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Rainscreen Performance Monitoring: Continuing Research Current Masters Thesis Research Highlights

Rainscreen Performance Monitoring: Continuing Research Current Masters Thesis Research Highlights. Presented by: Graham Finch, Dipl.T, BASc University of Waterloo, MASc Student. Introduction. Background Current Research Highlights Exterior Gypsum Hygrothermal Modeling

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Rainscreen Performance Monitoring: Continuing Research Current Masters Thesis Research Highlights

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  1. Rainscreen Performance Monitoring:Continuing ResearchCurrent Masters Thesis Research Highlights Presented by: Graham Finch, Dipl.T, BASc University of Waterloo, MASc Student

  2. Introduction • Background • Current Research Highlights • Exterior Gypsum • Hygrothermal Modeling • Building 3 – A Case Study • Monitoring Program Improvements • Still to Come May 2006 - BCBEC Symposium

  3. Background • Building Monitoring Program • RDH Building Engineering (RDH) • Canadian Mortgage and Housing Corporation (CMHC) • Homeowner Protection Office • British Columbia Housing Management Commission • Designed and installed on five buildings in Vancouver, BC being constructed or rehabilitated using a rainscreen wall assembly. • Data collected includes temperature, relative humidity, moisture content, wetness, pressure, wind, rain, and driving rain. May 2006 - BCBEC Symposium

  4. Background • University of Waterloo MASc Student • Rainscreen Performance Monitoring Study part of Graduate Thesis work • Build on initial RDH work • Further work as part of thesis • Further data analysis • Trends, Normals, Abnormalities • Wetting and Drying Rates • Hygrothermal Modeling • Validation • Material Testing May 2006 - BCBEC Symposium

  5. Presentation Outline – Research Highlights • Measuring moisture content of exterior gypsum using electrical resistance • Hygrothermal modeling of ventilated rainscreen walls • Seasonal performance of Building 1 • Improving performance by design • Building 3: A case study • Field validation of monitored results May 2006 - BCBEC Symposium

  6. Exterior Gypsum Sheathing Properties • Purpose • Measure performance of exterior fiberglass faced gypsum exposed to humid conditions • Correlate electrical resistance of gypsum with gravimetric moisture content • Well established correlation for wood • More difficult with gypsum • Provide approximate sheathing moisture contents for Buildings 3 and 5 to assess performance May 2006 - BCBEC Symposium

  7. Exterior Gypsum Sheathing Properties • Physical Properties • Strength loss with elevated moisture content • As a result of high relative humidity or liquid water exposure • Levelton study results (Later today) • Other Issues • Mould Growth • Corrosion when in contact with metals ie. Steel studs May 2006 - BCBEC Symposium

  8. Why does it matter? • Significant strength loss with as little as 1 - 2% moisture content • Saturated = Destroyed Exposed to 100% RH for 1 year May 2006 - BCBEC Symposium

  9. Mould Growth • Possible under humid conditions and prolonged periods of time 4 months 4 years May 2006 - BCBEC Symposium

  10. When is it an Issue? May 2006 - BCBEC Symposium

  11. How Long does it take? • Gypsum boards relatively permeable to water vapour • 1000-2000 metric perms • Fast response to moisture • Wetting - 2% moisture content increase (from dry) in 2 days exposed to 100% RH • Even faster drying rates • Likely prevent very high MC levels from being achieved in the field May 2006 - BCBEC Symposium

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  13. Moisture uptake rate much slower than drying rate 10 days to wet, 1 day to dry half May 2006 - BCBEC Symposium

  14. Moisture Content and Electrical Resistance • Used to correlate measured electrical resistance (ohms) with an approximate gravimetric moisture content for field monitoring studies • Determine “how wet” the gypsum is without destructive testing • Handheld moisture meters give only relative idea of moisture content • Different meters, different scales May 2006 - BCBEC Symposium

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  16. Hygrothermal Modeling • Purpose: To correlate field results with those predicted by hygrothermal simulation • Can we accurately model walls with ventilated claddings? ie Rainscreen Walls • Can you accurately model a 2D problem with 1D software? • Ventilation cannot be neglected • Current software has limitations May 2006 - BCBEC Symposium

  17. Modeling Requirements • Modeling ventilated wall assemblies with 1D software • Cladding input into model with an “effective permeance” which accounts for an assumed ventilated rate through cladding vent openings • Literature available for equivalent permeance values typically in range of 1000 + perms depending on flow rate May 2006 - BCBEC Symposium

  18. Modeling Requirements • Modeling correlation with field results • Effective permeance method works on average however: • Ventilation is a dynamic variable - Wind and temperature differences drive pressures which change on a daily basis • Better correlation achieved by using actual temperature/relative humidity values from ventilated cavity/drainage space May 2006 - BCBEC Symposium

  19. Building 1 May 2006 - BCBEC Symposium

  20. Building 1: Typical Ventilated Rainscreen Wall May 2006 - BCBEC Symposium

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  23. Discussion of Results • Stucco, Vinyl, and Cement board clad buildings all had similar annual trends and similar moisture levels of the sheathing • High RH (80-100%) and cool temperatures in the ventilated cavity space result in sheathing moisture contents between 20-25% during winter months May 2006 - BCBEC Symposium

  24. Discussion of Results • Correlation of hygrothermal simulation with field data is good • Material properties are important to correlation • Moisture Isotherm for plywood/OSB have direct impact on results May 2006 - BCBEC Symposium

  25. Uses for Hygrothermal Modeling • How can we improve the performance of ventilated rainscreen walls? • Insulated Sheathing • Is a polyethylene vapour barrier required? Would painted drywall work instead? • What is the impact of the indoor relative humidity and temperature? May 2006 - BCBEC Symposium

  26. Can Insulated Sheathing Improve Performance? • Base case R-19 (2x6 wall) • Compare to R-12 (2x4 wall) • R-19 stud insulation plus vapour permeable R-8 insulation on exterior (no poly) • R-12 stud insulation plus vapour permeable R-8 insulation on exterior (no poly) • Vapour permeable R-12 on exterior only (no stud space insulation, no poly) May 2006 - BCBEC Symposium

  27. Impact of Insulated Sheathing More Insulation on Exterior = Drier May 2006 - BCBEC Symposium

  28. Impact of Insulated Sheathing More Insulation on exterior = Drier May 2006 - BCBEC Symposium

  29. Role of Vapour Control Strategy • Typical R-19 insulated wall assembly (ventilated rainscreen) • Remove interior polyethylene vapour barrier • Use 50, 250 and 400 metric perm vapour retarding paints on drywall May 2006 - BCBEC Symposium

  30. Impact of a Paint VR vs. Poly VB Assuming no rain water Leaks! May 2006 - BCBEC Symposium

  31. Impact of Interior Conditions • 250 metric perm paint layer (interior latex paint) • 3 indoor cases analyzed using real vapour pressure data for Vancouver • Poorly ventilated (avg. winter RH 57%) • Building 1 as measured (avg. winter RH 39%) • Well ventilated (avg. winter RH 34%) May 2006 - BCBEC Symposium

  32. Relative Humidity at interior side of Sheathing May 2006 - BCBEC Symposium

  33. Moisture Content of Sheathing May 2006 - BCBEC Symposium

  34. Other Simulated Cases • OSB vs. Plywood, negligible difference in RH or MC results • Using standard OSB and Plywood properties from WUFI 3.3 database May 2006 - BCBEC Symposium

  35. Results • Insulated sheathing improves the performance of ventilated rainscreen walls • A paint vapour retarder can be used as a replacement for poly, however exterior insulation and designed ventilation are both required May 2006 - BCBEC Symposium

  36. Building 3: A Case Study May 2006 - BCBEC Symposium

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  39. Problems • High relative humidity within stud space 80-100% during winter months (All 8 monitored locations) • Corresponding high moisture content of fiberglass faced exterior gypsum • Interior suites – High relative humidity during winter (50-70%) May 2006 - BCBEC Symposium

  40. Seasonal Interior Suite Relative Humidity/Temperature July 2002-2003 May 2006 - BCBEC Symposium

  41. Seasonal Relative Humidity and Temperature at Exterior Sheathing May 2006 - BCBEC Symposium

  42. Seasonal Relative Moisture Level at Exterior Sheathing May 2006 - BCBEC Symposium

  43. Field Openings • Interior openings made in January 2006 • During seasonal period of elevated moisture levels within wall assembly • Confirm presence of moisture within stud cavity • Observe interstitial wall conditions after 4 years of service May 2006 - BCBEC Symposium

  44. Location of Test Openings May 2006 - BCBEC Symposium

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  49. Suite Observations • Interior of all suites had high interior relative humidity • Condensation on window frame and glazing surfaces • Mould growth on interior drywall surfaces at corners May 2006 - BCBEC Symposium

  50. Wall Opening Observations • Openings confirmed fiberglass faced exterior gypsum is getting wet • 80-100 relative moisture level (Delmhorst BD-10) • Calculated 1-2% moisture content (up to 6% in some locations) • Surface corrosion on steel studs • Sensors are returning valid data • Problematic details also contributing to moisture problems (thermal bridging) May 2006 - BCBEC Symposium

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