The quality of your registration as principle or secondary residence (HauptwohnsitzHauptwohnsitz Your Hauptwohnsitz is your principle place of residence, i.e. where you typically have the centre of your vital interests. Other residences are known as Nebenwohnsitze. or NebenwohnsitzZweitwohnsitz Secondary places of residence (e.g. holiday homes that you spend some time in yourself, pied-à-terres, granny flats) are known as Zweitwohnsitze (in legal terms) or Nebenwohnsitze (in common parlance). While you may reside at a secondary residence for part of the time, it does not constitute the centre of your vital interests. It is of course possible to change your residence status (i.e. from your Zweitwohnsitz to Hauptwohnsitz - known as Ummeldung) to reflect changes in circumstances, although you should be aware that "flipping" is not intended for short-term changes and that doing so can affect the status of grants etc. contingent on the location of your vital interests. respectively), is not decisive, but your actual residency in Austria. If you spend most of your time in Austria each year (more than 6 months) and wish to continue to live here you will have to apply for an “Art 50 EUVAufenthaltstitel "Artikel 50 EUV" The Aufenthaltstitel "Art 50 EUV" is a residency title to be issued to British citizens from the end of the transition period. Its name is derived from Article 50 of the Treaty on European Union. The "Titel" refers to the document or card itself, and not the right, or permission that it confirms.” card by the end of 2021, or for an Austrian non-EU residence permit which is restrictive and difficult to get. If, you only visit say a couple of times of year (e.g. to spend a vacation in a holiday home) and don’t spend most of the year in Austria, then you are not covered by the Withdrawal AgreementWithdrawal Agreement The Withdrawal Agreement sets out the terms of the UK’s withdrawal from the EU and provides for a deal on citizens’ rights. It sets out a transition period which lasts until 31 December 2020. During this time you can continue to live, work and study in the EU broadly as you did before 31 January 2020. If you are resident in Austria at the end of the transition period, you will be covered by the Withdrawal Agreement, and your rights will be protected for as long as you remain resident in Austria. Any rights that are not covered by the Withdrawal Agreement will be the subject of future negotiations. https://www.gov.uk/government/publications/new-withdrawal-agreement-and-political-declaration and will have to apply for a residency title under the Settlement and Residency Act (NAGNiederlassungs- und Aufenthaltsgesetz The Niederlassungs- und Aufenthaltsgesetz (Residency and Settlement Act) is the Austrian law governing residency for foreign citizens in Austria.; Niederlassungs- und AufenthaltsgesetzNiederlassungs- und Aufenthaltsgesetz The Niederlassungs- und Aufenthaltsgesetz (Residency and Settlement Act) is the Austrian law governing residency for foreign citizens in Austria.).
Further information about the various residency permits in Austria can be found at: https://www.migration.gv.at/en/welcome/?no_cache=1