Parasitic architecture sounds like a bad thing because of the connotations, but you could make an argument that it is, in fact, the exact opposite. It is a way to better leverage existing structures and reclaim under-utilized urban spaces. Perhaps additive architecture would be a more appropriate name.
Here's one example. WARchitect recently completed this "skyscape apartment" on top of an existing 5 storey apartment building in Bangkok. It's about 1,600 square feet. And the entire space is organized according to the structural grid of the apartment building below.
Many/most structural systems have excess capacity because of a built in factor of safety. So for a small addition like this, I'm guessing that they probably just loaded up the existing column grid. It also looks like there were already stairs leading up to the roof of the building.
Years ago I looked at doing an addition on top of an existing apartment building here in Toronto and it ended up being a lot more complex than I may be making it out to be in this post. Mind you, we were looking at adding on a few floors, which triggered all sorts of issues.
But now that Toronto is allowing accessory dwelling units along its laneways, is it time that we also look at the rooftops of our existing buildings?
Photo: Rungkit Charoenwat