As planned, we continued to develop our business in the Value-add Business segment. The increase in the output of our craftsmen’s organization once again significantly contributed to this trend and allowed us to continue our investments in improving our portfolio. In addition, we also continued to expand our business activities in the areas of condominium administration, the provision of cable television to our tenants, metering services, and insurance and residential environment services in the 2018 reporting period. As a leading real estate service provider, Vonovia Immobilien Treuhand now provides services to a total of around 107,000 units, of which 83,628 are apartments managed for third parties.
External revenue from our Value-add Business activities with our end customers rose by 8.6% from € 115.1 million in the first nine months of 2017 to € 125.0 million in the first nine months of 2018. Group revenue rose by 28.9%, from € 680.3 million to € 877.0 million in the same period. Overall, this results in a 26.0% increase in the revenue from the Value-add Business from € 795.4 million in the 2017 reporting period to € 1,002.0 million in 2018. The adjusted EBITDA Value-add Business was up 19.3% year-over-year to € 90.7 million in the first nine months of 2018.
The EBITDA margin of the core business, calculated based on the adjusted EBITDA Operations in relation to rental income within the Group, once again showed positive development in the reporting period. It rose from 73.6% in the same period of 2017 to 75.7% in the first nine months of 2018.