What OpenNAT measures
A construction project consumes nature in two places. On its site, it replaces a meadow, a brownfield or a woodland with buildings and planted spaces that will take years to be worth what they replace. Elsewhere, it draws on forests for its timber and on quarries for its aggregates, and its greenhouse gas emissions weigh on the climate.
OpenNAT counts both in a single unit, the square metre of equivalent habitat (m²HE): one square metre of a habitat of maximum quality. A meadow of value 0.5 over 1,000 m² is worth 500 m²HE. The calculation follows the site year by year over 50 years and compares the state without the project with the state with the project. Like the French RE2020 regulation for carbon, it is conventional: it compares projects with one another under common rules.
- Cnat, nature consumed on the site, in m²HE·year.
- Inat, embodied biodiversity of materials and construction works (climate, forests harvested for timber, quarries), in m²HE·year.
- Snat, nature balance of the project: Snat = -(Cnat + Inat).
- Bnat, biotope coefficient of the project state, in points, comparable with the coefficient of the local urban plan (PLU).
A method that can be checked
- Every coefficient carries its value, its uncertainty range, its precise source and the licence of that source: biotope values of the German federal compensation ordinance, the English statutory biodiversity metric, the GLOBIO model, IPCC reports, hourly climate data from Météo-France for the French reference warming trajectory.
- 191 habitat types, each with its condition sheet and maturation times; 70 method conventions, written and numbered.
- A calculation engine whose results are reproduced by a separately written reference workbook, on a test bench published with the code.
- Text and tables under the Creative Commons Attribution 4.0 licence, engine and calculation tool under the GNU Affero General Public License: anyone can read them, rerun a calculation and propose a better-sourced value.
Who does what
- NORMATYS publishes the method, its tables and its engine, and develops them.
- The method is submitted to the Biodiversity Standard Council, scientific and technical committee for the NORMATYS standards, which validates its conventions and thresholds.
- IRICE publishes the calculation tool: project entry, import of the RSEE file of the RE2020 study, calculation, standardised summary and summary sheet.
Reading and quoting a result
An OpenNAT result is the calculation of one project, at a given version of the method and of the data. Until the Biodiversity Standard Council has validated the method, its thresholds are proposals and its results are indicative.
The levels of the calculation, “no net loss” and “net gain”, describe the site of the project calculated. When used in a communication, they come with the version of the method, the scope (the site and the materials of the project) and the values of Cnat and Inat. Recommended wording:
“Calculated with the OpenNAT 1 method, data [version]: Cnat [value] m²HE·year on the site, Inat [value] m²HE·year for materials and construction works.”
Using OpenNAT
The calculation tool and the collected method texts are online at opennat.irice-certification.com, with an account validated by IRICE: project entry or RSEE import, calculation, results, standardised summary and summary sheet in Word. Submitted projects and their results are deleted from the server at the latest 24 hours after the calculation. The interface is in French.
The code, the tables, the text of the method, the user guide and the validation bench are public on github.com/normaxis-group/opennat. The method and its documentation are written in French. For confidential projects, the tool also installs on a workstation (Python): projects then stay on the machine of the person who runs the calculation.
A question about the method or a calculation: contact us.