> For the complete documentation index, see [llms.txt](https://docs.altum.ai/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.altum.ai/english/sustainability/sustainability-api-v2-apartments-delta.md).

# Sustainability API v2 Delta for Apartments

The Sustainability Delta API bridges technical upgrades with financial impact, enabling data-driven sustainability decisions across the Dutch housing ecosystem.

{% hint style="info" %}
This Delta variant builds on the [Sustainability API v2 for Apartments](/english/sustainability/sustainability-api-v2-apartments.md).\
For authentication, base endpoints and full documentation, see the main [Sustainability API v2](/english/sustainability/sustainability-api-v2.md) page.
{% endhint %}

## 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**


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