Can California build its way out of the housing crisis with mass timber?

By Senior Project Manager, Anders Carpenter and Senior Project Manager, Sarah Knize
Perkins&Will mass timber case study design for mid-rise graduate student housing in San Francisco.

Multi-family and student housing are two residential building types particularly well suited to maximizing mass timber’s attributes, a synergy that will help deliver needed housing in a faster and more cost-effective manner and with smaller construction crews. Mass timber, an alternative structural system and framing material to concrete and steel, is relatively new to California and much of the United States, but Europe and Canada have been building with it for decades. Mass timber is made up of massive wood panels, posts, and beams that are comprised of layers of fast-growing soft woods stacked with perpendicular grain directions and glued under pressure or nailed to create members as strong as, and in some cases more resilient than, steel or concrete.

While there are a handful of buildings that have used mass timber in California, the state’s building codes, up until now, heavily restricted the height and size of buildings that could use it. The recent building code updates, which went into enforcement effect on July 1, adopted parts of the International Building Code and expanded the codified acceptable use of mass timber–making the building material available to mid and high-rise multi-family and student housing projects, among others.  

The housing crisis continues to rage across California cities. Despite government efforts to streamline approvals, overrule local housing development restrictions, and increase public funding developers can’t build enough housing fast enough to meet the persistent demand. Multi-family housing, especially in dense urban settings, is particularly applicable to mass timber structural frames in that the dimensional modules for the dwelling units align with ideal structural grid spacing and material widths within a mass timber system. Urban sites also tend to have very little lay-down space or site storage for materials, so the appeal of mass timber is that it can be trucked to site and installed off the truck easily when space is tight. Most mass timber structures rely on a system of wood posts (or columns) and panels (or slabs). When examining ideal square footages and layouts for dwelling units, it is often the case that a 12’-0” structural grid aligns with the typical partition and demising of wall locations, allowing the columns to remain clear of the open space within the units. When interior columns are needed, they can fall in an unobtrusive location in the units and can be exposed as an intentional architectural feature. 

New code changes make mass timber a viable option for mid and high-rise multi-family and student housing projects in California.
Faster Development

A major advantage of mass timber over concrete and steel is how fast a building can be ready for tenants. This efficiency is accumulated over the course of the project, beginning with the manufacturing of the timber products. Multi-family housing, as a project type, typically features repeating elements. Because mass timber products are prefabricated with precision off-site, having multiple identical components is ideal. 

Once all the members are produced, they are organized according to assembly sequence and delivered to the site where they are put together by a small team and a crane. Without little to no required on-site adjustments, each component is lifted from the truck and put into place , sometimes taking as little time as  90 seconds each on average. This back-end coordination, combined with the reduced weight of mass timber, streamlines the on-site construction in terms of time and labor, saving as much as 15%  in construction time. For graduate student and faculty housing in particular, this time savings provides a critical advantage in meeting construction deadlines for academic calendar target move-in dates.

Sites with dense natural or urban constraints can benefit from the improved site logistics and speed of construction that mass timber provides.
Cost Savings

While material costs of mass timber are comparable to steel and concrete, the efficiencies in the project construction directly impact the bottom line by allowing building owners to more quickly generate rents. Mass timber is much lighter than concrete or steel and can consequently decrease overall foundation costs, which often provides additional labor, material and schedule savings.

Another area for savings comes from exposing the structure itself. The amount of exposed wood is governed by the new July 1 California codes. Now that code requirements for allowable exposure of mass timber have become clearer and less constrained for tall building applications, wallboard and paint are no longer always required to conceal the mass timber structure. Depending on the height of the building certain percentages of the wood structure can be left exposed. Builders can save money by eliminating these materials and the associated labor they require.  Designers can play up the  warmth, texture, color, and biophilic quality of the exposed wood. Horizontally, mass timber as a finish material offers both beauty and economy by reducing the need for gypsum wallboard, paint, and other coverings–which also increase embodied carbon, contribute to off-gassing within buildings, and diminish the aesthetic expression of a building’s structure. It is possible to have a beautiful wood ceiling finish that has consistent quality control of fabrication and installation without any additional cost or material. When post and panels are used, the posts (columns) can also be exposed as pilasters or freestanding columns.

The finish of the mass timber panels and columns become the final interior finishes for the living spaces in the residential units.
Smaller Construction Crew

In this particular post-pandemic time of labor shortages, another advantage of mass timber projects is that they require 75% less active workers on site to assemble the building. Given the streamlined product delivery, mass timber projects reportedly reduce truck traffic by 90 percent. Additionally, because construction with mass timber can offer less on-site coordination (as materials are precision fit off-site), it leads to less noise pollution and reduced waste. This translates directly to improved site logistics which can also have a huge impact on ensuring projects are delivered on time. When compared to steel or concrete construction projects, mass timber benefits the construction workers as well. Timber construction creates less noise and dust, and the tasks are physically easier, which generally lowers absenteeism due to illness or injury. Because of this, mass timber workers can work more efficiently over a shorter period of time and as a result, report higher project satisfaction.

On top of efficiencies in costs, staffing and schedule, mass timber construction is also sustainable and effectively addresses carbon neutrality. Timber is currently the only structural material that is renewable and able to sequester and store carbon over its lifetime. For a recently completed 131,000 square foot office building, utilizing a mass timber structure instead of concrete or steel, reduced CO2 emissions equivalent to taking 740 cars off the road for one year or powering 370 homes for one year. Mass timber warrants consideration from developers, builders, architects and higher education institutions as new multi-family and student housing projects are initiated.