The Soto Office
Engineer-Build
The Soto Mass Timber Office Building in Texas
The 6-storey, 168,000 sqft Soto Office Building gives San Antonio its first mass timber project. This elegant structure is in the first phase of a sustainable, walkable urban neighborhood project at Broadway and 8th streets.
The building has 5 storeys of timber structure over 1 storey of concrete. DLT (dowel-laminated timber) panels were used for the exposed floor and roof decks, supported by a Glulam post and beam frame.
We joined Lake Flato and Boka Powell early in concept design as the structural engineer for the timber superstructure. As design-builders, we were able to provide early pricing, giving the team confidence to proceed.
One of the features of the building is its full depth brick facade, making it one of the first North American projects to combine mass timber with heavy brick - this has presented design challenges which we successfully solved along with the design team.
Engineering
The roof deck consists of prefabricated Dowel Laminated Timber (DLT) panels. Each edge of the narrow 1.5" boards was moulded with a small chamfer to add texture and definition to the exposed ceiling. The double-height space the pop-up roof uses a cantilevered DLT mass timber panel to showcase the beauty of timber against the San Antonio skyline.
The typical floor gravity structure uses DLT panels supported by a Glulam post and beam frame, with the columns set at a 20' x 30' grid. An under-floor air distribution system gives building occupants an unencumbered view of the timber ceiling and direct air control. The DLT panels were prefabricated in 8' x 60' sections, allowing for rapid installation. The timber connections were engineered to minimize costs, while considering constructability and tolerance.
With the concrete core sustaining lateral loads and the gravity structure comprised of timber, the glazing and a heavy brick facade harmoniously envelope the wood structure.
The Soto is one of the first North American projects to combine mass timber with a masonry facade. This presented significant design challenges - combining timber - a material which has an inherent tendency to creep - with brick, a material which is particularly sensitive to deflection. The challenge was successfully solved through precise detailing that prevents long-term deflection and allows for a high-tolerance connection between the brick and mass timber system. At the loft roof, two-way 10' cantilevers comprised of DLT panels were created with a complete concealed connection system. This unique cantilever system showcases the beauty of the exposed timber through to the building exterior.
Dowel Laminated Timber (DLT) floors help to provide additional acoustical and vibration isolation between stories. On top of the DLT floor panels is 1" of concrete followed by a raised floor system with a 6" air cavity and 1" concrete floor tiles that will be covered in carpet.
There are plenty of fabricators in the mass timber market today who can competitively supply individual components such as beams and columns, and floor planks, but turnkey subcontractors, like StructureCraft, have proven to be reliable and trustworthy partners. (Don Powell | Principal BOKA Powell Architects)
Fabrication
We fabricated the SPF DLT panels in-shop with a shop-applied honey brown stain to create warmth within the building space. The exterior Glulam canopies and terrace are an architectural grade Larch species coated with a similar stain.
A shop-applied membrane was used atop the DLT panels to provide temporary moisture protection during construction.This system successfully protected the panels from significant moisture exposure during rain events.
Installation
We erected the mass timber frame following the cast-in-place concrete core. Large 60’ DLT panels were erected allowing the floor plates to be completed rapidly and stitched together. A special feature of this building is the above-mentioned brick façade that, along with the glazing, wraps the wood structure. The brick trades worked well alongside our team to provide seamless installation of both components.