Hygrothermal Modeling & Building Enclosure Design. Introduction

Hygrothermal Modeling & Building Enclosure Design Introduction

Hygrothermal Modeling & Building Enclosure Design Presentation Outline 1. Introduction 2. Why Use Hygrothermal Modeling 3. The WUFI Program 4. WUFI Inputs 5. WUFI Outputs 6. Frame Wall Examples 7. Case Studies 8. Limitations 9. Conclusions Presenters: Dave Bryan AIA, LEED AP Third Level Design Minneapolis, Minnesota Third-Level@comcast.net John Rahill AIA Black River Design Montpelier, Vermont JohnR@BlackRiverDesign.com Introduction

THE 1970 s BROUGHT FOCUS ON USING RENEWABLE ENERGY, NOT ON SAVING ENERGY. ACTIVE SOLAR! GREEN LUMBER 2X6 FRAMING, FIBERGLASS INSULATION NO INSULATION AROUND THE FOUNDATION OR UNDER SLAB FULL 8 OF INSULATION BETWEEN FRAMING IN ROOF Introduction

Hood House 3rd Project of Black River Construction View of Wood Trusses Solar Heat Storage System Introduction

WHICH HOUSE WAS AHEAD OF THEIR TIME? THE ENVELOPE: IS WHERE IT S AT THE GREATEST ADVANCEMENTS IN UNDERSTANDING HOW BUILDINGS PERFORM HAS BEEN IN THE ENVELOPE AND IN REDUCING HEAT LOSS NOT IN RENEWABLE ENERGY + TECHNOLOGY Introduction

Before we tightened up buildings, we didn t have many moisture problems 1800 S HOUSE LITTLE INSULATION, NO VAPOR BARRIER, GOOD DRYING FROM INSIDE AND OUTSIDE, POROUS WALLS Introduction

BROUHA HOUSE: Vapor barrier carefully installed, fiberglass batt insulation, tar paper, new siding. and Peeling Paint! Introduction

BROUHA HOUSE, A FEW YEARS LATER: When design fails: Everyone s opinion is valid. Why is the paint peeling? Wrong brand of paint Should have used stain Should have back primed Should not have used a vapor barrier it needs to be removed Introduction

TIMBER FRAME MODERN HOME VERMONT 1999 Introduction

Introduction

TIMBER FRAME MODERN HOME 5 YEARS LATER: The paint is peeling on the siding.. Introduction

TIMBER FRAME MODERN HOME TIMBER FRAME WALL SECTION Introduction

CONTRIBUTING FACTORS TO WALL FAILURE Introduction

PAST ASSUMPTIONS THAT GOT US INTO TROUBLE: 1. In Northern Climates moisture source is in the interior, so you can prevent problems with an impermeable interior vapor barrier when it is done perfectly 2. Siding can be made waterproof. 3. Human beings are predictable 4. Air Tightness will take care of itself. 5. Thermal Bridging is a minor issue 6. Caulking Works 7. Contractors and Subcontractors have the same concern for the details that we have. Introduction

How do we design resilient, energy efficient building enclosures that avoid problems with mold, rot and corrosion? How we used to do it: Consider examples of local buildings Consult best practices checklist Comply with building codes Guess the rest! Why Use Hygrothermal Modeling

Why Use Hygrothermal Modeling

HYGROTHERMAL MODELING An analytical tool for designing building assemblies to: Control moisture Reduce the risk of mold, rot and corrosion Allows fine-tuning assemblies for longevity and cost-effectiveness Allows sensitivity analysis to determine critical variables: Vapor retarder type Insulation quantity, type and location Sheathing type Air-tightness of assemblies Air barrier permeability Natural ventilation of wall and roof cavities Interior relative humidity Why Use Hygrothermal Modeling

Other Reasons Hygrothermal Modeling is Worthwhile: 1. Getting it wrong can be very expensive Why Use Hygrothermal Modeling

Other Reasons Hygrothermal Modeling is Worthwhile: 1. Getting it wrong can be very expensive 2. As insulation levels increase, the danger of moisture damage increases Why Use Hygrothermal Modeling

Other Reasons Hygrothermal Modeling is Worthwhile: 1. Getting it wrong can be very expensive 2. As insulation levels increase, the danger of moisture damage increases 3. As architecture firms expand their geographic markets, they are continually designing assemblies for new climates 4. New materials cannot necessarily just be substituted for old materials Why Use Hygrothermal Modeling

Why Use Hygrothermal Modeling

Infiltration Control WUFI Resilience & Tolerance to Uncontrollable Events WUFI Moisture Vapor Control WUFI Affordability Success Criteria for Wall and Roof Design Insulation Effectiveness Ease of Construction Low Maintenance, Maximum Longevity WUFI Rain Penetration Control WUFI The WUFI Program

WUFI??. Acronym for Transient Heat and Moisture Transport Verified by extensive (& on-going) field and laboratory testing in Germany & U.S. Allows realistic calculation of the moisture behavior of building assemblies The WUFI Program

The WUFI Program

Fraunhofer Institute, Holzkirchen, Germany: Building Materials Test Facilities Hartwig Kunsel, Director F.I. Holzkirchen The WUFI Program

The WUFI Program

Field Validation Example: Wall Assembly Test Facility in Charleston, South Carolina by Oak Ridge National Laboratories One of many sites used to validate WUFI results against actual performance The WUFI Program

The WUFI Program

WUFI Inputs

Exterior Climate WUFI Inputs

Exterior Climate Driving Rain Varies Tremendously by Region Zone 6 Zone 6 Zone 5 Minneapolis Montpelier Boston WUFI Inputs

Wind-Driven Rain and Building Envelopes Perfect building assemblies exist only on paper Most wall claddings and many types of roof claddings leak Moisture-tolerant enclosures must be designed to deal with water that penetrates the cladding ASHRAE Standard 160 Criteria for Moisture Control in Buildings requires walls to withstand 1% of wind-driven rain penetrating the cladding Modeled and Measured Drainage, Storage and Drying behind Cladding Systems, Straube, 2007 WUFI Inputs

Interior Climate WUFI Inputs

Moisture Movement Mechanisms Higher air pressure Lower air pressure Air flow through visible cracks and holes Water vapor is carried by the air Higher water vapor concentration Lower water vapor concentration No air flow Water vapor flow through tiny pores Control with Air Barrier Small holes & seams must be sealed. Continuity important Control with Vapor Retarder Small holes & seams not too important if there is a good air barrier Both Air Barrier and Vapor Retarder are important from: Insulations, Sheathings and Vapor Diffusion Retarders, Building Science Corporation 2003 WUFI Inputs

5/8 gypsum board with latex paint Example of WUFI Wall Section Input WUFI Inputs

Example of WUFI Output Film Clip of Wall Section Status in October Exterior Interior WUFI Outputs

Example of WUFI Output Film Clip of Wall Section Status in February Exterior Interior WUFI Outputs

Example of WUFI Output Center of Sheathing WUFI Outputs

Damage Threshold Criteria Identify moisture sensitive materials and critical components Structural damage of wood products: Limit moisture content of wood products to 18% peak (80% to 85% R.H.) Check for mold growth risk Structural damage of gypsum products: Limit moisture content of fiberglass-faced gypsum to 90% to 95% R.H. Check for mold growth risk Corrosion of metals: Keep the surface of metals < 80% R.H. for any 30 day period (unless specific material information is available) Corrosion Rates vs RH, Harriman, 2003 WUFI Outputs

Fraunhofer Institute, Holzkirchen, Germany: Building Mold and Fungi Studies WUFI Outputs

A Short Hygrothermal History of Frame Walls in Zone 6 Frame Wall Examples

International Energy Conservation Code U.S. Climate Zones Building Science Corporation Frame Wall Examples

Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis Leaky 2 X4 wall with R11 fiberglass and interior latex paint Legacy Wall 1 Damage Threshold WUFI Assumptions: ASHRAE 160P rain load 1% wind-driven rain penetration South-east facing wall Moisture Load: 1 person/5880 cu.ft. Unvented cladding is leaky: 4 ach.5 interior air changes per hour Class C infiltration rate into stud cavity Temperature and Relative Humidity of Sheathing Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis Leaky 2 x6 wall with R19 fiberglass and interior latex paint Legacy Wall 2 Damage Threshold Red Text indicates change since last case WUFI Assumptions: ASHRAE 160P rain load 1% wind-driven rain penetration South-east facing wall Moisture Load: 1 person/5880 cu.ft. Unvented cladding is leaky: 4 ach.5 interior air changes per hour Class C infiltration rate into stud cavity Temperature and Relative Humidity of Sheathing Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis Tighter 2 x6 wall with R19 fiberglass, interior latex paint and mechanical ventilation Legacy Wall 3 Damage Threshold Red Text indicates change since last case WUFI Assumptions: ASHRAE 160P rain load 1% wind-driven rain penetration South-east facing wall Moisture Load: 1 person/5880 cu.ft. Unvented cladding is leaky: 4 ach.35 interior air changes per hour Class B infiltration rate into stud cavity Temperature and Relative Humidity of Sheathing Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis Tighter 2 x6 wall with R19 fiberglass, polyethylene vapor barrier and mechanical ventilation Current Code Compliant Damage Threshold Red Text indicates change since last case WUFI Assumptions: Same As Previous Case Temperature and Relative Humidity of Sheathing Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis Tighter 10 wall with R30 fiberglass, interior vapor retarder paint and mechanical ventilation High Performance Wall Damage Threshold Red Text indicates change since last case Results are similar for other R30 vapor- permeable cavity insulations: cellulose & open cell spray foam WUFI Assumptions: Same As Previous Case Temperature and Relative Humidity of Sheathing Frame Wall Examples

Frame Wall Examples

WUFI: A MODELING PROGRAM TO HELP WHEN REAL LIFE GETS IN THE WAY INSULATION STRATEGY AFTER VALUE ENGINEERING Case Studies

Family Center Wall Design Evolution Initial Wall Design 4 Exterior Foam Sheathing Relative Humidity Damage Threshold Final Wall Design 1.5 Rigid with fiberglass in Cavity Sheathing Relative Humidity 4 Extruded Polystyrene Exterior Insulation No Stud Cavity Insulation 1.5 Extruded Polystyrene Exterior Insulation R19 Fiberglass Cavity Insulation R outside sheathing to R inside sheathing ~ 20 R outside sheathing to R inside sheathing ~.4 Case Studies

Family Center Wall Design Evolution Family Center: Second Set of Assemblies Max. R.H. (mid-winter) Max. % Water Content (mid-winter) Moisture Run Wall Description exterior insul sheathing spray foam cavity insul exterior insul sheathing spray foam cavity insul Creep? Case 1 wood clapboards, 3/4" airspace, 1.5" XPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b. 85% 90% 60% 1.7% 14.8% 4.7% N, 5 yr Case 2 cement board, 3/4" airspace,.05 perm Blueskin v.b.,1" XPS, plwd, 4" closed cell spray foam, 5/8" gyp.bd 90% 90% 60% 5.2% 18.0% 2.7% Y, 5 yr, sheath Case 3 cement board, 3/4" airspace, 8 perm Blueskin wrb,1" XPS, plwd, 4" closed cell spray foam, 5/8" gyp.bd 90% 88% 60% 4.1% 16.8% 2.4% N, 5 yr Case 4 wood clapboards, 3/4" airspace, 15 lb felt, 1.5" XPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b. 85% 90% 60% 1.8% 14.9% 4.6% N, 5 yr Case 5 wood clapboards, 3/4" airspace, 15 lb felt, 2" XPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b. 83% 90% 60% 1.7% 14.0% 4.2% N, 5 yr Case 6 wood clapboards, 3/4" airspace, 15 lb felt, 2" EPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b. 81% 90% 60% 1.3% 13.9% 4.2% N, 5 yr Case 7 clapboards, 3/4" airspace, 15 lb felt, 2" XPS, OSB, 1" closed cell spray foam, 3.5" unfaced f.g., 5/8" gyp.bd,1 83% 85% 70% 60% 1.9% 14.0% 4.1% 3.7% N, 5 yr Case 8 wood clapboards, 15 lb felt, OSB, 3.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b. 92% 82% 19.0% 6.0% N, 3 yr Case 9 wood clapboards, 15 lb felt, OSB, 3.5" unfaced f.g., 5/8" gyp.bd,.1 perm v.b. 90% 81% 16.5% 6.7% N, 3 yr Case 10 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,.1 perm v.b. 93% 62% 19.1% 8.1% N, 5 yr Case 11 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,.07 perm v.b. (poly) 92% 62% 19.1% 8.1% N, 5 yr Case 12 wood clapboards, 15 lb felt, plywood, 5.5" unfaced f.g., 5/8" gyp.bd,.07 perm v.b. (poly) 91% 62% 21.9% 8.3% N, 5 yr Case 13 wood clapboards, 15 lb felt, plywood, 5.5" unfaced f.g., 5/8" gyp.bd, no v.b. 100% 61% 73.0% 44.0% N, 5 yr Case 14 wood clapboards, 15 lb felt, OSB, 3.5" unfaced f.g., 5/8" gyp.bd, no v.b. 100% 61% 80.0% 76.0% N, 3 yr Case 15 wood clapboards, 15 lb felt, OSB, 3.5" unfaced f.g., 5/8" gyp.bd, 4 perm paint 100% 82% 34.0% 8.2% N, 3 yr Case 16 wood clapboards, 15 lb felt, OSB, 3.5" unfaced f.g., 5/8" gyp.bd,.07 perm v.b., 4 perm paint 90% 83% 15.3% 7.7% N, 3 yr Case 17 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,.07 perm v.b., 4 perm paint 92% 60% 18.0% 9.3% N, 5 yr Case 18 clapboards, 3/4" airspace, 15 lb felt, 1" XPS, OSB, 2" closed cell spray foam, 3.5" unfaced f.g., 5/8" gyp.bd,1 86% 88% 69% 60% 2.2% 15.3% 4.2% 3.5% N, 5 yr Case 19 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,.07 perm v.b., 4 perm paint - low density batt 91% 61% 16.3% 1.4% N, 5 yr Case 20 wood clapboards, 15 lb felt, OSB, 3.5" unfaced f.g., 5/8" gyp.bd,.07 perm v.b., 4 perm paint- low density batt 89% 86% 14.9% 1.0% N, 5 yr Case 21 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd, 1 perm v.b. - low density batt 93% 61% 19.5% 1.0% N, 5 yr Case 22 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd, 1 perm paint - low density batt 93% 86% 19.9% 0.8% N, 5 yr Case 23 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd, 1 perm v.b on ext of gyp.bd - low density batt 93% 60% 19.9% 0.8% N, 5 yr Case 24 wood clapboards, 15 lb felt, Plywd, 5.5" unfaced f.g., 5/8" gyp.bd, 1 perm paint - low density batt 92% 86% 22.1% 0.9% N, 5 yr Case 25 clapboards, 3/4" airspace, 15 lb felt,osb, 2" closed cell spray foam, 3.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b. 91% 71% 61% 16.8% 6.3% 4.0% N, 5 yr Case 26 clapboards, 3/4" airspace, 15 lb felt,osb, 2" closed cell spray foam, 3.5" cellulose., 5/8" gyp.bd,1 perm v.b. 92% 71% 61% 17.0% 6.9% 10.4% N, 5 yr Case 27 clapboards, 3/4" airspace, "tyvek",osb, 2" closed cell spray foam, 3.5" cellulose., 5/8" gyp.bd,1 perm v.b. 91% 70% 61% 16.7% 6.7% 10.4% N, 5 yr Case 28 clapboards, 3/4" airspace, 15 lb felt,osb, 3" closed cell spray foam, 2.5" cellulose., 5/8" gyp.bd,1 perm v.b. 91% 68% 61% 16.5% 4.4% 9.7% N, 5 yr Case 29 clapboards, 3/4" airspace, 15 lb felt, 1" XPS, OSB, 2" closed cell spray foam, 3.5" cellulose, 5/8" gyp.bd,1 pe 86% 88% 67% 60% 2.2% 15.3% 4.6% 9.9% N, 5 yr Case 30 clapboards, 3/4" airspace, 15 lb felt, OSB, 2" c.c. spray foam, 3.5" cellulose, 5/8" gyp.bd,.1 perm v.b., 4 perm paint 91% 74% 60% 16.6% 5.2% 11.7% N, 5 yr Case 31 clapboards, 3/4" airspace, 15 lb felt, 1" XPS, OSB, 2" closed cell spray foam, 3.5" cellulose, 5/8" gyp.bd, no v 88% 90% 65% 65% 2.3% 15.9% 5.8% 9.0% N, 5 yr Case 32 wood clapboards, 3/4" airspace, 1.5" XPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b.- low density batt 82% 88% 60% 1.4% 13.6% 0.5% N, 5 yr Case 33 wood clapboards, 3/4" airspace, 1.5" XPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd, v.b, l.d. batt, Membrain, 4 per 77% 80% 65% 1.3% 11.8% 0.4% N, 5 yr Case 34 wood clapboards, 3/4" airspace, 1.5" XPS, OSB, 5.5" unfaced f.g., 5/8" gyp.bd,1 perm v.b, low density batt, N 81% 87% 60% 1.3% 13.2% 0.4% N, 5 yr Case 35 wood clapboards, 15 lb felt, OSB, 5.5" unfaced f.g., 5/8" gyp.bd, l.d. batt, Membrain, 4 perm paint 92% 74% 17.5% 0.7% N, 5 yr Criteria for full acceptance < 90% closed < 18% closed < 5% increase Criteria for marginal performance >90 & <100 cell >18 & <20 cell in MC over Criteria for rejection > or = 100% > or = 20% period Case Studies

Stay on this side of line for OSB or Plywood Sheathing.50 Case Studies

Vapor Permeability of selected Building Materials Class 1 Vapor Barriers Class 2 Vapor Retarders Class 3 Vapor Retarders 0 to.1 perms.1 to 1 perms 1 to 10 perms Polyethylene Sheet Vapor Barrier Paint Latex Paint Aluminum Foil Oil-based Paint, 3 coats Oil-based Paint, primer +1coat most Bituminous Sheet Closed-cell Polyurethane Closed-cell Polyurethane Materials spray foam, thicker than 2 spray foam, less than 1 Vinyl Wall Covering, Extruded Polystyrene, Extruded Polystyrene, un-perforated unfaced, thicker than 1 unfaced, less than 1 Hot Asphalt Roofing Kraft Paper (nominal) Kraft Paper (NAHB measured) Smart Vapor Retarders (Membrain, Intello) Open-cell Polyurethane spray foam (Icynene) Building codes generally require Class I or Class II vapor retarders for Climate Zones 5 through 8 Case Studies

Family Center Vapor Retarder Options Vapor Barrier Paint Sheathing Relative Humidity Damage Threshold Smart Vapor Retarder Sheathing Relative Humidity Vapor retarder selection can improve assembly performance Case Studies

PRIVATE RESIDENCE: CENTRAL VERMONT Case Studies

PRIVATE RESIDENCE: CENTRAL VERMONT PROPOSED WALL SECTION: CONTINUOUS RIGID INSULATION AROUND ENTIRE BUILDING VE WALL SECTION: 1.5 RIGID EXTERIOR INSULATION SPRAY FOAM INSULATION IN THE WALL CAVITY. Cost saving measure at the time. Case Studies

Wall Design Evolution Initial Wall Design Sheathing Relative Humidity Damage Threshold Final Wall Design Sheathing Relative Humidity 4 Foil-faced Isocyanurate Exterior Insulation No Stud Cavity Insulation 1.5 Foil-faced Isocyanurate Exterior Insulation 3.5 Closed Cell Spray Foam Cavity Insulation R outside sheathing to R inside sheathing ~ 26 R outside sheathing to R inside sheathing ~.4 Case Studies

INSULATION STRATEGY Case Studies

Closed Cell Polyurethane Spray Foam Stud Cavity Insulation Without Exterior Insulation: No ventilation behind cladding Damage Threshold Ventilation behind cladding No Exterior Insulation 3.5 Closed Cell Spray Foam Cavity Insulation No Exterior Insulation 3.5 Closed Cell Spray Foam Cavity Insulation Vertical furring strip cavity vented top and bottom Case Studies

WUFI allows simulation of the effectiveness of Naturally-Ventilated Wall and Roof Cavities Modeled and Measured Drainage, Storage and Drying behind Cladding Systems, Straube, 2007 Case Studies

WUFI 1D & 2D Stud Wall Comparison WUFI 1D through cavity insulation Center of sheathing between studs Center of sheathing next to stud Center of sheathing outside stud Wood Stud Wall Minneapolis, fiber cement siding, Densglass sheathing, R11 in, R 10 out Limitations

Recommendations for Zone 6 Frame Walls Assume that wall the cladding will not be watertight Provide a drainage plane between cladding & water barrier Can be small ~ 1 mm Design assemblies to dry to both inside & outside Provide a Class II vapor retarder (.1 perm to 1 perm) on warm side Smart vapor retarder recommended for normal moisture loads Ventilate and control moisture sources to keep interior relative humidity between 30% and 60% Detail a continuous whole building air barrier Test and seal it during construction Specify.40 cfm/sq.ft. maximum building air leakage at 75 Pascals (or better) Conclusions

Guidelines for Zone 6 Frame Walls: Foil-faced exterior insulation: Avoid using foil-faced insulation with vapor permeable cavity insulation Exterior Insulation / Cavity Insulation Ratio is Important: Higher is drier Closed cell spray polyurethane foam in the stud cavity: For thickness > 3, use at least 1 exterior rigid insulation or vent the space behind the cladding top and bottom Conclusions

Hygrothermal Modeling & Building Enclosure Design Conclusions

Conclusions

University of MN Building Enclosure Research Building enclosure performance is very sensitive to material properties, construction practices and interior relative humidity - so designs should be fault tolerant Smart vapor retarder systems (polyamide films) perform better than polyethylene Certainteed Case Studies

U.S. Building Enclosure Air Leakage Comparison 2.5 Enclosure Air Leakage cfm/sq.ft. surface at 75 pa 2.0 1.5 1.0 0.5 Commercial Residential 2012 IECC Commercial (.4 cfm / sq.ft. @ 75 Pa) Residential (3 ac/hr @ 50 Pa) 0.0 2005 NIST Study: Existing Commercial Buildings < 4 stories NIST Study: Target airtightness, 26% to 37% Minneapolis HVAC Savings Av. for U.S. Residential Housing Stock Av. for U.S. Residential Housing Stock since 1993 DOE Building America Residential Enclosure Standard Passivhaus Standard

Moisture Damage from Freeze/Thaw Cycles Case Studies

Pool Area Wall Plan Section Exterior Brick and Mortar Air Space Door Frame 2 Extruded Polystyrene Peel & Stick Air / Vapor Barrier 12 Concrete Block Air Space 4 Glazed Concrete Block Case Studies

Pool Area Brick Cavity Wall Cross-Section with Failed Air/Vapor Barrier February Temperature and Moisture Conditions Airspace 2 Extruded Polystyrene Air / Vapor Barrier Airspace Face Brick 12 Concrete Block 4 Glazed Concrete Block Case Studies

Case Studies

Outside R / Inside R 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Condensation Potential at the Condensation Plane with Permeable Stud-Cavity Insulation 0 500 1000 1500 2000 2500 3000 3500 4000 Annual Condensation Potential Hours Minneapolis, MN - Zone 6 - Medium Moisture Load (40% RH winter to 60% RH summer) Minneapolis, MN - Zone 6 - High Moisture Load (50% RH winter to 60% RH summer) Minneapolis, MN - Zone 6 - Low Moisture Load (30% RH winter to 60% RH summer)

Condensation Potential at the Condensation Plane with Permeable Stud-Cavity Insulation 2.4 2.2 2.0 Outside R / Inside R 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 500 1000 1500 2000 2500 3000 3500 4000 Annual Condensation Potential Hours Montpelier, VT - Zone 6 - Medium Moisture Load (40% RH winter to 60% RH summer) Minneapolis, MN - Zone 6 - Medium Moisture Load (40% RH winter to 60% RH summer) Duluth, MN - Zone 7 - Medium Moisture Load (40% RH winter to 60% RH summer) Boston, MA - Zone 5 - Medium Moisture Load (40% RH winter to 60% RH summer)

WUFI results for unvented wood cladding in Minneapolis Tighter 2 x6 wall with R19 fiberglass, interior vapor retarder paint and mechanical ventilation Current Code Compliant Damage Threshold Red Text indicates change since last case WUFI Assumptions: Same As Previous Case Temperature and Relative Humidity of Sheathing Frame Wall Examples

WUFI results for vented wood cladding in Minneapolis Tighter 10 wall with R30 fiberglass, interior vapor retarder paint and mechanical ventilation High Performance Wall Damage Threshold Red Text indicates change since last case Results are similar for other R30 vapor- permeable cavity insulations: cellulose & open cell spray foam WUFI Assumptions: Same As Previous Case Temperature and Relative Humidity of Sheathing Frame Wall Examples

The WUFI Program

Good RH/Temp Data Points Bad RH/Temp Data Points Initial construction moisture in interior gypsum board dries gradually over a three year cycle Interior gypsum board annually cycles back into the mold growth danger zone Time Sequence of Data Points: yellow to green to black WUFI Outputs

Infiltration Control Resilience & Tolerance to Uncontrollable Events Moisture Vapor Control Affordability Success Criteria for Wall and Roof Design Insulation Effectiveness Ease of Construction Low Maintenance, Maximum Longevity Rain Penetration Control Why Use Hygrothermal Modeling

Note: a gap is recommended between OSB and SPF for moisture distribution when OSB has impermeable foam on both sides. Use grooved foam, crinkled building wrap, 1/8 polypropylene mesh, etc. Joe Lstiburek, Mind the Gap, Eh Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis 2 exterior XPS, 2 x6 wall with R19 fiberglass, interior vapor retarder paint and mechanical ventilation High Performance Wall Damage Threshold Red Text indicates change since last case WUFI Assumptions: Same As Previous Case Temperature and Relative Humidity of Sheathing Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis Tighter 2 x6 wall with R19 fiberglass, polyethylene vapor barrier and mechanical ventilation Current Code Compliant Damage Threshold Red Text indicates change since last case WUFI Assumptions: Same As Previous Case Mold Growth Potential on interior gypsum board Frame Wall Examples

Wall Cavity Ventilation is Beneficial for Most Assemblies in Most Climates Air Cavities Behind Claddings What Have We Learned, Karagiozis et.al., 2007 Frame Wall Examples

WUFI results for unvented wood cladding in Minneapolis 2 exterior XPS, 2 x6 wall with 1.5 SPF and R11 fiberglass, interior vapor retarder paint and mechanical ventilation High Performance Wall WUFI Assumptions: Same As Previous Case Temperature and Relative Humidity of Sheathing Frame Wall Examples

EIFS With Drainage Wall Assembly Frame Wall Examples

Effect of R-value Ratio on Wall Moisture Stay on this side of line for OSB or Plywood Sheathing.50 Frame Wall Examples

Effect of R-value Ratio on Wall Moisture Stay on this side of line for Gypsum Sheathing Frame Wall Examples

Generic Wall Components & Functions Frame Wall Examples

What s wrong with this picture? Limitations

Air Barrier Benefits and Costs Annual HVAC Energy Use, MBtu 800 700 600 500 400 300 200 100 0 Reduction in Energy Use by Air Barriers for Typical Existing Minneapolis Buildings 41% 27% 39% Office Buildings Retail Buildings Apartment Buildings Energy Use with Reduced Air Leakage Energy Savings from NIST Study on Commercial Building Airtightness and Energy Use Base airtightness is 1.4 cfm/ft2 at 75 Pa Readily Achievable target airtightness is.24 cfm/ft2 at 75 Pa

Air Barrier Benefits and Costs $14,000 Air Barrier Savings and Costs for Typical Existing Minneapolis Buildings $12,000 $10,000 $8,000 $6,000 $4,000 $2,000 $0 Office Buildings Retail Buildings Apartment Buildings Annual Savings Air Barrier Costs for Frame Buildings Air Barrier Costs for Masonry Buildings from NIST Study on Commercial Building Airtightness and Energy Use

Worst Case Air Leakage Scenario 1. air or vapor-permeable cavity insulation 2. major vapor retarder and/or air barrier failure 3. moist room air reaches a cold condensation plane High Damage Potential Low Damage Potential Fraunhofer Institute Case Studies

WUFI 2D Stud Wall Comparison Minneapolis, fiber cement siding, Densglass sheathing, R11 in, R 10 out WUFI 1D center of sheathing Same both cases Wood Stud Wall Metal Stud Wall Limitations

WUFI Limitations Results are sensitive to material properties The requisite material properties are very detailed Complete data rarely available from manufacturers Must use standard WUFI library and modify as needed Results are sensitive to indoor relative humidity Varies by building use, airtightness, climate and user activity No true convection modeling of airspaces Makes some assemblies (especially in 2D) difficult to analyze Ventilated cladding and infiltration models are simplifications Infiltration model only verified for cold climates No gravity Condensation does not end up sitting on the stud wall plate No active discussion group or third party operation & reference manual Must rely on personal research of available literature and WUFI forum The WUFI version in common use is one-dimensional Most assemblies aren t homogeneous Limitations

Quality Control and Quality Assurance Prerequisites: Understand material properties and basic physics of heat and moisture transfer Understand building assemblies and construction practices Understand building operation and interior climate Evaluate building assemblies for best practices and thermal bridging If you don t control air movement, you can t control moisture Use WUFI output statistics to evaluate simulation accuracy Use conservative assumptions Don t lowball interior relative humidity Don t assume construction is perfect Choose the critical wall or roof orientation Assume 1% of driving rain penetrates wall cladding (ASHRAE standard160) Use WUFI 2D to check the validity of 1D analysis Strive to validate results against actual building performance You need to know where you re going Interpolate don t Extrapolate Limitations

Bio-adverse materials with porous structures like plaster, some woods, insulation Easily bio-degradable materials like paper and processed wood products WUFI Outputs

Sorption Curve for Common Building Materials www.buildingscience.com WUFI Outputs

NEXT REVELATION: PASSIVE NOT ACTIVE SOLAR DIRECT ABSORPTION HEAT SINKS, AND SHADING BLACK RIVER CONSTRUCTION BUILT SOLAR COMPONENTS CONTRACTOR BUILT REST OF THE BUILDING Introduction

Condensation Potential in Minneapolis for 40% interior R.H.

Limitations of Condensation Analysis Assumes unlimited quantities of interior air reach the condensing surface Requires an assumption of: what exterior air temperature to use or a threshold for condensation hours Does not recognize that mold growth and damage to assemblies occurs below 100% relative humidity Provides guidance but is not a suitable tool for fine-tuning building assemblies