Fluid Applied Air/Moisture Barriers for Moisture Control and Mold Prevention in Wall Construction  

Fluid applied air/moisture barriers are effective and economical means of controlling moisture in wall assemblies. Moisture control assists in preventing mold growth in wall assemblies. Fluid applied air/moisture barriers also offer performance advantages over building wraps and traditional asphalt- impregnated felt or paper moisture barriers. They can be used in all types of wall construction over wood, gypsum and cement-based sheathings. They can also be used over prepared concrete and concrete masonry units. They generally consist of three components (Figures 1a and 1b on page 204):

1. A spray- or trowel-appliedjoint treatment for filling sheathing joints, spotting fasteners, and protection of rough openings, corners and other changes of plane in sheathed wall construction.
2. Areinforcing mesh or tape used in conjunction with the joint treatment to reinforce sheathing joints, corners, and changes of plane, and for repair of minor cracks in concrete or concrete masonry wall construction.
3. Awaterproof coating applied by spray, roller or brush to prepared sheathing, concrete or concrete masonry wall surfaces.

When properly applied to sound supporting construction, these components function together as an air barrier and seamless moisture barrier in the wall assembly. Some of the advantages of a fluid applied air/moisture barrier include:

Effectively blocks air leakage Increases occupant comfort Reduces energy costs by reducing heating and cooling loads Reduces risk of condensation caused by air leaks through the wall construction Seamless moisture barrier no tears, holes, or lap joints that can compromise performance in service reduces risk of installation errors Protects sheathing and rough openings from weather damage during and after construction minimizes risk of weather damage to sheathing and associated repair or replacement costs Simple installation procedures No special tools or skills required; reduces labor costs Durable Does not tear or lose its effectiveness with exposure to weather during construction or while in service Structural/fully adhered Rigid and stable under air pressure loads, does not tear or blow off the wall with wind Distinct colors Facilitates job site inspection and quality control Water based Safe to use, easy clean-up, VOC-compliant Provides opportunity for pressure equalized or pressure moderated wall design Minimizes risk of rain water penetration through wall assembly Doubles as air barrier and moisture barrier in wall assembly Efficient use of materials

In the last decade, studies have shown air leakage to be a significant potential source of condensation and moisture accumulation in building envelope assemblies (see CMHC,Commissioning and Monitoring the Building Envelope for Air Leakage, by David J. Odom, III; andPreventing Indoor Air Quality Problems in Educational Facilities: Guidelines for Hot, Humid Climates).

Figure 1a: Fluid applied air/moisture barrier applied to sheathing by roller.

By constructing an airtight building envelope, the risk of moisture problems-decay, corrosion, loss of insulation value, mold growth and indoor air quality (IAQ) problems-which can occur because of air leakage and condensation, are minimized. At the same time, airtight construction is likely to be less capable of drying than "air-porous" construction, in the event of water leakage or other unforeseen circumstances that cause water to enter into a wall assembly. The designer then must strive to prevent rain water penetration into the wall assembly, to construct an airtight building envelope assembly of compatible air barrier materials, and to enhance the drying potential of the wall assembly in his/her overall design strategy.

Figure 1b: Fluid applied air/moisture barrier applied to sheathing by spray application.

When incorporating fluid applied air/moisture barriers in wall assemblies, the following considerations are important to effectively control condensation and prevent moisture penetration:

Design Considerations

• Air permeability
• Continuity with other air barrier materials
• Structural integrity
• Durability
• Water penetration resistance
• Water vapor permeability
• Mechanical ventilation
• Construction details and sequencing
• Code compliance
• Climate

Air Permeability

The layers of material that make up a wall assembly have different air permeability. Figure 2 provides a comparison of typical materials used in wall assemblies and their air permeability values.

Energy codes in the United States have begun to require air tightness of the building envelope, but they are not specific about levels of air permeability for air barrier materials. The generally accepted level based on National Building Code of Canada requirements is 0.02 L/(s·m2) at 75 Pa pressure (0.004 cfm/ft2 at 1.57 psf). While many common building materials like plywood and gypsum wallboard meet this standard, a sheathed wall assembly will not perform well as an air barrier unless the joints are treated with an air barrier material. The sheathed wall assembly with treated joints then becomes an air barrier sub-system of the total building envelope air barrier system. The total building envelope air barrier system consists of all the interconnected air barrier materials-for example, treated wall sheathing, roof membrane, foundation waterproofing, windows and doors, and the air barrier connection materials between them.

Air Barrier Continuity

The overall design concept of air barriers in building construction is the creation of a continuous airtight membrane around the building envelope. Therefore, air barrier materials in wall assemblies, to be effective, must be continuous. Breaks in air barrier continuity cause air leaks. In cold climates the breaks can allow significant amounts of warm moisture-laden air to escape from the interior environment and condense on a cold surface in the wall assembly. Conversely, in hot, humid climates, breaks in the air barrier permit moisture-laden air from the exterior environment to infiltrate the building envelope and potentially condense on a cold surface in the wall assembly. Any penetration through the wall assembly or termination of the wall assembly must therefore be detailed to maintain the continuity of the air barrier materials to effectively create an air barrier system. Without continuity of the air barrier materials in the wall assembly, air barrier system performance is less effective. The design/construction professional must take material compatibility and construction sequencing into account when designing an airtight assembly to ensure continuity. A number of connecting air barrier materials exist that are compatible with fluid applied air/moisture barriers to make transitions from one material to the next, for example, rubberized asphalt membrane tapes to connect from wall sheathing to foundation, or low-expanding urethane foam sprays for use between windows and rough openings.

Air Barrier Structural Integrity

Structural integrity of air barriers is important because wind loads are transferred to the most airtight components in a wall assembly-the air barrier materials-and in turn, are transferred to the structure. Negative and positive wind loads stress air barrier materials. If the materials tear or displace with loading, they lose their effectiveness as air barriers. Some building wraps have low air permeability, but they do not perform well when commonly installed because they have many seams that reduce their effectiveness against air leakage, and they are non-structural. If the seams in building wraps are not taped, they do not perform well as air barrier materials. Because building wraps are non−structural, they are susceptible to displacement and tearing from negative wind gusts in cavity wall construction. This compromises their performance in service.1

Fluid applied air/moisture barriers are fully adhered. Adhesion to sheathing exceeds the strength of the sheathing. Tensile adhesion tests show that the paper or glass mat facing fails in gypsum based sheathings, while unfaced sheathings like plywood show adhesive failure at loads in excess of 344 kPa (50 psi, could equate to more than a 2560 km/hr [1600 mph] wind speed). The structural strength of the fluid applied air/moisture barrier in effect equates to that of the sheathing. Deformation while in service is limited to the deformation of the sheathing. This means no tears and no compromise in performance caused by structural loading, provided the sheathing and supporting frame are adequate to resist loads.

Air Barrier Durability

While capable of resisting wind loads without compromise in performance, air barrier materials must also demonstrate durability in a number of other ways, particularly if the air barrier is concealed and inaccessible for maintenance. Durability criteria include:

• Resistance to puncture
• Resistance to pests-rodents, termites, carpenter ants, and other insects
• Resistance to low but sustained negative pressures from building stack effect and HVAC fan effect
• Ability to withstand stress from thermal and moisture movement of building materials, and stress from building creep
• Resistance to UV degradation (during the construction period)
• Resistance to mold growth
• Resistance to abrasion

Fluid applied air/moisture barriers generally do not provide a food source for insects or other pests. By virtue of their excellent adhesion to sheathing and prepared concrete or masonry substrates, they are resistant to puncture and they resist loads imposed by stack effect and fan effect, as well as wind loads. Their resistance to stresses imposed by thermal and moisture movement, and building creep, is mainly dependent on the ability of the joint treatment material to span gaps in sheathing without cracking. This performance, in turn, is dependent on the physical properties of the specific joint treatment material. Similarly, the UV resistance, resistance to mold growth, and abrasion resistance are dependent on the physical properties of the joint treatment and waterproof coating materials.

p class="mainboldBlue">Water Penetration Resistance

The traditional moisture protection used in wall construction is asphalt-saturated felt or kraft waterproof building paper. The terms weather-resistive barrier or moisture barrier are often used to describe these components in wall construction. They are generally installed over sheathing by lapping them shingle-style and fastening with nails, screws or staples to the sheathing. Their general purpose in walls is to protect against ingress of incidental water into the building and to protect moisture-sensitive components like gypsum sheathing in the event of a breach in the outer wall covering, such as a crack in stucco. Building wraps are often used in place of asphalt felt in wall construction, often with the same perceived purpose. The water resistance, air infiltration resistance, and vapor permeability characteristics of building wraps vary widely, depending on the brand of wrap selected. (See references, PHRC Report No. 59). Seamless fluid applied moisture protection provides a significant improvement over traditional moisture protection and building wraps.In fact, they can be 10 times more resistant to water penetration than building wraps and nearly 200 times more resistant to air leakage than asphalt felt .

Water Vapor Permeability

A fluid applied air/moisture barrier may or may not be a vapor-retarding material. The generally accepted definition of a vapor-retarding material is one that has a water vapor permeance of 57.4 ng/(Pa·s·m2) [1.0 perms] or less. In Table 1, the fluid applied air/moisture barrier components are not vapor retarders. The joint treatment has a vapor permeance of 994 ng/(Pa·s·m2) [17.3 perms] and the waterproof coating has a vapor permeance of 327 ng/(Pa·s·m2) [5.7 perms], about the same as Type 15 building felt.

Building Material Water Vapor Permeance (Perma) Water Vapor Permeance ng(Pa-s-m2) 4 mil Polyethylene 0.08 4.60 6 mm (1/4 inch) Plywood3 (ext glue) 0.7 40.2 101mm (4 inch) Brick3 0.8 46.0 203mm (8 inch) Concrete Block3 2.4 138 25mm (1 inch) Expanded Polystyrene1 5 287 Type 15 Building Felt2 5.6 322 Fluid Applied Air Moisture Barrier Waterproof Coating 5.7 327 19mm (3/4 inch) Plaster on Metal Lath3 15 862 Fluid Applied Air Moisture Barrier Joint Treatment 17.3 994 9.5mm (3/8 inch) Gypsum Wallboard3 50 2873 Table 1: Water vapor permeance of fluid applied air/moisture barrier materials and common building materials. Check online material for Table 1 notes.

The purpose of a vapor retarder in wall construction is to minimize water vapor diffusion through the wall assembly and thus reduce the risk and the amount of condensation on cold surfaces in the wall assembly. Whether or not a vapor retarder should be placed in a wall assembly and where it should be placed must be carefully evaluated in relation to climate, the physical characteristics of other components of the wall assembly, and interior relative humidity conditions. In cold climates the predominant water vapor diffusion direction through most of the year is from the inside to the outside, as warm, humid air from the interior environment moves in the direction of cold, dry outside air. Conversely, in hot, humid climates, the predominant water vapor diffusion direction through most of the year is from the warm, humid outside environment towards the cooler, dryer, air-conditioned interior environment. Based on these general conditions, a vapor retarder is customarily placed on the interior of wall construction in cold climates and on the exterior in hot, humid climates. A vapor retarder should not be placed on the interior in hot, humid climates, since it will potentially cause condensation by restricting vapor diffusion to the interior. The use of interior vapor retarders has been shown to be a contributing cause in many cases of moisture problems and IAQ problems in buildings in hot, humid climates. One tool that is available to assist in making decisions about whether a vapor retarder is needed and where to place it in the wall assembly is a water vapor transmission analysis that can be performed manually (see ASHRAE Handbook-Fundamentals, chapters 21 and 22) or by computer (Trechsel, Moisture Analysis and Condensation Control in Building Envelopes).

Mechanical Ventilation

A properly functioning air barrier system will limit the influence of air infiltration and exfiltration on the heating and cooling loads of the interior environment. This can increase the efficiency of the HVAC system, which translates into energy cost savings. However, the mechanical ventilation system must still perform its basic functions of:

• Ventilation and exhaust
• Proper distribution of makeup air to interior spaces
• Dehumidification of air
• Filtration of outdoor air

Wind effects, stack effects, fan effects and space configuration and partitions influence how the mechanical ventilation system must be designed to perform adequately. ASHRAE handbooks provide guidance on mechanical ventilation, and design and control of interior relative humidity conditions to control microbial growth, to minimize condensation potential, and to provide occupant comfort, in relation to air leakage.

Figure 4: Fluid applied air/moisture barrier lapped onto flashing at the base of the wall to "splice" the two materials and shed water onto the flashing and to the exterior.

Construction Details and Sequencing

"As much as 90 percent of all water intrusion problems occur within one percent of the total building exterior surface area. The one percent of the structure's façade contains the terminations and transition detailing that all too frequently lead to envelope failures."3

Construction detailing is a critical component for the success of any wall assembly. The designer must create details that effectively:

Control rain water penetration that may occur via:

• Gravity flow-water that flows down and to the interior if surfaces are sloped towards the interior, for example, an improperly sloped brick ledge
• Kinetic energy-rainwater, for example, being blown directly into large openings
• Capillary action-the tendency of water to travel through narrow openings or cracks in materials toward dryer surfaces, for example, a crack in a mortar joint
• Pressure differentials-the effects of wind pressure, stack effect or mechanical ventilation that create pressure differences across the building envelope, and drive water through cracks or openings

Control condensation that may occur via:

• air leakage
• diffusion

Figure 5: Integration of the fluid applied air/moisture barrier at the rough opening with interior air seal and sill flashing beneath the window.

The contractor must in turn coordinate and sequence work so that details are properly constructed. Given that today's buildings are generally "tighter" than they were 50 years ago, the importance of eliminating water intrusion into wall assemblies increases substantially, since water in walls may not readily dry. Some details are fundamental, such as the proper sloping of sills and ledges to the exterior, use of drip edges at soffit returns, capillary breaks in construction joints, or lapping of the air/moisture barrier over flashing at the base of a wall (Figure 4) to direct water to the exterior. Other details are more complex, such as maintaining the continuity of the air barrier at a window penetration (Figure 5) and integrating the air/moisture barrier with sill flashing. Whatever the detail, whether straightforward or complex in nature, the development and execution of details is vital to the long term success of the wall assembly, regardless of how well the air/moisture barrier system performs. An important advantage of a fluid applied air/moisture barrier in the wall assembly is that it can mitigate or eliminate one of the major forces that cause water infiltration into walls: pressure difference. The fluid applied air/moisture barrier, in combination with venting and compartmenting, can effectively enable the pressure behind the cladding material to equalize with the pressure outside, and prevent rain water penetration caused by pressure differentials (pressure equalized rainscreen).

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Code Compliance

United States
Model building codes and state and municipal codes in the United States do not address air barriers, moisture barriers and vapor retarders in a uniform way. Energy codes in the United States, including the IECC (International Energy Conservation Code), the State of Massachusetts Building Code, and ASHRAE's 1999 energy conservation standard (ANSI/ASHRAE/IESNA Standard 90.1-1999, Energy Standard for Buildings Except Low-Rise Residential Buildings, an energy conservation standard which is required to be adopted by state building energy codes under the Federal Energy Conservation and Production Act) require air tightening of the building envelope. Although codes in the United States do not always provide specific limits for air leakage of air barrier materials, the generally accepted limit is 0.02 L/(s·m2) at 75 Pa pressure [0.004 cfm/ft2) at 1.57 psf)] based on National Building Code of Canada requirements.

Most model codes generally require the use of a water-resistive barrier in wall construction and prescribe asphalt saturated felt (IBC Chapter 14, paragraph 1404.2). They often require the use of vapor retarders in wall construction (IBC Chapter 14, paragraph 1403.3) unless other means are provided to avoid condensation.

Fluid applied air/moisture barriers are proprietary materials and are not listed in model codes. Provisions are made for non-traditional building materials like building wraps and fluid applied air/moisture barriers as an "alternate material, design or method of construction."2 Approval by the building official is based on his/her finding that "….the intent of the provisions of the code [are met]…and that it [the air/moisture barrier material] is at least equivalent in quality, strength, effectiveness, fire resistance, durability and safety to the materials or methods of construction listed in the code."3 In practice the building official cannot evaluate each and every new material or method of construction, so model code evaluation agencies do this for him/her and publish evaluation reports which describe the use and limitations of alternate materials. Therefore it is always important to verify compliance of a fluid applied air/moisture barrier material with the code via an evaluation report.

Southern Building Code Congress Public Safety Testing and Evaluation Services, Inc. publishes an Evaluation Guide on Floor, Wall, and Roof Systems (Testing for Moisture Protection Barriers-SBCCI PST & ESI Evaluation Guide 119), which lists specific performance criteria for air and moisture barriers, including fluid applied air/moisture barriers. Conformance with these criteria is the basis for code recognition of fluid applied air/moisture barriers. ICBO ES (International Conference of Building Officials, Inc.)

is similarly in the process of developing a criteria for water-resistive coatings that function as alternates to UBC (Uniform Building Code) prescribed weather-resistive barriers.

Canada
The National Building Code of Canada requires an air barrier system encompassing the entire building envelope, a vapor barrier if condensation is expected, and control of precipitation (Chapter 5, Environmental Separation, Sections 5.4-5.6). Multiple standards are listed in the code that identify performance requirements for building materials. New materials for which a standard has not yet been written undergo technical evaluation by CCMC (Canadian Construction Materials Centre), who publishes evaluation reports which verify compliance of a material or assembly with the intent of the code. Some air/moisture barrier materials have been shown to meet the requirements for air leakage as a material component of an air barrier system and are either listed or currently under evaluation by CCMC.

Typical Wall Assemblies with Fluid Applied Air/Moisture Barriers for Climate Zones in North America

The model wall constructions illustrated below are examples of wall constructions that incorporate a fluid applied air/moisture barrier in two climate zones of North America. In each case the fluid applied air/moisture barrier functions as an air barrier and moisture barrier material over the sheathing that:

• Protects the sheathing from moisture damage during construction
• Minimizes air leakage into the wall cavity and to the interior environment from warm humid outside air in hot humid climates (and during summer months in cold climates)
• Protects the sheathing against incidental moisture that may occur outboard of the sheathing but behind the cladding while in service
• Minimizes air leakage from the interior towards the exterior in cold climates

The fluid applied air/moisture barrier has a unique advantage as compared to building wraps beneath non-contact siding such as brick veneer with a cavity because it is in effect structural and does not tear and lose its effectiveness with negative wind gusts during construction or while in service.

Note, in hot humid climates it is important to:

• Use a water vapor permeable interior wall covering to permit drying to the interior and to prevent condensation immediately behind the interior wall covering.
• Use unfaced batt insulation to permit water vapor diffusion and drying to the interior
• Pressurize the interior space with conditioned (dehumidified) air so that warm humid outside air is not drawn to the interior
• Use a low permeance rigid insulation on the exterior to resist vapor diffusion to the interior, especially if porous cladding like brick veneer is used

Note that the rigid EPS insulation (as opposed to XEPS insulation) is chosen because it is vapor permeable. The vertical grooves in the insulation drain incidental moisture. The insulation is adhesively attached to the fluid applied air/moisture barrier to prevent thermal bridging that would occur if it was attached with metal fasteners, and, to minimize penetration with mechanical fasteners. The installation of the wood siding over strapping creates a cavity to promote drying of the wood in the event it gets wet during construction or while in service.

In cold climates the vapor retarder is essential (unless mechanical controls are in place to adequately control interior relative humidity conditions in winter). The vapor retarder minimizes water vapor diffusion to the exterior during winter months. However, it is essential to eliminate leaks, condensation, or any other source of moisture in the frame wall cavity, given that the vapor retarder on the interior and the fluid applied air/moisture barrier and insulation on the exterior create a very "tight" construction with limited drying potential.

Note, in cold climates it is important to:

• Insulate on the exterior, particularly when metal studs are used, to prevent:
  • Telegraphing (ghosting) of metal studs on the interior or exterior wall surfaces
  • Heat loss via conduction through the metal studs
  • A dew point from occurring in the metal stud cavity and condensation which can lead to corrosion
• Adjust the type and/or thickness of the rigid insulation to prevent a dew point in the frame cavity and condensation on or within the wall sheathing. As the size of the stud cavity increases and the thickness of batt insulation increases the dew point moves further to the exterior with the risk of the sheathing becoming a condensing surface.
• Provide a neutral or slightly negative indoor pressure to prevent exfiltration of warm humid air into cold walls

Note that each of the above model wall constructions illustrates a design strategy that incorporates a fluid applied air/moisture barrier, and other design considerations for the effective control of moisture in the wall assembly. As each building is different and has its own unique set of materials, climate, and interior conditions to consider, these model wall assemblies should be taken as a guide relative to any specific project. Appropriate adjustments in materials, and their position in the assembly should be made. The overall design strategy must include prevention and control of rain water penetration, minimizing the risk of condensation caused by water vapor diffusion or air leakage, and maintaining proper mechanical controls of the interior environment.

Fluid applied air/moisture barrier materials are effective components in wall assemblies that control moisture by minimizing air leakage and protecting water-sensitive components from moisture. Their material properties such as water vapor permeability, UV resistance and mold resistance must be taken into account. They are cost effective alternatives for moisture control in wall assemblies that have several performance advantages over building wraps and traditional asphalt saturated felt or paper moisture protection.

Table 1 Notes:

1. Dry Cup Method
2. Wet-Cup Method
3. Other Method
4. Note: this chart provided for information only. Direct comparisons of water vapor permeance values may not always be applicable, as different methods of measuring produce different results. Materials may also have varying water vapor permeability with changes in relative humidity.
5. Sources of Data: ASHRAE Handbook Fundamentals and Sto Corp.

Figure 3 Notes:

1. Source of Data: independent testing by Cerny & Ivey Engineers
2. Fluid applied air/moisture barrier material did not leak, but met limit of testing fixture.
3. Materials tested in accordance with AATCC-127 (American Association of Textile Chemists and Colorists Test Method 127−Water Resistance: Hydrostatic Pressure Test [modified]). A column of water 55 cm (21. 6 inches) tall is placed over the moisture barrier material and sealed to the surface. The moisture barrier material spans a 3 mm (1/8 inch) wide joint in supporting sheathing. Building wraps and building paper are not penetrated with fasteners. Time to water penetration is then measured. For the materials that met the 5 hour criteria, the height of the water column was increased to determine the limits of the material.

References

American Architectural Manufacturers Association, Installation Masters Training Manual. Schaumburg: AAMA, 2000.

American Architectural Manufacturers Association, Window Selection Guide. Palatine: AAMA, 1995.

American Association of Textile Chemists and Colorists, AATCC-127 Water Resistance Hydrostatic Pressure Test. AATCC, 1995.

American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1993 ASHRAE Handbook-Fundamentals, (I-P Edition), Atlanta: ASHRAE, 1993.

Anastasi, Leonard, "Air Barrier Systems for the Life or Your Building," The Construction Specifier, (March, 2002), 30−35.

Anis, Wagdy "Insulation Strategies for Exterior Walls," The Construction Specifier, (August, 2002), 40−45.

Canada Mortgage and Housing Corporation, Commissioning and Monitoring the Building Envelope for Air Leakage, (Report No. 33127/02), Ottawa: CMHC, 1993.

Canada Mortgage and Housing Corporation, Rainscreen, Ottawa: CMHC.

Cerny & Ivey Engineers, Inc., Water Penetration Resistance Testing Sto Gold Guard (Engineering Report No. 20409), Atlanta: Cerny & Ivey Engineers, Inc., 2001.

International Code Council, Codes Forum(September/October), Falls Church: ICC, 2002.

Construction Specifications Canada and Alberta Building Envelope Council, CSC TEK·AID Digest Air Barriers, Toronto: CSC & ABEC, 1990.

Foundation of the Wall and Ceiling Industries, Mold: Cause, Effect and Response, Itasca: FWCI, 2002.

International Code Council, Inc., International Building Code. Falls Church: ICC, Inc., 2000.

International Conference of Building Officials, Uniform Building Code, (Vol. 3), Whittier: ICBO, 1997.

Kubal, Michael, T., Waterproofing the Building Envelope, New York: McGraw-Hill, Inc., 1993.

Lstiburek, Joseph. Builder's Guide. Minneapolis: Energy and Environmental Building Association, 2001.

National Research Council of Canada, National Building Code. Ottawa: NRCC, 1995.

Southern Building Code Congress International Product Safety Testing Evaluation Services, Inc., Evaluation Guide on Floor, Wall, and Roof Systems (Testing for Moisture Protection Barriers). Birmingham: SBCCI PST & ESI, 1995.

Odom, David J. III, Preventing Indoor Air Quality Problems in Educational Facilities: Guidelines for Hot, Humid Climates, Orlando, 1997.

Odom, David J. III, "Solving Indoor Air Quality Problems in Hot, Humid Climates," Building Standards (September-October, 1994), Whittier: International Conference of Building Officials, 1994.

Pennsylvania Housing Research Center, The Use of Housewrap in Walls: Installation, Performance and Implications, (PHRC Research Series Report No. 59), University Park: PHRC, 1998.

Trechsel, Heinz R., Moisture Analysis and Condensation Control in Building Envelopes, (ASTM MNL40), West Conshohocken: ASTM, 2001.

Footnotes

1. The Use of Housewrap in Walls: Installation, Performance and Implications, PHRC Research Series Report No. 59 (University Park, 1998), p. 41.
2. International Code Council, Inc., International Building Code (Falls Church, 2000), p. 3.
3. Ibid.