Mass Timber’s Rise in Construction

 

It seems counter intuitive to consider wood construction in the category of advancements in building materials. However, mass timber products take one of the oldest building materials and apply modern fabrication techniques for new ways to design and build. Gaining traction in the US, mass timber’s applications range from affordable housing and public university developments to high profile technology campuses and laboratories. Increasingly, International Building Code and more localized new code provisions are clearing the way for tall timber high-rises.

Holmes engineers lead mass timber construction along the West Coast, incorporating performance-based designs and industry research to secure approvals. Our solutions meet architectural and performance objectives from both structural, fire, and life safety standpoints.

Structural Benefits

 

While clients are initially attracted by the aesthetic warmth of woodgrain, mass timber buildings provide a number of functional advantages. These structures can have the additional benefits of increased off-site fabrication, shorter construction schedules, reduced on-site work force and less material waste. These buildings can also be lighter than other construction methods, which can reduce the foundation and/or seismic demand on the structure.

Holmes Mass Timber Optimizer Tool

We’ve built an in-house timber optimizer tool with data from the main mass timber suppliers. It spits out optimum grids based on wood volume or even cost, so we can quickly iterate between different options with clients.

Megan Stringer, Associate Principal

In terms of sustainability, mass timber can also reduce the carbon footprint of a building relative to more conventional building materials. To begin with, wood is a renewable resource that sequesters atmospheric carbon. Our engineers evaluate the entrained carbon in alternate structural systems. When assessing and analyzing multiple construction materials for the same building the results are clear: using wood as the primary structural system results in the lowest embodied carbon of any structural alternate. We use this tool as one of many factors that go into making recommendations on the most appropriate systems for the projects we design.

 

Mass Timber Construction with Glulam Columns at District Office, Portland

Mass timber is a broad set of materials. All of these products are made up of smaller pieces of wood formed together into bigger pieces that are considered mass timber, as well as traditional big, heavy timbers.

Eric McDonnell, Principal

Common Products

 

Mass timber comes in many forms, including:

Cross-Laminated Timber (CLT). Essentially structural plywood with 2x members laminated together in alternating layers.

Nail-Laminated Timber (NLT). One of the oldest forms of mass timber construction with 2x framing member nailed together and spliced to create large panels.

Dowel-Laminated Timber (DLT). Similar to NLT with wooden dowels to ensure monolithic deflection of the panels.

Glue-Laminated Timber (GLT). Commonly used as beams or columns, glue-laminated sections can be used on the flat to create flooring panels similar to the other systems referenced.

Tongue & Groove (T&G). Wood decking laid flat with interlocking tongue and groove on narrow face.

Mass Plywood Panels (MPP). Built up from thin layers of veneer from small-diameter trees.

When applied to flooring systems, these mass timber products can be compositely connected to a concrete topping slab for greater strength and stiffness. This composite performance reduces vibrations and increases the spanning capabilities of the floor system.

Common Mass Timber Construction Types CLT NLT DLT GLT T&G MPP

Reliable Fire Design

 

Our fire engineers study the performance of mass timber construction in potential fire scenarios. Given its compressed form and large surface area, mass timber generally performs well in fire scenarios with predictable charring patterns. We help project teams identify applicable mass timber construction types in relation to building massing and local code requirements. Performance-based fire design offers an opportunity to increase the amount of exposed wood through fire modeling, research, testing, and improved fire-protection measures. We provide the necessary safety in design while challenging some of the industries preconceived notions of what is possible!

Thermal Finite Analysis of Mass Timber Connection Detail

A comprehensive performance-based fire assessment for mass timber should consider a realistic fire exposure, accounting for the fire load, amount of exposed timber and ventilation, compartment properties, performance of connections, and impact of cooling and fire suppression. 

Bevan Jones, Principal & CEO (Fire)
Timber char analysis and burn test
University of Oregon Knight Campus CLT Stair
University of Oregon Knight Campus - Eugene, OR

Designing buildings in wood is an art. There are a number of factors that we consider, from the in-service movement of the material to accommodating required tolerances and optimal exposure. When done well, the resulting systems are expressed in the finished architecture.

Brentwood Public Library finished exterior with lights on at dusk
Brentwood Public Library - Brentwood, CA

More Perspectives

Specialist team of fire engineers provides advanced finite element analysis.

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