# Sustainability API v2 Delta for Apartments

{% 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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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.altum.ai/english/sustainability/sustainability-api-v2-apartments-delta.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.