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Environmental Performance of Cross-Laminated Timber

Jennifer O’Connor

Group LeaderEnergy and EnvironmentBuilding Systems Program

February 2011

Lal Mahalle

Research ScientistEnergy and EnvironmentBuilding Systems Program

Dr. Alpha Berry

Group LeaderEnvironmentalComposites Program

Possible Environmental Questions for CLT

• Is there enough forest to sustainably support

manufacturing?

• Does it contain recycled material?

• Does it minimize the use of materials?

• Does it reduce operating energy in buildings?

• Does it have less embodied environmental effects than

alternate materials (energy, water, greenhouse gases,

etc)?

• Does it adversely affect indoor air quality?

Possible Environmental Questions for CLT

• Is there enough forest to sustainably support

manufacturing?

• Does it contain recycled material?

• Does it minimize the use of materials?

• Does it reduce operating energy in buildings?

• Does it have less embodied environmental effects than

alternate materials (energy, water, greenhouse gases,

etc)?

• Does it adversely affect indoor air quality?

Addressed in this presentation

4

Environmental Profile Using Life Cycle Assessment

LCA is a rigorous, scientific accounting of flows to and from nature

related to a product over its entire life span

Our Approach

• No existing LCA data on CLT publicly available.

• Not in our scope to do a primary LCA.

• Performed a snapshot mid-rise comparison using

glulam as a proxy for CLT.

• Used secondary data to approximate an LCA for CLT

manufactured in Canada.

• Compared a CLT floor section to a functionally-

equivalent concrete floor section.

• Reviewed related literature to help draw conclusions.

Mid-Rise Comparative Snapshot - Approach

What is the footprint of Stadthaus compared to a reinforced concrete alternate?

Modeled with the Athena Impact Estimator (whole-building LCA software )

• 910 m3 CLT.

• Modeled as a glulam

column-beam

system with

additional glulam.

• Results are missing

added fasteners and

added construction

effects.

• 950 m3 concrete and

120 tonnes steel

reinforcement.

• Modeled as concrete

slab-column-beam

system with additional

concrete and steel.

• Missing some

components and

effects, and may be

missing interior walls.

Base Case Alternative

Material estimates for Stadthaus according to published literature on this building.

Mid-Rise Comparative Snapshot – Embodied Results

Rough approximation for

Stadthaus using material

estimates by others and the

Athena Impact Estimator

software.

Comparison is using glulam

as a proxy for CLT.

This graph shows relative

results, benchmarked to the

CLT building, for several

environmental impact

categories.

Global warming category

does not take a credit for

carbon stored in the CLT.0%

200%

400%

600%

800%

1000%

1200%

1400%

1600%

1800%

2000%

Energ

y use

Resou

rce

use

Global

warm

ing

Acidific

ation

Respir

ator

y effe

cts

Eutro

phica

tion

Ozone

dep

letion

Smog

Wat

er u

se

Reinforced concrete

CLT (glulam)

Cradle-to-grave LCA. Does not include operating energy of the building.

Mid-Rise Comparative Snapshot - Carbon

CLT is environmentally

interesting for its carbon

profile.

There are two aspects to

the carbon story.

First – typical for wood

systems – there are

substantial avoided

greenhouse gas

emissions when using

wood instead of

something else.

Second, carbon in the

wood is a long-term pool

of greenhouse gas

removed from the

atmosphere.

Avoided GHG

emissions

when using

CLT instead of

RC

Mid-Rise Carbon Estimate

Mass of CO2 stored (metric tons): 631

Mass of estimated CO2 avoided (metric tons): 244

TOTAL combined estimated CO2 effect (metric tons): 875

Equivalent to one year of emissions from this many cars: 167

This is the amount of CO2

taken up by the tree to

make the wood used in this

building.

This is the difference in

embodied CO2 emissions

between CLT and a

functionally-equivalent

amount of reinforced

concrete.

Calculated using an in-house method for avoided carbon (CLT volume estimate by others) and using the

USEPA greenhouse gas equivalencies web site. Stored carbon is calculated at 50% of the dry mass of wood.

Floor Comparison - Approach

• Started with existing life cycle inventory (LCI) data for

Canadian glulam.

• Adjusted this data by modifying wood and adhesive

volumes to approximate an LCI for CLT.

• Received functionally-equivalent floor sections for

CLT and reinforced concrete. Highly conservative

design for CLT (thicker than the concrete floor

section).

• Performed cradle-to-building site LCA analysis for 1

m2 of CLT and concrete at the design thicknesses.

Fasteners and reinforcing steel not included.

Floor Comparison – Results

Modeled with SimaPro and using TRACI impact assessment methods plus CED. Databases used included USLCI and

ecoinvent. Global warming measure includes a credit for carbon in the wood and also treats biomass as carbon-neutral.

-150

-100

-50

50

100

150

Global

Warming

Acidification Respiratory

effects

Eutrophication Ozone

Depletion

Smog Non renewable

fossil fuelPerc

en

tag

e

CLT

Concrete

Environmental Footprint - Conclusions

• Rough estimate suggests CLT has a better

embodied profile than functionally equivalent

concrete systems.

• More data needed for a firm conclusion.

• Potential thermal effects of CLT need investigation.

• Design for deconstruction likely important to address

concerns about material consumption.

• Appears to have a sound argument for a carbon

credit when substituted for concrete.

Indoor Air Quality Impact - Method

Volatile organic compounds (VOCs) evaluated according to ASTM

D 5116-10 and ANSI/BIFMA M 7.1-2007 standards.

Formaldehyde was evaluated according to NIOSH 3500 method

Testing Chamber

Prepared

CLT

Sample

VOC Emissions - Results

VOC emissions as a function of CLT Types

0

20

40

60

80

100

120

140

160

180

200

µg

/m³

190-5S 152-5S 210-7S

190-5S 3,9 4,1 105,7 11,3 2,7 9,5 36,4 7,7 9,1 70,0 24,9

152-5S 2,8 2,8 59,6 5,9 2,3 21,1 17,7 2,8 6,1 73,5 30,5

210-7S 2,4 3,2 50,0 7,3 0,0 6,9 8,3 3,5 5,7 66,5 18,8

Acetic acid Hexanalalpha.-

Pinenebeta.-Pinene

alpha.-

Phellandrene3-Carene para-Cymene Limonene

Formaldehyd

e

Acetaldehyd

eAcetone

(various thicknesses of CLT)

Five different samples in total were tested. No correlation between VOCs and CLT

thickness / number of glue lines. All detected VOCs originate with the wood material itself.

CLT Formaldehyde Emissions vs Standards

CLT 24-hour vs European limits after 28 days sample exposure

The five samples easily pass European standards and the most stringent N. American

standard (CARB phase II).

0

20

40

60

80

100

120F

orm

ald

ehyd

e (p

pb

)

CLT Samples

Maximum Emissions for Various Standards

CLT Total VOC Emissions vs Standards

CLT 24-hour TVOC vs some European limits after 28 days sample exposure

0

200

400

600

800

1000

1200

CLT Samples

Maximum Emissions for Various StandardsT

VO

C μ

g/m

3

CLT Indoor Air Impact Preliminary Findings-Conclusions

• The CLT TVOC and formaldehyde 24-hour results were generally lower than those set forth by some European emissions labelling systems.

• The European E1 formaldehyde limit (100ppb) was 6 to 20 times higher than the CLT emissions.

• CLT formaldehyde results were 3 to 10 times lower than the most stringent CARB limit set at 50ppb for HWPW-CC.

• Based on these results if confirmed with more data the CLT products could be used indoor with no impact on the air quality.

18

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