hadw
6
You would need to read the licensing carefully, as you would have created a derived work, and would be required to publish that, under some circumstances. You would need to determine whether you were publishing the derived work or making the data available. http://wiki.openstreetmap.org/wiki/Legal_FAQ#3b._If_I_have_data_derived_from_OSM_data.2C_do_I_have_to_distribute_it.3F
You may need to take this up with the Licensing Working Group: http://wiki.openstreetmap.org/wiki/Legal_FAQ#5a._I_have_questions._Can_you_answer_them.3F
Also, as Portugal is part of the EU, it will have similar data protection legislation to that in the UK, so making personal information available to anyone other than person submitting and the emergency services would probably be a breach of the relevant law. Unless there is some specific exemption, you may need to register under the relevant legislation. https://www.cnpd.pt/english/bin/legislation/Law6798EN.HTM
At the moment, I can’t see any reason why you couldn’t publish a derived work that contained personal data, from an OSM licensing point of view, even though that could not be merged back into the main OSM.
Although it would be more work for you, it would be better if adding houses was done on the main OSM database, and your shadow database only contained the additional attributes. The two could be linked by the object identity, which would avoid contaminating the main map, but would make you more vulnerable to people deleting and re-adding (which is bad practice), or you could have some correlator in the main database. Whilst overuse of that, e.g. by normal businesses, might be frowned upon, your use case might be more acceptable, but I wouldn’t want you to do it just on my opinion.
There may already be some form of national identifier for buildings (although, in the UK, the one that exists is proprietary, and cannot be used on OSM).