Today we are pouring our massive level two transfer slab at One Delisle. Delisle Avenue has been temporarily closed and the first concrete truck arrived at 6 AM. We're currently averaging about 100 m3 per hour. There's also a bit of light rain in Toronto right now, so that should help keep the slab cool. We're a few weeks later than we were initially targeting back in June, but a lot of coordination has gone into this one slab. Our level three slab is also somewhat unique because of the double-height pool space and the gym; but following that, we're on to our "typical" floors. And by "typical", I mean as typical as one gets on a project like One Delisle.

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.

Another major consideration is heat. When concrete cures it generates a lot of it. And with a thick slab like this one, I am told that we run the risk of the middle starting to overheat (especially with the hot weather that we've been having lately). The guideline limit is 60 degrees Celsius, so we'll be monitoring it for probably about 1-2 weeks following the pour.

I find these details fascinating. Maybe some of you do too. So once it's poured, I'll share a few photos.

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.