Air Barriers vs.

Vapor Barriers Roger G. Morse AIA, Stephen M. Lattanzio PE

Paul Haas CIH, Gordon A. Brandon Brian Crowder

Morse Zehnter Associates Rensselaer Technology Park

165 Jordan Road Troy, NY 12180

Moisture Intrusion into Exterior Wall Cavity

• Liquid Moisture • Air Infiltration • Vapor Diffusion

Air Infiltration vs. Vapor Diffusion

Methods Used to Determine Location of Vapor Retarder

• Rule of Thumb – Mapping and prescriptive requirements

• Dew Point Calculation • Hour-by-hour simulation

Location of Vapor RetarderRule of Thumb

• Rule of Thumb: Locate on warm side of insulation – North – toward inside – South – toward outside – Mixed Climate - ????

• Problem – Most places have both a heating and a cooling season

Unforgiving Northern Construction

Forgiving Northern Construction

Unforgiving Southern Construction

Forgiving Southern Construction

Mapping Climate/Hygrothermal Zones

Specific Requirements for Zone

Calculation Methods

• ASHRAE Dew-Point Method – Steady state for given outside temperature

and humidity

ASHRAE Dew-Point Method

Location of Condensation

Dew Point Calculation

Calculation Methods

• Hourly Simulations – Hour by hour weather data – Typical

Meteorological Year (TMY)– WUFI

– MOIST (no longer supported)

Hygrothermal Modeling

• Hygrothermal Modeling Software • WUFI-ORNL/IBP Hygrothermal Model for

Architects and Engineers. Dr. Achilles N. Karagiozis, A. Oak Ridge National Laboratory, Kuenzel, H. Fraunhofer Institute fur Bauphysik, Holzkirchen, Germany

• http://www.ornl.gov/sci/btc/apps/moisture/

WUFI Input Screen

WUFI Output Screen

WUFI Output Screen

WUFI Water Content Profiles

Construction with vinyl wall covering Construction without vinyl wall covering

WUFI Temperature and Humidity ProfilesConstruction with vinyl wall covering Construction without vinyl wall covering Gypsum board wall side face (3) Gypsum Gypsum board wall side face (5) Gypsum board room side face (4) board room side face (6)

Test House # 1

Bonus Room in Attic

Mold Spots Under Plastic Wall Covering

Mold Through Gypsum Board

2×4 STUD (TYP.)

KRAFT PAPER FACED FIBERGLASS BATT

INSULATION

½" GYP. BOARD

CHAIR RAIL

PLASTIC COVERED WALL PAPER

WAINSCOT

VENTILATED ATTIC

AIR CONDITIONED ROOM

Batt Insulation on Attic Side

Attic Ventilated

Attic Side of Walls

Kraft Paper Toward Room

Kraft Paper Laminated Material

Engineered for Perm of 1.0

Mold on Attic Side of Gypsum Bd

Mold on Attic Side of Gypsum Bd

Locations with Painted Surface ATTIC

½" GYP. BOARD 2×4 STUD KRAFT PAPER FACED (TYP.) FIBERGLASS BATT

ROOM INSULATION

AIR FLOW

BATT INSULATION

KRAFT PAPER FACING

SPOTS OF MOLD GROWTH ON PAPER FACE OF DRYWALL

HUMID AIR

Locations with Plastic Wall CoveringATTIC

½" GYP. BOARD 2×4 STUD (TYP.)

ROOM

KRAFT PAPER FACED FIBERGLASS BATT

INSULATION

PLASTIC COVERED

WALL PAPER

AIR FLOW

SPOTS OF MOLD GROWTH ON PAPER FACE OF DRYWALL

HUMID AIR

GYPSUM CORE SATURATED WITH LIQUID WATER

PATCHES OF MOLD INFRINGING ON GYPSUM CORE

BATT INSULATION

KRAFT PAPER FACING

PLASTIC COVERED WALL PAPER

Wall Open to AtticObserved and Predicted Locations of Condensation

Surface

Painted Interior Vinyl Wall Covering

Field Rule of Thumb

Dew Point

Hour by Hour Field Rule of

Thumb Dew Point

Hour by Hour

Outside Face of Kraft × × × × × × Outside Face of Gypsum Board

Light Mold × × × ×

Gypsum Board × × × × Paint × × ×

Ducts Compress Insulation

Mold at Compressed Insulation

Mold at Wall Penetrations

AIR FLOW

CONDENSATION & MOLD GROWTH

½" GYP. BOARD 2×4 STUD (TYP.)

KRAFT PAPER FACED FIBERGLASS BATT

INSULATION

ATTIC

ROOM

OUTLET BOX

COVER PLATE

OUTLET OR SWITCH

Condensation at Penetrations in Wall

Test House # 2

½" PLYWOOD

2×4 STUD (TYP.)

KRAFT PAPER FACED FIBERGLASS BATT

INSULATION

½" GYP. BOARD

VENTILATED ATTIC

AIR CONDITIONED ROOM

OUTLET BOX

Insulated Attic

Attic Ventilated

Pour Insulation – No Vapor Retarder

Plywood Sheathing on Attic Wall

Kraft Paper Toward Inside

Painted Interior SurfaceATTIC ½" PLYWOOD

½" GYP. BOARD 2×4 STUD KRAFT PAPER FACED (TYP.) FIBERGLASS BATT

ROOM INSULATION

AIR FLOW STOPPED

NO MOLD ON ANY SURFACE

Wall with Plywood Air BarrierObserved and Predicted Locations of Condensation

Surface

Painted Interior Vinyl Wall Covering

Field Rule of Thumb

Dew Point

Hour by Hour Field Rule of

Thumb Dew Point

Hour by Hour

Outside Face of Kraft None × None None NA × × × Outside Face of Gypsum Board None None None NA × × Gypsum Board None None None NA × × Paint None None None NA × ×

Air Barriers vs.

Vapor Barriers Roger G. Morse AIA, Stephen M. Lattanzio PE

Paul Haas CIH, Gordon A. Brandon Brian Crowder

Morse Zehnter Associates Rensselaer Technology Park

165 Jordan Road Troy, NY 12180