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.

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
 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
North Park Passive House

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
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
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
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
Assemblies and Sensors

9. 9
Building Layout

10. 10
South Elevation
S
3
S
2
R
S
D

11. 11
North Elevation
N
3
N
2
R
N
D

12. 12
Installation

13. 13
Data Logger

14. 14
Enclosure Monitoring Data – T – N Wall

15. 15
Enclosure Monitoring Data – T – S Wall

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
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
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
Fungal Models
 VTT Mould Growth
 Surface mould
 Aesthetic and health effects
 Laboratory regressions

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
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
Discussion + Questions
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