There is a growing trend in Toronto right now where people want to build on top of existing buildings. We are proposing to do this in midtown at 1 St. Clair Avenue West and, this week, this proposal was announced for the Cambridge Suites Hotel in the Financial District (shout out to Len Abelman).

Generally speaking, this is something that an owner and/or developer might want to do when you have an older building and there is now "unused" density on the site. By "unused" I mean that if you were developing the land for the first time today, the resulting density would be higher than what is currently on the site.

Alongside this, it can also be a way to reposition the existing asset. In the case of the Cambridge Suites site, it sounds like the existing 231 hotel keys will be converted to residential.

At some point in the process you will probably also look at whether it is "better" to tear down the existing building and build new, or whether you should try and build on top. The former is obviously very bad from an embodied carbon perspective but, for whatever reason, this may be the preferred option.

If you decide to build on top, your structural engineer will love you because the result -- for them -- will be a far more interesting project compared to a typical high-rise. But interesting comes with its challenges. Here's how your structural solution might work:

It’s a complicated project that will require a 10-metre-high bridge structure to be built atop the existing hotel where the roof is removed. The bridge will help bear the weight of the new tower, explains Len Abelman, principal at Toronto’s WZMH Architects, the firm designing the redevelopment for the property’s owner, Centennial Hotels Ltd.

“It’s not a common technique, it’s challenging. We worked with a firm called RJC Engineers to do simulations of the massing and loading of weight and the lateral forces the building will face, to make sure it will work,” Mr. Abelman says.

“Other projects in Toronto have added floors before, but it’s usually done with a big exoskeleton that goes over the entire building. This one uses technology that transfers some of the weight to the columns and the floors of the existing structure below,” he says.

This is similar to what we are doing in midtown, except that we are proposing to retain all of the the existing facades along with the building. It is certainly not the easiest way to build. But we are likely to see more, not less, of it in the city.

It is evidence of the immense development pressures that certain areas of our region are facing. When you restrict new supply, the market will find somewhere to build, even if it involves a lot of structural gymnastics.