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Rainscreen Performance Monitoring: Insights and Advances from Current Research

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tevy
58 diapositives · 728 Views · Oct 02, 2014

This thesis presentation by Graham Finch from the University of Waterloo delves into the performance monitoring of rainscreen wall assemblies in Vancouver, BC. It highlights essential research on exterior gypsum, monitoring techniques, and hygrothermal modeling. Key findings include moisture content correlations, seasonal performance evaluations, and recommendations for design improvements to enhance wall performance. Additionally, it discusses the implications of moisture on structural integrity and the challenges of accurate modeling in ventilated wall systems.

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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

  12. May 2006 - BCBEC Symposium

  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

  15. May 2006 - BCBEC Symposium

  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

  21. May 2006 - BCBEC Symposium

  22. May 2006 - BCBEC Symposium

  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

  37. May 2006 - BCBEC Symposium

  38. May 2006 - BCBEC Symposium

  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

  45. May 2006 - BCBEC Symposium

  46. May 2006 - BCBEC Symposium

  47. May 2006 - BCBEC Symposium

  48. May 2006 - BCBEC Symposium

  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