Mass Timber and the Power of Reuse

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The University of Houston (UH) Retail, Auxiliary, and Dining (RAD) Center is a testament to sustainability and economy. Far from being at odds, the sustainable use of mass timber over existing columns and foundations minimized structural costs and maximized the building’s program. Located on UH’s main campus in Houston, Texas, the site previously housed a one-story subterranean dining hall prone to flooding. The RAD Center transformed the site into a vibrant hub of campus life, featuring a 41,000-square-foot, two-story building filled with natural light for dining, retail, and office functions. The project showcases the beauty of mass timber through architectural design by Perkins & Will and thoughtful engineering and detailing by structural engineer of record Walter P Moore, in collaboration with Martinez Moore Engineers, who contributed additional engineering and modeling expertise.

Walter P Moore recognized a unique opportunity to reduce cost, improve scheduling, and significantly enhance the sustainability of the UH RAD Center by reusing existing columns and foundations. The existing one-story, below-grade building was constructed in the 1970s and featured a heavy concrete joist lid structure weighing nearly 200 pounds per square foot. It was designed to support plaza and landscaping loads exceeding 250 pounds per square foot. By removing the lid and plaza to capitalize on this excess capacity and minimizing the weight of the structural system, the team supported the new building on the existing concrete columns and belled piers.

Although the UH RAD Center was initially conceived as a structural steel building, Walter P Moore proposed and evaluated a slightly lighter mass timber system, which would allow the reuse of the existing columns and foundations without widespread strengthening or replacement. In total, 66 foundations were reused, with only 11 new foundations required, primarily for areas of the new building that extend beyond the original footprint. The foundation reuse alone resulted in substantial cost savings and significantly improved sustainability by reducing embodied carbon by more than 175 metric tons of carbon dioxide equivalent.

Walter P Moore worked closely with Perkins & Will to set a 25-feet x 25-feet column grid, closely matching the existing grid, which ranged from 20 feet, 2 inches to 24 feet, 10 inches. Due to the expansive clay soils prevalent in Houston, UH requires elevated construction at all ground-level slabs, so this was utilized as the transfer structure for the new columns. The ground-level beam and slab system distributed loads in a similar pattern to the original building and was tied into the existing structure by attaching couplers to the column longitudinal bars. The existing basement was sealed off and backfilled with a combination of soil and geofoam in localized areas to prevent overloading the structural elements that would remain.

The RAD Center’s superstructure consists primarily of southern pine mass timber, with glued-laminated (glulam) columns and beams, cross-laminated timber (CLT) floor panels, and steel braced frames. The 25-foot bay width is slightly longer than the optimal span for CLT panels, so intermediate beams were introduced to reduce panel spans to 12 feet, 6 inches. With the favorable structural properties of southern pine and shorter spans, the floors utilized 3-ply CLT panels instead of the typical 5-ply, reducing wood volume to improve both cost and sustainability. Additionally, because the building is classified as Type IIIB construction, it did not require a fire-resistance rating, eliminating the need for additional wood volume to create a char layer. The floor panels were topped with a 2-inch acoustical mat and a 3-inch lightweight concrete topping slab.

One portion of the building, a one-story structure primarily outside the existing building footprint, was constructed in structural steel. This localized change addressed the owner’s concerns regarding maintenance and food safety in the kitchen and allowed for a larger column-free space. Walter P Moore developed details to connect the steel and timber structures, transmitting lateral forces and eliminating the need for a high-maintenance expansion joint.

Walter P Moore’s creative solutions reduced cost, shortened the schedule, and improved sustainability on the RAD Center. The use of mass timber and foundation reuse saved roughly $1 million and contributed to an overall carbon reduction of 650 tons.

Mass timber is unique in that it often functions both as the structure and as an exposed architectural feature. This dual role offers a unique opportunity for structural engineers to contribute to the architectural vision. At the RAD Center, our team thoughtfully considered aesthetics alongside structural performance and efficiency when selecting member sizes, designing feature elements, and creating details.

Nearly every column, beam, and CLT panel is visually exposed. As a result, member size selection involved additional considerations beyond structural strength and serviceability. These included accommodating exposed MEP systems, managing lighting impacts, and ensuring visual consistency. For example, the RAD Center features large openings that create multi-story volumes. Beam widths and depths around these openings were kept consistent to form a uniform perimeter band.

Openings in mass timber must be defined early for shop cutting, which ensures greater precision and cleaner edges than field cuts. Horizontal penetrations in beams for MEP systems were common due to the absence of ceilings, and the structural team used Technical Notes S560 and V700 from APA—The Engineered Wood Association to assess openings. Because member depths and opening sizes are interdependent, close coordination with MEP consultant, Henderson Engineers, was essential to achieving a visually cohesive effect.

Exposed connections also necessitate careful detailing. Fully concealed timber connections were specified wherever possible, and minimal exposed steel elements were used at locations with higher reactions. For exposed steel braced frames, Cast Connex Universal Pin Connectors provided an aesthetic end connection while conventional connections were used where bracing was concealed.

A major architectural feature of the building is an exterior canopy with an exposed timber soffit that cantilevers more than 13 feet over the main entrance and an additional 10 feet to the side. Working with mass timber subcontractor Timberlyne, the team achieved this dramatic form using custom CLT panels approximately one foot thick and concealed structural steel beams hidden by the soffit and building facade. Through-bolt connections between the steel channels above and the CLT panel were recessed at the bottom and concealed using wood block patches that matched the panel species.

Another structural challenge involved large openings in the floor and roof diaphragms. CLT panels comprised the primary diaphragm, but one area adjacent to the building facade narrowed to approximately nine feet wide, where CLT alone was insufficient. Deepening the structure would have negatively impacted the aesthetic. Instead, Walter P Moore removed the acoustical mat in this location, where it was not needed, and thickened the concrete topping slab to carry diaphragm forces across this narrow band. Concealed steel angles, screwed to the CLT and embedded in the concrete with headed stud anchors, transferred forces into and out of the concrete topping slab.

The University of Houston RAD Center project exemplifies the successful integration of architectural vision and structural engineering. By repurposing existing structural elements and leveraging the unique properties of mass timber, the project met its economic and aesthetic goals while significantly enhancing sustainability. The thoughtful engineering and close collaboration among stakeholders resulted in a distinctive structure that enhances the campus and stands as a model for innovative, sustainable construction. ■

About the Author

Sarah Evans, PE, is a Principal and Design Manager at Walter P Moore, where she focuses on digital delivery of higher education, sports, and commercial projects. Evans was a leader of the UH RAD Center structural team and is a member of the STRUCTURE Magazine Editorial Board.

Thomas Kostelak, PE, is a Senior Engineer at Walter P Moore focused on higher education, healthcare, and commercial projects. Kostelak oversaw the construction administration for the UH RAD Center.