A first for CLT structures in the US

By | 2019-09-06T12:29:50+00:00 September 6th, 2019|

By IKD

Yugon Kim and Tomomi Itakura, from Boston and San Francisco based architectural design firm IKD, completed the first hardwood-cross-laminated timber structure (hardwood CLT) in the US – The Conversation Plinth.

12m long finger joint hardwood boards being prepared to be loaded into a CLT press. Image credit: IKD

12m long finger joint hardwood boards being prepared to be loaded into a CLT press. Image credit: IKD

9m x 3m hardwood CLT panel set in place amongst site bollards. Image credit: Hadley Fruits/IKD

9m x 3m hardwood CLT panel set in place amongst site bollards. Image credit: Hadley Fruits/IKD

The structure was unveiled at Exhibit Columbus in midwestern modern art and architecture mecca, Columbus, Indiana. Its form takes cues from the conversation pit in the living room of the Miller House, as well as the plinths that elevate the important landmarks immediately surrounding the site – the library designed by I. M. Pei, the First Christian Church designed by Saarinen church, and the Large Arch by Henry Moore.

Using Hardwood CLT for construction

Construction images of the upper tier of the Conversation Plinth being lifted using a boom crane on site. Image credit: IKD

Construction images of the upper tier of the Conversation Plinth being lifted using a boom crane on site. Image credit: IKD

The Conversation Plinth was constructed from the first-ever commercial pressing of hardwood CLT in the US, developed by IKD and team partners. Although softwood CLT already existed in the US, hardwood CLT did not.

The hardwood CLT was derived from combined species of low value grade 3 common hardwoods. Hardwood CLT is harder and heavier than traditional softwood CLT. This created challenges during the project because of the impact on processing and fabrication timelines. In addition, there was also an increase in transportation costs. The project took ten days to be completed on site and a boom crane was used to assemble certain tiers of the Conversation Plinth. The installation is made of a high-tech engineered cross laminated timber.

IKD was awarded a 2017 Wood Innovation grant by the United States Forest Service to develop this material innovation for the installation and for product certification that could potentially lead to mass production.

Using the Conversation Plinth as a demonstration project, the IKD team hopes the installation can be a catalyst for a new timber industry by upcycling low-value hardwood sawn logs that are extracted from regional forests in Indiana and the mid-west. Indiana’s largest cash crop is hardwood, but over 55% of each log processed is of low value. The idea is that low-value hardwood, such as grade 3 common oak, maple, and ash, can be used to create high-value HCLT, which can then be used in commercial applications.

The hardwood CLT panels are used for floor, stair and balustrade. Image credit: Hadley Fruits/IKD

The hardwood CLT panels are used for floor, stair and balustrade. Image credit: Hadley Fruits/IKD

Benefits of HCLT

HCLT offers numerous benefits over softwood, including superior mechanical properties, material volume savings, increased resistance to fire, and higher quality appearance in visible settings. The proposal aims to jumpstart and accelerate the development and use of HCLT fabricated from parts of logs harvested from Indiana forests that can currently only be used to produce low value wood products. It seeks to demonstrate the viability and the benefits of a new, high value timber market in Indiana and the mid-west.

This has the potential to initiate a cascade of effects: positive job growth in rural forestry and manufacturing, expanding and diversifying hardwood lumber markets, higher forest land value, and improved forest management practices to reduce wildfires and encourage biodiversity. All these benefits lead to an abatement of climate change.

The project had the full support of the National Hardwood Lumber Association (NHLA) and the Indiana Hardwood Lumbermen’s Association (IHLA). A partnership was also established with SmartLam, the first CLT manufacturer in the United States, timber structural engineering expert Chris Carbone from Bensonwood, and Clemson University’s Wood Utilization + Design Institute. IKD has also collaborated with the Indiana department of Nation Resources, the Hoosier National Forest office, and the Indiana Society of American Foresters.