Evaluation of potential for moisture in high

IMPROVING THE BUILT ENVIRONMENT g

6 th Annual North American

Passive House Conference

Evaluation of Potential for Moisture in High R-‐value

Walls in Cold Climates

October 2011

Lois B. Arena

Steven Winter Associates, Inc.

© 2011 Steven Winter Associates, Inc. All rights reserved.

Overview of Presentation

Project Summary

Reasons for research

Questions to be answered

Modeling

Field Testing

Analysis


Project Summary

Evaluate potential for moisture problems in 3 new wall assemblies

Modeling – this year

WUFI

THERM

Field Monitoring – beginning 2012

Brick rehab

High-‐R walls: R-‐40 & 60

Code walls: hybrid insulation w/ spray foam & fiberglass


Reasons for Research

Changes in construction due to:

Drastic increase in retrofit activities

Programs like PH & NZEH challenges

Increased use of hybrid insulation strategies

New insulation products

Code changes


Research Focus

Assemblies

Brick walls with interior insulation;

Super insulated walls at least

12” thick: R-‐40 and R-‐60;

Code built walls using spray foam insulation and fiberglass batts.


Research Focus

Climate zones 4A, 5A, 6A and 7

experience both cooling and heating seasons

considerable humidity during the summer


Vapor Pressure Analysis


Modeling -‐ WUFI

Wall

Type

Brick

Wall

R-

40+ 1

R-

60+ 2

Table 1. Brick Wall and High-R Walls to be Evaluated in WUFI

Vapor

Retarder

None, 0.1,

1.0

Cavity

Insulation

Fiberglass

Cellulose

Cavity

Insulation

Thickness

(inches)

2-5

2-5

Spray Foam

Thickness

(inches)

3

Sheathing

Type

None, 0.1,

1.0

None, 0.1,

1.0

Fiberglass

Cellulose

Fiberglass

Cellulose

3

1 Evaluated in Climate Zones 4 & 5

2 Evaluated in Climate Zones 6-8

5-8

5-8

8-12

8-12

0.5 - 2

0.5 - 2

2-4

--

2-4

--

4-6

--

4-6

-- n/a n/a

OSB

XPS

OSB

XPS

OSB

XPS

OSB

XPS


Sheathing

Thickness 4

(inches) n/a n/a

0.5

2-4

0.5

2-4

0.5

4-6

0.5

4-6

Modeling -‐ THERM

WUFI can only analyze continuous components

Want to analyze condensation potential due to thermal bridging at framing members -‐

THERM

Image from THERM


Field Testing

Short Term

moisture content of components using a hand held moisture meter

Adjust values in WUFI if necessary

Long Term

RH & Temp at critical interfaces

Moisture content – OSB, brick, studs

Climatic conditions


Failure Criteria – Today’s Focus

Moisture Content (MC)

Total Assembly

OSB

Condensation Potential

Center of Cavity

At Stud


MC & Condensation Potential

Moisture Content (MC) of OSB < 20%

Condensation Potential – graph interior air dew point temp vs. surface temp

WUFI -‐ foam/cavity insulation

THERM – framing/insulation, foam/cavity insulation

Final Water Content of Assembly < Initial


EcoVillage Community


EcoVillage Co-‐housing Community

Third Phase of the

Community

39 Dwelling Units

17 Detached-‐SF

4 Duplexes

14 Apartments

Common House

PH Certification

Desired


EcoVillage Specifications – Climate 6

R-‐80 Ceiling

R-‐62 Walls

R-‐40 Slab (edge & under)

Windows: U<0.15

& >0.55 SHGC

Solar Thermal

DHW

Electric Resistance


EcoVillage – 2 Wall Options

1 st -‐ Architect

Larson truss w/ 6” foam + blown/batt cavity insulation


EcoVillage Wall Options

2 nd -‐ Builder

Modified truss w/ 4” foam + R-‐38 batt


WUFI


Outdoor Conditions

Albany, NY (closest profile to Ithaca)

Cold Year File

Outdoor conditions can be used to generate interior

Temp & RH


Indoor Conditions -‐ Initial Assumptions

3 bedroom

PH Infiltration – 0.6 ACH

@50

Default moisture generation


Case 1: PH ACH, ASHRAE

Heat Only, 3 Bedroom


Case 7: Sine Curve


Case 8: ERV , ASHRAE Heat

Only, 1 Bedroom +0.1 perm

Vapor Retarder


Climate Zone 5 – Collected Data


Indoor Climate Chosen

Sine Curve

65 to 68 ϶&

50 to 70% RH

Have to chose from predefined list in free version of WUFI


Architect’s Case – Sine Wave Results


Architect’s Case – Sine Wave Results


Builder’s Case – Sine Wave Results


Builder’s Case – Sine Wave Results


Builder’s Case – More Foam


THERM


Dew Point/Condensation Potential

Determine Interior Setpoint

Determine Outdoor Temperature to Use in THERM

Design?

Average of Winter Months?

Evaluate Center of Cavity and Near Stud


Finding Dewpoint


THERM


THERM Results At Design

Should Condensation Potential be Evaluated at

Design for High R-‐walls?


Recommendations


Important Factors to Consider

Indoor Conditions

HRV or ERV

# of Occupants

Outdoor Climate

R-‐value of Components, not thickness

Unusual moisture loads inside home


Code Minimum R-‐values for

Class III Vapor Retarder


Recommendations for EcoVillage

Install enough foam to contribute more than 50% of overall R-‐value to reduce the potential for condensation

Use a vented cladding system


Recommendations for Consultants in Cold, Moist Climates

Do NOT use code minimums for exterior rigid or spray foam for high R-‐walls

Use WUFI and THERM to evaluate your projects on a case by case basis

Evaluate the climate conditions for your project carefully and compare to software assumptions

These walls are not forgiving

Must prevent interior moisture from getting into the walls – investigate smart vapor retarders


Questions?


Thank You.


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