or more meets the target.
The free state tool that replaced STORM.
What the number is
A Blue Factor score is the result of the Blue Factor stormwater assessment, the free state tool that replaced STORM for Victorian planning permits. It is calculated on total nitrogen. A score of 100% or more means the nitrogen reduction target has been met, and a small, low-risk project is deemed to comply.
What else the result shows
The result screen also reports suspended solids, phosphorus and nitrogen, gross pollutants, and the share of runoff harvested and infiltrated.
The two runoff targets change with the site’s location, so they are read from each site’s own result, never from a general table.
Four things move the number.
How much roof reaches a tank
Every roof connected to a tank is treated area.
Whether the tank is used
A tank plumbed to the toilets and laundry empties between storms, so it has room to catch the next one.
Raingardens for paving
Driveways and paths drained to a raingarden sized at about 2% of its catchment, more where volume is short.
The take-off
Each surface is measured separately, one catchment per surface per dwelling. Lumping the site into one figure is what councils query.
In the cheapest order.
- Connect more roof to the tank and plumb it in.
- Take a larger tank where the drawings allow.
- Enlarge the raingarden toward 3 to 5% of its catchment.
Raingarden size as a share of the catchment it drains.
Blue Factor is built for small developments, up to about one hectare with no internal roads. Larger sites use MUSIC modelling instead.
Sources: Blue Factor (DEECA), Melbourne Water raingarden guidance, Victoria Planning Provisions Clauses 53.18, 55.05-1 and 56.07-4. General information, not an assessment of any particular site.
Common questions
What does a Blue Factor score of 100% mean?
The design treats enough of the site's stormwater to meet the nitrogen reduction target.
For a small, low-risk project that is enough to be deemed to comply.
Why is the score based on nitrogen?
Blue Factor calculates its single score on total nitrogen.
The result screen still reports suspended solids, phosphorus, gross pollutants and runoff, so the whole picture is there.
How do you raise a Blue Factor score?
Connect more roof to a rainwater tank and plumb the tank to the toilets and laundry, use a larger tank, then add or enlarge a raingarden.
A tank that is not used for anything does little.
Do the runoff targets change between sites?
Yes.
The harvested and infiltrated runoff targets change with the site's location, so they are always read from that site's own result.
Need a Blue Factor report?
For townhouse, dual occupancy and small commercial applications under Clauses 55.05-1 and 53.18, built to reach 100% properly, within 48 hours.
Which reports does my job need?
The usual list, from each council’s planning scheme and website.
Step 2: a quote or fee proposal for this list. Name and email are enough; the drawings can come later.
Get a price for this listOr call 0470 389 168Tell us about the project.
A quick quote from your plans, before any work starts.
Quick quote from your plans. Planning and residential reports within 48 hours; Section J, CMP and GTP within 72 hours.
Start here
See which reports your job needs, then get the quote for that list.
- What will it cost?
- A quick quote from your plans, before any work starts.
- Will council accept it?
- Every report is written to the council’s own policy or the NCC edition that applies.
Beyond Green Energy Assessments