In many American suburbs, nearly-identical homes line neatly organized streets, all with nearly-identical landscaping and fencing in colors approved by the local homeowner’s association. There isn’t a lot of room for creativity and experimentation. So when homeowners decide it’s time to build an addition, they usually have little choice but to go with the prevailing style. Some may argue that such limitations keep the neighborhood looking uniform and tidy. Others find it all terribly boring. With “House on House,” New York-based studio Architensions took a more daring approach.

There’s nothing conventional about this second-floor addition to a compact house in the Babylon area of Long Island, New York. Not only does it flout the very modest conventional styling of the existing home, it looks like an entirely different home was just plopped right on top of it. That effect is intentional. The architects didn’t want the home to simply blend in, but rather offer a contrast of past and present, both visually and programmatically. While the original home is clad in light gray vinyl siding, the addition features thick stucco exterior walls. The two volumes are merged together by a splash of pale pink tiling flowing across the facade.
The client didn’t care much about resale value, opening up the potential for the architects to experiment. Instead, he asked them to update the original layout of the existing home and draw down some ...