Exterior Systems for Wood-framed Building Envelopes

Code Compliant Exterior Systems for

Wood-framed Building Envelopes

Presented by Tim Farrell1 LU/HSW

Disclaimer: This presentation was developed by a third party and is not funded by WoodWorks or theSoftwood Lumber Board.

Sponsored by Huber Engineered Woods,Makers of

Course Description

This course investigates the most recent code changes

emphasizing building envelope performance. We will explore

next generation integrated solutions that simultaneously provide

protection against moisture penetration, air leakage, and

thermal bridging. Installation benefits and on-site quality control

issues related to multi-solution integrated systems will also be

evaluated.

Course ObjectivesAfter completion of this course, participants will be equipped to:

• Delineate the latest code and design standards for wood

framed exterior wall assemblies.

• Assess different product approaches available to meet air

barrier and water-resistive barrier (WRBs) requirements in the

International Building Code.

• Analyze the differences between multi-product solutions and

single product solutions for wood framed building envelopes.

• Articulate the benefits of continuous insulation added to

exterior sheathing.

Course Outline

Part 1• Moisture

Management

Part 2• Air Leakage

Management

Part 3• Vapor

Management

Part 4• Thermal

Management

Part 5• Alternative

Solutions

Introduction• In a tight building

– Heating and cooling

efficiencies can be

maximized

– Ventilation system

can manage

moisture levels and

indoor air quality

• High performance

rewarded by LEED and

other green building

programs

IntroductionConventional methods:

– Caulk

– Building felt

– House wrap

Replaced by High-performance panels:

– With integrated weather barrier

– Help eliminate the risk of water trapped

between building wrap and sheathing

– Engineered to allow permeability

– Enables the building to dry

SECTION 1Moisture Management

Moisture Management in Buildings Moisture is the single greatest

threat to a building’s

durability and long-term

performance.

• Rot• Mold• Mildew• Corrosion• Maintenance problems• Poor indoor air quality• Building system failure• Liability issues for building

designers and owners

Moisture Management in Buildings

• Liquid water carried into a building

through holes and cracks

• Air leakage carrying water vapor

• Water vapor diffusion

Greatest risk

Moderate risk

Lowest risk

Moisture Management in Buildings

Four key strategies,

known as the Four Ds,

keep moisture from

getting into a building.

The Four D's• Deflection• Drainage• Drying • Durability

Moisture Management in Buildings

The Four Ds have two objectives:

1. Prevent moisture from getting into the

structure in the first place (deflection)

2. Any moisture that does get into the

structure must be managed as quickly

and thoroughly as possible (draining,

drying, and durability)

Definitions

• EXTERIOR WALL COVERING – An assembly of materials applied on the exterior side of exterior walls for the purpose of providing a

weather-resistive barrier.

• WATER-RESISTIVE BARRIER - A material behind an exterior wall

covering that is intended to resist

liquid water that has penetrated

behind the exterior covering

Moisture Management

• Water-resistive barrier - One layer of No. 15 asphalt felt, free from

holes and breaks, complying with ASTM D 226 for Type 1 felt or other

approved water-resistive barrier shall be applied over studs or

sheathing of all exterior walls.

ICC Acceptance Criteria for WRB

Moisture Management

• The exterior wall envelope shall

be constructed in a manner

that prevents the accumulation

of water within the wall

assembly by providing a water-

resistant barrier behind the

exterior veneer and a means of

draining to water that enters

the assembly.

Drainage• Oregon Code – The envelope

shall consist of a water resistive

barrier and a minimum 1/8”

space between WRB and

exterior veneer.

• Exception – A space is not

required when using a WRB

that meets 75% drainage

requirement of ASTM E2273

Moisture Management

• Approved corrosion-resistant flashing shall be applied in a manner

to prevent entry of water into the wall cavity or penetration of

water to the building structural framing components. Self-adhered

membranes used as flashing shall comply with AAMA 711.

SECTION 2Air Leakage Management

Air Leakage

Uncontrolled air flow:

• Introduces moisture that can

cause rot and mold

• Can increase energy use

• Can reduce effectiveness of

insulation

• Can impact indoor air quality

Typical House Wrap

Building Envelope — A System of Many

• No one product can control air leakage

• Air tightness is a function of the entire building envelope

• Everything must work together to achieve effective air tightness

The airtightness of a building envelope cannot be underestimated. A

building’s energy efficiency, occupant comfort and sustainability

depend on it.

Air Leakage

2015 IECC - Air Leakage

Commercial C402.5

• Prescriptive Option or

• Testing Option

Residential R402.4

• Testing Only

2015 IECC - Air Leakage

Commercial Prescriptive Option

• A continuous air barrier shall be provided throughout the building

thermal envelope.

• Air barrier joints and seams shall be sealed to resist positive and

negative pressure from wind, stack effect and mechanical

ventilation.

• The continuous air barrier will comply with…

Air Barrier Material Testing

• ASTM E2178 Air Permeance of Building Materials

• 1.0 m x 1.0 m specimen with no seams or transitions

• Must achieve less than 0.02 L/(s•m2) @ 75 Pa

Air Barrier Assembly Testing• ASTM E2357 Air Leakage of Air

Barrier Assemblies

• 8.0 ft x 8.0 ft wall with penetrations/transistions

• Includes wind cycling

• Measures infiltration and exfiltration

• Must achieve less than 0.2 L/(s•m2) @ 75 Pa

2015 IECC - Air Leakage

Commercial Testing Option

• Blower door testing in

accordance with ASTM E 779 at

a pressure differential of 75 Pa

• Air leakage rate no greater than

0.40 cfm/ft2

• Regardless of Climate Zone

2015 IECC - Air LeakageResidential Air Leakage Testing

• Blower door testing in accordance with

ASTM E 779 at a pressure of differential

of 50 Pa

• Max leakage rate of 5 ACH in Climate

Zones 1and 2,

• Max leakage rate of 3 ACH in Climate

Zones 3 through 8.

• Sill plate shall be sealed at foundation

• Top plate shall be sealed at top of

exterior walls.

• Knee walls shall be sealed.

Residential Air Leakage Compliance MethodsAir Changes per Hour (ACH) at 50 Pascals of pressure (50 Pa)

Climate Zone 2006 IECCVisual inspection

only

2009 IECCVisual inspection or blower door

2012 IECCBlower door only

2015 IECCBlower door only

1 Follow checklist

Follow checklist or 7

ACH

5 ACH 5 ACH

2 Follow checklist

Follow checklist or 7

ACH

5 ACH 5 ACH

3 Follow checklist

Follow checklist or 7

ACH

3 ACH 3 ACH

4 Follow checklist

Follow checklist or 7

ACH

3 ACH 3 ACH

5 Follow checklist

Follow checklist or 7

ACH

3 ACH 3 ACH

6 Follow checklist

Follow checklist or 7

ACH

3 ACH 3 ACH

7 Follow Follow 3 ACH 3 ACH

Air Leakage

Building wraps

• Pros:

– Can help decrease air leaking provided all seams, edges and details

are sealed, and that it is caulked at the bottom

• Cons:

– Sometimes susceptible to ripping or tearing

– Must be handled carefully

Air Leakage

Taped wall sheathing panels

• Form a continuous protective

air barrier

• Reduce air leakage through

walls or roofs

• Lower air changes per hour

• Help optimize R-value

• Save energy

• Meet stringent codes and

certifications

SECTION 3Vapor Management

Vapor Management

• Water as vapor causes problems

when it becomes trapped in an

assembly and turns to liquid

(condensation)

• Water vapor moves by two

mechanisms—air transport and

vapor diffusion

AIR-TRANSPORTED MOISTURE > VAPOR DIFFUSION

Vapor Management

• Warm air holds more

moisture than cold air

• Air leakage can carry

significant amounts of

moisture into the

building enclosure

Air Leakage vs. Vapor Diffusion

In one year, 100 times more moisture is transported by air leakage compared to diffusion…and gypsum is 50 perms!

Solid 4x8 sheet of gypsum

4x8 sheet of gypsum with a 1 in2 hole

Interior at 70° F and 40% RH

Vapor Management

Warm Moist Interior Cold Dry Exterior

The 2015 IBC/IRC provides

methods to prevent

condensation by

controlling temperature

and humidity in primarily

two ways:

Interior Vapor Retarders

Exterior Insulation

Vapor Management

2015 IBC - Vapor

Vapor Permeance

Low

HighClass I or II Vapor

Retarders are required

on the inside of framed

walls in Climate Zones 5-

8 and Marine 4

2015 IBC - Vapor

Vapor Permeance

Low

HighClass III Vapor Retarders shall be permitted when exterior insulation is used

Climate Zone

2x4 2x6

Marine 4 R > 2.5 R > 3.75

5 R > 5 R > 7.5

6 R > 7.5 R > 11.25

7 & 8 R > 10 R > 15

Vapor Management

• DO: Encourage inward drying by using the most vapor permeable

option. Don’t use Class I if Class II is allowed

• DON'T: Install Class I vapor retarders such as polyethylene, foil-faced

batt insulation, or vinyl wall coverings on the interior of air-

conditioned assemblies

• DON'T: Install Class I vapor barriers on both sides of wall assemblies, ie.

thick rigid foam on the outside and poly on the inside.

SECTION 3Thermal Management

2015 IECC - Thermal

Commercial C402.1

• Prescriptive Table

• Assembly U-Factor

Residential R402.1

• Prescriptive Table

• U-Factor Alternative

• Total UA Alternative

ADD IMAGE

Thermal Bridging

Cavity Insulation

Framing

Commercial Wood Framed WallsR-Value Requirements

Climate Zone 2009 IECC 2012 IECC 2015 IECC ASHRAE 90.1-2013

1 13 20 or 13+3.8 20 or 13+3.8 132 13 20 or 13+3.8 20 or 13+3.8 133 13 20 or 13+3.8 20 or 13+3.8 134 13 20 or 13+3.8 20 or 13+3.8 20 or 13+3.8

Marine 4 13+3.8 20 or 13+3.8 20 or 13+3.8 20 or 13+3.8

5 13+3.8 20 or 13+3.8 20 or 13+3.8 19+5 or 13+7.5

6 13+7.5 20+3.8 or 13+7.5

20+3.8 or 13+7.5

19+5 or 13+7.5

7 13+7.5 20+3.8 or 13+7.5

20+3.8 or 13+7.5

19+5 or 13+7.5

8 13+15.6 20+10 or 13+15.6

20+10 or 13+15.6 13+18.8

Single Family Residential Wood Framed Walls R-Value Requirements

Climate Zone

2006 IECC 2009 IECC 2012 IECC 2015 IECC

1 13 13 13 13

2 13 13 13 13

3 13 13 20 or 13+5 20 or 13+5

4 13 13 20 or 13+5 20 or 13+5

5 & Marine 4 20 or 13+5 20 or 13+5 20 or 13+5 20 or 13+5

6 20 or 13+5 20 or 13+5 20+5 or 13+10

20+5 or 13+10

7 & 8 21 21 20+5 or 13+10

20+5 or 13+10

Thermal Definitions

• R-Value: Measure of thermal resistance• U-Factor: Measure of thermal transmittance

R-Value = 1/U-FactorU-Factor = 1/R-Value

Calculation: Area weighted

average U-factor

U = (0.25x0.160) + (0.75x0.067)U = 0.090R = 11.08

Wall Assembly U-Factor and R-Value (2x6 at 16” o.c. wall)

Wall Component

A1 A2

Lap Siding 0.81 0.81

OSB Sheathing

0.62 0.62

Framing or Insulation

4.38 13

Drywall 0.45 0.45

Total R-Value

6.26 18.88

U-Factor 0.160 .067

% of Wall Area

25% 75%

U-Factor ExampleA2

A1

SECTION 5Alternative Solutions

Alternative Solutions

OSB Panel with Integrated Moisture

Barrier

• Structural OSB panel with

integrated moisture barrier

• Continuous water and air barrier

that improves energy efficiency

by significantly reducing air

leakage

• After taping, a lasting

protective barrier has been

established

Alternative SolutionsKey Features and Components of OSB

Panel with Integrated Moisture Barrier

• High quality structural sheathing panel

made of engineered wood

• Built-in vapor permeable water-

resistive barrier eliminates the

complexities of installing of building

wrap and felt

• Engineered for enhanced drainage of

bulk water and optimal permeability

• Allows water vapor to pass through

and promote drying

Alternative Solutions

Key Features and Components of OSB

Panel with Integrated Moisture Barrier

• Continuous, rigid air barrier

• Decreases unwanted air leakage

• Greater energy efficiency

• Seam sealing flashing tape with high-

performance acrylic adhesive bonds

provides permanent protective seal

Alternative Solutions

OSB Panel with Integrated Moisture

Barrier

• Seam sealing acrylic tape can be

used as flashing tape, which

minimizes the chance for flashing

installation errors

• Unlike with many conventional

products, windy weather does

not impede tape application

Conclusion•Building codes drive increased performance requirements for building envelopes.

•Traditional solutions attempt to create an integrated system from individual components.

•Creating a high performance system out of traditional products is challenging.

•Code compliant multi-solution systems install easily and perform reliably, mitigating the risk of envelope failure.

This concludes the Huber

Engineered Woods LLC, AIA/CES

Continuing Education Program

For additional information, visit:

• www.huberarchitectlibrary.com

• For Technical questions:

800-933-9220 ext. 2716 or

techquestions@huber.com.

This concludes The American Institute of Architects Continuing Education Systems Course

QUESTIONS?

Tim Farrell

Huber Engineered Woods

Tim.Farrell@huber.com