@Droite
The copyright issue is a red herring, as it relates to the architect's design. Taking a photo of someone's house doesn't infringe the copyright, just as taking a photograph of a book wouldn't infringement the author's copyright.
From my limited understanding infringement relates to
commercial usage, which it is in this case as the images are being sold
but only if the building is still in copyright with the designer not being dead for 70 years.
Buildings are protected by copyright, it is not possible to use a photo of The Shard or The London Eye commercially without permission.
Still in copyright, but you could of St Pauls or Tower Bridge as they are out of copyright. You can take a personal photograph of either buildings for your own Facebook page without infringement as this isn't classed as commercial use.
Taking a photo of a book cover for personal use (or editorial use) isn't infringement, but if you used that image commercially and the book was still in copyright and /or not pubic domain, then it would be an infringement of the artist who designed the book cover.
We don't know the age of the building in question to establish if its Copyright or not so this is just guess work. But if in copyright the artist should seek permission from the architect. Out of politeness they should speak to the owner but i do not think it is a requirement by law.
Putting an address of the building on the paintings being sold would be a different 'privacy' matter, as would the artist going on to the persons property without permission.
As a rule all original creative bodies of work are automatically protected by copyright for 70 years after the authors death.
Interesting side note - the view from the Top of the Rock in NYC is protected by copyright, so if you wanted to take a photo of the Manhattan skyline / buildings from the viewing platform to sell you would require permission.