6.5K 
Our previous edition of Explainer described how fly forms are used to quickly create new repeating floor-plates for tall buildings, but as construction soars above grade on multi-storey developments — especially those with large podiums — these buildings often have very different locations for walls and columns on the upper storeys. In such cases, these buildings require special infrastructure to transfer the massive loads from the walls and columns above to the walls and columns below: ultimately, the upper storeys depend upon the foundations and substrate below.
In order to facilitate a load transfer, a tabletop-like slab is constructed out of far more than usual concrete, steel rebar, with post-tensioned tendons often added, than the average floor slab would require. Called a transfer slab, the complex undertaking is one of the most important — and longest to complete — tasks in the construction of a multi-storey building.
At Sugar Wharf Condos in Toronto, seen above, the two towers each needed a transfer slab above the podium-top amenities floors of the complex's base. Above left, you can see the northwest tower with its recently completed transfer slab having its first tower level forms erected, while above right, seven storeys have been built atop the southeast tower. (Both towers have since topped out, at 64 and 70 storeys respectively.) The 4.5-metre-thick slabs here each took a few months to complete, whereas the regular floors above went up at about a floor per week on average.
When only part of a building is unsupported directly below it — sometimes owing to a cantilever, sometimes because of a pass-through — only transfer beams are required. In the image below, a number of chunky transfer beams can be seen taking the loads from columns above at Totem Condos in Toronto, completed a few years ago, and transferring them down to columns and walls in places that make the ground level work better.
Another type of situation that requires load transfer is on the verge of becoming commonplace in Toronto as well, where existing tall buildings are proposed to have additional floors built above. Several such proposals are now being considered for intensification projects along University Avenue, and one recently completed project of this type is its poster child: at The Residences of 488 University Avenue by Amexon, 37 new storeys were recently constructed above an existing 18-storey office building. To accomplish that, a massive transfer slab was needed. In preparation for this feat, vertical steel beams along with diagonal cross bracing was installed around the existing building's perimeter (once its original cladding was removed) to support the additional floors.
Above, new cladding is already being installed over the existing building's lower levels, and temporary white walls can be seen behind the new steel framing. Below, over a full year after the image above was taken, the transfer slab was complete atop the original building, the original building was fully reskinned, and the first level of walls were just being formed above.
Below, a short while later, the first three floors above the thick transfer slab have been completed, and a fourth is under construction.
Finally, the completed structure a couple years later, supported on the huge transfer slab, and now with places for people to live as well as work.
Have any other construction and development related terms that you would like to see featured on Explainer? Share your thoughts and questions in the comments section below!
* * *
From 2015 to 2017, UrbanToronto and its sister publication, SkyriseCities, ran an occasional series of articles under the heading Explainer. Each one took a concept from Urban Planning, Architecture, Construction, or other topics that often wind up in our publications, and presented an in depth look at it. It's time to revisit (and update where necessary) those articles for readers who are unfamiliar with them. While you may already know what some of these terms mean, others may be new to you. We are publishing or updating and republishing Explainer on a weekly basis. This article is an update of one that first appeared in 2015.
* * *
Do you have other planning terms that you would like to see featured on Explainer? Share your comments and questions in the comments section below!
* * *
Want to read other Explainers? Click on the magenta Explainer box at the top of the page.
* * *
UrbanToronto has a research service, UrbanToronto Pro, that provides comprehensive data on construction projects in the Greater Toronto Area—from proposal through to completion. We also offer Instant Reports, downloadable snapshots based on location, and a daily subscription newsletter, New Development Insider, that tracks projects from initial application.
