Managing Rainwater at the
Window-Wall Interface
Presented by :
Michael Lacasse
on behalf of:
(M.M. Armstrong, S.M. Cornick, G. Ganapathy, A. Jacob,
M. Nicholls, S. Nunes, M. Rousseau)
Canadian Home Builders’ Association,
Technical Research Committee Meeting, Ottawa, 28 May 2010
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Introduction
• The problems – you know
what they are but to
summarise...Results from BE
surveys
• Wall- Window interface details
– Key elements from laboratory
studies
• Thermal performance at the
interface
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Introduction, cont’d
• CMHC Surveys of Building
Envelope Performance
• 1995 – Survey of Building Envelope
Failures in the Coastal Climate of British
Columbia
• 1999 – Wall Moisture Problems in Alberta
Dwellings
• 2001 – Study of High-Rise Envelope
Performance In The Coastal Climate of
British Columbia
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Surveys of Building Envelope
Performance
The Survey - Why Did Walls Fail?
•
Inappropriate balance between wetting and
drying mechanisms
– Exposure - walls got wet
– Details - let water in
– Sensitivity of assemblies - inability to
drain or dry
Drying
Wetting
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Surveys of Building Envelope
Performance, cont’d
Finding:
• (at least) 25% of the moisture
problems associated with water
ingress into wall assemblies
were directly attributed to
penetration through the windows
or the window-wall interface
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Windows and the
Building Envelope
“Rain penetration is a major problem with glazing and must be
controlled….”
Glazing Design - Canadian Building Digest #55 (CBD55) published in July 1964
“Many inquiries concerning rain penetration of exterior wall are
received by the B.C. Regional Station…. and are focused on
window installation practices.”
Rain Leakage of Residential Windows in the Lower Mainland of British
Columbia – Building Practice Note No. 42 (BPN42)
Division of Building Research,
National Research Council of Canada
November 1984
“….reports on window performance problems in
Atlantic Canada…..”
Building Research Note No. 210 (BRN No. 210) - 1984
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2002 Water Penetration
Resistance of Windows
STUDY OF MANUFACTURING,
BUILDING & INTERFACE DESIGN,
INSTALLATION AND
MAINTENANCE FACTORS
WINDOW
TERMINOLOGY
SUMMARY
OF STUDY
WINDOW
INSTALLATION
GUIDE
STUDY OF CODES, STANDARDS,
TESTING AND CERTIFICATION
RDH
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Partial Conclusions
and Recommendations
• Most frequent leakage path  L5
(L5 : Through window-wall interface to
adjacent wall assembly)
• L4 and L5 are considered “high” risk for
consequential damage
(L4 : through window to adjacent wall
assembly)
• Minor variation exists between window
types with respect to leakage paths
L3
L2
L6
L1
L4
L5
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Partial Conclusions
and Recommendations
•
The CSA A440 B rating performance criteria does not
address the current dominant leakage paths that are
associated with installed windows
Risk of
Consequential
Damage
Rating
Applicability
of A440
Testing to
Leakage Path
L1 - Through fixed unit to
interior
Moderate
Good
L2 - Around operable unit to
interior
Moderate
Good
L3 - Through window to wall
interface to interior
Moderate
Never
L1
High
Sometimes*
L4
L4 - Through window
assembly to adjacent wall
assembly
L5 - Through window to wall
assembly interface to
adjacent wall assembly
High
Never
L6 - Through window
assembly to concealed
compartments within window
assembly
Minor
Good
Leakage Paths
L3
L2
L6
L5
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Depends on where window frame is attached to test frame
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Partial Conclusions
and Recommendations
•
Manufacturers have to focus on the design of the entire
installed window. This includes …the interface with the
perimeter building walls.
•
Windows need to be …installed with redundant
assemblies.
•
e.g. 
The addition of sub sill drainage to interface design
would improve water penetration performance of
installed windows
•
Designers need “…to increase their focus on interface
detailing, considering continuity of all of the critical
barriers..”
•
Installers need to have greater understanding of the
manufacturing and building design strategy.
•
The creation of a mandated or generally accepted
certification protocol, would have a positive impact on
quality control issues.
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Key Points
CMHC-NRC
(with
industry
partners) water
initiateleakage
WWI project
Test
results
indicate
dominant
to
evaluate
paths
as: water management performance of various
window installation details
L4 : through window to adjacent wall assembly
• Possibility to evaluate different interface details and
L5their
: Through
interfaceentry
to adjacent
wall
abilitywindow-wall
to manage rainwater
– evaluate
assembly of design
robustness
– High frequency
occurrence andapproach
consequential
• Development
of of
a “standards”
in a damage
laboratory
setting
– precursor
a fieldstandards
certification
– L4 & L5 not
addressed
by currenttowindow
protocol
• Benchmark “performance” of proposed designs
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NRC/IRC Research Program
Detail A
Variation
• Develop procedure
to assess rainwater
ingress
• Evaluate specific
window-wall
interface details to
determine how
effective they
manage rainwater
intrusion
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Test Specimen
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Effectiveness of Seals at
Window Frame/Sheathing
Membrane Joints
• Several approaches to seal the joints
between the window and the wall
against water ingress were examined:
– Seal the back of the window flange
against the sheathing membrane
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Self-adhered Membranes
– Strip of self-adhered flashing
membrane over the joint
between the window flange
and the sheathing membrane
(not at sill)
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Self-adhered Membranes
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Test Observations
Reverse lapping
Shingle-lapping
Large water accumulation on the
window head
Water accumulation
at head
NO Water
accumulation at head
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Test Observations
• Fish mouths and reverse
lapping allowed water
ingress
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Sequencing is Critical
Reverse lapping can channel water behind the plane of
water resistance, and risk of damage increases
•Shingle lapping is essential
– Rough sill flashing laps OVER the sheathing membrane
– Sheathing membrane laps OVER the drip cap head flashing
– Rough jamb membrane laps OVER the corner upstand of
the sill flashing
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Lesson #1:
Rough Opening Will Get Wet:
Drain it Out
• Flash and drain the rough opening
– Protect moisture-sensitive materials from water
absorption
– Provide a drainage path to the outside
•
•
•
•
•
Sloped rough sill
Back dam
Water impermeable rough sill; up 150 mm on the jambs
Ease of drainage out of rough sill, and out of wall assembly
Integration with other elements contributing to the control of
rainwater ingress (i.e. shingle lapping, sequencing)
ROUGH SILL FLASHING SYSTEM
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Facilitate Drainage at Rough
Sill of Flanged Windows
Ensure positive drainage:
• Provide drainage at sill –
no seal along flange at sill
• Do not tape front of flange
at sill joint
• Can install window on
shims or furring strips to
create a clear gap (plus
enhanced venting)
Window installed
over
furring
strips
Shims
created
a gap
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Specimen Details
Window installed over
furring strips
Shims created a
gap
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Air Pressure Difference
• Effect on water accumulation on rough sill of:
– Location of highest air pressure drop in relation to
location of plane of wetness
– Air leakage rate
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Lesson #2:
Location of Higher Pressure
Drop in WWI should be DRY
Observations:
• Typical technique for sealing perimeter of window flange to
sheathing membrane created plane of high resistance to air
flow on exterior — however — at this interface, water could
flow through small gaps - was not 100% watertight
• High pressure drop occurred across imperfect interface seal
• Presence of film of water at this interface.
• Pressure difference drove water through interface seal
• Resulted in higher water accumulation onto rough sill.
• Lower water accumulation on rough sill achieved when:
• Resistance to air flow at interface seal lower as compared to
interior air barrier
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Fabrication of V-side
ASTM
Back side of
flange is caulked
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Observations – Effects of
Air Pressure Distribution
Specimen B-W1 (V-side; ASTM):
High pressure drop (P) across wetted airtight external plane
Exterior
302 Pa
Bead of sealant
at back of
window flange
No venting or
drainage at sill
55 Pa
P = 302 – 55 247 Pa
Self-adhered membrane
Tighter plane of the
assembly
Pressure tap to measure air
pressure in the cavity behind
the siding (cavity)
Pressure tap to measure air pressure
in the stud cavity (stud)
Higher water
deposition on
the rough sill
0 Pa
Interior
Intended interior air barrier
leakier than exterior wet
layers of wall specimen
Jamb detail (horizontal view)
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Observations – Effects of
Air Pressure Distribution
Specimen B-W1 (B-side):
Lower pressure drop across wetted “vented” external plane
Exterior
302 Pa
No seal
behind
flange
Self-adhered membrane
P = 117 Pa
Vented and
drained
185 Pa
at the sill
Lower water
deposition on
the rough sill
Airtightness at this plane of
wall
assembly
Pressure
tap to measurenot
air as tight as
pressure in(ASTM
the cavity behind
V-side
method)
the siding (cavity)
Pressure tap to measure air pressure
in the stud cavity (stud)
0 Pa
Intended assembly air barrier
leaks as much as V-side
Interior
Jamb detail (horizontal view)
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Observations – Effect of
Location of Plane of Airtightness
Reservoir Water Entry - 08 ABS
140
Same rate of air
leakage across
specimen,
2 different designs
Rate of water deposition
on the rough sill (ml/min)
120
100
Airtight plane on exterior- WET
80
60
40
DRY- Airtight plane on interior of joint
20
0
0
100
200
300
400
500
600
700
800
Chamber Pressure (Pa)
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Lesson #3:
Keep Air Barrier Tight and Dry
• Current practice aims at sealing joints that can get
wet: joint between window frame (flange) and
sheathing membrane
• Imperfect seals that got wet and were subjected to
higher pressure difference sucked water through seal
imperfections
• Plane of higher pressure drop (Air Barrier System)
should be in a dry location, further inside and towards
interior of joint
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Effect of Leakage Rate
of Interior ABS
Leakier intended air barrier system resulted in higher water
deposition on rough sill (exterior plane was sealed)
Higher air leakage rate on
interior ABS
Lower air leakage rate on
interior ABS
0 Pa
700 Pa
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Other Factors to Consider
• Location of window in relation to thermal plane of wall
• Thermal effects of draining sill
• Effect of placing insulation into wall-window joint
cavity on drainage capability
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Other Factors to Consider
• Location of window in relation to thermal plane of wall
• Vancouver, -5°C outside; 20°C inside
3.0 C
7.0 C
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To Foam or not to foam?
Is that the question?
Photos from Gas
Technologies Institute
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Points to Remember
• Rough opening should be protected with flashing to
ensure water tightness at sill - Rough opening will get
wet during service life
– Ensure all elements are shingle-lapped to outside Ensure proper sequencing takes place. Review
procedures with those responsible for installation
• Design sill at rough opening to facilitate drainage of
incidental water entry from protected sill
– sloped sill; drainage gap at sill; back dam
• Locate wall-window seal on interior of wall assembly
– Ensure 1st and 2nd line of defense against water
penetration are not most airtight layers of wall. Rain
screen principle applies to WWI too.
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Project literature
Trade journals:
“Effective Sealing of the Wall-window Interface” ;
Home Builder Magazine, March / April 2010,
Lacasse, M. A. and Armstrong, M.M.
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Project literature
Phase “A” — Interface details typical of Canadian
practice
Phase
— Variations
incorporating a drainage
Further“B”
reading
–
medium
Lacasse, M.A.; Rousseau,
M.Z.; Cornick, S.M.; Plescia, S."Assessing the
effectiveness of wall-window interface details to manage rainwater," 10th
Phase
“C” — Use of flexible self adhered flashing
Canadian Conference on Building Science & Technology (Ottawa, ON, May 12
membrane
2005), pp. 127-138,
(NRCC-47685)
Lacasse, M.A.
et al.,
Results
on Assessingvariations
the Effectivenessfor
of Wall-Window
Phase
“D”
—
Installation
light
Interface Details to Manage Rainwater, 11th Canadian Conference on Building
commercial
design
Science and Technology,
Banff, Alberta,
2007
Cornick, S.M.; Lacasse, M.A. "A Review of climate loads relevant to assessing the
watertightness performance of walls, windows and wall-window
interfaces,"Journal of ASTM International, Vol. 2 (10), Nov/Dec 2005,
pp. 1-16 (NRCC-47645)
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Project literature
Phase “B” — Variations incorporating a drainage
medium
•
Lacasse M., Armstrong, M., Ganapathy, G., Rousseau, M., Cornick, S., Bibee, D., Shuler
,D., Hoffee, A., “Assessing the Effectiveness of Wall-Window Interface Details to
Manage Rainwater—Selected Results from Window Installation to a Wall Sheathed
in Extruded Polystyrene”, JAI (October 2009) Volume: 6, Issue 9, DOI:
10.1520/JAI101270
•
Lacasse, M., Rousseau, M., Cornick, S., Armstrong, M., Ganapathy, G., Nicholls, M.,
Williams M., “Laboratory Tests of Water Penetration through Wall-Window Interfaces
Based on U.S. Residential Window Installation Practice”, JAI (September 2009),
Volume: 6, Issue 8; DOI: 10.1520/JAI101428
•
M. A. Lacasse, S. M. Cornick, M. Rousseau, M. Armstrong, G. Ganapathy, M. Nicholls,
and S. Plescia, “Towards Development of a Performance Standard for Assessing the
Effectiveness of Wall-Window Interface Details to Manage Rainwater Intrusion”; JAI
(October 2009) Volume: 6, Issue 9, DOI: 10.1520/JAI101446
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Does this approach work?
Visual evidence from the laboratory
The following video is courtesy of Mario
Goncalves at Patenaude-Trempe and Air-Ins
Inc.
Varennes, Québec.
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