Exploring Precast Concrete’s Potential
- Feb 27, 2018
Even for a city where interesting and innovative new projects have become a familiar sight in recent years, 28 Grand is a uniquely noteworthy Detroit development. Located in the heart of Detroit’s historic Capitol Park district, the 13-story project represents the first downtown residential construction since the 1980s and houses 218 micro-apartment units (each just 260 square feet)–another Motor City first.
While the vision for this signature project stands out, the execution is perhaps even more intriguing. Approximately 90 percent of the project was constructed using precast concrete, a product that enabled developer Bedrock to meet an aggressive construction time frame while incorporating the necessary façade aesthetic.
Project designer Kraemer Design Group’s decision to utilize precast concrete in 28 Grand conferred significant design and construction advantages, while influencing much of the design of the finished project. A closer look at how precast was used in this development gives some insight into how this unique building material can (and cannot) be used, and what kinds of design, construction, economic and aesthetic considerations need to be accounted for when working with precast.
While 28 Grand uses multiple types of precast products–planks, walls, stairs, architectural detailing on exterior walls, and insulated panels–precast only becomes an efficient and cost-effective product if you can repeat the mold: Tinker Toys writ large. The architectural precast on the outside of the building is necessarily less standardized but the structural material is standard shapes and cuts. Walls and planks–28×4 pieces of concrete–are produced en masse and cut to size as needed.
Inside and out
The lower two floors of the 28 Grand’s exterior design incorporate dark bricks cast directly into the precast pieces, meeting the design aesthetic while maintaining the quick construction cadence. This also reduces the opportunity for water to penetrate the wall assembly, preventing future water damage. On the interior, standardized unit dimensions work well with the structural capacity of the precast. Painted concrete walls and ceilings eliminate the need for additional investment in drywall or other interior finishes.
The sound dampening properties of precast are phenomenal–a bonus for multifamily and hospitality–and it ranks extremely high on fire safety ratings. It’s also extremely energy efficient, and using precast allowed 28 Grand to achieve a coveted Energy Star rating. The exterior skin of the building is self-supporting, requiring a low amount of tie backs to the main building structure, and a gap between the exterior wall and floor slab edge allows for the running of continuous insulation. Thermomass insulated precast sandwich panels were used at strategic exterior areas, minimizing thermal bridging. A single Thermomass panel incorporates the structure, insulation, vapor barrier and exterior façade for a seamless installation process.
The 28 Grand design team was cognizant of the project’s location in a historic district, meaning the finished design had to meet specific regulatory guidelines. The selection of exterior materials was critically important, as every piece would be reviewed and approved by the historic committee to be cohesive with surrounding buildings.
The aesthetic flexibility of precast was valuable. The intent was to replicate the look of limestone, a commonly used exterior cladding material on many historic Detroit buildings. A custom pigment mix and acid finish achieved a convincing limestone appearance, resulting was a finish that is sympathetic to the architectural vernacular of the neighborhood.
Speed and utility
The project gets its name from its location on Michigan’s well-known Grand River Avenue. But a premium location in the heart of the city also comes with some logistical challenges. The building takes up 100 percent of the small urban lot, so the precast served as an innovative solution to keep traffic patterns in check while reducing construction site congestion. The precast was shipped in, off-loaded directly from the truck and hoisted into place on the building, minimizing the potential for damage to the precast and reducing the amount of time that a large construction crane had to be on site.
These efficiencies also made it possible to meet an incredibly aggressive schedule with an accelerated construction timeframe. The structure and exterior cladding could be assembled simultaneously, allowing for lower floors to be enclosed and interior work to commence–all before precast assembly above was completed.
Dollars and sense
While precast takes time up front to manufacture, once the material has been produced and delivered to the site, things move very quickly. The 28 Grand project team utilized two precast manufacturers–and brought them in early in the process to accelerate production.
Precast is ideal for multifamily and hotel construction, but would be impractical or impossible for the large open floor plates of preferred office layouts. From a cost standpoint, there may be cheaper alternatives. Precast is only cost effective if it can be manufactured regionally, and maximizing the efficiencies generated by the precast demands a mid-rise (10-12-story) format. But in terms of value engineering–overall speed of construction, durability/longevity, and product quality and attributes (sound dampening, fire resistance)–precast is an appealing option. There is no doubt that 28 Grand would have been a radically different–and much less successful–project without the creative use of precast concrete.
Bob Kraemer is co-founder and principal of Detroit-based Kraemer Design Group, a leading, high-end architecture and interior design firm with more than 20 years of experience in historic renovation and comprehensive architectural consulting.