Tag Archives: Moisture management

Weep Now or Weep Later: Moisture management and risk zones for masonry

All images courtesy Masonry Technology Inc.

All images courtesy Masonry Technology Inc.

by John H. Koester

Three decades ago, this author was issued his first patent; it was for a weep system. The main ‘claim’ was the forming of a mortar bed joint’s bottom side to create tunnels or channels into the cores or cavities of masonry walls. In the process of researching information for the patent’s content, something became very apparent—many of the industry-standard accepted practices for weeping had little to no scientific basis.

The spacing of weeps 406, 813, 1219 mm (16, 32, or 48 in.) on center (oc) is one example of a common practice without scientific support given moisture management and modular spacing patterns have little correlation. While there may be rules calling for certain spacing (i.e. 2006 International Building Code [IBC] 2104.1.8−Weep Holes), that does not mean there is supporting research.1 Some things are just done long enough they become standard practice.

With the old weep technology and its spacing, water indeed got out of the cavities and cores of masonry walls. However, it was not necessarily all the water, always through the weeps, or a fast process. Moisture management in masonry walls is about getting the water away from, off of, and out of the construction detail as quickly as possible. The length of time moisture remains is in direct proportion to the amount absorbed into the materials.

What is a weep?
In the first volume of its Masonry Training Series (1996), the Mason Contractors Association of America (MCAA) defined weeps as “openings placed in mortar joints of facing material at the level of flashing, to permit the escape of moisture.” In other words, they allow the exit of any liquid water that drained down to the top surface of a flashing from the masonry wall’s core or cavity.

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The bed joint of mortar needs to be spread (a). Then, a masonry unit is laid (b). Mortar is displaced to allow for wee placement (c), and the air vent material is placed (d). A bed joint of mortar needs to be re-spread in front of the air vent material (e). Finally, a masonry unit is laid to the air vent material and into the bed joint of mortar (f).

The bed joint of mortar needs to be spread (a). Then, a masonry unit is laid (b). Mortar is displaced to allow for wee placement (c), and the air vent material is placed (d). A bed joint of mortar needs to be re-spread in front of the air vent material (e). Finally, a masonry unit is laid to the air vent material and into the bed joint of mortar (f).

Some have incorrectly adopted use of head joint air vent material and devices as weeps. Many of these air vent devices are not the proper dimensions to accommodate potential variations of a first-course bed joint of mortar and masonry unit. The non-voided portion of the bed joint of mortar becomes a dam that causes water to form a reservoir at the bottom of the cavity (Figure 1). Further, installation of this type of material—even when field-fabricated to the right height—is labor-intensive and a cumbersome, multistep process (Figure 2).

The appropriate detail for a masonry air vent and mortar weep.

The appropriate detail for a masonry air vent and mortar weep.

The appropriate detail for a masonry air vent and a masonry weep would look like Figure 3. The weep holes are at the lowest point of the masonry wall (and cavity) and are spaced 267 mm (10.5 in.) apart to improve the mathematical chances one of them will be at the lowest point of the masonry wall (and cavity) where the water is. (The bottom side of the bed joint of mortar is not part of the modular layout of the wall; therefore, the forming of the bottom side of the bed joint of mortar to create a weep system is also separate from any modular considerations.) The masonry wall air vents should be spaced every third brick head joint, one to two courses above the bottom of the cavity, and above the weeps. They should also be a course below the top of the vertical height of the flashing mechanically fastened to the backup wall.

This detail provides excellent weeping capacity and potential air intake to improve airflow in the masonry wall’s cavity. The positive outcomes include improved chances for pressure equalization of the cavity with the pressure on the masonry wall’s exterior surface. This may move moisture-laden air (i.e. water vapor) deeper into the exterior building envelope due to the the scientific principle of high to low pressure equalization. Additionally, providing equal air intakes and air exits at the wall’s top and bottom improves airflow in the core or cavity. This will have some positive impact on the masonry wall’s ability to dry out.2

Commonly used on lintels and shelf angles, open-head joints have the potential to provide both weeping capacity and airflow (Figure 4). They also eliminate problems with the related bed joint of mortar because the first brick course is usually laid dry on the flashing material covering the lintel or shelf angle that waterproofs the bottom of the cavity.

Open-head joints are weep details commonly used on lintels and shelf angles.

Open-head joints are weep details commonly used on lintels and shelf angles.

Sometimes, the bed joint of mortar is left in place because raking it out is not architecturally appealing (it breaks the coursing lines of the bed joint).

Sometimes, the bed joint of mortar is left in place because raking it out is not architecturally appealing (it breaks the coursing lines of the bed joint).

When employed with a bed joint of mortar, there is a chance the bed joint directly below the open head joint will not be raked clean of mortar. If this occurs, water flow out of the detail is dammed up. In other cases, the bed joint of mortar is left in place because raking it out is not architecturally appealing as it breaks the coursing lines of the bed joint (Figure 5).

The introduction of rainscreen drainage planes have improved the predictability of masonry veneer walls.

The introduction of rainscreen drainage planes have improved the predictability of masonry veneer walls.

It is critically important the cavity or core (the void behind the veneer) is open and clear of obstruction to allow liquid water to move from a high point of entry to the lowest point of the cavity or core, which is the top surface of the flashing. In the past, attempts to produce this part of a masonry veneer wall have been the responsibility of masons. The results have varied from good, open, clean cavities to those bordering on being poured solid. Predictable, high-quality results are required to effectively manage moisture. The introduction of rainscreen drainage planes to maintain this void has improved the required predictability (Figure 6).

Detailing the solution: a case study
Proper moisture management for masonry assemblies involves more than just knowledge of weeps. In devising the best approach, dividing the envelope into ‘risk zones’ is crucial. These ‘separations’ are determined by factors such as the building site and climate, the structure itself (i.e. multistory versus low and sprawling), and the materials specified for the envelope. Ranging in intensity from very low to extremely high, the zones are specific sections of the exterior building with unique exposures to moisture. There are many examples of premature failure of the exterior building envelope illustrating entrapped moisture has migrated from one location (zone) to another. This migration, along with the costs associated with premature failure, can be prevented with the appropriate detailing.

The process of determining moisture management zones begins at any part of the exterior envelope. In most cases, since moisture moves from a high point of entry to a low point in the exterior building envelope, starting at the top makes sense.3

A sample building highlighting moisture management risk zones.

A sample building highlighting moisture management risk zones.

A detail of a parapet wall.

A detail of a parapet wall.

In some cases, the process is two steps: first, a determination of a ‘general’ risk zone, followed by a second determination of ‘associated zones’ within (e.g. parapet walls and window openings). Figure 7 is an example of assessing moisture management risk zones for the purpose of designing the appropriate flashing and weep detail to help modify the moisture management risk. They include:

  • parapet wall (Zone 1);
  • decorative cornice belt (Zone 2);
  • window openings (Zone 3);
  • louver openings (Zone 4);
  • door openings (Zone 5);
  • intersection of non-frost-affected concrete stoop and masonry wall (Zone 7);
  • intersection at grade of masonry wall and frost affected sidewalk (Zone 10); and
  • intersection at grade of a masonry wall and landscaping (Zone 11).

Parapet
Zone 1 (Figure 8,) is an example of a parapet wall with multiple associated moisture management details:

  • coping;
  • roof flashing and counter flashing; and
  • transition point from bottom of parapet wall to top of exterior building envelope that encloses the interior spaces—the ‘decorative stone cornice band.’

The coping on the parapet wall is the roof of the parapet and must be waterproofed (Figure 9). One of numerous exterior building envelope details with many responsibilities, coping stones are frequently positioned out of sight. The intersection of the roof and bottom back side of the parapet is another moisture management detail with numerous roles. The roof flashing and the parapet wall counter flashing must be designed to be both waterproof and movement-absorbing; they must be able to accommodate expansion and contraction of the roof assembly.

Decorative cornice
The point where the bottom of the parapet wall ends, and the top of the exterior building envelope enclosing the interior begins, is sometimes unclear. Zone 2 is the top of the decorative stone cornice band (Figure 10). One should not be misled by the term ‘decorative;’ it is also a moisture-diverting detail and a ‘roof’ for the wall and windows below it.

Detail of coping stone.

Detail of coping stone.

Detail of a decorative cornice.

Detail of a decorative cornice.

While attractive, this stone has many open areas that trap snow and moisture and allow it to build up and hold. The flat window ledge also traps and holds moisture.

While attractive, this stone has many open areas that trap snow and moisture and allow it to build up and hold. The flat window ledge also traps and holds moisture.

There is a misconception patterns on the exterior of the building envelope veneers (e.g. stucco, wood, brick, or stone) are simply decorative. In truth, their primary function is protection. They direct moisture away from sensitive details, such as windows and doors. In the past, the construction industry understood this multipurpose concept and had the sense to make them both functional and aesthetically appealing. The current trend seems to concentrate solely on the aesthetic aspect. The unintended consequence of this singular focus is the creation of surface patterns (or details) that actually cause moisture management problems (Figure 11).

Window flashing
Zone 3 is the group of six windows on the second and first floors on the right and left sides of the exterior building envelope (Figure 12). In many cases windows or numbers of windows should be grouped into a single risk zone because their moisture management details are so interconnected and interdependent.

Louvers and windows
Zone 4 is the pair of louvers and windows on each side of the entryway (Figure 13). Obviously, the two types of openings are different, but the moisture management detail is virtually the same. Further,

their proximity to one another joins them into one, unified moisture management risk zone.

In many circumstances, the wall opening directly above another opening will have an impact on the latter’s detail even though they may be of different types. The explanation is obvious: water runs downhill.

Detail of the window flashing.

Detail of the window flashing.

Louver and window flashing.

Louver and window flashing.

Arch above the door
Zone 5 is the arch above the front entry (Figure 14). The arch is probably the most misunderstood moisture management detail of all the wall-opening details—for example, weeps protruding from the radius of an arch is not a good idea, but it still occurs.

If the weeps installed on the radius were to be functional at all, there would need to be an upturned stop flashing at that point of the arch flashing to stop moisture, and the weep would need to be installed at the bottom of the valley in the flashing. It would also have to have the same elevation in the masonry joint. The skill to execute this type of detail is difficult, if not virtually impossible, to find.

Like many good practices and details in the construction industry, the moisture management detailing for arches has been lost to history. Arches have been in common use since the time of the Romans, and so has the moisture management detailing required for their preservation. Nevertheless, most people today simply pass them off as decoration. The gaping mouths in the heads of animals and gargoyles that serve as column caps supporting arches on ancient and medieval structures are actually the weep exits (holes) for the arches’ moisture management system.

Decorative band stone.

Decorative band stone.

Arch detail.

Arch detail.

Decorative band stone
Zone 6 is the decorative band stone separating the bottom of the first floor exterior building envelope from the garden level exterior building envelope (Figure 15). This veneer detail has many responsibilities, including diverting moisture out, over, and away from the windows and wall below it. This decorative band stone also has an aesthetic appearance aspect.

Intersection of vertical wall and stoop
Zone 7 is the intersection of the vertical wall and the top surface of the non-frost affected stoop platform (Figure 16). This vertical wall veneer surface will be subjected to water splash back from the top surface of the platform of the stoop. Additionally, various types of ice control chemicals (e.g. salts and de-icers) may contaminate it, and snow removal tools (e.g. shovels and scrapers) may contract it. This wall detail needs to be durable, aesthetically pleasing, and backed by a waterproofing system because it is an exterior wall system with an interior living space behind it.

Front stoop steps and stoop platform
Zone 8 is the front stoop steps and platform. The seventh and eighth risk zones are the perfect example of the interdependence of moisture management systems. In the case of the stoop platform and steps, the slope-to-drain of the surfaces and their ability to resist moisture penetration is absolutely critical.

Decorative band stone .

Decorative band stone .

Garden-level window.

Garden-level window.

A detail that will allow for replacement of the stoop platform and steps without major impact on the veneer wall system is the appropriate design (Figure 16). This is an example of how a comprehensive understanding of moisture management risk zones influence the original building design and its detailing to allow for future maintenance, repair, and replacement of the exterior building envelope components with the least amount of interruption to adjoining details.

In this instance, the stoop platform is the construction detail that has the most exposure to moisture. In all likelihood, it will need to be repaired or replaced before the other adjoining details. The band of stone at the bottom of the vertical brick wall should be more durable than the brick. It separates the edges of the top surface of the stoop platform from the brick veneer and diverts water away from the intersection of this moisture sensitive detail.

Bottom of wall
Zone 9 is the set of two garden level windows on each side of the front entryway stoop (Figure 17). Window openings at this elevation on an exterior building envelope have several unique moisture management concerns, including their proximity to grade level and accumulating moisture, along with the potential for splashes.

Details at the bottom of the wall: frost-affected sidewalk and landscape stone.

Details at the bottom of the wall: frost-affected sidewalk and landscape stone.

Designing/detailing the grade surface that adjoins these types of grade-level windows is an important factor that will play out in the daily maintenance and their long-term sustainability. The other obvious concern with windows in this location is security. A damaged window is also not waterproof.

On-grade
Zones 9 and 10 are the two on-grade details that contact the bottom perimeter of the building on each side of the front stoop (Figure 18). The grade surface in the first detail is a frost-affected sidewalk; the grade surface in the second is landscaping stone. These two very different ‘on-grade’ materials need to follow many of the

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same rules of good moisture management:

  1. They both need to maintain good slope-to-drain away from the structure they contact.
  2. Their top surface elevation must not interfere with the drainage weeps of other exterior building envelope components (these risk zones). Further, one must consider their movement up or down in elevation due to expansion or contraction of supporting soils due to the wetting, drying, or freeze-thaw of supporting fill material, or because of expansive soils.
  3. These details can never become attached to the structure they abut. The attachment and potential movement of these details will result in severe damage to the structure and the ‘at-grade’ details.

Conclusion
Understanding weeps and identifying unique moisture management risk zones on and in the exterior building envelope are critical for creating and maintaining a sustainable building. However, while these moisture management risk zones can be identified as separate and unique for the purpose of designing and detailing, they are not and cannot be disconnected from each other when it comes to moisture management.

From top to bottom and from bottom to top, they all interconnect and impact each other. No good wall system can survive a bad roof and no good roof can survive a bad wall system; they support and protect one another. This is what holistic and sustainable is all about—knowing that nothing is separate, all things are connected and nothing stands alone.

Notes
1 This reference comes from the 2006 edition—it is puzzling the reference to weeps was discontinued in the 2009 and 2012 versions of IBC given the importance of moisture management in the exterior building envelope. (back to top)
2 It should be emphasized, however, the ability of masonry cavity airflow to dry out or remove moisture is extremely limited. This airflow should not be expected to effectively remove or alleviate any type of ponding water condition—this should be the job of a well-designed weep system. (back to top)
3 Although this article concentrates on the wall portion of the exterior building envelope, it is important to remember many serious wall moisture management problems are actually caused by roof leaks, both low- and high-sloped. (back to top)

John Koester is the founder and CEO of Masonry Technology Inc. With construction experience dating back almost 40 years, he has been a card-carrying mason and cement-finisher, and for many years operated his own masonry construction business in the Minneapolis-St. Paul area. Koester has extensive background in waterproofing systems in the areas of forensics, design, and installation oversight—both in restoration and complete re-roofing projects. He can be contacted via e-mail at john@mtidry.com.

To read the sidebar, “Weep Now or Weep Later: Of Ropes and Tubes,” click here.

Weep Now or Weep Later: Of Ropes and Tubes

by John H. Koester

One of the first commonly employed weep details was the sash cord or ‘rope’ weep. In some cases, this detail was expanded with sections of the sash cord laid in the cavity and then extended through

the wall, usually at a head joint. In other cases, the sash cord was fastened vertically up the backside of the cavity. In yet other instances, it would be pulled out of the wall, leaving a hole through the head joint or bed joint of mortar.

How and when these sash cord sections were placed or embedded in the bed joint of mortar impacted whether they had any weeping capacity. If they were placed on the flashing and the bed joint of mortar was spread on top, the finished detail looked like Figure A. However, if the bed joint of mortar was spread and the sash cord section was laid or embedded into it, the finished detail looked like Figure B. The theory was the cotton sash cord (or a synthetic one) would ‘wick’ water out of the core or cavity and dry the units. However, if there is one takeaway from this article, let it be that one should not get into a wicking contest with mortar or masonry units—how can a 9.5-mm (3/8-in.) diameter sash cord compete against an entire masonry assembly?

Many have seen an example of a rope weep that has moisture stains around the outside end of the cord; it appears to have moisture ‘weeping’ from it. What is really happening is a small amount of moisture is actually exiting the cavity through small voids in the bed joint of mortar at the 5 o’clock and 7 o’clock positions on the bottom radius of the sash cord.

Various tube weeps—pieces of plastic pipe cut to length—have also been introduced to the masonry industry. Their installation procedure is virtually the same as the sash cord material and so are the shortcomings. Even when the tubes are correctly installed on the flashing’s surface, the weep’s wall thickness is still a water dam.

All images courtesy Masonry Technology Inc.

Image courtesy Masonry Technology Inc.

To read the full article, “Weep Now or Weep Later: Moisture management and risk zones for masonry,” click here.

 

Claddings and Entrapped Moisture: Lessons learned from early EIFS

 

All images courtesy Masonry Technology Inc.

All images courtesy Masonry Technology Inc.

by John Koester

While some building science concepts can be difficult to grasp, there is nothing new or complex about the relationship between temperature and moisture management. The phrases ‘wet and cold’ or ‘warm and dry’ are ingrained in the minds of the public for good reason.

The law of physics dominating this phenomenon is thermal conductivity. Dense materials transmit temperature more efficiently than less dense ones because the molecules are closer together. Water is denser than air and transmits temperature 25 times more efficiently. When a person is wet, the ambient air temperature can be received more readily and the body loses temperature to the surrounding ambient air more easily if the latter is colder. A practical example can be found in the kitchen—moving one’s hand into a 200-C (400-F) oven, without touching any surfaces, is quite different from plunging a hand into boiling water.

Controlling the temperature relationship of a building from inside to outside (or outside to inside) means insulating the exterior building envelope.

Controlling the temperature relationship of a building from inside to outside (or outside to inside) means insulating the exterior building envelope.

Good thermal insulators—sprayed polyurethane foam (SPF) and rigid boardstock, for example—have a lot of air molecules in proportion to other dense molecules; further, the former is effectively positioned between the latter to make this separation. A good example of this is the cardboard sleeve that slides around a paper cup of hot coffee, allowing someone to comfortably hold a steaming beverage.

The clear takeaway for the building industry is to have an impact on a temperature relationship of a building from inside to outside (or outside to inside), one must insulate the exterior building envelope—the walls, floors, and roof (Figure 1).

Another critical requirement is keeping the insulation material dry. Wet insulation is not an insulator, but rather a conductor. Different types of insulation materials absorb moisture at different rates. In many instances, an exterior building envelope with no insulation is preferable to one with wet insulation. Of course, the problems of wet insulation in a wall do not end with just poor insulation values. They also include mold, pest infiltration, and building material degradation.

As shown in Figure 2, there are many causes of wet insulation in the exterior building envelope. Examples include:

  • uncovered insulation stored in an exposed location on a jobsite can be installed in a damp/wet state;
  • liquid water can egress into the exterior building envelope during and after the construction phase;
  • moisture (in the form of water vapor) can enter the building envelope from the exterior and interior;
  • liquid water can leak from faulty plumbing; and
  • poorly insulated plumbing or HVAC ductwork can condense and drip water.

Moisture problems with EIFS are often in areas where the system abuts other materials such as wood trim, at the top wall, at roof flashing, around wall openings, and where other items penetrate the cladding’s surface. EIFS can also develop penetrations over time—foundations move, walls crack, storms can blow debris into façades, etc. There can often be installation issues. Even though manufacturers of EIFS products have recommended best practices and procedures, onsite labor does not always follow them; components like flashing can be improperly installed or omitted.

As the National Institute of Building Sciences’ (NIBS’) Whole Building Design Guide states:

Problems observed with in-service EIFS installations are primarily related to moisture intrusion. EIFS provides protection against moisture infiltration at the base coat; however, moisture migration through openings for windows, flashings and other items, or holes and cracks in the EIFS itself, have allowed leakage to occur on EIFS clad buildings. With barrier EIFS installations, or where weather barriers and flashing are improperly installed in conjunction with wall drainage EIFS installations, moisture has entered the wall system at these locations and caused damage to the wall sheathing and framing. The extent of these occurrences on wood frame structures has led to class action lawsuits.1

There are many causes of wet insulation in the exterior building envelope.

There are many causes of wet insulation in the exterior building envelope.

EIFS and entrapped moisture
There are additional scenarios that have caused a great deal of problems. For example, issues occur when board stock rigid insulation is layered against other rigid insulation or exterior sheathing, or when decking traps moisture between the layers of material. This phenomenon first happened on a wide scale in early exterior insulation and finish systems (EIFS). Moisture entered these systems and became entrapped behind the rigid insulation and in front of the wall sheathing on the backup wall, deteriorating the water-resistant barrier (WRB), sheathing, and structural studs (Figure 3).

In early exterior insulation and finish systems (EIFS), moisture occasionally entered and became trapped, deteriorating the water-resistant barrier (WRB), sheathing, and structural studs.

In early exterior insulation and finish systems (EIFS), moisture occasionally entered and became trapped, deteriorating the water-resistant barrier (WRB), sheathing, and structural studs.

Moisture entering these early EIFS assemblies (through any of the methods previously mentioned became held for an extended period in the pockets/voids in the exterior building envelope created by the variations between the rigid insulation surface and the wall sheathing surface. This negative scenario was amplified by the composition of the two layers of materials involved.

The EIFS industry started addressing this problem by incorporating a 3.175-mm (1/8-in.) drainage plane between the back side of the board stock rigid insulation and the exterior face of the sheathing or the WRB installed over the sheathing. Created through vertical adhesive patterns and/or strips of manufactured drainage material (Figure 4), this void became the accepted solution because it caused the least decrease in R-value while maintaining effective drainage characteristics. It also allowed accumulating moisture to effectively drain down and out the wall.

Additionally, this size was chosen because anything smaller could have allowed capillary action. When a wet layer is in close proximity to a dry one (i.e. less than 3.2 mm [1/8 in.] of separation), moisture moves between them. As the Whole Building Design Guide states:

Once wetted, capillary transfer within, or between, layers of an exterior wall assembly can also occur, and can be further exacerbated by moisture loads inherent to an exterior wall product or material shortly after initial installation.2

These voids are not widely promoted features of EIFS because the cladding systems qualify, under the International Building Code (IBC), as “barrier systems.” In other words, they are not supposed to allow moisture to penetrate into the building envelope and accumulate. The following information comes from an International Code Council Evaluation Service (ICC-ES) report of a major EIFS manufacturer’s product:

Compliance with the following codes:
● 2012 and 2009 IBC; and
● 2012 and 2009 International Residential Code (IRC).
EIFS: IBC Chap. 14, IRC Chap. R7
Weather resistance: IBC Chap. 14, IRC Chap. R7
Weather protection: complies with IBC Section 1403.2 and IRC Section R703.1

Granted, in a perfect world, EIFS would indeed work as a barrier system. However, walls do leak because of contractor error or issues with the installation of other products used in conjunction with the system. Therefore, since evidence showed moisture penetrated these systems, the EIFS industry’s decision to add a drainage plane to overcome the entrapped moisture problem is important. As this information was at one time proprietary and not widely disseminated, the requirement for and effectiveness of a drainage plane as a remedy for entrapped moisture is not fully appreciated by the construction industry.

It is important to note this article is not intending to single out and disparage the EIFS industry. In fact, it should be seen as just the opposite—EIFS manufacturers have made significant strides in successfully remedying the entrapped moisture problem by adding a drainage plane. Further, it is critical to remember the entrapped moisture problem is not exclusive to just one type of building envelope system.

Voids created through vertical adhesive patterns and/or strips of manufactured drainage material maintain effective drainage, without overly decreasing R-value.

Voids created through vertical adhesive patterns and/or strips of manufactured drainage material maintain effective drainage, without overly decreasing R-value.

Many are specifying rigid board stock insulation to be applied outside the wall sheathing, but this may create a system remarkably similar to early EIFS—and without the benefit of the drainage plane.

Many are specifying rigid board stock insulation to be applied outside the wall sheathing, but this may create a system remarkably similar to early EIFS—and without the benefit of the drainage plane.

The problem with two barriers
Enter the new energy code requirements: the 2009 International Energy Conservation Code (IECC) for residential buildings and American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2007, Energy Standard for Buildings Except Low-rise Residential Buildings, for commercial buildings. (The 2012 IECC, requiring even stricter standards, may soon be adopted in some locations.) To comply, the building industry is specifying rigid board stock insulation to be applied outside the wall sheathing.

In so doing, the industry may be unwittingly creating a system remarkably similar to the early EIFS, but without the benefit of the drainage plane. There are numerous ongoing discussions in the construction industry related to this application (Figure 5):

  • Should the WRB be installed over the rigid insulation (Figure 6)?
  • Should the exterior sheathing and rigid insulation (with taped seams) be installed atop the WRB (Figure 7)?
  • Does rigid insulation with taped seams qualify as a WRB?
  • Is rigid insulation with taped seams a vapor retarder?

This author sees most types of board stock rigid insulation with taped seams as ‘vapor retarders.’ If this is the case, then the consequences of two or more vapor retarders as components of the same exterior building envelope system are very real.

There is nothing wrong with two or more vapor retarders in one exterior building envelope—provided no moisture is trapped between them. Similarly, there is nothing wrong with moisture being trapped between two or more vapor retarders in an exterior building envelope—provided the amount is small, and there are no other construction details involved that could rot or harbor microorganism growth. Of course, both of these scenarios provide potential problems given the criteria.

Whether there are issues with installing the WRB over the rigid insulation is a discussion ongoing within the industry.

Whether there are issues with installing the WRB over the rigid insulation is a discussion ongoing within the industry.

Should the exterior sheathing and rigid insulation (with taped seams) be installed atop the WRB?

Should the exterior sheathing and rigid insulation (with taped seams) be installed atop the WRB?

 

 

 

 

 

 

 

 

 

Conclusion
When it comes to claddings and entrapped moisture management, denial and ignorance are rife. “I do not have to worry about moisture being trapped in the exterior building envelope because it cannot get there” is the former, while “I didn’t know that material was a vapor retarder” is the latter.

Holistic building is critical to ensure the envelope functions as intended.

Holistic building is critical to ensure the envelope functions as intended.

While a sense of denial is inexcusable for design/construction professionals, the ignorance can be more understandable. There are many choices for exterior building components that may qualify as vapor retarders under various conditions and configurations:

  • rigid insulation (and other types of insulation);
  • certain veneers/rainscreens;
  • both interior and exterior sheathings;
  • interior vinyl wallcoverings;
  • some paints and coatings;3 and
  • polyethylene sheets and other products specifically billed as ‘vapor retarders.’

Knowing how the wide range of components in the exterior building envelope interacts with each other under various conditions is not easy. Nevertheless, it is the responsibility of the specifying professional to research and determine what components and configurations will function properly. The term ‘holistic building’ is not just a catch phrase—it is a requirement that allows an exterior building envelope to function effectively in the long term (Figure 8).

Notes
1 Visit www.wbdg.org/design/env_wall.php. (back to top)
2 See note 1. (back to top)
3 Vapor retarder paints typically have a perm rating of 0.8 to 0.45, but the actual perm in the field depends on the number of coats and the degree of coverage. For more information, read the Journal of Light Construction article, posted at www.jlconline.com/paints/q-a–vapor-retarder-paints.aspx. (back to top)

John Koester is the founder and CEO of Masonry Technology Inc. With construction experience dating back almost 40 years, he has been a card-carrying mason and cement-finisher, and for many years operated his own masonry construction business in the Minneapolis-St. Paul area. Koester has extensive background in waterproofing systems in the areas of forensics, design, and installation oversight—both in restoration and complete re-roofing projects. He can be contacted via e-mail at john@mtidry.com.