The Piazza Homes comes with the special set bonus. When it is adjacent to other buildings belonging to the Piazza Set the properties of the building are improved.
The Piazza Homes can be upgraded by Piazza Homes Upgrade Kit item. To upgrade the Piazza Homes, use the Piazza Homes Upgrade item on the Piazza Homes that is already situated in your city. Its upgraded version will then be placed directly on the same spot in your city and the production timer will not be reset. Note that the upgraded building will be from your current era, even if the old one was from one of the earlier ages.
Piazza Homes will produce the following effects. Base effects will always be produced. Bonus effects are determined by how many other unique Piazza Set buildings it is connected to.