Purchasing an apartment occurs on the day that you sign the bill of sale on your apartment. This is not the same as the date on which the ownership of the apartment is transferred to you. The ownership of the apartment may be transferred to the buyer later due to the remaining sale price of the apartment being paid later when the apartment is assigned to the buyer, for example. For those who are building a detached house, the apartment is deemed purchased when they start construction. Construction is deemed started when the casting of the foundation is started or the installation of the structural parts of the foundation is started. This is verified by providing a statement from the municipal building inspector, or in some other reliable manner. For those who are buying a prefabricated house, the home is deemed purchased when the prefabricated house is bought.