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
BRANDON DONNELLY 
Brandon
Many many years ago we added a residential tower to the roof of a major library branch on Orchard View Boulevard in the Yonge Eglinton area. In this instance we had medium difficulties because the library had been designed in anticipation of an office tower and was laid out with a column grid for that purpose and we had to create a residential plan using the grid. Most buildings would not be viable for this sort of thing if they are designed to take this additional load in the first place and it takes a visionary owner to pay for the extra structure going in. As well since this was a seniors building and our parking requirements were very low and we could get them into the existing underground garage.. This would be another or perhaps the real deal breaker for most buildings..either building a lot of expensive spots in advance or getting a reprieve when the building grows. One of the objectors was a local McDonalds who complained that this building would increase local traffic…I loved that one, especially since we were providing them more customers within a 5 minute walk! There is an image here
https://www.google.com/search?newwindow=1&hl=en&tbm=isch&source=hp&biw=1280&bih=587&ei=ZOxfXeL6IcO0tQWc8YTIAQ&q=stanley+knowles+housing+coop+toronto&oq=stanley+knowles+housing+coop+toronto&gs_l=img.12…1500.10577..14429…0.0..0.276.4984.14j16j6……0….1..gws-wiz-img…….35i39j0j0i10j0i24j0i30.lVfkJWQc52s&ved=0ahUKEwjivMXmjpnkAhVDWq0KHZw4ARkQ4dUDCAU#imgrc=NvasdWIHHujnbM:
or since this is a muddle you can enter Stanley Knowles Housing Coop Toronto in Google images and you will see what I mean
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