Tilden Elementary Center

Outstanding thermal performance achieved with high performance walls

Over the past several decades we have learned much about the superior construction and cost saving benefits of precast concrete. Perhaps none more so than when precast concrete is used for the construction of educational facilities in school districts across the region. Precast is at the top of its class for many of the benefits school boards and municipalities desire most. With features like faster more cost effective construction, exceptional mold and damage-resistance, superior fire ratings, lower maintenance, longer life cycle, and easier expansion opportunities, it’s no wonder precast gets high marks from both architects and administrators alike. Plus, precast, and especially thermally-efficient, insulated sandwich wall panels, is one of the most environmentally friendly building technologies available and may contribute significantly to LEED points for a project. With its wide range of finishes, matching or complementing existing buildings on a school campus is easier than ever. It’s easy to see why smart districts, choose precast concrete.

Amid skyrocketing energy costs and heightened public awareness of green construction practices, more building owners are seeking environmentally friendly solutions – but without incurring higher costs. Tilden Elementary Center in Hamburg, Pa., is no exception. The school for kindergarten through fifth grade students will save on heating and cooling costs with innovative, thermally-efficient precast insulated wall panels engineered, manufactured and erected by High Concrete Group LLC.

Carbon fiber grid a key component

When first designing the structure, the project team considered a conventional block and brick cavity wall for the exterior. However, masonry ties create an energy-inefficient thermal conductance path. In addition, brick-and-block walls are often susceptible to mold and mildew issues—a problem school districts don’t even want to utter let alone face. High Concrete’s 10”-thick load-bearing precast sandwich exterior walls on the 110,000-square-foot project deliver steady state R-15 performance. They use three inches of continuous insulation (“ci”)* sandwiched between a 4” interior wythe and a 3” exterior wythe. A carbon fiber connector was used to join the two wythes. Several proprietary connector systems exist on the market at this time. With relatively low thermal conductivity, the 1mm thick carbon fiber shear virtually eliminates thermal transfer between wythes, so that there on the painted interior wythe there aren’t the hot or cold spots like those caused by steel connectors, enhancing comfort for students, teachers and administrators alike.

“With thermally–efficient wall panels, the building will be much slower to cool down and warm up, meaning the exterior environment will have less impact on energy costs,” said Phil Leinbach, architect, AEM Architects, Inc. “Because of the thermal mass of the panels and the resulting thermal lag effect on heat transfer we were able to reduce the size and cost of the central HVAC plant.” Use of the carbon fiber shear truss also created 100 percent structurally composite action, which enables the load-bearing walls to deliver structural support, much like a solid wall. Thermal efficiency and load-bearing performance combined on this project to provide an attractive alternative to other wall assemblies which, in general, were thicker and did not offer the same high, steady-state R-value. In addition to exceptional performance, the precast exterior provided aesthetic freedom. The building features a traditional brick facade composed of thin brick embedded in the panel face. “Thin brick can be somewhat tile-like in appearance,” noted Leinbach, “but its advantage is in thinner, better performing walls. We were pleased with the traditional aesthetic it achieved when viewed from the curb.”

Exposed precast banding and window sills impart the feel of limestone accents. A large, central cupola is the focal point of the building. Spring arched windows were created in the panels to emphasize the traditional look of the building. The pre-curved steel featured on the exterior of the building is exposed inside, providing a unique touch. “The owner wanted sloped rather than flat roofs for drainage reasons,” said Leinbach. “We proposed the curved beams as a way to preserve the building’s aesthetics. As a design element they’re distinctive because they’re not native to the area. The curves help tie together the past with the present.” The interior wythes of the precast walls were float-finished to complement the masonry walls throughout the building, and eliminate the dust and potential moisture issues associated with masonry. The project team also incorporated precast stairs and landings on the interior of the building.

Learning on the fast track

The project team lauded the fast enclosure time enabled by precast. The precast walls were fabricated while the structural steel was erected. Quick wall panel placement on the sloping site–at a pace of six to eight panels a day–expedited installation of the windows and roof. This allowed other contractors to conduct interior finishing in a dry, friendly environment conducive to quality. Conduits were cast directly into the walls, which streamlined the work of mechanical, electrical and plumbing trades and reduced change orders.

* “ci” – continuous insulation as defined in ASHRAE Building Energy Code 90.1-2004.

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