Managing Rainwater at the Window-Wall Interface

1. 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

2. 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

3. 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

4. Drying Wetting 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

5. 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

8. 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 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.”

9. 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

10. 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

11. CMHC SCHL 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

12. e.g.  CMHC SCHL 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.

13. Key Points • 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 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

14. Detail A Variation NRC/IRC Research Program • Develop procedure to assess rainwater ingress • Evaluate specific window-wall interface details to determine how effective they manage rainwater intrusion

15. Test Specimen

16. 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

17. Self-adhered Membranes • Strip of self-adhered flashing membrane over the joint between the window flange and the sheathing membrane (not at sill)

18. Self-adhered Membranes

19. Test Observations Shingle-lapping Reverse lapping Large water accumulation on the window head NO Water accumulation at head Water accumulation at head

20. Test Observations • Fish mouths and reverse lapping allowed water ingress

21. 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

22. 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)

23. 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) Shims created a gap Window installed over furring strips Facilitate Drainage at Rough Sill of Flanged Windows

24. Shims created a gap Window installed over furring strips Specimen Details

25. 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

26. 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

27. Fabrication of V-sideASTM Back side of flange is caulked

28. Higher water deposition on the rough sill Observations – Effects of Air Pressure Distribution Specimen B-W1 (V-side; ASTM): High pressure drop (P) across wetted airtight external plane Self-adhered membrane 302 Pa Bead of sealant at back of window flange No venting or drainage at sill Tighter plane of the assembly P = 302 – 55 247 Pa 55 Pa Intended interior air barrier leakier than exterior wet layers of wall specimen 0 Pa Jamb detail (horizontal view)

29. No seal behind flange Vented and drained at the sill Lower water deposition on the rough sill Observations – Effects of Air Pressure Distribution Specimen B-W1 (B-side): Lower pressure drop across wetted “vented” external plane Self-adhered membrane 302 Pa Airtightness at this plane of wall assembly not as tight as V-side (ASTM method) P = 117 Pa 185 Pa Intended assembly air barrier leaks as much as V-side 0 Pa Jamb detail (horizontal view)

30. Airtight plane on exterior- WET DRY- Airtight plane on interior of joint Observations – Effect of Location of Plane of Airtightness Same rate of air leakage across specimen, 2 different designs

31. 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

32. 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 Rate of water deposition on the rough sill Lower air leakage rate on interior ABS 0 Pa 700 Pa

33. 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

34. Other Factors to Consider • Location of window in relation to thermal plane of wall • Vancouver, -5°C outside; 20°C inside 7.0 C 3.0 C

35. To Foam or not to foam? Is that the question? Photos from Gas Technologies Institute

36. 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.

37. Project literature Trade journals: “Effective Sealing of the Wall-window Interface” ; Home Builder Magazine, March / April 2010, Lacasse, M. A. and Armstrong, M.M.

38. 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)

39. 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

40. 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.