Under Decree 21/2001/ND-CP, dated May 28, 2001 detailing the implementation of the Ordinance on Entry, Exist and Residence of Foreigners in Viet Nam,
1.Foreigners who stay overnight at hotels or residential quarters reserved for foreigners (including residential quarters of the diplomatic corps) shall have to make temporary residence declaration through the hotel owners or residential quarters' managers.
The hotel owners or residential house quarters' managers shall have to transfer contents of temporary residence declaration by foreigners to the migration management units of the police of provinces and centrally-run cities.
2. Foreigners who stay overnight at private houses of local citizens shall have to personally or through house owners make temporary residence declaration with the police offices of wards or communes where they temporarily reside.
The ward or commune police officers shall have to transfer contents of temporary residence declaration by foreigners to the migration management units of the police offices of provinces or centrally-run cities.
According to item c, chapter 3 of Circular 04/2002 guiding the implementation of the Government’s Decree 21/2001-ND-CP, detailing the implementation of the Ordinance on entry, exist and residence of foreigners, foreigners who stay overnight at private houses of their relatives shall have to personally or through the house owners, make temporary residence declaration at ward or commune police offices.
The Circular stipulates that “private houses of their relatives” are not “private houses of local citizens”.
Accordingly, the relations between you and your friend are colleagueship not relative relationship. Hence, you must have a business certificate of rental housing certificates for foreigners if you want to temporally live with a foreigner./.