# Sustainability API v2 Delta for Apartments

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This Delta variant builds on the [Sustainability API v2 for Apartments](https://docs.altum.ai/english/sustainability/sustainability-api-v2-apartments).\
For authentication, base endpoints and full documentation, see the main [Sustainability API v2](https://docs.altum.ai/english/sustainability/sustainability-api-v2) page.
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## Introduction

The **Sustainability Delta API** from **Altum AI** empowers professionals in the Dutch housing market to assess sustainability upgrades with precision. Built on the **new NTA 8800 energy label norm**, the API flips the traditional analysis approach: instead of starting with existing measures and calculating improvements, users can now **define their target measures directly**.

The API then calculates the resulting **energy label**, along with:

* **Investments required** per measure (€)
* **Expected savings** (€/year and CO₂ reduction) per measure
* BENG2 improvement per measure
* Annual and monthly savings in **€** on energy bills and ROI (%)
* Gas, electricity, city heating usage
* **Impact on property value**