Factory-built modules cut construction time on site
By Jim Taggart
The King William Street project provides housing for those who are experiencing or are at risk of homelessness. The project demonstrates that equitable access to
housing is possible by transforming a
former urban surface parking lot into a
welcoming and dignified place to call home. The three-storey building accommodates 24 studio dwelling units along with shared amenities on the ground floor, which include a community room, meeting room, lounge, and laundry facility.
Why Prefabrication?
The project began during Covid, when there was a desperate need for truly affordable housing. As it progressed, it became apparent that the greatest immediate need was for supportive housing.
The City of Hamilton drove the discussion on the benefits of prefabrication as it wanted rapid delivery and cost control for this project. As clients, CityHousing Hamilton has a history of researching and implementing innovative solutions, both in the delivery method (such as off-site prefabrication) and performance standards (such as Passive House certification).
Materials and Methods
Stick frame was chosen for the construction as it is less carbon intensive than cross laminated timber and has a proven track record for projects of this scale.
In fact, this became an example of two-step prefabrication, as the 2×6 stick frame elements were prefabricated in a factory by Panels.ca, and shipped in ‘flat packs’ to NRB/ATCO for assembly into volumetric modular units.
Converting the 2D units into 3D modules in the factory is a relatively recent approach to stick framing but is becoming a preferred solution. The NRB/ATCO factory is arranged in a series of workstations, with the modules being moved from one station to the next as the construction sequence progresses. NRB/ATCO first erected the frames, then installed the batt insulation, interior finishes, service lines and rigid exterior insulation, using Thermowall PH Panel by Legalett.
Before the units left the factory, they were fully finished on the interior, including fixtures and equipment. The delivery of the wall elements and other items to the factory location, rather than the project site, reduced the construction time of the project on site.
Transportation Constraints
When using off-site modular construction, transportation constraints determine the maximum width and height of the modules that can be shipped without a permit. In Ontario, those limits are maximum height 12ft (3.66m); maximum width 8ft 6in (2.59m) and maximum single vehicle length 40ft (12.2m). Over-sized loads require permits, and may also require road closures and police escorts, increasing the time and cost of transportation.
For this project the standard width of modules was 14 feet (4.27m) which required a permit and vehicle escort, but no road closures or police escorts. The module provider drove the route from the factory to the project site, to ensure that delivery would be feasible, and to determine whether alternative routes were available. NRB/ATCO also organized the appropriate permits.
It is important that the dimensional limitations are discussed with the client at the schematic design stage to ensure that the programmatic requirements of the building can be met within the cost and schedule constraints of the project.
The large ground floor multipurpose room was designed to be three modules wide, with large openings through the demising walls. These openings had to be temporarily filled in to facilitate transportation, then reopened when the modules were installed on site.
Design/Build Process
A design/build contract was suggested by NRB/ATCO, and the client agreed to proceed on that basis. The design/build format promoted up front collaboration and problem solving, between the fabricator, design team and general contractor.
JIM TAGGART, FRAIC IS EDITOR OF SABMAG
Project Credits
- OWNER/DEVELOPER CityHousing Hamilton
- ARCHITECT Montgomery Sisam Architects Inc.
- MODULAR MANUFACTURER NRB Limited, ATCO Structures
- GENERAL CONTRACTOR Husky General Contracting
- PASSIVE HOUSE CONSULTANT Peel Passive House
- LANDSCAPE ARCHITECT OMC Landscape Architecture
- CIVIL ENGINEER Ainley
- ELECTRICAL ENGINEER DesignWorks Engineering
- MECHANICAL/STRUCTURAL ENGINEER DesignWorks Engineering
- STRUCTURAL ENGINEER DesignWorks Engineering
- PHOTOS Doublespace