Managing Rainwater at the Window-Wall Interface

Transcription

1 Managing Rainwater at the Window-Wall Interface Prepared by : Silvio Plescia (CMHC) and Michael Lacasse (NRC) ANHWP, Edmonton and Calgary, September 2009 CMHC SCHL

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 Does this work? Visual evidence from the laboratory

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 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 Wetting Drying

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

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8 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)

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 L3 L2 L6 L1 L4 L5

11 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 L3 L2 L1 - Through fixed unit to interior Moderate Good L6 L2 - Around operable unit to interior Moderate Good L1 L3 - Through window to wall interface to interior Moderate Never L4 L4 - Through window assembly to adjacent wall assembly High Sometimes* L5 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

12 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 e.g. 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 Test results indicate dominant water leakage paths as: CMHC-NRC (with industry partners) initiate WWI project to evaluate water management performance of various window installation details L4 : through window to adjacent wall assembly Possibility to evaluate different interface details and L5 their : Through ability window-wall to manage rainwater interface entry to adjacent evaluate wall robustness assembly of design Development High frequency of a of standards occurrence and approach consequential in a damage laboratory L4 & L5 not setting addressed precursor by current to window a field standards certification protocol Benchmark performance of proposed designs

14 NRC/IRC Test Program Detail A Variation 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 Reverse lapping Shingle-lapping Large water accumulation on the window head Water accumulation at head NO 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 Flash and drain the rough opening Lesson #1: The Rough Opening Will Get Wet: Drain it Out 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

23 Ensure positive drainage: Do not caulk back of window flange Do not tape front of flange sill joint Install window on shims or on furring strips to create a clear gap (plus enhanced venting) - Provide drainage at sill no seal along flange Facilitate Drainage at Rough Sill of Flanged Windows Window installed Shims over created furring a gap strips

24 Specimen Details- W3 Window installed over furring strips Shims created a gap

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 Observations: Lesson #2: Location of Higher Pressure Drop in WWI should be DRY A typical technique for sealing window flange to sheathing membrane created a plane of high resistance to air flow on exterior but was not 100% resistant to water flow. High pressure drop occurred across that imperfect seal, which was also covered by a film of water. Air pressure difference drove water through interface seal - resulting in higher water accumulation onto rough sill. A technique consisting of maintaining sheathing membrane/ window flange connection but having lower resistance to air flow than interior air barrier resulted in lower water accumulation on rough sill.

27 Fabrication of V-side ASTM Back side of flange is caulked

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

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

30 Reservoir Water Entry - 08 ABS Observations Effect of Location of Plane of Airtightness Rate of water deposition on the rough sill (ml/min) Airtight plane on exterior- WET Same rate of air leakage across specimen, 2 different designs 20 DRY- Airtight plane on interior of joint Chamber Pressure (Pa)

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) Rate of water deposition on the rough sill Higher air leakage rate on interior ABS 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 3.0 C 7.0 C

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

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

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

38 Three Points to Remember Correctly install a subsill flashing system to protect moisture-sensitive materials in R.O. The rough opening will get wet during service life Ensure first and second line of defense against water penetration are not most airtight layers of wall. Air barrier must be dry. Rain screen principle applies to WWI too Ensure all elements are shingle-lapped to outside - Ensure proper sequencing takes place. Review those responsible for installation

39 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.

40 Project literature Phase A Interface details typical of Canadian practice Phase Further B reading Variations incorporating a drainage Lacasse, M.A.; Rousseau, medium M.Z.; Cornick, S.M.; Plescia, S."Assessing the effectiveness of wall-window interface details to manage rainwater," 10 Phase C Use of flexible self adhered flashing th Canadian Conference on Building Science & Technology (Ottawa, ON, May ), pp , membrane (NRCC-47685) Phase Lacasse, M.A. D et al., Results Installation Assessing the variations Effectiveness of for Wall-Window light Interface Details to Manage Rainwater, 11 commercial design th 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 (NRCC-47645)

41 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: /JAI 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: /JAI 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: /JAI101446