Sometime next month we're going to be pouring a large concrete transfer slab at the second floor of One Delisle. Its function is to take the loads coming down from the entire tower above it and "transfer" them onto new structural elements, before being brought down to our mat foundation at the bottom of the parking garage.
Put differently -- and, as always, I should warn you that I'm not a structural engineer -- a transfer is used whenever you have a change in your structural grid and the loads don't have a straight path down to your foundations. Because whenever this happens, you're now introducing moment forces and those need to be dealt with structurally.
Transfer slabs are relatively common here in Toronto (which isn't the case in every market), but they are expensive and they consume a lot of depth. In the case of One Delisle, our level two transfer slab is 1.8 meters deep and it's going to contain about 1,200 m3 of concrete. (Some of you might also recall that One Delisle's mat foundation is over 4m deep.)
We were reviewing this with the team today and we think that we'll be able to pour about 100 m3 of concrete per hour. That means that this slab will take about 12 hours to pour! This requires a lot of coordination. Neighbors need to be notified, pumps need to be on standby in case of a breakdown, and so on.
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.
