This €500 million ($539 million).bond was a pioneering joint initiative by the development banks of the German federal states of Brandenburg, Hamburg and Rhineland-Palatinate.

It was the first joint, cross-state and social bond to be issued in Germany.

Environmental Finance Bond Award judges praised the bond for having what they described as a "very interesting and noticeable structure" that brought together multiple institutions with a clear objective to target social housing, and said the bond was well worthy of first place.

Its goal was to refinance affordable housing projects – especially social rental housing and the construction of owner-occupied housing.

The three development banks involved agreed that affordable housing was a nationwide concern for Germany that cut across state borders, and that having an impact would require a collective effort to provide the right finance.

The multi-state support provided by this bond issuance was targeted specifically at people affected by or threatened with poverty, such as the elderly, people with disabilities, students and households with children.

Christina Tyca, product lead, second party opinions and sustainability analyst at imug rating, said to Environmental Finance: "With the consensus that affordable housing is a cross-state concern, the banks have served a social benefit beyond state borders.

"The issuance demonstrates how successful joint efforts by financial institutions can be in addressing nationwide challenges in favour of vulnerable groups.

"We were very pleased to facilitate the project by providing guidance and independent assessment in the form of a second party opinion. The positive feedback on our assessment process, which the banks perceived as very structured and transparent, was especially rewarding."