Challenges Related to Waterproofing Manufacturers’ Standard Details David Sacks, AIA, LEED AP Simpson Gumpertz & Heger Inc. 135 S. LaSalle, Suite 3800, Chicago, IL 60603 Phone: 312-754-7423 • E-mail: desacks@sgh.com RC I I n t e r n a t i o n a l C o n v e n t i o n a n d T r a d e S h ow • Ma rc h 1 4 – 1 9 , 2 0 1 9 S a cks • 7 9 Abstract Architects, engineers, and contractors frequently use manufacturers’ standard details (MSD) for construction drawings and/or shop drawings. While these MSDs show system configurations for a variety of situations, they often represent the bare minimum assembly necessary to meet minimum performance requirements. Furthermore, MSDs are typically tested in a laboratory setting, bearing little to no resemblance to actual environmental conditions experienced in the field. Accordingly, relying on MSDs may not provide the desired performance for actual site conditions and should be used with caution or modified to meet the design team’s specific project needs. This paper will provide background information about the development of MSDs, discuss challenges associated with their use, and propose detail enhancements that may improve system performance for real-world conditions. Speaker David Sacks – Simpson Gumpertz & Heger – Chicago, IL SACKS is a member of Simpson Gumpertz & Heger Inc.’s (SGH’s) Building Technology group. He is experienced in the investigation and evaluation of building enclosures, including roofing, below-grade waterproofing, and wall and glazing systems, with a specialty in repair and rehabilitation of existing buildings. Sacks is a member of ASTM D08 on Roofing and Waterproofing, and serves on the board of the Association for Preservation of Technology’s (APT’s) Western Great Lakes Chapter. He completed his graduate education at the University of Michigan, receiving master’s degrees in both architecture and engineering. 80 • SacksCKS RCI International Convention and Trade Show • MarcRCh 14-19, 2019 PART I – THE INTENT OF MSDS AND THEIR ASSOCIATED CHALLENGES Introduction Repairing a defective envelope waterproofing system on a newly constructed building often requires deconstruction and/or demolition of otherwise new and functioning cladding materials to access the source of the issue, not to mention replacing water-damaged interior finishes. Repairing below-grade waterproofing systems can be exponentially more challenging, destructive, and costly, due to access. Effective repairs typically require excavation. For zero-lot-line projects, there may be no exterior access, and intrusive grout injection methods may be the only option. This article reviews the myriad challenges associated with below-grade waterproofing systems and the limitations of many standardized manufacturer installation details and provides recommendations for detail modifications to enhance system performance in order to align the system with project-specific needs. Background Below-grade waterproofing does not contribute to the aesthetic of a building. Accordingly, most designers (for purposes of this paper, this includes architects, engineers, owners, consultants, and potentially contractors) focus their efforts on above-grade envelope design and may rely on waterproofing manufacturer specifications and details to provide a below-grade waterproofing design. Unfortunately, in doing this, they may not achieve the level of performance they expect because those details may not fully address the site-specific geotechnical conditions, construction sequencing challenges, local climate issues, and skill level of installers, among other project-specific variables MSDs are typically validated through ASTM or modified ASTM tests and limited trial installations and may address minimum requirements for a variety of physical properties, including resistance to hydrostatic head, elongation, puncture resistance, crack cycling, and peel adhesion, among others. Standardized testing aims to confirm that certain products, assembled per specified details, will achieve a prescribed minimum performance; this minimum performance often triggers receipt of a default material warranty offered by the manufacturer. While said standardized testing may validate performance under specific conditions, it is difficult, if not impossible, to account for the variety of site conditions, contractor means and methods, and structural conditions that affect the performance of below-grade waterproofing. Similarly, a warranty is not a guarantee of performance; on the contrary, it is an outline of what a manufacturer is legally obligated to do should their system fail to perform. Furthermore, many warranties limit liability to product defects (rarely the issue) and place the onus on the owner/designer/contractor to confirm said defect, creating a major hurdle to enacting a warranty that may ultimately be worthless. MSDs MSDs es-sentially provide a default assembly where waterproofing design is not otherwise articulated in design documents. They are limited in nature, illustrating minimum requirements for installation of each membrane system for typical conditions only. As noted, the method ensures that the system, as tested in laboratory conditions, will meet specified performance requirements. MSDs and manufacturer installation instructions typically include information such as necessary side or end lap preparation and width, configurations for changes in plane, substrate preparation requirements, and system terChallenges Related to Waterproofing Manufacturers’ Standard Details RCI International Convention and Trade Show • MarcRCh 14-19, 2019 SaCKS • 81 Figure 1 – Example manufacturer’s standard side lap selvage edge detail. Polyguard Products, Inc. Detail BS-2; http://www.polyguardproducts.com/products/architectural/details/index.htm#BLINDSIDE. Figure 2 – Example manufacturer’s standard side lap selvage edge detail enhanced with fabric tape at interior (concrete-facing-side) of the membrane. Polyguard Products, Inc. Detail BS-6; http://www.polyguardproducts.com/products/architectural/details/index.htm#BLINDSIDE. mination. In addition, MSDs often provide specifier flexibility by permitting a variety of products/assemblies for the same function, especially at more complex details, which can be confusing to designers. This may include variation in the layering of products (e.g., at transitions from wall waterproofing membrane to footing membrane), or the interchangeability of certain products (e.g., types of sealants, including one- or two-component products). While MSDs are valuable starting points for designers, manufacturers frequently neglect to highlight the associated differences in performance or clarify when and where the MSDs may no longer apply. And even when details do articulate that they are intended for specific applications (e.g., for Shotcrete, below the water table), there is little explanation describing how the changes may impact actual performance (Figures 1, 2, 3 and 4 show one manufacturer’s iterations of a blindside vertical wall side lap detail). Further, the competitive bidding process common in construction today disincentivizes contractors from offering system alternates that may improve system performance but increase upfront cost. The Designer’s Challenges The designer of record is tasked with designing a system that works for a specific project, under specific conditions. Many designers frequently find themselves caught in a balancing act, bound by performance requirements, budgetary constraints, and an aesthetic design vision. This often creates a zero-sum game in which designers spend their time and effort focusing on visual building elements—often at the expense of fundamental, but hidden, building systems. As a result, most design professionals rely on readily available manufacturers’ data to guide their waterproofing decisions. Every project that includes below-grade construction contains a unique set of challenges, and as the complexity of the below-grade structure increases, so may the obstacles to a successful waterproofing installation increase. Access may be confined to narrow trenches; soil conditions may limit the potential machinery available; geological conditions (including depth to water tables, soil characteristics, and location of bedrock), may dictate waterproofing system strategy, triggering removal of site water and/or soil, and necessitate thicker or thinner structural slabs than desired; and the construction schedule itself may push the installation to a season where a specified product is no longer viable. The challenges associated with waterproofing are extensive. For the purposes of this discussion, they are summarized into the following categories: • Access: Below-grade waterproofing can be difficult to access during construction, and doubly so post construction; enhancing the design is a prudent approach to eliminate the risk that further waterproofing access will be necessary during the service life of the system (i.e., add redundancy where possible). • Site: The site may include lot line limitations, require deep trenches, utilize rocky soil for the substrate, or have a water table that is higher than anticipated. Make the detailing as simple as possible and provide belts and suspenders where feasible. • Protection: The waterproofing installer will not have control of the project site; what happens between the time they install their assembly and the time when the assembly is covered is out of their hands. Detail the system for durability, and provide dedicated protection layers. • Environment: Mother nature unfailingly presents unexpected challenges—weather extremes, rain, snow, sunshine, temperature swings—designers should plan for these as much as possible. Detail the system to limit the impact of potential weather extremes. The following section explores these challenges further. Access Simply put, waterproofing is inherently in a location that is difficult to access. Here is a limited explanation of access-related challenges. • Below-grade placement: Waterproofing systems are generally below grade, making initial placement and future repair efforts difficult and costly. • Heavy construction equipment: Excavation equipment lacks precision in movement, presenting risks during installation and/or future repair operations. Figure 4 – Example manufacturer’s standard side lap selvage edge detail enhanced with fabric tape at interior (concrete-facing-side) of the membrane and detail tape at exterior (substrate-facing-side) of the membrane. Polyguard Products, Inc. untitled detail. Figure 3 – Example manufacturer’s standard side lap selvage edge detail enhanced with fabric tape and seam edge sealant at interior (concrete-facing-side) of the membrane. Polyguard Products, Inc. untitled detail. 82 • SacksCKS RCI International Convention and Trade Show • MarcRCh 14-19, 2019 • Subsurface traffic: Various utilities (e.g., gas, cable, water) may be buried in the soil, adding complexity should excavation need to occur. • Blindside nuances: Blindside systems, by their very nature, increase the potential for waterproofing breaches and intensify the consequences, should those occur. While we may not be able to mitigate these access-related challenges through design, they establish a basis of justification for enhancing details that can be improved. Site Each project site is unique and will include conditions that should be accounted for in the design. • Soil conditions: Geotechnical reports provide valuable information; however, those reports capture data at specific locations and times, which may not represent the critical information for the actual project design. • Foundation wall type/placement: The project may require narrow or zero-lot-line foundation wall placement, deep trenches (Figure 5), and/or unique soil conditions. These conditions will likely dictate the waterproofing system selected for the project. • For a blindside application, the challenges are exponentially greater, beginning with the substrate itself, which is not the structural slab, but rather existing soil or backfill (Figure 6). Manufacturers often list broad substrate guidelines subject to the installer’s discretion. While the inclusion of a thin concrete mud slab in horizontal applications may eliminate many substrate-related challenges, the additional construction costs, both in terms of time and money, make it a frequent target during value engineering. • For vertical blindside assemblies, the soil retention system also provides the waterproofing substrate; this is commonly either wood lagging or sheet piling (Figure 7). While gaps and offsets in wood lagging may require minor modifications prior to membrane installation, attaching a membrane directly to sheet piling requires flexibility in the sheet good to accommodate the undulating surface plane, as well as forethought to align the seams in a single plane to avoid laps occurring at transitions. System Protection For any waterproofing application, the order of operations may impact the design decisions. Waterproofing will not be the only system installed on a project, and the other trades may have little knowledge of, or care for, the waterproofing. Therefore, the project staging plan may directly impact the waterproofing system, informing decisions about how quickly backfill must occur or when concrete placement may begin. • For a blindside system in particular, waterproofing materials will typically be one of the first systems installed; RCI International Convention and Trade Show • MarcRCh 14-19, 2019 SaCKS • 83 Figure 5 – Site conditions may require narrow, deep trenches, which can dictate the type of waterproofing selected for a project. Courtesy of Simpson Gumpertz & Heger Inc. Figure 6 – Poor substrate selection may cause dimpling of the waterproofing membrane, creating numerous weakened areas more susceptible to puncture failures. Courtesy of Simpson Gumpertz & Heger Inc. Figure 7 – The attachment of blindside membrane directly to sheet piling provides numerous inherent installation challenges due to the geometry of the sheet piling, the flexibility of the membrane, and the spacing of the lap joints, which may coincide with direction changes or splice joints in the sheet piling. Courtesy of Simpson Gumpertz & Heger Inc. these areas are subsequently used as staging and laydown areas by other subcontractors before concrete placement, subjecting the waterproofing system to impact from foot traffic, heavy equipment, material placement, and general construction site debris (Figure 8). • Blindside applications also reverse the installation order, placing the steel rebar over the membrane, followed by the concrete, rather than rebar protected within concrete, so that it’s never in contact with the membrane. The blindside procedure exposes the membrane to the steel bars, potentially resulting in surface damage to the membrane. • Large slabs and block-outs: for large continuous slabs or where repetitive block-outs occur throughout a slab, the necessary concrete formwork will likely need to puncture the waterproofing membrane, requiring patches at a variety of locations throughout the system. Poorly planned sequencing will make it difficult to achieve the manufacturer’s required overlap (Figure 9). • Backfill operations place and compress soil adjacent to a new waterproofing system, where the protection layer is bonded to the waterproofing. Backfill installation may transfer vertical loads onto the membrane for which the system was not designed. Environment Buildings are not constructed in a bubble. Waterproofing assemblies need to withstand a variety of conditions (rain, snow, freezing temperatures), as well as rapid condition changes. In addition, the system design should account for the challenges of installing such systems in adverse settings. Critical details may be difficult to install in perfect conditions, let alone as the work crew nears the membrane working temperature limits (which may differ from human working limitations). • All membranes include specific application temperature limitations. Currently there is a market trend toward fluid-applied products driven by construction schedules and the rapid speed of fluid system installation. These site-fabricated systems are entirely reliant on proper installation and highly dependent on installation conditions and methods, with a much narrower set of limitations (i.e., the specified system may not be viable for actual climate at the time of installation or may require methods not planned for in the design or specification of the system). • Many environments experience large temperature swings, especially in the shoulder seasons. For a product that relies on adhesive bond at lap conditions, temperature swings may undo an otherwise well-installed system. An asphaltic-based system installed at an ambient 55°F, which then dips to 5°F within 24 or even 48 hours, Figure 8 – Construction site post waterproofing membrane installation with stacks of rebar and welded wire fabric staged on the membrane, as well as a generator and other miscellaneous equipment. Courtesy of Simpson Gumpertz & Heger Inc. Figure 9 – Poor planning of formwork at breaks in large continuous slab may result in penetrations immediately adjacent to the edge of the pour, leaving little space to install a patch repair. Courtesy of Simpson Gumpertz & Heger Inc. 84 • SacksCKS RCI International Convention and Trade Show • MarcRCh 14-19, 2019 will likely contract, the forces of which can easily overcome a single-layer adhesive bond (Figure 10). • UV exposure, while typically not an in-service concern, can impact the waterproofing system during the installation process, causing failure before it ever sees moisture. Environmental conditions (and construction sequencing) may dictate that a product remain exposed much longer than initially anticipated. These challenges all highlight the reasons why waterproofing design is so critical. PART II – ADDRESSING THE CHALLENGES Enhanced Design Appropriate below-grade waterproofing design should address construction challenges, not just in-service conditions. Accordingly, design enhancements seek to limit the hurdles to operational performance by lowering the risk that waterproofing may become damaged before it is ever placed in service. Numerous opportunities exist to limit these risks. The following is an overview of some of those opportunities. Countering Site Challenges The geotechnical report costs will likely be nominal compared to the cost of construction, and even less significant compared to the cost of any future repairs. Allow the geotechnical engineer to place wells that may be monitored over a period of time, to give a better understanding of seasonal variations in water table elevation, and consider additional wells after the schematic design phase is complete. Require a mud slab in the design. This increases construction schedule and budget; however, it provides a stable working surface for more expeditious waterproofing installation and subsequent construction activities, and will reduce the risk for damage due to foot traffic over rough or uneven surfaces. This is especially valuable where heavy machinery will be incorporated by other trades. Similarly, including a sheet/board substrate at the support of excavation to provide a continuous orthogonal surface (for a blindside system) will simplify the installation and limit the potential for failure. Add backside (positive-side) tape to blindside side lap seams. Again, this will slow down the installation process, but will reinforce the waterproofing at one of its most vulnerable locations. This is especially beneficial for protecting three-way T-joints, which occur where an end lap joint meets a side lap joint. At those locations, the three membrane layers inherently exist in offset planes; where the upper layer meets the bottom layer, the offset results in a narrow gap between the layers, creating a potential funnel for water to breach in the system. For a positive-side system, T-joint protection is standard, including joint sealant and/or a membrane patch plus joint sealant after the membrane is set. Given the inability to access this critical location post membrane installation, we strongly advocate for the use of backside tape. Detail transitions and plane changes to resist the loads imparted during the construction process. For example, where a system transitions from a grade beam to a thickened slab edge, the waterproofing may need to change substrates while also changing direction/plane. Reliance on the adhesive bond alone may not survive this process. Instead, consider a redundant layer to help resist construction forces. This applies not only to transitions within the waterproofing, but also transitions from the waterproofing to an adjacent system (e.g., vapor barrier); these transitions are frequently overlooked, even though they may be just as critical to the viability of the waterproofing system (Figure 11). RCI International Convention and Trade Show • MarcRCh 14-19, 2019 SaCKS • 85 Figure 10 – A large temperature swing in a short period of time caused membrane shrinkage, resulting in frequent voids at the side laps. Courtesy of Simpson Gumpertz & Heger Inc. Figure 11 – Detail sketch for waterproofing to vapor barrier transition. Courtesy of Simpson Gumpertz & Heger Inc. Limiting Staging Risks Most roofing contractors stage their installation to limit foot traffic and wear on their new system; occasionally, they even include insulation board or other stiff overlay, should their finished system become a work surface for other contractors. However, below-grade waterproofing design rarely includes true protection once the membrane is installed in a blindside application. Given the critical role waterproofing plays and the access challenges associated with possible repair, we recommend requiring temporary protection during the staging process. In certain cases, we would advocate for going a step further and adding a full protection slab over the waterproofing membrane, especially at thick mat slabs where the extensive rebar placement will simultaneously escalate the chances for rebar membrane contact, while impeding access to the membrane for repair during the construction process (Figures 12 and 13). While any or all of these measures may limit the risks for system failure, none of them should invalidate or supersede the need for waterstops in the cold joints. For positive-side vertical systems, require drainage and protection boards as separate items. Separating these layers creates a buffer between the waterproofing membrane and the backfill, not to mention the equipment used to install the backfill. Although many designs allow the drainage layer to perform double duty as both drainage and protection layer, this combination product is often adhered or taped directly to the waterproofing. During backfill operations, any vertical forces applied to the protection layer may transfer directly to the membrane, shearing it from the Figure 13 – Construction site with reinforced protection slab over blindside waterproofing as designed in the detail shown in Figure 12. Courtesy of Simpson Gumpertz & Heger Inc. Figure 12 – Enhanced detail showing protection slab over the waterproofing with a layer of redundant waterproofing atop the protection slab. Courtesy of Simpson Gumpertz & Heger Inc. 86 • SacksCKS RCI International Convention and Trade Show • MarcRCh 14-19, 2019 substrate. Incorporating a slip plane in the design to isolate the drainage board and/or protection layer from the waterproofing layer (Figure 14) will help negate the potential for shear failure. Protect Against Environmental Factors Any waterproofing installer understands the most ideal conditions for system installation—e.g., mild temperature, low humidity, no precipitation, and limited temperature swings. Unfortunately, the construction schedule, not the designer, typically dictates the timeframe for waterproofing installation; furthermore, environmental conditions (e.g., extended periods of cold or wet weather) may prolong the system’s exposure to the elements. Measures may be introduced to lessen the impact of these variables beyond the control of the construction team. The designer should mandate UV protection over the waterproofing layer, regardless of anticipated construction schedule. This may be a simple polyethylene sheet or perhaps a multilayered composite membrane also serving as redundant waterproofing. Seal all seam edges at positive-side membranes. While the seams are tested to meet hydrostatic head requirements, no substrate will be perfectly smooth, and some breaches/fishmouths at the seams will be inevitable. Sealing the seams provides relatively inexpensive insurance against potential installation defects such as wrinkles at laps that provide a leakage path. Similarly, consider stripping in the interior face side laps (for blindside membrane) and picture-framing the edges of strips with sealant. This protects a major system weakness during the construction phase, providing one more measure of redundancy; additionally, these strips may be easier to handle and align at the side laps than a typical full-size waterproofing sheet (Figure 15). Require components that may be less sensitive to exterior exposure. Where manufacturers’ details allow for multiple accessory products, consider potential construction risks associated with each one and select products accordingly. For example, a manufacturer may support either a one-component moisture-cured detail sealant or a two-component solvent-cured product. In this scenario, contractors will often default to the one-component product, as they tend to be more cost effective and require less preparation. While the manufacturer’s detail may imply equivalent performance on paper, the one-component sealant may cure more slowly than the two-component solvent-cured product, thereby exposing it to more environmental variables before it has setup and is ready to perform. Word of Warning While the information presented above purposefully pushes the user toward redundancy in the design system approach, it is important to remember the big-picture goals of your specific project, including how the system will be operated and maintained. For a below-grade art gallery with highly regulated relative humidity conditions, the RCI International Convention and Trade Show • MarcRCh 14-19, 2019 SaCKS • 87 Figure 14 – Include multiple layers of separation to provide a slip plane between backfill and the waterproofing membrane. Courtesy of Simpson Gumpertz & Heger Inc. Figure 15 – Condition where all side lap seams have been enhanced with additional detail membrane, including perimeter sealant along the edges of the membrane. Courtesy of Simpson Gumpertz & Heger Inc. 88 • SacksCKS RCI International Convention and Trade Show • MarcRCh 14-19, 2019 risks of water infiltration likely necessitate enhanced system design. For a below-grade parking garage, however, water infiltration may be a tolerable nuisance, and the inclusion of redundant layers or details may provide little to no benefit. CONCLUSION Design details which address only in-service conditions may function in a vacuum, but they often fall short in the field. Where the costs associated with repair are exponentially greater than the initial installation, as is the case for waterproofing, best practices should go beyond the bare minimum. In summary, we recommend the following: 1. Design for construction conditions as well as in-service conditions. 2. Simplify the installation variables through use of mud slabs or other protective measures. 3. Create redundancy when necessary; tape over seams on the positive and negative sides to reduce installation defects, and add sacrificial waterproofing layers for high-risk locations (e.g., in the water table). 4. Use products and/or accessories that may reduce the impact of environmental factors. 5. Rely on well-developed details, not well-meaning warranties. 6. Consider the ultimate use of the system, including how the building will be operated and maintained. 7. Don’t let construction schedule circumvent good design decisions.
