Sidewalk Labs Reveals a Timber Tower Digital Model

Sidewalk Labs, the urban infrastructure startup from Google parent company Alphabet, has released a “digital proof-of-concept” that details a new model for designing tall timber towers.

Exterior rendering of office and residential levels of Proto-Model X, Sidewalk Labs’ prototypical timber building. (Image: Michael Green Architecture and Gensler) via

To explore how factory-produced timber buildings can grow even taller, the Sidewalk Labs team designed a 35-storey mass timber proto-model, called Proto-Model X, or PMX.

With PMX, the team demonstrates how a modular 35-storey tower can be built in mass timber—a height that’s yet to be achieved in practice. The detailed model is rendered in Revit, and hosted in BIM 360.

According to Sidewalk Labs’ Medium page, PMX was developed through collaboration with a team of architects, engineers, and environmental designers who advanced the building through eight key steps. The consultant team includes Michael Green Architecture, Gensler, Aercoustics, Aspect Structural Engineers, Atelier Ten, CadMakers, Integral, JE Dunn Construction, RDH, Sweco, and Vortex Fire.

The eight steps of PMX. (Image: Michael Green Architecture and Sidewalk Labs) via

Sidewalk Labs describes mass timber as a “nimble and light” material compared to other structural building elements. PMX is approximately 2.5 times lighter than its concrete counterpart, and when researchers began doing wind analysis, they discovered that PMX was reacting more like a building of 40 or 50 stories.

As a result, in response to lateral pressure on the 35-story timber building, the team drew from engineering tactics more typical of super-tall building design, employing a cross-braced frame and a tuned mass damper.

To create sufficient stiffness, a structural timber core wall would have had to have 5-foot- thick walls—a non-starter. As an alternative, the team chose to use an exoskeleton form, with large timber beams criss-crossing the facade of the building. Since PMX was still prone to swaying due to its lightness, the team included a 70-ton steel tuned mass damper to reduce lateral movement.

Once the Sidewalk Labs team stabilized the design of PMX at 35-storeys, the researchers designed an affordable method to manufacture the building off-site.

Representative images of the kit of parts that form the PMX building. (Image: Michael Green Architecture) via

The team created an interlocking kit of parts including a floor-cassette system. Each cassette has a shell made of wood panels with acoustic and insulating layers. The interior of each cassette houses the building’s mechanical, electrical, and plumbing systems, which are installed in a factory as part of the pre-fabrication process. The cassettes are slotted one by one into the envelope of the building, linking up to one another to form new floors.

Like the floor cassettes, PMX’s building envelope consists of a series of panels that can be produced by a factory. The Sidewalk Labs team began with a basic metal module with 40 percent window coverage, accompanied by a balcony for each unit. The team then explored a number of highly expressive designs, with the intention of showcasing a wide range of architectural possibilities. The building can be skinned with panels of any shape, material, or design, so long as they meet building code requirements and follow a standardized modular pattern.

Using different skins allows PMX to transform into buildings with a different look and feel. Sidewalk Labs says that these skins, or others, could be applied to mass timber buildings of different shapes and sizes, all factory-produced.