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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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• 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

Introduction, cont’d

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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

WettingDrying

Surveys of Building Envelope Performance

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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

Surveys of Building Envelope Performance, cont’d

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Windows and the Building Envelope

“Rain penetration is a major problem with glazing and must be controlled….”

“Many inquiries concerning rain penetration of exterior wall are received by the B.C. Regional Station…. and are focused on window installation practices.”

Glazing Design - Canadian Building Digest #55 (CBD55) published in July 1964

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

RDH

STUDY OF CODES, STANDARDS, TESTING AND CERTIFICATION

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• 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

L6

L1

L4

L5

L2

Partial Conclusions and Recommendations

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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

Leakage Paths 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

L4 - Through window assembly to adjacent wall assembly

High Sometimes*

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

Depends on where window frame is attached to test frame

L3

L6

L1

L4

L5

L2

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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.

• 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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e.g.

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Key Points

Test results indicate dominant water leakage paths as:

L4 : through window to adjacent wall assembly L5 : Through window-wall interface to adjacent wall

assembly– High frequency of occurrence and consequential damage – L4 & L5 not addressed by current window standards

CMHC-NRC (with industry partners) initiate WWI project to evaluate water management performance of various window installation details

• Possibility to evaluate different interface details and their ability to manage rainwater entry – evaluate robustness of design

• Development of a “standards” approach in a laboratory setting – precursor to a field certification 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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– Strip of self-adhered flashing membrane over the joint between the window flange and the sheathing membrane (not at sill)

Self-adhered Membranes

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Self-adhered Membranes

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Large water accumulation on the

window head

Reverse lapping Shingle-lapping

Water accumulation at head

NO Water accumulation at head

Test Observations

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Test Observations

• Fish mouths and reverse lapping allowed water ingress

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Sequencing is Critical

•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

Reverse lapping can channel water behind the plane of water resistance, and risk of damage increases

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ROUGH SILL FLASHING SYSTEM

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)

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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)

Facilitate Drainage at Rough Sill of Flanged Windows

Shims created a gapWindow installed over furring strips

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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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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

Lesson #2: Location of Higher Pressure Drop in WWI should be DRY

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Fabrication of V-sideASTM

Back side of flange is caulked

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Pressure tap to measure air pressure in the cavity behind the siding (cavity)

Pressure tap to measure air pressurein the stud cavity (stud)

Interior

Exterior302 Pa

55 Pa

Self-adhered membrane

0 Pa

Bead of sealant at back of window flange

No venting or drainage at sill

Specimen B-W1 (V-side; ASTM): High pressure drop (P) across wetted airtight external plane

Tighter plane of the assembly

Intended interior air barrier leakier than exterior wet layers of wall specimen

Jamb detail (horizontal view)

Higher water deposition on the rough sill

P = 302 – 55 247 Pa

Observations – Effects of Air Pressure Distribution

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Pressure tap to measure air pressure in the cavity behind the siding (cavity)

Pressure tap to measure air pressurein the stud cavity (stud)

Interior

Exterior302 Pa

185 Pa

Self-adhered membrane

0 Pa

Intended assembly air barrier leaks as much as V-side

No seal behind flange

Vented and drained at the sill

Airtightness at this plane of wall assembly not as tight as V-side (ASTM method)

Lower water deposition on the rough sill

Specimen B-W1 (B-side): Lower pressure drop across wetted “vented” external plane

P = 117 Pa

Jamb detail (horizontal view)

Observations – Effects of Air Pressure Distribution

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Reservoir Water Entry - 08 ABS

0

20

40

60

80

100

120

140

0 100 200 300 400 500 600 700 800Chamber Pressure (Pa)

Rat

e of

wat

er d

epos

ition

on

the

roug

h si

ll (m

l/min

)Observations – Effect of

Location of Plane of Airtightness

Airtight plane on exterior- WET

DRY- Airtight plane on interior of joint

Same rate of air leakage across

specimen, 2 different designs

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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

Rat

e of

wa t

er d

e po s

itio n

on

the

r ou g

h si

ll

Lower air leakage rate on interior ABS

Higher air leakage rate on interior ABS

Leakier intended air barrier system resulted in higher water deposition on rough sill (exterior plane was sealed)

700 Pa0 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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• Location of window in relation to thermal plane of wall• Vancouver, -5°C outside; 20°C inside

3.0 C 7.0 C

Other Factors to Consider

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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 “B” — Variations incorporating a drainage medium

Phase “C” — Use of flexible self adhered flashing membrane

Phase “D” — Installation variations for light commercial design

Further reading – Lacasse, M.A.; Rousseau, M.Z.; Cornick, S.M.; Plescia, S."

Assessing the effectiveness of wall-window interface details to manage rainwater," 10th Canadian Conference on Building Science & Technology (Ottawa, ON, May 12 2005), pp. 127-138, (NRCC-47685)

Lacasse, M.A. et al., Results on Assessing the Effectiveness of Wall-Window Interface Details to Manage Rainwater, 11th Canadian Conference on Building 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

• 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

Phase “B” — Variations incorporating a drainage medium

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The following video is courtesy of Mario Goncalves at Patenaude-Trempe and Air-

Ins Inc.Varennes, Québec.

Does this approach work? Visual evidence from the laboratory