At the end of the 2017 fiscal year, our housing stock in the Rental segment had virtually full occupancy. The apartment vacancy rate came to 2.5% at the end of the year, virtually level with the prior-year value of 2.4%, with around 1 percentage point attributable to construction-related vacancies due to our extensive investment program. Rental income rose by 8.4% from € 1,538.1 million in the 2016 fiscal year to € 1,667.9 million in the 2017 fiscal year. This corresponds to an average monthly in-place rent of € 6.27/m2 at the end of 2017, compared with € 6.02 €/m2 at the end of 2016, and to an overall increase in rent per square meter of 4.2% (2016: 4.7%). The increase in rent due to market-related factors came to 1.6% (2016: 1.5%). In addition, we were able to achieve an increase in rent of 2.5% thanks to property value improvements achieved as part of our modernization program (2016: 1.8%). If we also include the increase in rent due to new construction measures and measures to add extra stories, then we arrive at an organic increase in rent of 4.2% (2016: 3.3%). The corresponding like-for-like increase in rent came to 4.1% in the 2017 fiscal year (2016: 3.3%). The average monthly in-place rent in the conwert portfolio came to € 6.06 m2 at the end of the reporting period.
As planned, we increased our modernization and maintenance measures significantly to a volume of € 1,124.8 million in the 2017 fiscal year (2016: € 792.4 million). This was driven primarily by the increase in the modernization volume from € 472.3 million to € 778.6 million. In the 2017 fiscal year, a volume of € 52.5 million was attributable to modernization and maintenance measures in the conwert portfolio.
In relation to the average number of apartments managed during the reporting period, this corresponds to spending on modernization and maintenance of € 51.00 per m2 in the 2017 fiscal year (2016: € 36.84 per m2).
A total of € 65.7 million was invested and settled in relation to the construction of new apartments in the 2017 fiscal year (2016: € 13.9 million). A total of 182 apartments were completed during the reporting period. In addition, 443 apartments accounting for an investment volume of around € 80 million were under construction at the end of 2017. In its new construction activities, Vonovia is placing particular emphasis on targeted densification and vertical expansion using prefabricated modules and the following three modular construction concepts: wood hybrid, steel skeleton and precast concrete construction.
In the 2017 fiscal year, operating expenses in the Rental segment were up by 6.3% on the figures for 2016, from € 244.5 million to € 259.9 million, mainly due to acquisitions. All in all, adjusted EBITDA Rental rose by 9.9%, from € 1,046.2 million in 2016 to € 1,150.0 million in 2017.