Carbon Impacts of CLT

Abstract:

Whole building life cycle analysis (WBLCA) refers to a method to quantify and evaluate the environmental impacts associated with a building's life cycle. This series highlights five whole building life cycle assessments of buildings incorporating the building material known as cross-laminated timber (CLT) into some or all of their structure, using a primary cradle-to-grave system boundary. This case study series will serve as an educational resource for academics, professionals, and CLT project stakeholders. While there is some uncertainty about the best way to reduce greenhouse gas emissions from architecture and construction, using CLT and other wood building materials is one possible means to reduce the emissions associated with a building’s materials.

 

Project Duration: 7/1/18-6/30/19

Project Lead: Alison Kwok

Student Researchers: Isabel Rivera, Hannah Zalusky, Hannah McKay

Advisor: Lindsay Rassmussen, Architecture 2030

Facilities: NetZED Laboratory - University of Oregon

 

Introduction:

CLT offers the potential to reduce greenhouse gas emissions by using timber, which requires much less energy to produce than steel or concrete and naturally sequesters carbon through its lifetime. However, there is a gap in the literature and a lack of general understanding about how much carbon CLT sequesters compared to the carbon emitted in the manufacturing process and in creating the adhesives used, as well as how the carbon value is calculated. This project analyzes and summarizes relevant literature and will create six case studies to illustrate the embodied carbon impacts of various kinds of mass timber buildings. In doing so, it aims to reduce confusion in the sector and assist designers and developers in making informed decisions regarding future green buildings.

 

Research Details:

 

Research involved cooperation with several firms to obtain construction drawings for these case studies. These were then entered into Tally, a life-cycle plugin for Autodesk Revit to understand the embodied carbon impacts of the six buildings. For each case study, the software program Tally and the software program Athena IE generate multiple whole building life cycle assessment reports for a reference building. Tally links material quantities from a Revit model to a database of material environmental impacts. Tally users assign a Tally-specific material to each Revit material usage. After all the materials are assigned, additional information about the building is entered into the Tally program, such as location and area. Tally then exports a formatted WBLCA report in pdf and Excel.

 

For the Athena IE WBLCA reports, a new project is created with background information about the building type and location. Within the project, building assemblies are added with their respective material compositions. For these case studies, the generic assembly “project extra materials” is used to enter the building’s materials in Athena IE. Tally materials are matched to their closest equivalent in Athena IE, and their quantities are entered into Athena IE through measures of mass, area, or volume. Although Tally’s reports only provide the calculated mass of each material, the volume and area can be manually calculated using the density shown within the Tally software. When all the materials are added, Athena IE can generate a report of environmental impacts as well as a bill of materials. The bill of materials displays the mass of the materials, which allows for validation of Athena IE and Tally inputs. Athena IE does slightly increase material quantities via construction waste factors, which cannot be manually changed, so Athena may have slightly higher mass calculations in many cases. However, in other cases, entering Tally’s material volume into Athena results in a slightly lower material mass than Tally’s value — presumably due to different material density assumptions.

 

Tally and Athena IE’s material calculation differences as well as other differences between the software (methodology and database sources) produce varying WBLCA results. In some cases, Tally may result in larger calculated impacts, while in other cases, Athena IE may result in larger calculated impacts. For each case study, to see the range of results, Tally and Athena IE’s WBLCA data values are united in new excel graphs for the impact categories of global warming potential, acidification potential, eutrophication potential, smog formation potential, and primary energy demand.

 

 

Results:

 

MASS TIMBER LCA CASE STUDIES:


CLT BUILDINGS: A WBLCA CASE STUDY SERIES

Whole building life cycle analysis (WBLCA) refers to a method to quantify and evaluate the environmental impacts associated with a building's life cycle. In this series, five buildings which incorporated cross-laminated timber (CLT) into their structures were assessed. These include a single-family house, a multi-family residential building, a parking garage, an office building and an industrial building.


INDIVIDUAL BUILDING CASE STUDIES (POSTERS):


Cross-Laminated Timber House

 

Mass Timber Parking Garage Structure


Mass Timber Multifamily Residential Structure


Mass Timber Office Structure


Mass Timber Industrial Building

 


 

CLT Info Sheets

A general overview of the use of CLT in buildings, including design information and synthesis of research on sequestered and stored carbon.


CLT: Annotated Bibliography 




 







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