The skyline of Montreal is home to a new member of the Hilton Hotels family, the Hilton Garden Inn, with 37 above-grade floors that employ a variety of colours on two colour precast panels — light beige, with both heavy and light sandblasts, and black-pigmented with acid wash. The 36-month construction schedule saw the precast panels erected in six months in the $67-million combination hotel and residential structure. But the real story was in the use of Slenderwall® studcast panels that reduced the dead load of the structure by some 50 per cent!
The plan from the beginning was always to design the building for precast and glass, and there are traditional precast panels as well as lightweight panels on the building. In some locations — mostly near the base of the structure — traditional, heavier precast was used for logistical and structural reasons. For example, according to Construction Canada magazine (Jan. 2010, Vol. 52, No.1) panels near the ground floor had granite veneers cast into them, and it was felt that the thicker panel would hold the stone better. Thicker panels were also used beneath windows where the windows rest on the curtainwall panel. In the end, however, of the 10,700 square meter (115,000 square feet) of panels cast, fewer than 20 per cent of them were conventional thick panels.
The remainder of the building was clad using Slenderwall panels. “We had a certain limitation on the site because it is an infill site,” says Eric Huot, Partner with Geiger & Huot Architects, “and because of the technical constraints of the location for the tower crane, we had to go to a very lightweight precast panel — because I think that at the end of the boom, we had something like a 12,000 pound capacity and a traditional panel would have been way over that.” That requirement led to a relationship with Montreal’s Betons Prefabrique du Lac (BPDL) to supply the Slenderwall studcast product.
It wasn’t just weight considerations that made the studcast panels an ideal fit for this project; there were time considerations as well. “The precast allowed us to close the building (quickly)”, explains Richard Varadi, Project Manager for contractor Groupe Canvar. “It’s a high building and we couldn’t wait until (the frame) was all the way to the top to start closing it off so precast really became our only option. So, as we were going up the building, we were able to close it off floor-by-floor, and then follow pretty quickly with windows, insulation and so on. It was a good match between our needs and what the precast offers.”
Still another advantage that the Slenderwall studcast brought to bear of the Hilton project is the space saving realized within the envelope itself; “keeping dimension”, as Robert Bouchard, Vice President and General Director of precast contractor BPDL puts it. “They sprayed the insulation directly between the sill-ed stud and the Slenderwall product, and then they put the drywall on that frame,” he explains, “and that saved space because normally for a job like that, we’d need to use 150 mm (six-inch) concrete precast and they’d also need to build a 100 mm (four-inch) drywall stud. With this system, they use the stud as well as part of the mechanism to insulate the panel.” Bouchard notes that the initial cost is a little bit more expensive, but using larger size panels reduced the overall cost per square meter, with costs further offset by reduced transportation costs with fewer panels being trucked to the site.
Beyond the mechanical and logistical advantages of using precast, the most obvious reason to use it is simply that it can do things that no other cladding material can. “There is a very slight curve to both sides of the building,” notes Huot, “and it cantilevers out at either end, and in deciding on the cladding of this building, we knew we wanted a masonry look, and the precast was our number one choice because it gave us the opportunity to create this curve in a very standardized way, and it gave us the appearance of having a stone cladding on the building — in texture and colour as well.”
In short, precast means possibilities. “As a designer,” concludes Huot, “we want to have every possible tool to work with because sometimes you scribble an idea down on paper, but then you have to make it happen, and because of precast, the more choices you have, the easier that is to do.”
ARCHITECTS: Geiger and Huot Architects
DESIGN TEAM: Eric Huot, Mélanie Sarrasin, Lauren Gonzalez
INTERIOR DESIGN: Geiger and Huot Architects
STRUCTURAL ENGINEERS: Pasquin St-Jean Ass.
MECHANICAL AND ELECTRICAL ENGINEER: BPA
CONSTRUCTION: Groupe Canvar Inc.
PRECASTER: Prefabriques Du Lac Inc. (BPDL)