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Good practice Imported

Oslo's Blue-Green Factor — A Mandatory Stormwater & Greenery Score for New Developments

Norway · Oslo · See the Norway profile · See the Oslo profile

Evidence: Descriptive / self-reported Top 27% 53/100 · Ask Evidence Copilot about this practice

Oslo requires new developments to hit a minimum 'Blue-Green Factor' score for stormwater, vegetation, biodiversity and recreation; a peer-reviewed study found wadi-based measures returned up to 17.3x their cost, and the norm is now a Norwegian national standard.

12.0–17.3
Benefit-cost ratio, wadi-based stormwater measures (Grefsen catchment)

Details

Maturity
Established
Promoter
City of Oslo (Bymiljøetaten / Klimaetaten — Urban Environment & Climate Agencies)
Period
2019–present
Keywords
urban planning, stormwater management, green infrastructure regulation

Context

Oslo's Blue-Green Factor (Overvannsfaktor) has been a binding city planning norm since 2019, requiring new developments to reach a minimum weighted score for stormwater retention, vegetation, biodiversity and recreation elements, with the threshold varying by urban zone.

Results

A peer-reviewed 2022 cost-benefit analysis of six stormwater strategies in Oslo's Grefsen catchment found wadi-based measures returned benefit-cost ratios of 12.0–17.3, and the tool has since been adapted into a Norwegian national standard.

Implementation
Indicative cost
Low (< €50k)
Time to results
Medium (1–3 years)
Staffing & skills
Municipal planning/permitting staff (Bymiljøetaten/Klimaetaten)

Conditions for success

  • Assessment cost (under €50,000) carried by developers through the permitting process
  • Minimum score threshold varies by urban zone to fit local conditions

Commonly funded by

National / regional programmes

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Data sources

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