Tag Archives: moisture

Getting Along With Stucco: Sometimes it just needs space

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All images courtesy Alta Engineering Co.

by Brett Newkirk, PE
There are two maxims about stucco application over wood-framed structures: first, it will crack, and second, owners will not do much about it. Water intrusion through stucco claddings is so common in Florida, re-skinning buildings here after five or 15 years is commonplace, even though it is not always warranted.

In some cases, re-skinned buildings are needing to be re-skinned again due to moisture intrusion years later. Damage to building structures is frequently related to poor installation of the veneer system and associated flashings.

In some examples, the stucco systems have been installed in general compliance with the building code requirements and product manufacturer instructions, yet damage to the wood substrate still ensues (Figure 1). Why then, does a code-compliant system fail?

This article includes a study of code requirements for stucco veneer systems to help explain the situation for design/construction professionals.

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Figure 1: Damage to an unpenetrated wall through a stucco veneer over Grade D paper and a polymeric water-resistive barrier (WRB).

Bond-break layer
A major change was introduced to the 2003 International Building Code (IBC) and the 2004 Florida Building Code (FBC), which required two layers of an approved water-resistive barrier (WRB), equivalent to two layers of Grade D paper, behind stucco veneers. The purpose of the second (outboard) layer is to create a ‘bond-break’ between the back plane of the stucco rendering and the WRB’s front face.

The bond-break layer (BB) is intended to provide a disruption to the potential capillary movement of moisture from the stucco across the WRB and into contact with the wood wall sheathing. To that end, the bond-break layer is supposed to create a small air space, allowing gravity to draw moisture to the base of the wall, where it presumably will drain out of the wall system before it absorbs across the cross-section of the WRB. While this code change was a huge stride and of sound substance, it was not quite enough.

The problem is the method by which stucco is secured to the walls and through the WRB and BB. Fasteners, typically staples, are installed with a pneumatic tool that draws the lath tight against the BB and WRB. The tightly bound sandwich of lath, BB, WRB, and wood wall sheathing at each connection does not offer sufficient separation to break the capillary path of moisture travel or allow for drying of moisture in the system, even when a BB is present. Thus, the BB’s purpose is negated, and capillary movement across the system is possible.

However, the greater concern is a hole (or two, thanks to a staple) is conveniently created by the fastener at the precise location where the weatherproofing sandwich is tightly squished together (Figure 2). Consequently, permeation through the WRB is not required. Instead, moisture accumulates within the tightly bound assembly, clings to the fastener shank, and travels through the fastener hole in the WRB into contact with the wall sheathing (Figure 3). Equally important is the inability of moisture within the assembly to dry due to the tightly bound, unventilated space between the veneer and the wood substrate. Instead, the chronically damp conditions are favorable for wood decay.

Figure 1

Figure 2: Typical stucco section at fastener—the two tiny holes are located right where the waterproofing is squished.

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Figure 3: Damage to wood sheathing from state penetration.

 

 

 

 

 

 

 

 

By code, the metal lath is fastened to the wall sheathing with more than one fastener per square foot of wall area. Some rough math reveals there are on the order of 6000 holes through the WRB for a one-story 230-m2 (2500-sf) structure footprint.

Stucco accessories, such as casing beads, weep screeds, and control joints, are typically installed prior to lath. Accessories are also typically secured with pneumatic fasteners, which draw them tight to the BB, eliminating any meaningful drainage space behind the accessory. Consequently, water within the system tends to accumulate along the horizontal edges of the accessories, where it may find weaknesses in the WRB, prompting migration to the interior. Of course, fasteners securing the accessories also serve as conduits for water to migrate through the WRB.

Water-resistive barrier performance
Sheet-good WRBs are tested in a laboratory setting to ensure they perform under a battery of tests established by the International Code Council Evaluation Service (ICC-ES). The most commonly used WRBs are polymeric sheets called ‘house wraps’ or ‘building wraps.’

ICC-ES AC38, Acceptance Criteria For Water-resistive Barriers, evaluates the WRB material’s tensile strength, vapor transmission, air permeance, and resistance to water penetration, to name a few. The polymeric material’s adequacy in resisting water penetration is judged by its ability to prevent water passage for two hours when subjected to a 25 to 550-mm (1 to 24-in.) column of water on one side. Once proving performance, the WRB is considered code compliant. However, the battery of laboratory tests fails to include one little detail of real life: holes in the WRB from veneer fasteners.

A single fastener penetration would result in a ‘failure’ of the AC38 water penetration resistance test. Why should one expect field performance of a product that is installed in a different (and far inferior) manner than that under which it was tested and approved?

To this author, even more perplexing is AC38’s seeming double standard for the use of paper-based WRBs, which are not subjected to the same tests as those required of polymeric WRBs. Grade D paper is used as the backing for paper-backed lath, whose installation is the most common means of creating the BB layer. By definition, Grade D paper allows water to pass after only 10 minutes of exposure with no meaningful hydrostatic pressure, while polymeric WRBs are expected to perform for hours, at pressures of up to 5.36 kPa (112 psf). Why then are two layers of Grade D paper the code-mandated baseline for WRBs behind stucco veneers? Obviously, the very low tolerance of Grade D paper to resist moisture absorption can cause substantial moisture-related distress to wood-framed buildings where it is used.

Mockup testing
Full-scale testing was performed by this author to gage the performance of several ‘code-compliant’ stucco wall assemblies, with various polymeric-based and felt-based sheet-good WRBs. The tested wall assemblies consisted of 1.2 x 1.2-m (4 x 4-ft) specimens constructed with wood framing and oriented strandboard (OSB) sheathing, and then clad with various types of WRBs.

A three-coat stucco system was then applied over paper-backed metal lath secured with 25-mm (1-in.) crown staples, confined within 22-mm (7/8-in.) plastic casing bead accessories that were secured around the wall’s perimeter (Figure 4). A 0.6 x 0.6-m (2 x 2-ft) observation port was created in the center of the OSB substrate, where gypsum wallboard wrapped in kraft paper was substituted for the OSB (Figure 5). This way, the wallboard could be removed and the back side of the WRB could be observed after testing. The kraft paper also served as an indicator of water contact during the test.

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Figure 4: Front side of a typical mockup wall test setup.

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Figure 5: Back side of a typical mockup wall test setup.

 

 

 

 

 

 

 

Testing was performed using a variation of ASTM E2273, Standard Test Method for Determining the Drainage Efficiency of Exterior Insulation and Finish Systems-clad Wall Assemblies (AC38 drainage test), with the additional step of performing observations for moisture ingress during the test. (ASTM E2273 only calls for a comparison of the volume introduced to the specimen to that which escapes at its base. This measurement was not of interest to the author as it related to this evaluation.)

Water was introduced to the drainage cavity at the top of the wall at a rate of 3.38 L/min/m2 (5 gal/sf/hr) for 30 minutes. Perhaps unsurprisingly, the testing revealed water penetration occurred through the fastener penetrations in both polymeric and felt-based WRBs (Figure 6). Water migration also occurred directly through the field of some woven polymeric WRBs and Grade D paper. Intrusion through Grade D paper-based WRB mockups was substantially more severe than that of the polymeric or felt-based WRBs.

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Figure 6A: Water penetration through fastener holes in a spun-bound polymeric WRB following testing. B: Water penetration through fastener holes in a woven polymeric WRB following testing. C: Water droplet below staple shank penetration through WRB during testing. D: Hyrion paper shows water ingress through fastener penetration.

Magnified observation of staple-penetrated WRBs reveals an oblong, torn annular opening is created around the shank (Figure 7). The torn annulus was more significant at woven than spun-bound WRBs. In some cases, an additional indentation and hole through the WRB was noted due to the actuation of the pneumatic tool which impacted its surface. Additionally, use of ‘slap’ or ‘hammer-tacker’ staples caused rupturing of the WRBs at the staple shank hole and the tool’s impact location, which could allow water passage.

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Figure 7: The left image shows a 10x view of a staple shank shows an oblong torn hole in the WRB (and water migration through it). The right image depicts an enlarged, torn hole in the WRB at the staple penetration.

Where to go from here
It probably does not take the foregoing technical discussion to understand holes are paths for water entry or wood that stays wet will rot. So why do we build walls with thousands of holes in them, prevent them from drying out, and expect them to have watertight performance?

If repeating an activity and expecting a different result is the definition of insanity, then why do we tear stucco veneers off of water-damaged building structures and then replace it the same way? Accepting the realities of stucco cracking and inadequate owner maintenance, something else needs to change to give stucco-clad buildings
a longer life.

Based on the author’s testing and experience, there are a few installation practices that can help mitigate the compression of the veneer’s weatherproofing sandwich, which helps prompt drying and greatly reduces the likelihood of moisture migration through fastener penetrations in the WRB.

Separate stucco from WRB with furring or other drainage media
There are many randomly oriented polymeric filament products, typically 6 mm (1/4 in.) in thickness, that provide this function (Figure 8). Often called drainage media, drain screens, furring, or drainage mats, these products should be installed behind all accessories.

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Figure 8: Test wall with drainage media installed in front of the WRB.

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Figure 9: The recommended stucco section at a fastener.

 

 

 

 

 

 

 

 

The resulting air space creates a functional capillary break between the back side of the stucco rendering and the WRB, even at fastener locations (Figure 9). This gap provides an easy, unobstructed path for moisture to travel vertically down the face of the WRB (within the media). In combination with through-wall flashing vents and drainage weeps at the stucco base, the air gap also prompts ventilation within the cavity that prompts drying of moisture.

Control the installation force and depth of fasteners
This can be achieved by reducing the air pressure for pneumatic tools, but is most effectively completed by use of pan-head screws, which have installation depths that can be easily controlled and adjusted (Figure 10). The use of screws also inherently reduces the number of penetrations through the WRB by half, when compared to staples that have two shanks. Further, the cross-sectional diameter of the screw is greater than that of a staple shank, rendering it less vulnerable to corrosion over time. (The drainage system anticipates water to drain across the unprotected fastener shank.)

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Figure 10: Pan-head screws are used to secure lath to the wood frame.

Use fluid-applied weather barriers.
Fluid-applied weather barriers cannot be torn; they create a ‘gasket’ effect around penetrating fasteners. However, these products’ detailing and reinforcing requirements demand a more skilled and conscientious craftsman to properly install. Designers should also recognize fluid-applied barriers are typically vapor-impermeable, which should be a consideration in the envelope design.

Conclusion
The recommendations in this article are an additional step to prevent water intrusion through stucco-veneered walls and to prompt drying beyond current code requirements. Of course, these suggestions are no guarantee against water penetration—after all, one still has thousands of un-gasketed holes through the sheet-good water-resistive barrier. However, with proper WRB installation, appropriate flashings and drains, incorporation of drainage media, and controlled depth fasteners, a stucco veneer has a much better chance at providing long-term performance.

Brett Newkirk, PE, is a practicing structural engineer with Alta Engineering Company in Jacksonville, Florida. He specializes in the diagnosis and repair of moisture-affected structures, and is a recognized author and leader in the building envelope repair industry in the southeastern United States. Newkirk is an associate member of the American Society of Civil Engineers (ASCE) and sits on ASTM committees for wood and gypsum. He can be reached at brett@altaengineeringco.com.

Continuing Education on Continuous Insulation

continuous - Tom's article 2015 - 5th-&-Alton Shopping-Center

All images courtesy Sto Corp.

by Tom Remmele, CSI
Continuous insulation (ci) has been a component of exterior wall assemblies for more than 40 years in North America and even longer in Europe. It has always been the smart way to design wall assemblies from the standpoint of energy conservation and water management. By minimizing energy loss caused by thermal bridging and the risk of condensation caused by water vapor diffusion, exterior ci can improve building durability and benefit the environment.

Standards-writing and regulatory bodies, government agencies, and the building science community are in alignment in viewing exterior ci as a sensible strategy to conserve energy in buildings. The American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) has steadily driven energy conservation standards—and hence, the International Energy Conservation Code (IECC)—to ci prescriptive R-value requirements (in combination with stud cavity insulation) as a pathway to greater energy conservation in buildings.

In sponsoring the 2012 IECC code changes, the Department of Energy (DOE) helped achieve the “largest one-step energy efficiency increase in the history of our energy code.” Building Science Corporation identifies the ‘perfect wall’ (i.e. one working in any climate zone), as having ci outbound of the structure. Thus, for the foreseeable future ci is likely to be a fixture in most exterior wall assemblies.

Types of foam plastic ci
Figure 1 summarizes properties of rigid cellular polystyrene and polyisocyanurate (polyiso) thermal insulations as published in ASTM C578-14, Standard Specification for Rigid, Cellular Polystyrene Insulation, and ASTM C1289-14, Standard Specification for Faced, Rigid Cellular Polyisocyanurate Thermal Insulation Board, respectively. Commonly used insulating materials conforming to these property requirements are Type I expanded polystyrene (EPS), Type IV extruded polystyrene (XPS), and Type I, Class 1 or 2 polyiso.

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Common types of rigid foam plastic continuous insulation (ci) used in exterior wall assemblies.

Each insulating material has its own benefits and limitations influencing which one should be used for a given project. For example, EPS is the insulation commonly used in exterior insulation and finish systems (EIFS) because of its dimensional stability, water vapor permeability, and adhesion compatibility with EIFS adhesives and base coats. Due to their higher R-values, XPS and polyiso boards are more commonly used behind brick veneer to allow for thinner wall sections. This becomes important when considering the total thickness of a brick veneer cavity wall with ci and the implications on size and thermal bridging of supporting shelf angles and lintels.

Water vapor permeability of the insulating material can be an advantage or disadvantage. For example, in hot, humid climate zones where vapor drive is predominantly inward, exterior polyiso or XPS insulation can retard inward vapor drive and reduce the potential for condensation on the relatively cold conditioned surface of interior drywall over metal studs. In mixed climates, where vapor drive is both inward and outward for long periods during the course of a year, EPS ci is advantageous because its higher vapor permeability allows water vapor to diffuse, which aids in drying of the wall assembly in the event of condensation.

A wall analysis during design is a valuable tool for selecting the best type of ci material in this regard. Dynamic computer models are a good approach, since they characterize wall assembly hygric performance through seasonal change, but even a simplified steady-state analysis for worst case winter and summer months can be a helpful tool to assist in making material choices for a given wall assembly.

Other things to consider beyond physical properties are jobsite handling, storage, and compatibility with other materials, as well as the construction Type, whether Types I−IV or Type V, and design wind pressure requirements. EPS and XPS have limited ultraviolet (UV) resistance and should not be left exposed to sun for extended periods as the surface will degrade (chalk).

While this degradation has no significant effect on R-value, it can interfere with adhesion of joint treatments, tapes, EIFS base coats, and membrane materials that rely on adhesion to the surface, unless the surface is rasped or sanded to remove the chalked material. Chalking is not an issue when the insulation is ‘faced’ with glass mat facing or aluminum foil facing as with most polyiso boards, although adhesion to the facing materials still has to be evaluated.

Equally important to consider (if not more so) on jobsites is the combustibility of foam plastics. They should be protected from sparks, flame, or any other source of ignition. All foam plastic insulation boards are produced with flame retardant, but they behave differently in the presence of flame; while EPS and XPS melt, polyiso chars.

Despite their combustibility, all these foam plastic insulating materials can be used on buildings required to be of noncombustible construction (Types I−IV) with proper material and ‘end use’ testing to support the proposed assembly. Likewise, they can all be used in wind-resistant assemblies provided they are constrained (i.e. sandwiched) in the negative and positive direction by another material (e.g. sheathing/cladding) capable of resisting design wind pressures. Alternatively, appropriate tests can be performed to determine wind load resistance of the insulation relative to project and/or building code requirements.

Fire safety considerations
Fire safety in the design of foam plastic-based wall assemblies is an important factor when considering their use. Since such materials are combustible, building codes strictly regulate the use of foam plastics. Chapter 26 of the 2015 International Building Code (IBC) has seven requirements that must be met for foam plastics to be approved for use in walls (Figure 2).

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Summary of the 2015 International Building Code (IBC) Chapter 26 requirements for use of foam plastic insulation in exterior wall assemblies.

For the design professional, listing and labeling of the insulation by an approved independent third party is the first step in verifying code compliance. Most insulation board manufacturers hold International Code Council Evaluation Service (ICC-ES) evaluation reports (ESRs), or Underwriters Laboratory (UL) or other listings, simplifying verification.

These listings also demonstrate other aspects of code compliance, for example, compliance with flame spread and smoke development criteria to qualify as a Class A building material, or special uses such as below-grade or attic insulation. Other code compliance requirements are more difficult to verify because they involve wall assembly tests that may exist with the insulation board manufacturer, the cladding manufacturer, or, in some cases, with the air barrier/water-resistive barrier (WRB) manufacturer.

Potential heat, a measure of the foam plastic’s stored heat energy, is a function of the type of foam plastic insulation, its thickness, and density. IBC effectively limits potential heat for construction Types I−IV to the insulation thickness and density successfully tested in the National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components.

NFPA 285 is a qualifying wall assembly test for the use of foam plastic in wall assemblies of Types I, II, II, or IV construction. As a ‘worst-case’ surrogate for exterior wall fires, the test addresses the effects of a simulated fire in an interior room and vertical flame propagation from floor-to-floor and room-to-room vertically and laterally. An example of an assembly that meets NFPA 285 acceptance criteria is shown in Figure 3, and the actual test is depicted in Figure 4.

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Figure 3: Exterior brick veneer wall assembly with ci that complies with National Fire Protection Association (NFPA) 285 acceptance criteria (refer to International Code Council Evaluation Service Reports (ICC-ESRs) 1233 [6] 2141[7]).

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Figure 4: As shown above, NFPA 285 test exposes the wall assembly to fire from an interior compartment and evaluates vertical and lateral flame propagation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

While the test enables approval of the assembly in Types I−IV construction, it also establishes limits—maximum allowable thickness and density of insulation and detailing around the opening that must conform to (or be more conservative, from a fire protection standpoint) what was tested. Test results can sometimes be extended to other claddings or backup wall construction when evaluated by a qualified fire protection engineer.

For example, in Figure 3, the results of the fire tests with masonry veneer over steel stud wall construction were extended to backup wall construction of concrete or concrete masonry unit (CMU) in lieu of steel stud with gypsum sheathing. Once again, ICC-ES evaluation reports can be a valuable resource for the design professional to know what assemblies have been tested and meet acceptance criteria, or where results of tests have been extended, evaluated, and recognized by ICC-ES.

NFPA 285 is not the only assembly test to be considered. ASTM E119-12a, Standard Test Methods for Fire Tests of Building Construction and Materials, is necessary when walls are required to have an hourly fire-resistance rating—a common requirement for commercial office, institutional, and some retail and multi-family type construction. The test evaluates the ability of the assembly to resist temperature rise, collapse, flaming, or ignition on the unexposed side of the assembly.

If the assembly is asymmetrical, it must be tested from both sides—in other words, with the fire originating from the interior or exterior. Further, the effects of a hose stream (used to provide additional structural evaluation) are evaluated to ensure the unexposed side remains intact and there is no breach or collapse of the assembly as a result of the hose stream.

Engineering analysis or modeling by a qualified fire protection engineer can be done to qualify substitute materials or to make minor revisions to what was tested to provide the design professional with a wider range of material options for the wall assembly. For example, if an hourly rating is achieved with a frame wall assembly with gypsum sheathing on the exterior and gypsum wall board on the interior, it is readily assumed a ‘mass wall’ fire-resistive wall construction (e.g. 152-mm [6-in.] cast-in-place concrete or 203-mm [8-in.] CMU) would provide equal or better resistance than the frame wall with the same exterior ci and cladding assembly. ICC-ES evaluation reports, UL listings, and Gypsum Association’s (GA’s) Fire Resistance Design Manual are valuable resources for the design professional to identify tested fire-resistance rated wall assemblies.

The last of the assembly tests is NFPA 268, Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source. The test evaluates a wall assembly’s susceptibility to ignite from the radiant heat produced by a fire in an adjacent building. It is an important test for EIFS and other foam plastic-based wall assemblies that do not conform to one of the six wall covering exceptions listed in Section 2603.5.7 of the 2015 IBC:

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minimum 15-minute thermal barrier;
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minimum 25-mm (1-in.) of concrete or masonry;
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at least 9.5-mm (38-in.) glass-fiber-reinforced concrete (GFRC);
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metal-faced panels meeting the prescribed composition and thickness;
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minimum 22.2-mm (78-in.) stucco; and
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minimum 6-mm (14-in.) fiber cement lap, panel, or shingle siding.

A final requirement of the code for all types of construction is separation of the combustible foam plastic insulation from interior space with a 15-minute thermal barrier, typically 13-mm (12-in.) interior drywall or exterior gypsum sheathing. Commercial attic space or the interior wall area above suspended ceilings must have this 15-minute thermal barrier in place on the interior if it does not exist on the exterior side of the wall to separate the foam plastic insulation (with some exceptions permitted in the 2015 IBC’s Section 2603.4.1). Between-the-stud fiberglass batt insulation does not count as a thermal barrier since it is discontinuous.

Thus, building codes strictly regulate the use of foam plastics in wall assemblies. Manufacturers of wall assembly components—cladding, ci, air barrier, and sheathing—must demonstrate compliance with these requirements. ICC ESRs are an excellent resource to facilitate verification of wall assembly compliance.

Moisture-related durability considerations
One of the ways exterior ci can help in managing water is by changing the location of the dewpoint in cold climate zones so water vapor diffusion condensation potential is minimized or eliminated. Continuous insulation can also aid in controlling moisture in hot humid climate zones as demonstrated in recent research conducted by the US DOE and the EIFS Industry Members Association (EIMA). The research compared the hygrothermal performance of various wall assemblies—EIFS, stucco, brick, and fiber cement siding (15 assemblies in total)—installed on a test hut (Figure 5) exposed to natural weather in Hollywood, South Carolina (Climate Zone 3A).

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Figure 5: The image to the left shows an EIFS Industry Members Association/Department of Energy (EIMA/DOE) test hut in Hollywood, South Carolina with wall panels monitored for a two-year period for hygrothermal performance. On the right, the test hut rainwater collection device ‘delivers’ rain into the panel at the plane of the water-resistive barrier (WRB) during the second year of exposure. The device was intended to simulate a flaw (breach) in the panel exterior wallcovering.

Temperature, heat flux, relative humidity (RH), and moisture content measurements were taken 24 hours a day with sensors placed in the wall panels. After a little more than a year of exposure, a flaw (i.e. opening) was created in some of the wall panels to introduce rainwater onto the plane of the WRB behind the cladding. The cladding with ci performed the best from the standpoint of temperature and moisture control as measured by the heat flux sensor on the inside face of interior gypsum wallboard and the relative humidity sensor on the face of the wall sheathing directly behind the WRB (Figure 6).

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Figure 6: Assembly with exterior ci shows improved moisture control in comparison to assemblies without ci as indicated by relative humidity (RH) measurements at the exterior face of the sheathing. The assemblies were installed over nominal 2×4 wood framing. In order, they are (a) 102-mm (4-in.) brick veneer cavity wall over paper water-resistive barrier (WRB) on 11-mm (7/16-in.) oriented strandboard (OSB) with unfaced R-11 batt insulation, (b) 102-mm exterior insulation finish system (EIFS) with fluid-applied air barrier/WRB on 13-mm (1/2-in.) plywood with no batt insulation, and (c) 22-mm (7/8-in.) portland cement stucco over two layers of paper WRB on 11-mm OSB with unfaced R-11 batt insulation.

The closer the heat flux sensor stayed to the zero base line (which would represent constant interior temperature), the better the assembly’s thermal performance. An average monthly relative humidity of below 80 percent was considered acceptable based on ASHRAE STP 160, Criteria for Moisture-control Design Analysis in Buildings. The ci assembly proved not only to be best from a thermal standpoint, but also kept wall components dry, even when rain was deliberately directed into the assembly during the second year of exposure. This is important not only from the standpoint of durability, but also because insulation, if it stays moist, loses some of its insulating value.

Key factors in the moisture control success of the ci assembly were:

  • 
exterior ci kept wall sheathing above the dewpoint during winter;
  • 
combination of low water absorption exterior finish materials and relatively low water vapor permeability of the insulation prevented high exterior RH in summer from significantly increasing the sheathing’s relative humidity;
  • 
seamless fluid-applied air barrier/WRB behind the cladding was effective in resisting air leakage (and condensation potential) and was unaffected by the rain introduced into the wall during the second year of exposure (the other claddings had paper WRBs); and
  • 
drainage feature of the ci assembly prevented excess amounts of rain from accumulating in the assembly.

Conclusion
As building codes have evolved to the point where ci is now mandatory for many wall assemblies, rigid foam plastic ci wall assemblies have become more prevalent than in the past. They have special design considerations that need to be addressed at the design stage with an awareness of what the building code requires in relation to the use of foam plastics and their effects on the physics of the wall construction, as well as design details.

While this feature looked at the basic types of materials available, and focused on fire safety and moisture-related durability, this author is also developing another technical article that explores the added complexity of design details, along with structural considerations, environmental impacts, and cost control for a future issue of The Construction Specifier.

Tom Remmele, CSI, is the director technical services/R&D for Sto Corp., a manufacturer of air barriers, coatings, exterior insulation and finish systems (EIFS), and stucco products. He has held technical management positions in the construction industry for more than 25 years. Remmele is a past Technical Committee chair of the EIFS Industry Members Association (EIMA). He can be reached at tremmele@stocorp.com.

An Overview of Waterproofing Solutions

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All photos courtesy Hoffman Architects

by Richard P. Kadlubowski, AIA
Waterproofing failures are more easily overlooked than roofing problems, so design professionals tend to hear less about them. When compared with a reroofing project, however, a below-grade or interior rehabilitation can be far more disruptive and expensive.

Whereas a roof leak can generally be identified with simple test probes, waterproofing breaches can be challenging to diagnose. Even a seemingly superficial leak can be symptomatic of hidden moisture-related deterioration. For basements, vaults, tunnels, and water features, excavation of overburden is often necessary; in commercial kitchens or lobbies, removal and replacement of fixtures and finishes is frequent.

In most commercial and institutional applications, a complete reroofing project can usually be anticipated every 20 years or so. Waterproofing, because it is so difficult to access, should have a design life as long as that of the building—unfortunately, with so many opportunities for damage, incorrect design, or poor execution, it can fail well before its time. When this happens, architectural investigation is needed to determine the location and cause of the leak, the extent of the damage, and the appropriate remedy.

While it can be a major undertaking to properly identify and correct faulty waterproofing, it is far worse to adopt a patch-it-and-hope-for-the-best attitude. All too often, even well-meaning attempts at treating the symptoms of waterproofing failure serve only to trap or redirect moisture, compounding the problem. While prevention is the obvious first choice for waterproofing success, there are many occasions for error: in design, during construction, and throughout operation. Until the waterproofing deficiency is resolved, the problem will only get worse.

Waterproofing basics
Various components contribute to a waterproofing system, such as drainage composites that direct water away from the structure, tie-ins between façade and foundation membranes, and watertight plumbing in food service areas.

Impervious membranes are one critical component of waterproofing, both for below-grade applications (e.g. foundation walls, basements, tunnels, and vaults) and areas subject to high moisture levels (e.g. fountains, lobbies, kitchens, and mechanical rooms). Waterproofing membranes may be applied on the ‘positive’ or ‘negative’ side.

Waterproofing on a building is typically an impervious material that will prevent water entry; building cladding materials may or may not be actual waterproofing. Most building cladding materials (e.g. brick masonry in a cavity wall assembly or rainscreen systems) are not waterproofing—they are only weather barriers. Similarly, although Tyvek-type materials shed water, they are not true waterproofing.

There is a distinction between waterproofing and roofing that has to be understood. Plaza decks over occupied spaces are waterproofed; the deck is technically not a roof. The manufacturers will make this distinction, because also typically waterproofing applications do not come with as complete a warranty coverage as do some roofing systems.

Positive-side waterproofing
By creating a waterproof barrier on the side of applied hydrostatic pressure, positive-side waterproofing prevents water from entering the wall. For a foundation, this would be the outside surface, closest to the soil; for a fountain, it would be the inside (i.e. where the water is).

For below-grade applications, the earth can be banked back such that a positive-side membrane is installed after the foundation is set. In urban areas, this may not be an option. Blind-side waterproofing incorporates the waterproof membrane on the face of the shoring before the foundation is cast. Concrete is then poured, and the waterproofing fuses to the foundation wall as it cures.

Options for positive side systems include:

  • fluid-applied membranes—similar to those used in roofing applications, they roll or brush on as a liquid and cure to form a monolithic, seamless membrane;
  • sheet systems—also similar to those used on roofs, including single-ply thermoplastics and rubberized asphalts;
  • hybrid systems—combining a fluid-applied membrane with embedded fabric reinforcing to create a stronger, more resilient waterproof barrier; and
  • bentonite clay—a natural mineral derived from volcanic ash and applied as a sheet, mat, panel, or spray to swell in the presence of moisture to create
    a solid clay barrier.

Positive-side systems, used both above and below-grade, are generally preferred over negative-side applications for their effectiveness. The structural barrier is completely protected from corrosive chemicals in groundwater, as well as freeze-thaw cycle damage.

The shortcoming to positive-side systems lies in leak detection and remediation. Once backfill is in place, the actual condition of the waterproofing cannot be inspected without excavation. If the system fails, rehabilitation can involve major excavation and reconstruction of paving, landscaping, and wall systems.

Blind-side waterproofing is similar to positive-side methodologies, but once the concrete is poured, the waterproofing is buried and cannot be inspected. Even for membranes installed after concrete is cast, it is too late to correct for sloppy installation once the waterproofing is buried.

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Negative-side waterproofing injection via ports along a foundation wall crack. The gauge monitors the pressure of the injected resin.

Negative-side waterproofing
Negative-side waterproofing protects the surface opposite the side of applied hydrostatic pressure (e.g. the inside of a basement wall), such that water is redirected after it enters the substrate. Negative-side waterproofing materials include:

  • cementitious systems—a combination of chemical waterproofing additives or acrylics with cement and sand to achieve an impervious surface;
  • acrylic, latex, or crystalline additives—products that penetrate into the surface to provide water protection.

Since the negative side is more accessible, it is easier to identify leak locations than with positive-side systems. Negative-side coatings or injections also can be applied as a retrofit measure.

On the downside, with negative-side waterproofing, moisture still enters the wall assembly, which can cause components to degrade over time. The constant presence of moisture can also lead to mold growth, corrosion, concrete deterioration, or damage to interrelated building elements like floors or windows.

Combination systems
For sensitive spaces below-grade, more sophisticated systems have been used. As an example, a rare book vault built below the water table employed a wall-within-a-wall arrangement, with a pump system in the channel between the inner and outer walls to augment the positive side membrane.

Dampproofing vs. waterproofing
Even some seasoned design/construction professionals mistakenly use the terms dampproofing and waterproofing interchangeably, but they are not the same. Dampproofing is a bitumen-based or cementitious treatment applied to the positive side of foundation walls. The quick, inexpensive coating aims to discourage moisture from wicking up into below-grade walls through capillary action. Named for the tiny, thin apertures, or capillaries, in porous materials like masonry and concrete, capillary action moves water from damp to dry areas, sometimes against gravity.

Waterproofing represents a much broader class of moisture protection. Unlike dampproofing, which cannot bridge cracks, a waterproof membrane can stretch to accommodate some degree of differential movement, settlement, and shrinkage. Even when subjected to the hydrostatic pressure of a high concentration of water, waterproofing is designed to be flexible and durable.

Dampproofing is not a substitute for waterproofing. While sometimes used because they are far less expensive than a waterproof membrane, dampproofing products are of a lesser grade and are applied as a sparse coat with little attention to detail. Waterproofing membranes demand precise application and detailing, and they can be reinforced with integral fabrics for increased stability. Dampproof coatings may be cheaper at the outset, but the long-term durability and effectiveness of properly selected and installed waterproofing are well worth the extra up-front cost.

 

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Before: Below-grade windows can present maintenance challenges, as leaves and debris clog drains, encouraging moisture retention.

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After: Adding channel drains and replacing packed earth with drainage media helps direct water away from the building.

 

 

 

 

 

 

 

 

Waterproofing failures
Even seemingly minor evidence of moisture may presage waterproofing distress. Examples include:

  • blisters or peeling paint;
  • mold, mildew, and vegetative growth;
  • dampness or dribbles of water;
  • stains and rust;
  • odors;
  • efflorescence, or white powdery deposits;
  • cracked walls; and
  • wood rot.

Moisture-related deterioration becomes more costly to repair the longer it is allowed to progress. Keeping a record of water infiltration symptoms is important to establishing how, where, and when moisture is penetrating the waterproofing system. An action plan for signs of water entry can involve six steps.

1. Review the leak history.
It is important to note how the building responds to weather events, such as high humidity, rain, or snow. Temperature fluctuations affect building materials, so any correlations with moisture observations should be recorded.

If the leak is worse after it rains, surface runoff is the likely cause. The joints between walls and slabs, as well as conduits, must be checked. However, when the leak is constant (i.e. uncorrelated with rain), it may be caused by a water line—either potable or sanitary sewer. Even an adjacent excavation or infill construction can indirectly lead to leakage by causing differential settlement cracks or changing water flow.

When the leak occurs after using certain equipment in a kitchen or mechanical room, one should perform usage tests to identify the faulty component. If water bubbles up between the foundation wall and the slab-on-grade, rising groundwater levels may be the issue, or a combination of groundwater and surface runoff. Flash storms can overflow combined sanitary and storm sewers, raising the water table. Clogged or inadequate perimeter/footing drains can also contribute to the problem.

2. Identify the water source.
A water test can determine which type of water is leaking. If the water contains chlorine, it is potable (drinking) water, and the source is likely a plumbing leak. If the water has a high coliform count (e.g. e.coli bacteria), a sewage waste line is the problem. If the water tests negative for both of the above, it is most likely groundwater or stormwater.

3. Rule out ambient moisture.

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Excavation exposed deficient waterproofing with this bent water stop in the vault wall.Where there is a significant temperature differential between inside and outside, condensation—not leakage—may be the culprit. To test, a piece of impervious material, such as aluminum or plastic, can be secured to the wall where moisture has been observed.

After a few days, if the sheet is wet on the side facing the wall, water intrusion through the wall surface is most likely the problem. If moisture appears on the side facing the room interior, condensation may be the cause of observed moisture, which can be addressed by adjusting HVAC equipment or improving ventilation.

4. Determine the leak location.
Water is deceptively migratory—the spot where stains or cracks are observed can be quite remote from the site of water entry. Recording when, where, and under what conditions signs of moisture are present can help determine the water access pathway. Original as-built drawings and construction specifications provide clues as to potential weak spots in the waterproofing system.

Non-destructive testing may be useful in identifying leak locations. Flood tests saturate an area, such as the backfill at a foundation wall, to generate conditions conducive to moisture penetration. Waterproofing failures can then be noted and addressed. Additives, such as dyes or scents, incorporated into the flood test water can help identify leaks that are otherwise difficult to detect.

Once the investigation determines a probable location, exploratory openings and test probes can verify the source of the leak.

5. Resolve the leak.
A course of corrective action may include drainage improvements, injections at interior surfaces, and water barriers at penetrations.

Drainage improvements
Stormwater leaks can often be resolved by redirecting water away from the foundation. Repair areas include:

  • improperly connected leaders and gutters;
  • downspout extensions too close to foundation walls;
  • clogged roof drains and gutters;
  • flashing failures in pools or planters;
  • expansion joint failure at plazas and pedestrian tunnels;
  • leaking underground oil storage tanks causing membrane disintegration;
  • backfill settlement directing surface water to footings;
  • improper drainage and seals at stairways, window wells, and openings; and
  • inadequate subsurface drainage.

Injections at interior surfaces
Resolving cracks through injection with epoxy, hydrophobic, or hydrophilic resins can be an economical way to solve minor waterproofing problems without excavation and reconstruction. However, this approach relies on trial-and-error, as it is nearly impossible to know what conditions are on the other side of the wall without seeing firsthand.

In one anecdote from a waterproofing contractor, injections were used to resolve failures in an aquarium tank. The job went over budget as more and more material was required to fill cracks. When the team finally finished and tried to refill the tank, nothing happened. The sealer had penetrated directly into the water system, filling conduits and clogging the pump. Repair costs far exceeded the initial project budget. The lesson—where injected materials have the potential to penetrate subsurface systems, it is probably best to take the known cost of investigation, excavation, and repair over the unknown cost of blind injection.

Water barriers at penetrations
Appropriate moisture protection, including sealants, should be installed at penetrations. However, unless moisture problems are stopped at their source, such barriers may only serve to re-direct water to another weak point. Good sealant integrity is important, but it is really a secondary waterproofing provision. The primary measure is to control moisture levels.

6. Repair the damage

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Liquid waterproofing and application of deck waterproofing with reinforcing fabric.

Once the leak has been resolved and deterioration arrested, water damage to walls, fixtures, and finishes may be required. In concrete structures where water infiltration has led to reinforcement corrosion, steel should be repaired and sealed, followed by application of a compatible concrete patching mortar. Migrating corrosion-inhibitors, either integrated into the patching compound or applied as a surface sealer, can provide additional protection to the structure.

For outdoor areas, including plazas, sidewalks, and landscaping, some rehabilitation may be necessary following waterproofing remediation. If repair work involved excavation, or if leaks have damaged fixtures or dislodged pavers, then outdoor finishes and plantings may need to be reconstructed. Portions of the façade may also require rehabilitation.

Where leaks migrate into occupied space or originate at an indoor area, water-damaged drywall, trim, paint, ceiling tiles, flooring, and fixtures may need to be replaced once the new waterproofing system is installed. Moisture also can lead to mold growth—
a health hazard that may require professional removal and cleaning.

The longer a leak is allowed to progress unchecked, the more extensive the underlying deterioration can become. Stopping a minor leak is far easier than rehabilitating the damage resulting from a major one.

Causes of waterproofing failure
There are a variety of potential causes for the wide array of many possible waterproofing issues.

Design omission
In cases where unusual intersections, multiple penetrations, or differential pressures demand elaborate detailing, designers are sometimes guilty of leaving these vital junctions to the contractor’s discretion. Where a waterproofing construction team has had success with similar configurations in the past, this may not cause a problem. In the more likely event the general contractor is facing an unusual arrangement demanding sophisticated design, relying on standard details is probably insufficient. It is the designer’s responsibility to detail any situations in which waterproofing might be compromised.

Installation error
Even the most rigorous and exacting drawings and specifications are of little use when workers fail to take care with materials and installation. Careless backfilling is a primary source of waterproofing failure, as is damage from heavy equipment. For example, the contractor at a below-grade book vault rushed to pour concrete walls without regard for delicate water stops, crumpling them in the process and rendering them useless. The resultant water infiltration required extensive excavation, concrete repair, and waterproofing rehabilitation to resolve.

Deficient quality assurance
Oversight and review during construction by an owner’s representative is an essential part of the quality control process. Should site conditions differ unexpectedly from design documents, or unforeseen circumstances present themselves, an onsite architect or engineer can respond to last-minute changes without delaying the construction schedule. The design professional can direct the general contractor to protect the work of the waterproofing installer from damage during construction.

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Suspending all kitchen operation for waterproofing rehabilitation is hardly desirable. However, if leaks are ignored, water damage to structural systems and finishes will only make things worse.

Having a site representative present during construction is important to see installation proceeds according to design intent. Eliminating this important part of the design process is often justified by owners with claims of guarantees or, failing that, litigation. Although field reports and photographs can serve as evidence at trial, the real benefit to onsite quality assurance lies in avoiding waterproofing failure in the first place. Submittal review and formalized inspection can make the difference between a successful waterproofing project and catastrophic failure.

Conclusion
For even the best-performing systems, it is prudent to remain vigilant for signs of trouble, so burgeoning problems can be stopped before they get out of hand. In new construction situations, owners can avoid costly waterproofing rehabilitation through appropriate design, correct application, and due diligence during construction. Owners and managers of older buildings have to deal with what they have got—and, often, that means addressing inexpertly designed or incorrectly installed moisture protection systems.

With thoughtful investigative work and creative water management strategies, even the most demanding waterproofing problems can be successfully addressed. The best approach is to waterproof basements, tunnels, mechanical rooms, below-grade levels, kitchens, vaults, water features, and sensitive spaces diligently and correctly from the outset.

 

Glossary of Waterproofing Terms
Blind-side waterproofing: Installation of waterproofing membranes and drainage before the concrete foundation is poured.Capillary action: Movement of liquid in porous materials or thin tubes (capillaries), due to attraction between the molecules of the liquid and those of the solid.

Condensation: The change in phase from a gas to a liquid, as when water vapor cools to liquid water.

Dampproofing: A coating that has been designed to limit soil moisture penetration.

Efflorescence: A white crystalline or powdery crust, made up of dissolved salts deposited by water seepage after evaporation.

Hydrostatic pressure: The force exerted by a fluid, such as water, due to gravity.

Negative-side waterproofing: A barrier opposite the side of applied hydrostatic pressure (e.g. the interior of a foundation wall), whereby water can enter the wall but not pass through it.

Positive-side waterproofing: A barrier on the side of applied hydrostatic pressure (e.g. the exterior of a foundation wall), such that water is blocked from entering the surface.

Waterproofing: A system designed to prevent and manage water infiltration that may include coatings, membranes, drainage media, perimeter drainage, interior channels, sump pumps, or other elements.

 

Richard P. Kadlubowski, AIA, is senior vice president and director of architecture with Hoffmann Architects, an architecture and engineering firm specializing in the rehabilitation of the building envelope. As manager of the Washington, D.C., office, Kadlubowski resolves complex waterproofing situations for existing buildings and new construction, including fountains, kitchens, lobbies, below-grade structures, terraces, and plazas. He may be reached
at r.kadlubowski@hoffarch.com.

 

 

 

 

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