Location: St. Louis, Missouri
Delivered in: 2017
Owner: Washington University in St. Louis
Key figures: 6 Ductal® sandwich panels (12 ft x 22 ft x 1 in thick)
The U.S. Department of Energy Solar Decathlon is described as a “life-changing competition for collegiate students and an intensive course in sustainability for consumers”. Participating student teams spend almost two years designing and building solar-powered houses that are cost-effective, energy-efficient, sustainable and attractive.
At the 2017 competition in Denver, Colorado, “Team WashU” (100+ students from the Sam Fox School of Design & Visual Arts and School of Engineering & Applied Science at Washington University in St. Louis, Missouri), secured second place in the Architecture category for their unique project called “The CRETE House”, an innovative, 995 square foot structure built entirely with prefabricated concrete. This includes an energy-efficient cladding system comprised of six large (12 ft x 22 ft wide), thin (1 inch) precast sandwich panels made from Ductal® Ultra-High Performance Concrete (UHPC).
Oversized gutters provide shade and extend the living space outdoors, while a water collection system and vertical planters support hydroponic gardening. The design also demonstrates that concrete is a viable, sustainable building material and a beautiful, highly durable alternative to wood construction. Thanks to its ultra-strong envelope, the home is extremely resilient against fire, moisture, mold, insects, seismic activity and harsh weather conditions.
Team WashU worked with the Precast/Prestressed Concrete Institute (PCI) to design and cast the Ductal® sandwich panels, which are about 30% lighter than standard precast concrete panels.
LafargeHolcim will continue to develop cladding and sandwich panel solutions based on experience gained from this project. Two specific opportunities are being explored: lighter sandwich panels (perhaps 60% lighter than standard panels) that utilize Ductal® on both the interior and exterior surfaces; and large scale cladding panels for curtain wall construction on high-rise buildings.
The panels are connected with bolts, which contribute to significantly reduced labor and material waste compared to traditional connection methods. Altogether, five inches of insulation was placed on top of the 1 inch Ductal® panel. (Typical sandwich panels have 3 inches of insulation because of the 3 inch concrete layer replaced by Ductal®).
The aesthetics of the 1 inch Ductal® layer are excellent, replacing the usual 3 inch layer of conventional concrete. The UHPC sandwich panel walls are a first attempt at combining the material strength into a typical utilitarian system, to achieve something with high design aesthetic and very good thermal properties.
With the competition now completed, the CRETE House has been dismantled and transported back to Washington University, for re-assembly and use as a long-term residence for scientists at the Tyson Research Center – a 2,000 acre, outdoor laboratory.
The thin, lightweight Ductal® sandwich panels met the project team’s requirements for lightweight, thin, durable, panels that contribute to the building’s energy efficiency. The panels also met requirements for aesthetics, cost and sustainability. They are easy to install, dismantle and re-assemble.