Building it Right on a Tight Site
In the downtown urban environments of today, real estate is hard to come by and increasingly expensive. As a result, every available space, no matter how small, is being investigated for potential development. With more and more people wanting to migrate to the center of cities to take advantage of urban lifestyles, architects and developers are being challenged to adopt to new standards of ever-increasing density in non-expanding spaces. Enter the “tight site” development.
Tight site buildings are popping up in many downtown cores and may prove to be a partial answer to the need for more downtown living space. These skinny building utilize a small land footprint that might not have been considered for development in the past and maximize it by going up while trying to utilize as much of the limited space as possible. Think high density living in micro spaces and you’ve got the picture. This presents some very interesting challenges to designers. How best to get the most out of the least?
When it comes to concrete, conventional construction techniques are better suited to larger projects and often don’t work well within the tight site format. Typical cast-in-place, one-sided formwork for foundation walls takes up much of the limited site space available making a small footprint even smaller. Forms with one sided braces must be assembled, placed, then once concrete cast, moved and stored out of the way until the sequence for pouring concrete is ready again. Once work on the suspended slab has started, there is nowhere for the formwork to go; either it is stored on site, limiting the size of a suspended slab that can be poured or the panels are disassembled, by taking the one-sided braces off, and loaded onto a truck to be removed to a storage yard and then trucked back in. This can dramatically increase construction costs and schedule length.
Pneumatically Applied Concrete (PAC) or shotcrete as it’s commonly referred to, completely eliminates the need for exterior forms. It eliminates the need for storage of forms, movement of the crane to other locations and the time and cost to truck them back to the site.
The advantages of utilizing shotcrete are also evident as work reaches ground level and then continues above grade into the tower. Placing exterior concrete walls against existing buildings was previously achieved in one of two ways. The first was to put a form in behind and cast in place conventionally with two-sided forms – a methodology that substantially reduces the amount of usable square footage in the building.
The other way was to use what was commonly referred to as blind formwork, where thin forms were placed at the back/exterior and had hook ties wrapping around to the front where it was tied off. Less was room required, but the formwork had to be left in place in between the new structure and the old.
Both of these practices still exist, but each has a major drawback; it’s not possible to use an envelope to waterproof the exterior utilizing drain mats and water proofing material. Once cast, there is no way to get behind and waterproof. With shotcrete, waterproofing material is pre-applied against the existing building. Once completed, reinforcing is placed and then concrete is pneumatically applied or “shot” against the reinforced wall. No forms are needed and because the waterproofing is applied prior to concrete placement, the building is waterproof once the concrete is applied.
Additionally, shotcrete walls can be thinner without sacrificing strength. With shotcrete, the gravel in the concrete mix is smaller than with a conventional mix allowing for increased cement in the mix. More cement means stronger concrete: 35 MPA shotcrete mix has a typical MPA rating of 45. The end result is a stronger wall that doesn’t need to be as thick as a cast in place wall to provide the same structural strength. There are no form lines, no penetrations from anchors to hold the panels, and the steel-trowelled finish results in a smooth surface that’s ready for paint with no rendering required.
Thinner, stronger walls result in more functional space. Space that can be used for additional parking stalls or a fully functional car ramp rather than an elevator. This is the beauty of shotcrete for tight site buildings: more efficient construction methods that result in larger living spaces.
Increasingly, developers are seeing that shotcrete is really the only way to maximize the minimum when it comes structural concrete requirements for restricted footprint developments.
Torrent Shotcrete is the innovation leader in the structural concrete industry with a wide range of award-wining experience and expertise in commercial and residential construction. We’ve helped hundreds of clients across Canada get more top quality work done in less time which adds up to projects coming in ahead of schedule. Everyone wins.
The Torrent difference? It’s really quite simple. More wall. Every day.