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AN OVERVIEW OF WATER LEAKAGE PATHS INTO EXTERIOR WALLS

Kurt R. Hoigard, PrincipalGarth D. Hall, Associate, Senior Architect

Raths, Raths & Johnson, Inc.

Abstract: Water leakage into exterior wall construction is one of the principal causes of damageand deterioration to facade materials and underlying construction. This paper discusses the basicapproaches currently used to keep water out of buildings and their relationship to several commonexterior wall systems. Also discussed are some of the more common water leakage paths the authorshave encountered while investigating building leakage problems, including deficiencies associatedwith masonry walls, siding, EIFS, windows and doors, weather-resistive barriers (WRBs), andflashing.

INTRODUCTION

Water penetration into building interiors has been an issue as long as man has been constructingshelters for himself. Early construction techniques using materials such as adobe, stone, and logsto create solid walls relied on a single material to provide both structure and weather resistance.These materials absorbed water yet provided a barrier to weather intrusion into the building interiorthrough sheer bulk. The addition of openings through walls for ingress and egress and to providelight and ventilation complicated matters by providing direct paths for water penetration to theinterior space. Fitting these openings with movable closures such as doors, windows, and shuttersreduced the potential for direct passage of water through the gross opening while creating a need toaddress the water resistance of the closures and their interfaces with the walls.

Advances in construction materials and techniques realized during the 19 and 20 centuries wereth th

accompanied by a growing public intolerance to intrusion of the exterior environment into theinterior environment. At present, an expectation exists that building interior conditions can andshould be kept completely controlled with respect to temperature and humidity, while allowing inlight and keeping out the weather. This increased demand on the building exterior envelope hasoccurred at a time when new construction materials, configurations, and installation techniques haveproliferated. The advent of new exterior wall materials and systems has resulted in manyarrangements that are physically intolerant to water intrusion and are susceptible to deterioration andfailure of cladding components and primary structural members, as well as the development ofbiological growth. In this paper, the authors use examples from exterior wall leakage investigationsthey have performed to illustrate some of the more common entry paths for water in the liquid form.For information on water vapor migration through exterior wall construction, the reader is directedto papers by Kudder, Lies, and Hoigard .1,2

BASIC WALL COMPONENT CONFIGURATIONS

The means by which exterior wall components keep water out of building interior spaces can beseparated into two general categories: barriers and water management . Barrier systems are intended3

to block the movement of water into the building interior. Water is either shed directly at the

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exterior surface, as with barrier Exterior Insulation and Finish Systems (EIFS) which are consideredface-sealed barriers, or is allowed to penetrate partially through the wall during rain events and thenevaporate during dry weather, as is the case with multi-wythe brick masonry which is considered amass barrier.

While some exterior wall systems are intended to act directly as weather barriers, many othersystems, including masonry veneer, function through water management. As the name suggests,water-managed systems are designed on the assumption that water will penetrate the exposed wallcomponents or material interfaces. Concealed flashing and weather-resistant barriers are requiredto collect, control, and discharge water that passes through the exterior wall plane. In theseconfigurations, the role of keeping water out of the building interior falls to materials that areconcealed and not easily maintained, making proper installation crucial.

Real buildings typically incorporate combinations of barrier and water-managed components,frequently in the same wall. As an example, consider an office building constructed with triple-wythe brick masonry walls with filled collar joints and aluminum-framed windows fitted intopunched openings. In this case, the masonry functions as a weather barrier, but the window openingsrequire head flashings to collect water that has penetrated the outer masonry wythe before it can dropinto the building interior at the top of the window opening.

WATER PATH EXAMPLES

As part of their work investigating, diagnosing, and developing repair designs to address buildingfailures across the United States, the authors have observed a wide range of cladding materials, walltypes, and building occupancies in various climates. Regardless of the materials and configurationinvolved, water leakage through exterior walls has followed two basic paths: passage through amaterial or component or passage through the interfaces between adjacent materials or systems.Each of the individual wall components are part of the building envelope, and as such, in additionto performing individually, each piece must be properly integrated with the surrounding materialsin order to perform acceptably. Although designers and contractors may pay attention to theindividual components, integration of those components is often overlooked entirely. Frequently,leaks to building interiors involve a combination of the basic leak paths, passing first through theexterior wall plane and then bypassing concealed water barriers via holes, gaps, or incompleteflashing and terminations. Some of the more common exterior wall water penetration pathsencountered by the authors are described in the following sections. The examples presented are notintended to provide a complete list of all potential wall water leakage sources, nor are they meantto imply one material or system is superior to another.

Masonry

Masonry construction includes brick, stone, or concrete units, separately or in combination, joinedtogether with cement-based mortar and can be erected as a barrier or water-managed systemdepending upon the configuration selected. Masonry barrier walls are typically constructed by usingmultiple wythes, or layers, and completely filling the collar joints (spaces between wythes) withgrout or mortar. This arrangement can provide good barrier performance when properly constructedwith full head, bed, and collar joints. Incomplete filling of any of the joints, poor adhesion of the

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mortar to the masonry units, and cracking due tounaccommodated volume changes or tensile stresses canall provide paths for water infiltration through theplanned barrier and into the building interior (Figure 1). Hollow concrete masonry units (CMUs) are oftenused for the inner wythes in masonry bearing wallconstruction. If left unfilled, the hollow core spaces

inherent in most CMUs significantly reduce the length of potential water paths through the bed jointsand also provide direct paths for vertical water movement within the wall (Figure 2). Thesecharacteristics of CMU construction increase the importance of obtaining full, well-bonded head andbed joints within the outer masonry wythe and complete filling of the collar joint present betweenthe outer wythe and the CMU back-up.

It is common in brick/CMU bearing wall construction to construct a solid layer called a bondbeam to distribute floor and roof framing loads and provide a connection point for framing members.Water that may be traveling downward through mortar joint voids or unfilled CMU core spaces canbe diverted into the building interior by the bond beam if through-wall flashing is not present tocollect and redirect the water to the exterior (Figure 3).

When brick masonry is constructed as a single-wythe cladding over other materials such as woodor metal stud framing, the masonry portion of the wall assembly is assumed to be permeable to waterand therefore requires a water management approach (refer to Raths and Hoigard, Kudder and4

Lies ). In this configuration, a clear cavity space is required between the brick and the back-up5

structure in order to allow water that penetrates the masonry to drain downward. Concealed weather-resistant barrier and flashing materials are generally required in the wall cavity to protect the back-upstructure and direct water to the exterior. Incomplete or defective construction of the hidden weatherbarrier and flashings can allow water entry to the building interior resulting in deterioration of otherwall components, as well as interior finishes (Figure 4).

Figure 1Removal of bricks in this masonrybarrier wall revealed voids in headjoints and the collar joint between theface brick and CMU back-up.

Figure 2Water leakage through brick/CMU masonrybarrier wall due to incomplete filling of thehead, bed, and collar joints and open CMUcore spaces.

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Siding Materials

For the purposes of this paper, siding materials will refer to those exterior wall finish materialsthat are typically purchased in long lengths, cut to fit at the project site, and installed as strips withlapped or interlocked interfaces. Common examples include aluminum and vinyl siding, woodclapboard and hardboard siding, and composite fiber-cement board materials. The authors’experience with these materials indicates that while water leakage may occur through the main fieldof the completed wall installation, leaks at the perimeter terminations, interfaces with other materialsor systems, or penetrations through the wall are more common. Although not historically mandatedby building codes and industry standards, the authors believe the many possible water-entry pointsmake it prudent to include concealed weather-resistive barrier materials (commonly referred to asWRBs) and flashings within exterior walls clad with siding materials. In this arrangement, the WRBand flashing are the primary weather barriers.

Exterior Insulation and Finish Systems (EIFS)

EIFS cladding is comprised of a rigid insulation board, a glass fiber-reinforced base coatapproximately /16-inch thick, and a textured finish coat. Similar to brick masonry and other types1

of cladding, EIFS-clad exterior walls can be designed and constructed as either a barrier or a water-managed exterior wall system, although the vast majority of the EIFS installed in the United Statesis the barrier type. Barrier EIFS is most often adhesively attached directly to a gypsum board,masonry, or wood panel substrate. The EIFS lamina (the reinforced base coat and finish) providesan effective barrier against water infiltration when properly integrated with other buildingcomponents using flashing and sealant. For more information on EIFS performance, the reader isdirected to a paper by Kudder and Lies .6

Figure 3Potential water path at a bond beamin a brick/CMU wall.

Figure 4Construction deficiencies in the hidden weatherbarrier and flashing at the base of a brickmasonry screen wall contributing to waterleakage to the interior. Deficiencies includenon-continuous flashing, incomplete WRB andbackward-lapped WRB behind the base flashing.

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In wall systems where a water-managed cladding is desired, a sheet or liquid-applied WRB canbe installed between the insulation board and sheathing. When sheet membranes are used as a WRBin these systems, the EIFS must be mechanically attached to the building structure. Regardless ofthe WRB used, proper integration of the WRB and flashing is necessary for water that penetrates thelamina to be collected and drained to the exterior. As with other water-managed cladding systems,fasteners through the hidden weather barrier can create paths for water intrusion and leakage to thebuilding interior.

Weather-Resistive Barriers (WRBs)

Water-managed exterior wall construction, regardless of whether the exterior wall finish ismasonry, siding, or drainage EIFS, typically includes a weather-resistive barrier (WRB) behind thecladding. By definition, the exterior wall finish in this arrangement is assumed to allow water topass, requiring the installation of a hidden primary weather barrier to preclude moisture intrusioninto the building interior. Common WRBs are typically purchased as rolled sheet goods and includeasphalt-impregnated paper and felt and various woven and perforated polymeric materials,commonly referred to as “house wraps,” with varying degrees of water resistance. For moreinformation on WRB water resistance, the reader is directed to a paper by Hoigard and Hall .7

WRBs must be continuous and properly integrated with other wall components in order toperform acceptably. Holes and gaps in the WRB installation defeat the water-managed wall designconcept. A common deficiency observed by the authors during water leakage investigations is theimproper lapping of WRB materials. In order to keep water away from water-sensitive wallmaterials inboard of the weather barrier plane, WRBs must be installed with properly configuredshingle laps at horizontal interfaces of adjacent sheets. The upper sheet needs to lap over the lowersheet to allow water to drain down the WRB surface for collection and discharge to the exterior.Backward laps, with the lower sheet installed over the upper sheet, can direct water into the buildinginterior, resulting in significant damage to the inner wall construction and interior finishes (Figure 5).

Figure 5Deterioration of plywood wall sheathing below backward lap of asphalt-saturated WRBs in the fieldof wall right of the window. Deterioration is also visible below the window where the WRB wasbackward-lapped at the window sill flange.

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Windows and Doors

Windows and doors, when installed in exterior walls, form part of the weather-resistive barrierfor the building envelope. Whether the wall employs a barrier or water-managed design, thefenestration must be properly integrated. In barrier wall construction, sealants installed around thefenestration perimeter become part of the exposed weather barrier and must remain watertight. Insystems with a concealed barrier, the WRB must be integrated with the windows and doors. Forflanged units, this means effectively integrating the flange and the WRB. For windows and doorswithout a nailing flange, the WRB typically is integrated with a separate flashing around theperimeter of the window or door opening which must be continuous to effectively prevent moistureintrusion.

Windows and doors themselves are also common leak sources. The authors have found thatwindow and door leakage depends on many factors, including the frame material and unitconstruction detailing. Window and door frames can be plain wood or wood clad with aluminumor vinyl, all vinyl, or all metal (typically aluminum but sometimes steel). Each material requiresdifferent construction details and each has its own advantages and disadvantages.

Most windows and doors are made up of multiple assembled components with joints betweenthem. The interfaces of the various components are susceptible to water leakage through the frame,especially at the lower corners. The exceptions are many vinyl products, which are heat welded tocreate a “seamless” frame. However, in most other products, the manufacturer must address theissue of frame joints. In wood products, the joints may utilize miter or rabbit configurations inconjunction with mechanical fasteners. The joints are then “sealed” by some manufacturers with theprimer and finish paint applied to the surface. In this case, if the paint fails to fill or bridge theinterface between the individual components, water penetration can occur. In other windowmaterials, including aluminum and some vinyl units, closed cell foam gaskets or other sealantmaterials are used to seal the joints. These techniques can work well when properly implementedbut require applying the correct sealant quality and quantity into the joints during manufacture.

Aluminum-framed windows and doors are popular for use in both commercial and residentialprojects. Although strong, aluminum is a good conductor of heat. Heat transfer through aluminumfenestration products can be significant and can lead to the formation of condensation on interiorsurfaces in cold climates and exterior surfaces in warm climates. In order to reduce the potential forcondensation and improve energy efficiency, several methods are used to “thermally improve” metalframes. One common method is to add a polymer “thermal break” between the inside and outsidesections of the metal window frame.

Windows using poured and debridged thermal breaks have been in use for over 35 years. Sincethe beginning of their use, thermal break shrinkage has been observed on a limited basis. Theproblem was significant enough that in 1990, the Architectural Aluminum ManufacturersAssociation (AAMA) formed the Dry Shrinkage Task Group to investigate the issue and develop testprocedures to monitor material performance (refer to Thermal Breaks in Aluminum Windows–ADebate ). Despite the formation of the task group, the authors continue to observe thermal break8

shrinkage in thermally improved aluminum window and door frames across the nation, even in newproducts installed within the past several years.

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Since the thermal break is an integralpart of the frame, shrinkage of the materialeffectively leaves voids in the frame(Figure 6). These voids allow water topenetrate a seemingly solid frame memberand reach the underlying construction. Ifthe fenestration is not installed with sillflashing, water leakage to the buildinginterior can occur. The authors haveobserved deterioration of exterior wallsheathing, wood and metal wall framingmembers, insulation, and interior finishescaused by water leakage originating atthermal break frame voids (Figure 7).

Flashing

As discussed in the preceding sections of thispaper, flashings play important roles in both barrierand water-managed exterior wall systems.Deficient flashing installations are one of the mostcommon causes of water leakage observed by theauthors and are frequently found at wall tops,vertical supports such as floor slabs and shelfangles, and at wall penetrations. At the top of walls, flashing comes in manyforms. In some cases, like parapet walls, exposedmetal coping flashing may be the only materialpreventing water entry. In other cases, metalflashing is installed in a concealed position beneathother materials, like stone or precast concretecoping units, but still provides the primaryresistance to water penetration. In buildings that donot incorporate parapet walls, metal flashing may beused as a drip edge at the roof termination of theroof or at the intersections of roofs and walls. Allof these installations are critical details and, whenpoorly executed, can lead to water intrusion thatcauses deterioration to wall materials for significantdistances below the water entry point.

Flashing can play an important role in wall penetrations like windows, doors, HVAC sleeves, andvents, especially when the primary wall system and the penetrating item differ in their approach towater resistance. Wall systems that incorporate masonry barriers or hidden drainage spaces need tobe drained to the exterior at the top of penetrations to prevent water intrusion to the interior. The

Figure 6Thermal break shrinkage of approximately /2 inch1

in a thermally improved aluminum window frame.

Figure 7Deterioration of OSB sheathing belowthermal break shrinkage at the windowcorner. The metal probe illustrates the pathbehind the nailing flange created by thermalbreak shrinkage.

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authors have observed many projects where failure to properly execute head flashings over openingshas led to water leakage incorrectly initially attributed to the penetrating elements.

The bottom of penetrations is another location where the installation of flashing can prevent waterintrusion. The installation of complete pan flashings beneath windows and doors can control leakagethrough unit frame joints and thermal breaks or through failed perimeter sealants, draining the wateraway before it can cause damage. In this approach, the flashing becomes a second line of defenseagainst water leakage.

At the bottom of the wall (as well as at intermediate locations on taller buildings), through-wallflashing is often used to collect water which has infiltrated through the cladding and direct it backto the exterior. At the base of the wall, through-wall flashing is often responsible for controllingwater intrusion through the cladding material for one or more floors. This can result in largequantities of water that need to be collected and directed to the exterior.

Flashing materials are typically purchased in sheets or rolls, requiring periodic splices to fabricatecontinuous installations. Continuity and proper detailing are critical to proper flashing performance.Unsealed lap splices and missing end dam terminations can allow water to bypass the weather barriervia lateral migration and travel to the building interior. Likewise, flashing corners and changes inelevations also need to be carefully detailed and installed to maintain the continuity of thewaterproofing plane. Failure to do so can result in severe wall component deterioration.

SUMMARY

The authors have encountered water leakage in all types of exterior wall cladding andconstruction. Resolving leakage problems requires an understanding of the wall design andintended behavior, the as-built construction, and the active water penetration paths. Repairsdeveloped without this information rarely fix the problem and often make the situation worse.____________________

1. Construction Details Affecting Wall Condensation, Kudder, Robert J., Lies, Kenneth M., and Hoigard, Kurt

R., 1986

2. Vapor Control and Psychometric Monitoring in Exterior Walls, Kudder, Robert J., and Hoigard, Kurt R., 1991

3. ASTM E 2128, Standard Guide for Evaluating Water Leakage of Building Walls, 2001

4. Brick Masonry Wall Nonperformance Causes, Raths, Charles H., 1986

5. Including ASTM E 514 Tests in Field Evaluations of Brick Masonry, Hoigard, Kurt R., Kudder, Robert J., and

Lies, Kenneth M., 1993

6. Comparison of Class PB EIFS Lamina Water Transmission Test Methods, Kudder, Robert J. and Lies, Kenneth

M., 1995

7. Water-Resistive Barriers How Do They Compare, Hoigard, Kurt R. and Hall, Garth D., Interface, The Journal

of the Roof Consultants Institute, November 2005

8. Thermal Breaks in Aluminum Windows–A Debate, Brimmer, William B., The Building Official and Code

Administrator, July/August, 1995