If someone in your household already pays the Rundfunkbeitrag, you are exempt from paying a duplicate. The principle of ‘one household — one contribution’ works in your favour.
What you need
Ask your roommate for their Beitragsnummer (10-digit number on any letter from the Beitragsservice). Then fill in the ‘Befreiung oder Ermäßigung beantragen’ form on the website and select the option for living with an existing payer.
Important
You may still receive invoices before the exemption is confirmed — don’t panic. Once processed, all charges will be cancelled retroactively.