Mass Timber Comparisons: Two San Francisco Case Studies

― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

Matt Covall, Senior Associate, Senior Project Manager Dalton Ho, Associate, Senior Sustainability Advisor Sarah Knize, Associate, Senior Project Manager

― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

Contents Introduction

5

Mass Timber vs. Traditional Construction Methods

6

Case Study #1 — 1 De Haro

8

Case Study #2 — Child Care Center

9

Conclusion

11

Endnotes

13

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― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

Introduction Steel and concrete may be the materials of choice for the majority of construction worldwide, but mass timber is gaining attention as a sustainable alternative with additional benefits from its wellness properties as well as time and cost efficiencies. Mass timber refers to engineered wood products that are made up of smaller wood pieces combined together in ways that create a structural strength comparable to steel and concrete, but without the weight and production-intensity. For decades, the U.S. has watched as these products have been put to the test in European and Canadian commercial, healthcare, institutional and even high-rise construction. While restrictions are beginning to relax, U.S. building codes still vary widely by state and city. Unfortunately, what is new to the Bay Area market is also seen as untested and therefore untrusted.

Perkins&Will began working with mass timber in 1995 and has done more than 30 mass timber projects world-wide.

In recent years, the San Francisco studio of Perkins&Will has been able to apply the firm’s mass timber experience to the local market in two distinct projects. In an effort to help break down the barriers to wide scale adoption of mass timber, the San Francisco studio and its project partners are opening up the curtains to offer a clear view of the behindthe-scenes decisions, challenges, and lessons learned. Coincidentally, each of these projects analyzed mass timber alongside either a steel or a concrete alternative through the schematic design phase for comparative purposes.

1 De Haro

Child Care Center

San Francisco, California

South San Francisco, California

1 De Haro, a speculative construction project for

An employee childcare center for a confidential,

developer SKS designed for light manufacturing (PDR) on

sustainably-minded client in South San Francisco

the ground floor and topped by Three subsequent floors

compared traditional steel frame construction to mass

of office space, looked at CLT and concrete.

timber.

Project Team:

Project Team:

SKS Partners, Developer

Perkins&Will, Architect and Interiors

Perkins&Will, Architect

Rutherford+Chekene, Structural

DCI engineers, Structural

Rudolph & Sletten, General Contractor

Hathaway Dinwiddie, General Contractor

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Mass Timber vs. Traditional Construction Methods

From a sustainability standpoint, mass timber offers a

shorter financing schedule, reduced weather exposure, and

compelling suite of products. The only building product

a much less intrusive and disruptive construction site to the

made from the sun, wood acts as a long-term carbon

neighboring community.

sequestering material when used as part of a building’s

When compared to steel or concrete construction projects,

structure. As such, a mass timber building has immediate

mass timber benefits the construction workers as well.

embodied carbon benefits over its steel or concrete

Timber construction creates less noise and dust and

counterparts.

the tasks are physically easier which collectively lowers

In contrast, steel and concrete production are carbon

absenteeism due to illness or injury. Overall, mass timber

intensive. The steel industry is one of the world’s top three

workers report higher project satisfaction.

producers of carbon dioxide. The production of the binder material in concrete, cement, constitutes about 8% of global greenhouse gas emissions. As a point of context, if cement production was an individual country, it would be the 3rd

A mass timber building has immediate embodied carbon benefits over its steel or concrete counterparts.

largest emitter, behind only China and the U.S. This is high-quality craftsmanship. Mass timber manufacturers meticulously prefabricate panels and timber members to the millimeter of an architect’s prescription.

This level of precision lends itself well to high-performing building envelopes that will continue realizing operational carbon benefits over the decades of the building’s life.

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 25% in construction time despite a significantly smaller crew. The manufacturer organizes the panels and beams so that each is delivered to the project site in the proper sequence for assembly. Compressed construction timelines allows for a

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― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

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Case Study #1 1 De Haro — San Francisco, California As San Francisco’s first multi-story mass timber building,

Despite timber’s lower mass and subsequently lower lateral

as well as its first cross-laminated timber building, the

forces on the building compared to steel or concrete, the old

conditions on the triangular 1 De Haro site had the project

codes also didn’t address seismic factors and requirements

team considering wood from early on. The site is directly

with mass timber. 1 De Haro satisfied these concerns by

adjacent to an underground portion of Mission Creek and

using steel BRB frames, to transfer these lateral loads, in

the poor soils required deep piles to anchor the building on

conjunction with Glulam beams and columns used for

stronger footings. The ultimate weight of the building would

gravity load transfer.

determine the number of piles necessary. At one fifth of the

The upper floors were constructed with a CLT slab and

weight of a comparable concrete or steel structure, mass

glulam post and beam structure, utilizing wood-to-wood

timber had a clear advantage. For comparison, Perkins&Will

connections. To dampen the noise resulting from the solid

carried both concrete and mass timber designs through

surfaces, the CLT floor slabs were topped by concrete with

schematic design.

an acoustic mat break. The vertical and horizontal wood

The City of San Francisco was supportive of the design and

elements of 1 De Haro’s stunning wood ceilings and wide

materials, but mass timber is still relatively new and 1 De

open spaces between its massive columns inspired a glass

Haro was subject to more restrictions than what is required

curtain wall that wraps the building. The expansive windows

in the new 2021 generation of building codes regarding

naturally light the space and showcase the material to

mass timber. The 1 De Haro project is a hybrid development

the outside world as well. As Perkins&Will Design Director

of combined Production, Distribution and Repair (PDR) uses

Peter Pfau notes,

and office space. A concrete ground floor was necessary for

“It’s amazing how beautiful it is in there. You don’t have to spend money covering up the ugly construction, instead you just celebrate the beauty of the wood and detailed craftsmanship.”

the light industrial PDR use and qualified the development as a Type IV: heavy timber over a Type IA concrete podium.

This also allowed a greater mass timber floor area than would have been with Type III or V construction. Zoning restrictions at that time capped the building’s height at 58 feet. When targeting 12.6’ floor height, the design

As a speculative construction project, mass timber presented

team quickly narrowed out steel as only concrete or wood

additional benefits as well. The wood beams and supports

construction with exposed slabs and shallower beam

are a more forgiving and flexible framework than concrete

depths would work.

or steel. The needs of future tenants are met by coring holes

Laboratory fire testing of mass timber components have

in the wood--which can be easily plugged as needs change.

been studied to validate the performance of the wood

Mass timber was also a key selling point as SKS marketed

assemblies in fire conditions; however, limited testing has

the space. Prospective tenants identified with the building’s

been performed on mass timber interfacing other building

story of sustainability and light environmental impact.

materials. Perkins&Will collaborated with fire-stopping

Many of the prospective tenants noted an internal shift or

manufacturers such as Hilti and STI and officials to consider

feeling they got from being in the presence of the wood

alternate means of evaluating the building. The 1 De Haro

elements. This is a real phenomena, known as Biophillia,

team worked with Hilti to develop details and engineering

that is experienced when inhabiting a space that connects

judgements to demonstrate how the building meets the

with nature in meaningful ways. Research has shown

intent of the building code.

that employees’ well-being, productivity and creativity improved in a natural office environment. SKS received three offers to take the entire building once Schematic Design was completed.

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― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

Case Study #2 Child Care Center — South San Francisco, California A sustainability-driven corporate client commissioned

The Type V-B construction utilizes mass timber columns

Perkins&Will to design a childcare center for their employees.

and beams and stick frame infill walls. The classroom

The client saw this development as an opportunity to inspire

buildings are I-4 occupancy (Institutional- Day Care) and the

the design team to test new materials and advance ideas

administration building is a mixed-use of E and B occupancy

toward improved energy efficiency, health and wellness.

(Education, Business). There is a fire-rated wall separating

They also saw the opportunity to apply this research and

the classrooms from the corridors in the classroom buildings,

testing to future developments on its campus.

and each classroom has a direct exit to the exterior. Due to the size and construction type, fire-rated walls were not

The Child Care Center is a five-acre mini campus of five

required in the administration building. All five buildings are

separate single-story buildings, totaling 57,140 square feet.

clad in a high-performing mineral-wool and fiber cement

The administration building consists of a secure lobby, a full

rainscreen system.

commercial kitchen, a kindergarten classroom, an art studio, science lab and office spaces. The other four buildings are identical classroom buildings with eight classrooms, corridor space, a multipurpose room, laundry and office spaces. Like in the 1 De Haro project, the team considered two structural systems — one utilizing mass timber and another with steel structure with decking — through the design schematic phase for comparison purposes.

Mass timber vs. other structural systems

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Concrete

Steel

Wood

Construction Time

Slow

Quick

Quick

Construction Cost

$$$

$$$

$$$

Environmental Impact

High

Medium

Very Low

Embodied Carbon

24-37 lbCO2/SF

19-27 lbCO2/SF

-20-6 lbCO2/SF

Material Locality

Local

Intercontinental

Continental

Foundation Intensity

Very High

High

Medium

In-Situ Flexibility

Very Low

Medium

High

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― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

Conclusions Mass timber made sense from the beginning, due to the

sloped wooden ceiling, reducing the need for electric

repeated programmatic structure combined with the

lights for much of the day. The slope of the south-facing

clients’ ambitious energy targets and their prioritization

roofs maximize photovoltaic panel efficiency. The sloped

on health and wellness--especially for our youngest

ceilings also provide acoustic relief by reducing parallel hard

population. Consistent proportions of the design elements

surfaces that create flutter echoes. In the administration

allowed for a high degree of prefabrication by the timber

building, the coffered wood ceiling enabled acoustical

manufacturer. Panels were precut, flat packed and delivered

panels to be placed between beams for improved sound

to the site. Without any required on-site adjustments, each

resistance.

component took an average of 90 seconds to be lifted

The timber frame, which minimizes heat loss through

from the truck and put into place. Interior stick frame walls

conduction, represents 25% less embodied energy than the

were fabricated on site. This also allowed the work to be

steel alternative. It also helps the building surpass the initial

completed mostly during the dry season, reducing exposure

target of 70% energy savings to achieve NetZero energy as

to natural elements.

well as LEED Platinum certification. Different configurations

The buildings’ sawtooth pattern creates an undulating effect

of slab insulation were considered but removed due to cost

as you move through the corridor. Each classroom is defined

constraints and limited performance improvements. Roof

by a 20'-0" bay width with glulam beams and expansive

insulation was maintained at six inches, and continuous

sloped CLT ceilings. North-facing, operable clerestory

exterior wall insulation at two inches, exceeding code

windows provide natural ventilation and illuminate the

requirements.

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Exposing the building’s wood structure was an intentional

Given the breadth of mass timber experience at

decision. In addition to being a visual reminder of the

Perkins&Will, the design team for the childcare project was

renewable resource; wood’s natural beauty minimized the

able to work with Structurlam, a vendor that had already

need for finishing materials--limiting the range of products

been vetted and established as a reputable partner. Even

and substances added inside the building. This strategy

with trusted recommendations, Perkins&Will teams still

reduces the cost of materials, simplifies maintenance, and

inquire about the wood species, forestry management

curbs exposure to substances of concern. The presence

processes, certifications as well as the location of the mill

of wood also helps create a warm and healthy learning

and the delivery methods. This due diligence provides

environment. The natural patterning and texture of exposed

necessary information beyond just selecting a manufacturer.

wood can prompt positive psychological and emotional

Wood sourced from different forests has different physical

responses. Moreover, the biophilic response of wood in

properties that impact engineering and the color, grain, and

classrooms has been shown to reduce stress and heart

knots inherent in the species affect the overall appearance

rates in students, helping to encourage a calm and relaxing

of the project. Every vendor does things in their own way.

atmosphere. In fact, the glulam columns were positioned in

The 1 De Haro team found Nordic’s turn-key services to be

the wall assembly as pilasters so that more wood could be

an appealing benefit. The manufacturer not only supplied

featured. Their verticality offers a place where children can

the product; but also installed and provided design assist

touch and experience the material quality at their level.

coordination services. In addition, Nordic was able to deliver the wood by a single train to Sacramento, leaving the final

Mass timber was the right structural choice for both projects

few miles easily bridged by a flatbed truck. When counting

and they realized savings in time and costs, but the reduced

carbon, understanding how mass timber manufacturers

embodied carbon and its carbon sequestering abilities are

manage their forests, produce their product and their

perhaps mass timber’s most compelling attributes. In fact,

methods of delivery are important factors. Ultimately,

a recent study found that a broad adoption of mass timber,

design teams need to find a manufacturing partner

especially for mid rise construction, could be a tipping

that shares their vision--not just for the project, but for a

point that shifts the construction industry from a significant

carbon-free future.

carbon source to a carbon sink.

However, not all wood products are created equally and it falls to product specifiers to ensure that their wood products are sourced responsibly and from sustainably managed forests. Also, in order for mass timber to live up to its carbon sink potential, the timber members need to live a long life-- beyond the lifespan of a typical structure. If the wood is left to decompose it releases its stored carbon back into the atmosphere. This requires care and attention in maintaining the integrity of the wood by protecting them from moisture and pests. To ensure the timber’s reuse value, it’s also essential for timber products to be joined by removable fasteners.

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― Mass Timber

Mass Timber Comparisons: Two San Francisco Case Studies

Endnotes 1

Churkina et al, "Buildings as a global carbon sink," Nature.com, January 27, 2020, https://www.nature.com/articles/s41893-019-0462-4

2 Johanna Lehne and Felix Preston, "Making Concrete Change: Innovation in Low-Carbon Cement and Concrete," June 13, 2018. https://www. chathamhouse.org/2018/06/making-concrete-change-innovationlow-carbon-cement-and-concrete 3 Christian Hoffmann, Michel Van Hoey, and Benedikt Zeum, "Decarbonization Challenge for Steel," June 3, 2020. https://www. mckinsey.com/industries/metals-and-mining/our-insights/ decarbonization-challenge-for-steel 4 reThink Wood Magazine, "Mass Timber in North America: Expanding the Possibilities of Wood Building Design." https:// www.awc.org/pdf/education/des/ReThinkMag-DES610AMassTimberinNorthAmerica-161031.pdf 5 Graham Lowe, "Wood, Well-Being, and Performance: The Human and Organizational Benefits of Wood Building," April 2, 2020. https://www. naturallywood.com/wp-content/uploads/2020/08/wood-wellbeing-and-performance_report_graham-lowe.pdf

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