By Herbert Slone, RA, and Art Fox

This is part three of a seven-part series of blog entries about the benefits of specifying and building with manufacturer-tested and warrantied wall systems compared to specifying individual components. Benefits include a much faster design and specification process, proven component compatibility, faster component installation and better performance, plus the peace of mind that comes from knowing all components are proven compatible and will perform as specified. Part three provides a look at vapor barriers.

 

 

Vapor barriers
Vapor barriers control the rate at which moisture moves in and out so the wall can dry. Many variables go into choosing and placing the correct barrier. For example, should it be located on the warm or cold side of the cavity? Since vapor will always move into the wall from the high-vapor-pressure (moister)
side of the wall, and migrate to the low-pressure (drier) side, the rule of thumb is the barrier always goes on the high-pressure side. This generally means the barrier goes on the interior or ‘heated’ side in northern locations, and on the exterior ‘high humidity’ side in the south. In the middle states, vapor barrier placement and the question of whether one should be used are a bit ambiguous. In such situations, further hygrothermal evaluation should be done by a qualified expert—often consultants or insulation manufacturers—using tools considering climate, building materials, HVAC systems, and building function.

In addition to placement, it is equally critical to decide between high- or low-perm barriers. Part of the vapor management consideration also involves the absorptive capability of the other components in the wall itself. All building materials absorb water, reservoir it, and then release it as conditions change, so one must account for these conditions as well.

A good place to start researching vapor barriers is the International Building Code (IBC) Section 1405.3, “Vapor Retarders,” which has definitions of and perm ratings for vapor barriers. The higher a material’s perm rating, the more permeable it is to water vapor. A Class I vapor barrier is a material with a perm rating of less than 0.1, which is at the level of polyethylenes or trilaminates like foil scrim kraft materials. Class II barriers have a permeance of greater than 0.1, but less than or equal to one, which is typical of fiberglass facers like a foil or kraft paper facer. Finally, there are the Class III barriers, which include all barriers with a perm rating greater than one and less than or equal to 10, such as common wall paint.

When it comes to placing the vapor barrier, IBC says a wall with continuous insulation is more tolerant of moisture because it stays warmer; therefore, condensation inside the wall becomes less of a possibility. If the cladding is back-ventilated, as it is in a masonry cavity wall, the wall can dry faster and more completely, which influences the vapor barrier choice. Given there are so many interdependent variables, and because each building and region creates a dynamic and unique set of conditions, a hydrothermal analysis, such as can be provided by WUFI software, is often helpful.

WUFI allows realistic calculation of the transient coupled one- and two-dimensional heat and moisture transport in walls and other multilayer building components exposed to natural weather, enabling a full understanding of how all the layers of the wall perform together to manage vapor and air movement under thermal conditions that vary by hour over years.

In addition to understanding the way vapor barriers handle moisture, it is necessary to consider their flame spread ratings. Typically, steel stud/brick veneer construction is classified by IBC as Type I or II construction and its insulation must use a facer with a flame spread less than or equal to 25 when tested in accordance with ASTM.

Be sure to come back to part four of this blog to learn about through-wall flashing, mortar dropping collectors and weep vents.

By Herbert Slone, RA, and Art Fox

This is part two of a seven-part series of blog entries about the benefits of specifying and building with manufacturer-tested and warrantied wall systems compared to specifying individual components. Benefits include a much faster design and specification process, proven component compatibility, faster component installation and better performance, plus the peace of mind that comes from knowing all components are proven compatible and will perform as specified. Part two includes an introduction to moisture management, including the definition and functions of water resistive barriers and air barriers. Part three will continue the discussion of water resistive barriers with a look at vapor barriers.

Moisture management
Moisture management means not only getting water out of the wall, but also allowing air into the wall so it can dry quickly and completely. Since water infiltration poses a significant danger to walls, it is wise to take a redundant approach to moisture management. Redundancy means there are multiple planes of defense against moisture intrusion.

These multiple planes include first the watershed at the face of the cladding or veneer. Behind that is an air space encouraging water to drain out of the wall, breaking the directly connecting path for water to enter the wall. The third redundancy is the use of a highly water-resistant, continuous insulation layer such as extruded polystyrene (XPS), which will shed rather than absorb any water that makes it to the board’s face. (Another insulation option would be polyisocyanurate [polyiso]. Expanded polystyrene [EPS], sprayed polyurethane foam [SPF], and mineral wool could also be used as continuous insulation, but they are not as water-resistant as XPS.) The final line of defense is the water-resistive barrier itself, often installed behind the continuous insulation and over the exterior-grade gypsum sheathing. All the redundant layers are a natural part of masonry veneer construction.

Water-resistive barrier
Air- and water-resistive barriers are often a single product, the same layer in the wall which resists bulk water penetration and wind-driven rain penetrating the exterior cladding. This contrasts with vapor, which either enters the wall system by permeation or is carried into it by air leakage. In a complete wall system, depending on the regional design considerations, the functions of the air barrier, vapor barrier, and WRB are sometimes combined in one product—frequently, a liquid product that is roller- or spray-applied. Greater efficiencies can be achieved if only one trade is involved in applying the all-in-one type of product instead of multiple trades applying each of the air-, vapor-, and water-resistive barriers.

Air barriers
Air barriers have a strong influence on energy efficiency. It is estimated air leakage is responsible for about six percent of total energy used by commercial buildings in the U.S. About 15 percent of primary energy consumption in commercial buildings attributable to fenestration and building envelope components in 2010 was due to air leakage. (For more, visit www.airbarrier.org/wp-content/uploads/2017/06/Buildings-XIII_OnlineAirtightnessCalculator_V5.pdf[3].) Air barriers are often also weather-protective and water-resistant. They allow the building envelope to prevent accumulation of water in the building and establish a drainage plane inside the wall.

Be sure to come back to part three of this blog to learn about vapor barriers.

By Herbert Slone, RA, and Art Fox

This is part one of a seven-part series of blog entries about the benefits of specifying and building with manufacturer-tested and warrantied wall systems compared to specifying individual components. Benefits include a much faster design and specification process, proven component compatibility, faster component installation and better performance, plus the peace of mind that comes from knowing all components are proven compatible and will perform as specified. Part one describes the components of a masonry veneer wall system and the tests a wall system must pass to provide optimal performance.

A masonry cavity wall system must successfully perform multiple functions throughout the life of the building. A proper wall is expected to manage moisture, air, and heat, contain fire, and hold up the structure itself. For a wall to perform all these functions, specifications should include all the products necessary for the components to work together.

For the contractor, building a masonry cavity wall is just as challenging as specifying it is for the architect. Contractors rely on the architect for highly precise drawings and specifications so they can produce an accurate bid. They want to be able to build with familiar, proven methods and materials that are compatible and readily available through distribution.

For these reasons, specifying a complete wall system with all the components tested and warrantied together can offer many advantages to the design professional, such as helping support risk management. The design professional’s ability to thrive depends on his or her ability to provide timely documentation for the building’s performance.

Components of a masonry veneer wall system
The structural components forming the basis of the substrate may be steel or wood studs or concrete masonry units (CMUs). On the outside is the weather-resistant component—the cladding or masonry veneer. Between those are three functional component categories that complete the wall system and make the wall perform: moisture/air, thermal, and structural management.

Moisture/air management relies on:

• an air- or water-resistive barrier (WRB);
• a vapor barrier;
• through-wall flashing (including mortar dropping collection and weep vents); and
• water- and air-sealing washers on fasteners.

Thermal management involves:

• insulation between the stud framing;
• continuous insulation (CI) outside and over the framing; and
• fire safing insulation.

Structural management depends on:

• masonry anchors;
• wall ties; and
• water- and air-sealing washers on fasteners.

Systemization
Having all the right components in the wall is not enough. A true wall system must have passed extensive testing proving the components, as a system, meet the code-mandated performance criteria and are physically and chemically compatible. Further, the system must pass industry-standard tests, such as:

• National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Nonloadbearing Wall Assemblies Containing Combustible Components;
• ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials;
• ASTM E2307, Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using Intermediate-scale, Multistory Test Apparatus
  (used only for joint firestopping);
• ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference; and
• ASTM E2357, Standard Test Method for Determining Air Leakage of Air Barrier Assemblies.

Individual product components of the system can also provide the protection of a warranty that covers them against defects. In the event there is a problem, unified and cooperative solutions are best rather than multiple companies acting separately.

Be sure to come back to this blog for part two to learn about moisture management, including a discussion of water-resistive barriers and air barriers.

Adhered masonry veneer can be installed using five different building techniques

An adhered masonry veneer is a cost-effective way for a home owner or commercial property owner to keep the appearance of masonry in the façade, even when budgets or design considerations don’t allow the use of full-sized masonry units. However, veneer installation is based on recommendations of the specific product and system chosen for your project. With that in mind, here’s a breakdown of basic installation using five standard building techniques that can help you in your next project.

 

1. Weep Screed

The purpose of the weep screed is to provide drainage for the system. It typically is a galvanized metal or a durable plastic strip placed at the base of the wall and, in some cases, at each floor level of a large veneer. The galvanized weep screed must be at least 26 gauge (0.018 inches) thick. The plastic weep screed must be a minimum thickness of 0.05 inch, and both products must extend up the wall a minimum of 3.5 inches. They both must also be fastened to a stud in frame construction, or directly to the concrete or concrete masonry unit (CMU) substrate.

To function properly, weep screeds should be a minimum of four inches above grade and two inches above a roof line. If applying veneer to a CMU or cast-in-place grade or foundation wall, the minimum tolerance is two inches from a sidewalk or driveway surface. This placement will reduce the possibility of the weeps becoming clogged with debris that splashes on the wall. Attach your weep screed prior to placing the weather resistant barrier (WRB) on your project, since it is easier to install the overlap when the weep screed is in place. Many building code officials have become more rigid on the enforcement of these standards in recent years.

2. Weather Resistant Barrier (WRB)

The WRB sheds the moisture that passes through the veneer away from the substrate and allows drainage to the weep screed or flashings. Two individual layers of house wrap or building felt sealed with tape surrounding the structure typically are required. When a drainage mat is used directly against the lath as part of the wall system, one layer of WRB is eliminated (check local codes). When a drainage mat is used, air and moisture can move with significantly less resistance behind the veneer, and the wall is usually dryer than one without a drainage mat. The WRB is installed after the weep screed is in place, and must drape over the weep screed to allow moisture to be channeled past the face of the wall.

3. Continuous Insulation

Continuous insulation, or rigid insulation, has become increasingly popular, and the installation of adhered masonry veneers on the exterior side of the insulation is allowed as a non-engineered system for insulation that is a thickness of ½ inch or less. Designs using insulation greater than ½ inch in thickness require an engineered anchoring system. Specialty washers for anchoring lath over rigid insulation are available where you purchase your insulation or from the rigid insulation manufacturers. There are several options, and the manufacturers can guide easily you in the right direction when specifying or constructing a project with the thicker insulation.

Continuous insulation, when placed as the outermost layer on the structure prior to lath installation, can eliminate the need for a second layer of WRB. The inner layer of WRB must have all of the joints sealed and taped for the system to work properly.

4. Fasteners

Adhered masonry veneers can be applied to concrete, CMU, steel stud and wood stud substrates. The allowable non-corrosive or corrosion-resistant anchors used for anchoring lath or lath systems are as follows:

Wood frame: Staples, roofing nails and screws can be used. The minimum embedment is ¾ inch, but a minimum of one inch is a good practice to follow.

Steel stud: The only anchor recommended for steel stud is the self-tapping screw or hex head anchor with a neoprene washer attached to the anchor. Minimum embedment is 3/8 inch, but again, a greater depth will increase your odds of success.

Concrete or concrete masonry units: Powder actuated fasteners, also known as cap anchors, are allowable for this installation. Powder actuated anchors do not need pilot holes, but are not used commonly. Concrete masonry screws are a good choice as they can be monitored for embedment; will not blow through the substrate; and typically are more economical.

Innovations in lath during the last several years have opened the market to different ideas, when thinking about the lath that is integral to adhered masonry systems.

5. Metal Lath

Metal Lath is manufactured by several outstanding domestic manufacturers. Metal lath used today is a galvanized, self-furring, dimpled product that allows the lath to project ¼ inch out from the substrate, so the base or scratch coat mortar can fully encapsulate the lath. Lath weight is expressed in pounds per square yard, and is offered in three different weights: 1.75 pounds, 2.5 pounds and 3.4 pounds. The most common is 2.5, but, in some areas, all of the specifications are written for 3.4 material.

Lath placement or orientation is no longer stipulated by local codes. It is still most productive to install lath horizontally – one over two for example – and the days of “cups up, smooth down” have been eliminated. Do not terminate lath at a corner. Always extend the lath past an outside corner a minimum of 12 inches. Lath can be terminated at an inside corner. Anchor lath a minimum of every seven inches vertically, and at every stud, or 16 inches on center.