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Window Sill Pan Flashings: Are Liquid Membranes Suitable?

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Presented by Michael Wilkinson at the 17th Canadian Conference on Building Science and Technology.

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Window Sill Pan Flashings: Are Liquid Membranes Suitable?

  1. 1. 1 Window Sill Pan Flashings: Are Liquid Membranes Suitable? 2017 CCBST Conference – Day 1 November 6th, 2017 Presented by: Michael Wilkinson | MEng, EIT
  2. 2. 2  Industry sill flashing practices  What about liquid membranes?  Long term water ponding testing  Drying potential evaluation  Gap bridging ability  Conclusions Outline
  3. 3. 3 Vapour permeable sheet/self-adhered products not acceptable
  4. 4. 4 Impermeable self-adhered membranes work adequately
  5. 5. 5 TOO MUCH Impermeable self-adhered membrane
  6. 6. 6 TOO MUCH Impermeable self-adhered membrane
  7. 7. 7 What about liquid membranes?  Vapour permeable liquid applied membranes becoming more common for treating window rough openings  Impermeable self-adhered membrane still applied at sill  Can be cost effective and simpler
  8. 8. 8 Vapour permeable liquid flashings suitable at sill? Photo Credit: Green Building Advisor
  9. 9. 9 Vapour permeable liquid flashings suitable at sill?  Existing industry standards and guidelines do not yet adequately cover liquid applied membranes applied in horizontal applications  Key considerations and potential issues:  Water ponding resistance  Drying potential  Flexibility and gap bridging ability  Compatibility and adhesion with other materials  Weather dependent curing (rainwater, cold, heat)  Workability and ease of application  Longevity, durability, exposure to UV & heat
  10. 10. 10 Long term water ponding resistance  Devised test to demonstrate the potential for water uptake through vapor permeable liquid flashing membranes on horizontal surfaces (wood sill, OSB and plywood edges)  Industry awareness that impermeable self-adhered membranes work adequately in this application and that permeable sheet goods (housewrap) are not suitable.  No comparative data to suggest what vapor permeable water repellant liquids may be suitable for this application  Compared liquid membrane results with self-adhered control membranes that were known to work well or fail
  11. 11. 11 Window sill setup Window sill mockup with 2x6 sill and OSB and plywood sheathing Moisture content pins installed into wood at critical locations Setup to pond water on liquid membrane surface
  12. 12. 12 Window sill setup
  13. 13. 13 0 5 10 15 20 25 30 35 40 45 0 Days 7 Days 14 Days 21 Days 28 Days 35 Days 42 Days MoistureContent(%) L01 (STPe-Based) L02 (Water-Based Acrylic) L03 (Silicone-Based) L04 (Water-Based Acrylic) S01 (Vapour-Permeable SAM) S02 (Vapour-Impermeable SAM) Window sill wetting – Results Safe MC <20%
  14. 14. 14 0 5 10 15 20 25 30 35 40 45 0 Days 7 Days 14 Days 21 Days 28 Days 35 Days 42 Days MoistureContent(%) L01 (STPe-Based) L02 (Water-Based Acrylic) L03 (Silicone-Based) L04 (Water-Based Acrylic) S01 (Vapour-Permeable SAM) S02 (Vapour-Impermeable SAM) Window sill wetting – Results Safe MC <20%
  15. 15. 15 0 5 10 15 20 25 30 35 40 45 0 Days 7 Days 14 Days 21 Days 28 Days 35 Days 42 Days MoistureContent(%) L01 (STPe-Based) L02 (Water-Based Acrylic) L03 (Silicone-Based) L04 (Water-Based Acrylic) S01 (Vapour-Permeable SAM) S02 (Vapour-Impermeable SAM) Window sill wetting – Results Safe MC <20%
  16. 16. 16 Window sill wetting – Observations Swelling failure liquid membrane at OSB resulting in leak Excessive absorption of liquid membrane and discoloration
  17. 17. 17 Window sill wetting – Observations Mould after 30 days due to absorption into OSB sheathing below a relatively absorptive & permeable liquid applied window sill flashing
  18. 18. 18 Drying potential evaluation  Devised test to demonstrate whether improved drying characteristics manifest through vapor permeable liquid flashing membranes on horizontal surfaces (wood sill, plywood edge)  Wood-framing often wetted during construction in the Pacific Northwest with little opportunity to dry throughout winter months  Potential for enhanced drying at rough opening particularly if interior window framing (king studs, cripple studs, headers) limit drying to the interior  Compared liquid membrane results with permeable and impermeable self-adhered membranes
  19. 19. 19 Window mock setup Moisture content pins installed into wood at critical locations (red dots) Wetted samples left outside beneath roof through winter months Exposed underside of wetted samples located beneath roof
  20. 20. 20 Safe MC < 20% 0 5 10 15 20 25 30 35 40 45 0 Days 7 Days 14 Days 21 Days 28 Days 35 Days 42 Days 49 Days 56 Days MoistureContent(%) L01 (STPe-Based) L02 (Silicone-Based) S01 (Vapour-Permeable SAM) S02 (Vapour-Impermeable SAM) Window mock-up drying – Results
  21. 21. 21 Safe MC < 20% 0 5 10 15 20 25 30 35 40 45 0 Days 7 Days 14 Days 21 Days 28 Days 35 Days 42 Days 49 Days 56 Days MoistureContent(%) L01 (STPe-Based) L02 (Silicone-Based) S01 (Vapour-Permeable SAM) S02 (Vapour-Impermeable SAM) Window mock-up drying – Results
  22. 22. 22 Gap Bridging Ability
  23. 23. 23 Gap Bridging Ability  Test consisted of applying the membrane to substrate with different gap widths and evaluating bridging ability.  Three gap widths: 1/4”, 1/8” and 1/16” were created using factory edge of gypsum sheathing  Monitored over 72 hours for formation of pin holes and voids (often not visible/apparent immediately)
  24. 24. 24 Gap Bridging Ability Gap Bridging Test Results after 72 Hours Note: All specimens applied at manufacturer’s specified thickness. Sample ID Chemistry Thickness (wet mils) 1.6mm (1/16”) Gap 3.2mm (1/8”) Gap 6.4mm (¼”) Gap L01 STPe 15 mils FAIL FAIL FAIL L02 STPe 15 mils FAIL FAIL FAIL L03 Silicone 30 mils FAIL FAIL FAIL L04 STPe 25 mils BRIDGED BRIDGED FAIL L05 Silicone 65 mils BRIDGED BRIDGED BRIDGED L06 STPe 15 mils BRIDGED FAIL FAIL L07 Acrylic 48 mils FAIL BRIDGED FAIL
  25. 25. 25 Gap Elongation – From Zero to >1/16” Opening Sample ID Widen to 1/16” Close to 0” Widen to 1/8” Close to 0” Widen to 1/4” Close to 0” Widen to 1/2” L01 FAIL FAIL FAIL FAIL FAIL FAIL FAIL L02 BRIDGED BRIDGED FAIL FAIL FAIL FAIL FAIL L03 BRIDGED BRIDGED FAIL FAIL FAIL FAIL FAIL L04 BRIDGED BRIDGED FAIL FAIL FAIL FAIL FAIL L05 BRIDGED BRIDGED BRIDGED BRIDGED BRIDGED BRIDGED BRIDGED L06 FAIL FAIL FAIL FAIL FAIL FAIL FAIL L07 BRIDGED BRIDGED BRIDGED BRIDGED BRIDGED FAIL FAIL
  26. 26. 26 Conclusions  Preliminary results confirmed common industry assumptions  Plywood and OSB more susceptible to moisture uptake and decay than 2x framing  Permeable and impermeable self-adhered membranes performed as expected  Liquid-applied flashing performance impacted by membrane chemistry and application thickness  Potentially some chemistries acceptable as sill flashings  Thicker membranes exhibited better gap bridging capabilities, but all membranes still require reinforcement across gaps/cracks  No discernable drying benefit to liquid applied membrane flashings over impermeable self-adhered products  Development of new ASTM or AAMA test methods required to accurately reflect in situ performance of liquid membrane flashings
  27. 27. 27 Discussion + Questions FOR FURTHER INFORMATION PLEASE VISIT  www.rdh.com  www.buildingsciencelabs.com  Michael Wilkinson- mwilkinson@rdh.com

Presented by Michael Wilkinson at the 17th Canadian Conference on Building Science and Technology.

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