Field Study of Hygrothermal
Performance of Cross-Laminated
Timber Wall Assemblies with Builtin Moisture
Ruth McClung
MASc. Building Science Candidate
Department of Architectural Science
Ryerson University
Co-authors: Dr. John Straube, University of Waterloo
Dr. Hua Ge, Ryerson University
Jieying Wang, FPInnovations
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Problem
• Moisture performance and properties
are not fully understood
• Susceptible to the same moisture
problems as wood (rot, mould,
swelling, etc)
• Construction moisture may pose an
issue
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Field Testing Layout
• CLT samples wetted on both faces by immersion in water
• Instrumented to monitor moisture content, temperature,
and relative humidity within the wall assemblies
• 4 wall configurations, with 4 CLT wood species are being
tested
• Wetted panels installed in field testing facility and
monitored for at least one year
Waterloo BEGhut Test Facility
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Planned Field Testing Layout
• BEGHut Layout
10420
1
2
4
5
7
8
N
27
9
510 Ø column
on 1200 x 1200
footing
10
100 Slab on Grade
CL
26
Heating/
Cooling
25
24
CL
electrical
service panel
23
Each quadrant is
symmetric with
the centre lines
22
100
6
Entrance
Foyer
28
3810
3
21
610 1270
Data
acquisition
system
11
12
computer
13
12.5 Ply clad corner
140/140 P.T. post
140 batt insulation
20
19
18
1270
1270
1270
17
16
14
15
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CLT Test
Wall Location
Field Testing Layout
A: European
CLT
Panel
Species
Type
All
panels
wetted
on both
sides
except as
indicated
Wall
Assembly
A1
Int Dry
A2
A3
A4
B: Black
Spruce
B1
B2
Int Dry
B3
B4
C: Western
SPF
C1
C2
Int Dry
C3
C4
Ext Dry
D: Hem-fir/
E: Eastern
SPF
D1
Type
1: Low
Interior
Materials
Exterior
Materials
E2
D3
Int Dry
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5
6: Dry
European SPF
CLT Panel
A6
E4
2: High
3: Medium 4: Low Int
⅜” Gypsum
Minimum 3½ “Air Space
Poly Sheet
Blueskin
Blueskin VP
3” Roxul RockBoard
3” Plastifab EPS
¾” Vented Cavity
½” Fiber Cement Board
Built-in Moisture Experiment
5: Stud Wall
Stud Wall
Materials
½”Gypsum + Poly
2x6 studs @ 16” c
5½” Roxul Comfo
Tyvek
¾” Vented Cav
½” Fiber Cement B
CLT Wall
Materials
Same as 2: Hi
Field Testing Layout
Wall Configurations:
1. Low Permeability
3” Roxul RockBoard
Blueskin
Nothing
2. High Permeability
3” Roxul RockBoard
BlueskinVP
Nothing
3. Medium Permeability
3” Plastifab EPS
BlueskinVP
Nothing
4. Low Interior Permeability
3” Plastifab EPS
BlueskinVP
Poly sheet
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Sensor Layout
With most panels drying freely to the interior, an estimate of the
variability in drying behaviour between samples of the same wood species
may be obtained.
Typical Sensor Layout
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Test Wall Construction
Condensation on polyethylene sheeting
Soaking of CLT panels in pool
Panel Installation
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Test Wall Construction
CLT test wall with insulation,
strapping and clading.
Interior of wall before drywall
installation
After installation of water resistive barriers
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Results
Freely Drying to Interior
• Relatively Uniform Behaviour
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Results
Low Interior Permeance
• Many Panels still above 26% MC, risk of decay initiation
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Results
Low Interior Permeance
• MC in centre of panels slowly drying or increasing,
redistribution
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Results
High Exterior Permeance
• Panels dry quickly, react quickly to outdoor RH
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Results
Medium Exterior Permeance
• Panel Surface RH is high, causing some panels to
increase in MC
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Results
Medium Exterior Permeance
• Panel Surface RH is high, some risk of mould
between insulation and VR WRB
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Results
Low Exterior Permeance
• MC remains high, and likely close to 100% RH
on surface
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Conclusions
•
•
•
•
•
•
Wetted panels dried very quickly during construction under typical
Southern Ontario Summer conditions.
The drying may be slower under cooler and more humid conditions, such
as in the rainy winter conditions in Vancouver, causing higher initial MC
High permeance envelope materials can effectively promote drying of
CLT panels
Impact of assemblies with medium permeance, including the use of EPS,
should be further investigated before any firm recommendations can be
made.
Low permeance materials should not be used
– Prolong the time period required for wetted panels to dry to a safe
level
– CLT panel itself is a good vapour retarder, and any additional vapour
barrier should not be used in a CLT assembly.
Wood species does not appear to have a significant effect on the drying
behaviour of the CLT panels.
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Acknowledgments
• Thanks to
– NSERC for funding this research project as a
part of the NEWBuildS strategic research
network
– FPInnovations, Nordic Engineered Wood, and
Henry for building materials
– Robert Lepage, Emily Vance, and Sam Siassi for
their generous donations of time, effort, and
knowledge in commissioning the test wall.
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References
•
•
•
•
Gagnon S., Pirvu C., 2011. CLT Handbook: Cross-Laminated Timber.
Vancouver: Forintek Canada Corporation.
Garrahan P., 1988. Moisture Meter Correction Factors. In: USDA
Forest Products Laboratory, Proceedings of a seminar on In-grade
Testing of Structural Lumber. Madison, WI, USA 25-26 April 1988.
Vancouver:Forintek.
Straube J., Onysko D., Schumacher C., 2002. Methodology and
Design of Field Experiments for Monitoring the Hygrothermal
Performance of Wood Frame Enclosures. Journal of Thermal
Environment and Building Science, 26(2), pp.123-151.
Wang, J., Morris P.I., 2011. Decay Initiation in Plywood, OSB and
Solid Wood Under Marginal Moisture Conditions. International
Research Group on Wood Protection, Document No. IRG/WP/1120469. IRG, Stockholm, Sweden. 12pp.
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