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Passive House Wall Assembly Performance - A Case Study

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Improvements in building efficiency can significantly reduce carbon emissions and are an intrinsic component in greenhouse gas reduction targets. The Passive House concept provides a framework for high-performance building that is growing in popularity in Canada, and particularly in the Pacific Northwest. The Passive House standard requires its buildings to achieve specific performance values for heating energy use intensity, total energy use intensity, spatial temperature variation, heat recovery ventilation performance and air leakage rate. The promised co-benefits of Passive Houses include superior thermal comfort and indoor air quality.

Passive House design is not prescriptive and can incorporate many different design aspects. The wall assembly is no exception. This paper evaluates the hygrothermal performance of a deep-stud wall assembly of a Passive House in Victoria, BC, with regards to moisture durability. The concern with deep or doublestud wall assemblies is the combined effects of reduced drying with wall configurations that place moisture sensitive materials in riskier locations. Consequently, enclosure monitoring was undertaken in an occupied six-plex over the period of one year.

The enclosure monitoring sensor packages were installed in strategic locations in the wall assembly to monitor the conditions of the assembly. The assemblies were evaluated based on the results of an empirical mold risk index. The wall assembly appears to perform acceptably, with minor concerns of mold growth on the North wall. Air leakage is a significant concern for cavity insulated walls, but the airtightness requirements of Passive house minimize this risk.

Presented at the 15th Canadian Conference on Building Science and Technology.

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Passive House Wall Assembly Performance - A Case Study

  1. 1. 1 Passive House Wall Assembly Performance – A Case Study CCBST XV PAPER 87 2017/11/06 ROBERT LEPAGE, M.A.SC., P.ENG.
  2. 2. 2  Intro – Passive House, Performance Requirements  Lit Review: Concerns with High-R Value Walls  Monitoring Methods  Monitoring Results  Analysis of Results  Performance Calculations (VTT Model) Outline
  3. 3. 3 North Park Passive House
  4. 4. 4 High-R Cavity Insulated Walls  Many variations: typically thick walls with cellulose insulation  Moisture Risks:  Construction Moisture  Bulk Water Leaks  Air Leakage Condensation  Vapour Diffusion (In and Out)  Organic sheathing on exterior  High-R Value: Decreased Drying (less heat flow)  Concern: Risk of Mould
  5. 5. 5 Literature Summary  Tsongas (1991): “Walls with more cavity insulation led to increased moisture levels”  Arena (2013): Simulations overpredict wall performance. North Walls ~20%MC  Lepage (2013): Parametric hygrothermal study, incl. air and water leak. Cavity insulated walls found to be sensitive  Ueno (2015): Double-Stud Wall, Sheathing MC ~30% with high interior RH, MC~20% with lower interior RH*  Smegal (2016): Comparative case-study on deep-stud walls. Found even nominal exterior insulation improved dryness  Trainor (2016): Field exposure test hut, incl. air leakage. Double-stud is at risk of air leakage (MC 30%+)
  6. 6. 6 NPPH Exterior Walls  2x8 wood stud wall 24” OC  Dense pack blown in cellulose  Dew-point analysis  2x4 service cavity filled with rock wool batts.
  7. 7. 7 Monitoring Method  Objectives: assess risk from construction, bulk water, air leakage, and vapour diffusion moisture loads  Sensors:  MC pins in sheathing  RH&T Sensors  Boundary Conditions:  Indoor: T&RH Sensor  Exterior: Local MET tower and drainage cavity sensor
  8. 8. 8 Assemblies and Sensors
  9. 9. 9 Building Layout
  10. 10. 10 South Elevation S 3 S 2 R S D
  11. 11. 11 North Elevation N 3 N 2 R N D
  12. 12. 12 Installation
  13. 13. 13 Data Logger
  14. 14. 14 Enclosure Monitoring Data – T – N Wall
  15. 15. 15 Enclosure Monitoring Data – T – S Wall
  16. 16. 16 0 10 20 30 40 50 60 70 80 90 100 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature(°C)andRH(%) Sheathing T VB T Drywall T Int. Dew Point Exterior CFI RH InteriorCFI RH Results – RH & T 0 10 20 30 40 50 60 70 80 90 100 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature(°C)andRH(%) Sheathing T VB T Drywall T Int. Dew Point Exterior CFI RH InteriorCFI RH  North Wall South Wall
  17. 17. 17 Vapour Drive -1500.0 -1000.0 -500.0 0.0 500.0 1000.0 1500.0 500 750 1000 1250 1500 1750 2000 2250 2500 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec VapourPressure(Pa) VapourPressure(Pa) S2- Exterior S2- Interior N2- Exterior N2- Interior -1500 -1000 -500 0 500 1000 1500 500 750 1000 1250 1500 1750 2000 2250 2500 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec ΔPressure(Pa) VapourPressure(Pa) S2- Differential N2- Differential -1500.0 -1000.0 -500.0 0.0 500.0 1000.0 1500.0 500 750 1000 1250 1500 1750 2000 2250 2500 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec VapourPressure(Pa) VapourPressure(Pa) S2- Exterior S2- Interior N2- Exterior N2- Interior -1500.0 -1000.0 -500.0 0.0 500.0 1000.0 1500.0 500 750 1000 1250 1500 1750 2000 2250 2500 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec VapourPressure(Pa) VapourPressure(Pa) S2- Exterior S2- Interior N2- Exterior N2- Interior S2- Differential N2- Differential
  18. 18. 18 Moisture Contents 8 10 12 14 16 18 20 22 24 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec MoistureContent(%) S2 - MC S3 - MC N2 - MC N3 - MC
  19. 19. 19 Fungal Models  VTT Mould Growth  Surface mould  Aesthetic and health effects  Laboratory regressions
  20. 20. 20 VTT Mould Model 0 0.5 1 1.5 2 2.5 3 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec MouldIndex N2 N3 S2 S3 0 0.5 1 1.5 2 2.5 3 2016 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026 MouldIndex N2 N3 S2 S3
  21. 21. 21 Conclusion  Deep/Double Stud Walls: They can work  Air tightness persnicketiness  Slight risk of surface mould  Higher safety factor with exterior insulation  Even nominal!
  22. 22. 22 Discussion + Questions FOR FURTHER INFORMATION PLEASE VISIT  www.rdh.com  www.buildingsciencelabs.com OR CONTACT US AT  RLEPAGE@rdh.com RLEPAGE@RDH.COM

Improvements in building efficiency can significantly reduce carbon emissions and are an intrinsic component in greenhouse gas reduction targets. The Passive House concept provides a framework for high-performance building that is growing in popularity in Canada, and particularly in the Pacific Northwest. The Passive House standard requires its buildings to achieve specific performance values for heating energy use intensity, total energy use intensity, spatial temperature variation, heat recovery ventilation performance and air leakage rate. The promised co-benefits of Passive Houses include superior thermal comfort and indoor air quality. Passive House design is not prescriptive and can incorporate many different design aspects. The wall assembly is no exception. This paper evaluates the hygrothermal performance of a deep-stud wall assembly of a Passive House in Victoria, BC, with regards to moisture durability. The concern with deep or doublestud wall assemblies is the combined effects of reduced drying with wall configurations that place moisture sensitive materials in riskier locations. Consequently, enclosure monitoring was undertaken in an occupied six-plex over the period of one year. The enclosure monitoring sensor packages were installed in strategic locations in the wall assembly to monitor the conditions of the assembly. The assemblies were evaluated based on the results of an empirical mold risk index. The wall assembly appears to perform acceptably, with minor concerns of mold growth on the North wall. Air leakage is a significant concern for cavity insulated walls, but the airtightness requirements of Passive house minimize this risk. Presented at the 15th Canadian Conference on Building Science and Technology.

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