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 Building 3 – A Case Study Monitoring Program Improvements Still to Come May 2006 - BCBEC Symposium 2

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 3

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 4

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 5

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 6

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 7

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 8

Mould Growth

 Possible under humid conditions and prolonged periods of time 4 months 4 years May 2006 - BCBEC Symposium 9

When is it an Issue?

Sorption Isotherm for Fiberglass Faced Exterior Gypsum

10 9 8 7 2 1 0 0 4 3 6 5 10 20 30 40 50 60 70 80 90 10 100

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 11

Moisture Content versus Time - 100% Relative Humidity

4.5% 4.0% 3.5% 3.0% 2.5% 2.0% 1.5% 1.0% 0.5% 0.0% 0 24 48 72 96 120 144 168 1 week 192 216 240 264 288 312 336 2 weeks 360 384

Hour from beginning of test

May 2006 - BCBEC Symposium 12

Wetting (50 to 100% RH) and Drying (100% to 50% RH) Rate Comparison

10.0

9.0

8.0

7.0

6.0

5.0

Moisture uptake rate much slower than drying rate 10 days to wet, 1 day to dry half 4.0

3.0

Drying to 50% RH Wetting to 100% RH

2.0

1.0

0.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Time - Days

May 2006 - BCBEC Symposium 6% 5% 4% 3% 10% 9% 8% 7% 2% 1% 0% 13

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 14

Moisture Content vs Log Resistance for Fiberglass Faced Exterior Gypsum

14% 12% 10% 8% 6% 4% 2% 0% 4.0

4.5

5.0

Critical Moisture Content (2%): Below 5 log Ohms (100 Kohms)

5.5

6.0

6.5

7.0

Log Resistance - Log(Ohms)

7.5

May 2006 - BCBEC Symposium 8.0

8.5

9.0

15

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 16

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 17

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 18

Building 1

May 2006 - BCBEC Symposium 19

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

May 2006 - BCBEC Symposium 21

May 2006 - BCBEC Symposium 22

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 23

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 24

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 25

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 26

Impact of Insulated Sheathing

More Insulation on Exterior = Drier May 2006 - BCBEC Symposium 27

Impact of Insulated Sheathing

More Insulation on exterior = Drier May 2006 - BCBEC Symposium 28

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 29

Impact of a Paint VR vs. Poly VB Assuming no rain water Leaks!

May 2006 - BCBEC Symposium 30

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 31

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

Moisture Content of Sheathing May 2006 - BCBEC Symposium 33

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 34

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 35

Building 3: A Case Study

May 2006 - BCBEC Symposium 36

May 2006 - BCBEC Symposium 37

May 2006 - BCBEC Symposium 38

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 39

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

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

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

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 43

Location of Test Openings May 2006 - BCBEC Symposium 44

May 2006 - BCBEC Symposium 45

May 2006 - BCBEC Symposium 46

May 2006 - BCBEC Symposium 47

May 2006 - BCBEC Symposium 48

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 49

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 50

Corner Detail

Condensation on steel studs and gypsum sheathing observed May 2006 - BCBEC Symposium 51

Thermal Modeling

Interior 19C, Exterior 5C Interior Dewpoint 10C Failed Air Barrier @ Corner = Condensation 52

What went wrong?

    High interior relative humidity/dewpoint during the winter – Poor Ventilation When building was retrofit in 2002, original R-8 insulation was left in stud cavity and polyethylene vapour barrier was removed Wall Design Flawed?

Morrison Hershfield (next) will talk about potential rehabilitation strategies and improvements to mitigate the high wintertime RH in next presentation May 2006 - BCBEC Symposium 53

Prevention by Design?

 Use hygrothermal modeling (WUFI) to analyze the impact of modifications on the original design  What if the poly was left in?

  What if the batt insulation were removed?

Vapour Permeable Air/Water Resistant Barrier in lieu of peel and stick May 2006 - BCBEC Symposium 54

Hygrothermal Results

    Leave in Poly – dual vapour barrier, in theory would work (perfect system) however in practice would fail, small leaks Remove R8 batt Insulation – increases the temperature of the sheathing and improves drying Trowel or Spray applied Air/Vapour/Moisture membrane (300-600 metric perms) in lieu of peel and stick improves drying even with high indoor RH Must improve indoor ventilation – lower RH during the winter May 2006 - BCBEC Symposium 55

Monitoring Program Suggestions

    Data Collection interval (1 hour vs. 15 minute) All data collected with loggers  No separate Hobos for interior or exterior data Collect Solar Radiation Data Monitor all elevations, not just wind-driven rain exposed, ie North May 2006 - BCBEC Symposium 56

Research Still to Come

    Analyze wetting events and material response Analyze drying rates Further hygrothermal modeling Final report of results and recommendations May 2006 - BCBEC Symposium 57

Thank you

RDH

Building Engineering Ltd.

Ontario Graduate Scholarship May 2006 - BCBEC Symposium 58