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5 WaysZero Ready Walls
Spring Training CampHidden Valley Resort, Huntsville ON | 2016.04.26
Chris Schumacher, B.Tech.(ArchSci), B.A.Sc.(CivEng), M.A.Sc.(BldgSci)
Principal, Senior Building Science Specialist
2
Requirements for Zero-Ready Walls
• Energy Efficient
• Affordable
• Buildable
• Durable
3
Approaches to Zero-Ready Walls
Deep Cavity
• Create a thick wall assembly and fill the cavity with insulation
• Double Stud Wall
• Truss Wall
• I-joist wall
• All insulation in the framed space!
Exterior Insulated
• Minimize framed assembly then add continuous exterior insulation
• Foam Board (XPS or PIR)
• Spray Foam (2pcf ccSPF)
• Semi-rigid mineral fiber (stonewool)
• Framing configuration and size for structure and utility distribution not insulation!
4
Deep Cavity vs. Exterior Insulated
( Straube and Smegal, 2009)
5
Deep Cavity Challenges
• Structural sheathing is at the coldest point in the assembly
• Cold = Higher RH
• Cold = Higher Moisture Content
• Cold = Greater Potential for Condensation
• Air tightness is paramount!
6
Exterior Insulation Challenges
• Cladding Support
• Window Support
• Trim Details
• Drainage Plane Location
• Integrating Drainage at Windows
• Rainwater control is paramount!
7
5 Zero Ready Walls(that could be adopted now)
• Deep Cavity
– Double Stud
– I-joist
• Exterior Insulation
– Polyisocyanruate (PIC)
– Extruded Polystyrene (XPS)
– Stonewool (e.g. Roxul)
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Double Stud
I-JoistStud
R-43RSI 7.5
(installed)
R-36 RSI 6.4
(installed)
9
Polysio
XPS
Mineral Wool
R-38 RSI 6.6
(installed)
R-37 RSI 6.5
(installed)
R-37 RSI 6.5
(installed)
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Wall Assembly – Thermal Details
• Average Nominal RSI of the High RSI walls was RSI 6.2
• I Joist Stud wall had highest calculated RSI through the stud• 2-D heat transfer simulation gives (RSI 4.7) for 241 mm stud• 286 mm I-Joist would be RSI 5.5 – significantly better than DS
Installed RSI
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University of WaterlooField Exposure Study
Objective: to improve the understanding of the moisture-related durability performance of exterior insulated, high-R, wood-framed wall systems
Approach: Natural exposure field testing with additional (controlled) moisture exposure
Recognition: The bulk of this work was done by T. Trainor & M. Fox. Both are past M.A.Sc. Students and current RDH-BSL team members.Also, a special thanks is owed to NRCan for supporting this project.
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The BEG HutSto
new
ool
R-3
4
X P
SR
-35
P I
CR
-35
Datu
mR
-24
• Natural weather exposure• North and South elevations were used for testing
I-Jo
ist
R-3
9
Db
lStu
dR
-39
University of Waterloo
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Test Walls
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• Fibre-cement lap siding• ¾ “ (19 mm) strapping• SBPO WRB and air barrier• 7/16” (11 mm) OSB sheathing• 2” X 6” SPF framing- 24” O.C.• 6 mil poly vapour barrier• ½ “ (12.7 mm) gypsum wall board
R-24 (installed)
Conventional (Datum) Assembly
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Deep Cavity AssembliesI-Joist Double Stud
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PIC XPS Stonewool
Exterior-Insulated Assemblies
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• Passive background performance evaluation
– Controlled indoor conditions 30-50% RH and 21° C
• Active testing to determine potential for wetting and drying
– Air Injection – constant flow rate of indoor air injected into cavity space to simulate air leakage
– Water injection test
Performance Evaluation
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Calibrated Air leak
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Air Injection Testing
• Energy Star air leakage limit = .02 l/s/m2 at 50 Pa
• Power Law: Q = C * (delta P)n (n=0.65, delta P = 4 Pa)
this was converted to an in-service air leakage rate of 0.2 l/s/m2
• Applying this to the area of the center bay (1.3 m2), results in a leakage rate of .26 l/s per test wall
• 30 CFH (.24 l/s) was used
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Calibrated Rain Leak
• Location and distribution to simulate a window leak
• Manually inject 30 ml of water twice a day
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Testing Protocol
Phase 1- Baseline (as-built condition)
October 2012 to February 18th, 2012
Phase 2- Air Leak Testing
February 19th to April 9th
Phase 3- Drying
April 10th to June 4th
Phase 4- Rain Leak Testing
June 3rd to July 5th
Phase 5 – Drying
July 6th to October
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BASELINE RESULTS
So what actually happened?
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Sheathing Temperature: Cold Weather
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Sheathing Temperature: Cold Weather
Wall Datum - N PIC - N XPS-N RW - N Double - N
Average -7.7 -0.1 1.6 2.5 -8.9
Min. -16.3 -5.6 -3.7 -2.5 -17.7
St. Dev. 5.0 3.6 3.2 3.1 5.1
Coldest Week of the Year
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Effective R-Values at 3 Temperature Conditions
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
-15° C 3.5 30° C -15° C 3.5 30° C -15° C 3.5 30° C
PIC PIC PIC XPS XPS XPS RW RW RW
Eff
ecti
ve
R-V
alu
e
at 3 Exterior Temperatures
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RH at Inside of Sheathing
0
50
100
150
200
250
300
Dbl. Stud - S Datum - S PIC - S XPS - S RW - S Dbl. Stud - N Datum - N PIC - N XPS - N RW - N
Re
lati
ve
Hu
mid
ity
(R
H)
Peak and Average Cavity RH - No Air LeakagePeak and Average Sheathing RH – Baseline (No Air leakage)
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Condensation hours - RH sensors less reliable near 100% RH
• Stud Cavity RH/T sensor data
• Pw – Stud cavity RH/T data [partial vapour pressure in cavity]
• Pws – T-data at sheathing / plates [saturation vapour pressure]
Possible errors include sensor location, non-uniform moisture distribution in the cavity
t
RH
t
ASHRAE Fundamentals, 2009
Potential for Air Leakage Condensation
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Potential for Air Leakage Condensation
Percentage of hours that could be expected to see condensation(if there was air leakage)
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Moisture Content of Sheathing
Moisture Content: Lower Sheathing, North Elevation – Baseline (No Air leakage)
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Moisture Content Distribution
Double Stud Wall – Baseline (No Air Leakage)
Double Stud Wall (South)
Double Stud Wall (North)
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Moisture Content Distribution
I-Joist Wall – Baseline (No Air Leakage)
I-Joist Stud Wall (South)
I-Joist Stud Wall (North)
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OSB MC – Exterior Insulated South
PIC Wall (South)
XPS Wall (South)
StonewoolWall
(South)
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OSB MC – Exterior Insulated North
PIC Wall (North)
XPS Wall (North)
StonewoolWall
(North)
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AIR INJECTION RESULTS
What about measured Air Leakage?
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L
M
L
L
Measured Moisture ContentAir Injection Wetting followed by Drying
Double Stud Wall (North)
I-Joist Stud Wall (North)
38
M
M
PIC Wall (North)
XPS Wall (North)
Stonewool Wall (North)
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Condensation Hours – Baseline Period
Condensation Hours – Air Injection Period
Condensation Hours – Drying Period
Datum Datum
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
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Condensation Potential-Change in M.C. Due to Air Injection
0 10 20 30
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Do
ub
le-
So
uth
Da
tum
-S
ou
thP
IC-
So
uth
XP
S-
So
uth
RW
-S
ou
th
0 10 20 30
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Bottom Plate
Lower OSB
Middle OSB
Upper OSB
Top Plate
Do
ub
le-
So
uth
Da
tum
-N
ort
hP
IC-
No
rth
XP
S-
No
rth
RW
-N
ort
h
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• Mould growth thresholds
• Moisture content and temperature
• Lower limit of 16% for onset (Temp>5°C)
• Lower limit of 20% for fast growth (Temp>10°C)
• Decay
• Wood below 20% MC - decay does not occur
• Above 26-28% MC decay initiated
• Decay continues until MC returns below 20%
ASHRAE, 2009; FPL, 2010; Straube, 2005; Wang et al., 2010
Potential Impact?
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Mould – Slow Growth (MC >16%, T > 5°C)
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
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Mould – Fast Growth (MC >20%, T > 10°C)
Decay risk
Total hours above 20% MC after exceeding 28% MC
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
DblS
I-JoistS
DatumS
PICS
XPSS
StnwoolS
DblN
I-JoistN
DatumN
PICN
XPSN
StnwoolN
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The Warming Effects of Air Leakage
-10.0
-5.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
1/5 1/12 1/19 1/26 2/2 2/9 2/16 2/23 3/2 3/9 3/16 3/23 3/30 4/6 4/13 4/20 4/27 5/4 5/11
Te
mp
era
ture
(D
eg
. C
)
Date (D/M)
The Warming Effect of Exfiltrating Air
Actual Sheathing Temp.
Predicted Sheathing Temp.Air Injection Phase
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WATER INJECTION RESULTS
What if a Window Leaks?
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• Injected via tubing into the absorbent sheet on exterior of OSB [ 30 ml – twice daily ]
• 1st Interval – 300 ml
• 2nd Interval – 420 ml
Water Injection Test
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Deep Cavity
Exterior Insulated
Water Injection Test
Wett
ing 1
Wett
ing 2
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Drying Capacity
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
5/25 6/1 6/8 6/15 6/22 6/29 7/6 7/13 7/20 7/27 8/3 8/10 8/17 8/24 8/31 9/7 9/14 9/21 9/28 10/5 10/12
Mo
istu
re C
on
ten
t (%
)
Date
Moisture Content of North Walls
Datum-N
PIC-N
XPS-N
RW-N
Double-N
Wetting mat
injections (1)
Wetting mat
injections (2)
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Drying Capacity
0.0
2000.0
4000.0
6000.0
8000.0
10000.0
12000.0
14000.0
16000.0
South North South North South North South North South North
Datum PIC XPS RW Double
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SUMMARY
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Zero Ready Wall Options
• University of Waterloo Study considered 5 Zero Ready Wall assemblies
• Design and construction use variations on techniques and materials common to current industry standard walls
• Field study to assess hygrothermal performance and potential durability
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Baseline
• Deep Walls showed elevated sheathing moisture contents in baselines condition
– Upper sheathing up to 17% and upper plate up to 24%
• All exterior insulated walls exhibited baseline sheathing moisture content similar to the datum wall
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Air Leakage
• Both Deep Walls showed an increased sensitivity to air leakage and a greater potential for condensation
• All exterior insulated walls studied showed a significant reduction in condensation potential due to air leakage
• Don’t underestimate the potentially greater moisture risk associated with tighter walls
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Rain Leakage
• The XPS and PIC walls showed a significant reduction in outward drying capacity, while the Stonewool wall was similar to non-exterior insulated walls
• For wetting at the structural sheathing layer, Deep Walls exhibited similar rain leakage response standard wall
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