Rainscreen Performance Monitoring: Continuing Research Current Masters Thesis Research Highlights Presented by: Graham Finch, Dipl.T, BASc University of

Rainscreen Performance Monitoring:Continuing Research

Current Masters Thesis Research Highlights

Presented by:

Graham Finch, Dipl.T, BASc

University of Waterloo, MASc Student

May 2006 - BCBEC Symposium 2

Introduction

Background Current Research Highlights

Exterior Gypsum Hygrothermal Modeling Building 3 – A Case Study

Monitoring Program Improvements Still to Come


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.


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


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


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


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


Why does it matter?

Significant strength loss with as little as 1 - 2% moisture content

Saturated = Destroyed

Exposed to 100% RH for 1 year


Mould Growth

Possible under humid conditions and prolonged periods of time

4 years

4 months


Sorption Isotherm for Fiberglass Faced Exterior Gypsum

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100

Relative Humidity

Mo

istu

re C

on

ten

t (%

)

When is it an Issue?


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


Moisture Content versus Time - 100% Relative Humidity

0.0%

0.5%

1.0%

1.5%

2.0%

2.5%

3.0%

3.5%

4.0%

4.5%

0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

Hour from beginning of test

Mo

istu

re C

on

ten

t

1 week 2 weeks


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

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.028

Nov

29 N

ov

30 N

ov

01 D

ec

02 D

ec

03 D

ec

04 D

ec

05 D

ec

06 D

ec

07 D

ec

08 D

ec

09 D

ec

10 D

ec

11 D

ec

12 D

ec

13 D

ec

Time - Days

Res

ista

nce

log

(Oh

ms)

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

10%

MC

%

Wetting to 100% RH

Drying to 50% RH

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

Moisture uptake rate much slower than drying rate

10 days to wet, 1 day to dry half


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


Moisture Content vs Log Resistance for Fiberglass Faced Exterior Gypsum

0%

2%

4%

6%

8%

10%

12%

14%

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0

Log Resistance - Log(Ohms)

Gra

vim

etri

c M

ois

ture

Co

nte

nt

Critical Moisture Content (2%):

Below 5 log Ohms (100 Kohms)


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


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


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


Building 1


Building 1: Typical Ventilated Rainscreen Wall




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


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


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?


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)


Impact of Insulated Sheathing

More Insulation on Exterior = Drier


Impact of Insulated Sheathing

More Insulation on exterior = Drier


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


Impact of a Paint VR vs. Poly VB

Assuming no rain water Leaks!


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%)


Relative Humidity at interior side of Sheathing


Moisture Content of Sheathing


Other Simulated Cases

OSB vs. Plywood, negligible difference in RH or MC results Using standard OSB and Plywood

properties from WUFI 3.3 database


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


Building 3: A Case Study




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%)


Seasonal Interior Suite Relative Humidity/Temperature July 2002-2003


Seasonal Relative Humidity and Temperature at Exterior Sheathing


Seasonal Relative Moisture Level at Exterior Sheathing


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


Location of Test Openings






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


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)


Corner Detail

Condensation on steel studs and gypsum sheathing observed


Thermal Modeling

Interior 19C, Exterior 5C

Interior Dewpoint 10C

Temperature Isotherms – THERM 5.2

Failed Air Barrier @ Corner = Condensation


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


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


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


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


Research Still to Come

Analyze wetting events and material response

Analyze drying rates Further hygrothermal modeling Final report of results and

recommendations


Thank you

Building Engineering Ltd.RDH

Ontario Graduate Scholarship

Documents

Rainscreen Performance Monitoring: Continuing Research Current Masters Thesis Research Highlights Presented by: Graham Finch, Dipl.T, BASc University of