Sealing In Savings

March 1, 2009

Children’s Hospital of Wisconsin, located in Milwaukee, WI, has experienced increasing patient volume for several years, with admissions and outpatient visits reaching record levels and exceeding projections of expected growth. From 2000 to 2005, admissions increased 13.3%, specialty outpatient clinic visits rose 46%, emergency visits were up 28.2%, and surgical cases increased 14%. Space was running out, so, in 2006, plans were drawn up to add a 12-story, 425,000–square foot expansion tower to increase the number of beds from 236 to 294, with capacity for an additional 72 in the future. The new $165-million West Tower will also feature two expanded 24-bed pediatric intensive care units and a larger, more comprehensive Herma Heart Center.

But before plans could be finalized, some special considerations had to be accommodated. “We had two primary concerns,” states Steve Roth, director of facilities operations. “We worry about mold because of the fragile immune systems of our patients. The other issue was pure energy.”

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Preventing uncontrolled ingress of air and moisture was a key requirement, because the formation of condensation in the wall cavity caused by warm air leaking through the façade could lead to the development of mold and other negative impacts on air quality, premature deterioration of building envelope components, and increased energy consumption. In addition to condensation, humidity, and other moisture damage, air leakage through the building envelope also leads to winter heat loss and summer heat gain. That translates into excessive energy consumption.

According to a 2005 National Institute of Standards and Technology (NIST) report, Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use, “infiltration in commercial buildings can have many negative consequences, including reduced thermal comfort, interference with the proper operation of mechanical ventilation systems, degraded indoor air quality, moisture damage of building envelope components, and increased energy consumption.”

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Outlining the Challenge
The higher humidity in hospitals and cold winters in Wisconsin create the potential for frost and condensation; a continuous building envelope solution eliminates issues. To be effective, it must provide flexibility where the curtain wall intersects with the precast, and it must withstand the difference in air pressure on both sides. Gaps in the system can compromise the performance between individual components and assemblies, reducing the effectiveness of the overall system. Design flexibility is incorporated to allow greater movement and deflection beyond what sealants can provide with varying geometries.

Equally important is compatibility between materials and components at the window-wall interface so they don’t compromise the system’s ability to function correctly. Many commonly used transition materials are limited by specific inherent characteristics. For example, spray foam may interfere with drainage planes when used with a drained window system with sill pan flushing; overspray can spoil the finishing materials; and to retain structural integrity, sheet membranes are limited by the width of unsupported gaps that can be spanned. Sealants are not always practical, due to the need for backing material or the required width-to-depth ratio on the complex geometries of some buildings. In addition, they are a continual maintenance item, subject to degradation from ultraviolet (UV) radiation and weather conditions.

Despite their shortcomings, improvements have been made in materials, design, and construction. Nevertheless, performance problems at the window-wall interface continue and are generally attributed to design, materials, workmanship, or sequencing. It’s a cause for concern since air leakage at the window-wall interface affects the air leakage performance of the entire window unit. To reduce the potential for compromised performance, the hospital owner sought a single source provider of a long-lasting durable solution.

Building Envelopes and Energy Efficiency
The building envelope—its outer shell—is designed and constructed to provide separation between the interior and the exterior environments. To do so, it must act as an air barrier to control the movement of air across the building, a thermal barrier to insulate against fluctuating temperatures, a drainage plane to manage water infiltration, and a vapor barrier to manage diffusion of vapor through the building envelope. In general, the wall and window assemblies perform these functions adequately. The Achilles’ heel occurs at the areas where windows and walls connect, particularly if varying geometries are part of the building design. “The interface between the window and the metal trim produces the greatest heat loss,” summarizes Roth. “Interfaces between systems will kill you. This is a complex building with a lot of curved surfaces and a multitude of materials. We knew we needed an air and vapor barrier.”

Ideally, the functional layers of each adjoining assembly are placed along the same plane so that performance of the components is not compromised. If the components are not installed along the correct planes, the point of failure usually occurs at the intersection of the different components—the interface between the assemblies.

Difficult though it may be to build, the window-wall interface’s functional performance affects overall building envelope system performance. As much as 90% of all water intrusion problems can occur within the 1% of the total building exterior surface area that contains the terminations and transition detailing, according to Michael T. Kubal’s, Waterproofing the Building Envelope. Air leakage and exterior moisture infiltration are primary factors in premature building envelope failure. Moisture-laden air penetrating the building envelope can condense, resulting in corrosion or damage to building envelope components, increased heating and cooling loads in excess of up to 40%, and occupant health and comfort issues.

Building envelopes, therefore, can be a valuable tool for facilities focused on increasing their energy efficiency. In fact, research conducted by the Building America Research team—a program spearheaded by the US Department of Energy that brings together is private sector, state and local governments, national laboratories, and universities to research and develop energy-efficient building technologies—emphasizes the important role of building envelopes. The report determined that integrating high-performance building envelopes can significantly improve energy efficiency, especially when teamed with onsite power. Because that thermal barrier created by the building envelope, less energy is required to the indoor environment, opening the door for smaller HVAC systems and allowing for onsite power options for those systems.

Seeking Solutions
Answering the call for a design that could address all of the Children’s Hospital’s needs, the architectural firm Shepley Bulfinch Richardson & Abbott designed a curtain wall with six-story spans, along with projections and recessions in the wall and a continuous vapor barrier. However, the junctions where the curtain wall and the adjacent wall assemblies—constructed of dissimilar materials—connect remain areas of dynamic movement with the potential for air and moisture infiltration, leading to mold growth.

Providing a reliable/adequate barrier between divergent substances is next to impossible with a sealant, so the construction team turned to the patent-pending Proglaze Engineered Transition Assembly from Tremco Commercial Sealants & Waterproofing to provide the tie-in between the curtain wall system and adjacent wall assemblies. The pre-engineered air barrier transition assembly is mechanically attached to the window and curtain wall structural framing to bridge continuously between the window-curtain wall opening and the adjacent air and vapor protection materials, ensuring a durable connection and seal.

“We don’t rely on sealants as the primary seal,” says Brian Stroik, the senior quality process manager for The Boldt Company.

Sealants are a secondary seal that provides aesthetics to the bridge materials. “Proglaze is the primary seal,” he says. “That’s important for the exterior because of UV rays and maintenance requirements.”

UV rays never hit the engineered transition assembly (ETA), which, he adds, is maintenance-free for an energy-efficient, sustainable building.

Mike Sebold, team leader for Tremco, says the junction between the window–curtain wall and the building structure is always difficult. “It’s a critical application; you need an impermeable system,” he says. “That’s why we invented a system to bridge between the window systems and the air barrier system. You don’t want the wall breathing; you have to stop moisture on the exterior to prevent mold issues inside.”

The system has already been used in 15 hospitals. At one Minneapolis, MN, hospital, Sebold says energy performance was improved, but at the Children’s Hospital, the concern was air and moisture seals. “A continuous seal is critical,” he says. “At the hospital in Wisconsin, irregular material and open columns in the design made it a difficult seal.”

Proglaze ETA provides an effective air barrier with an air leakage rate of less than 0.01 cubic feet per minute per square foot at 1.57 pound per square foot, which is below most published references for maximum allowable system air leakage. Consisting of a solid silicone sheet, it is a continuous system that provides air barrier continuity between assemblies, and can absorb dynamic movement and wind-loading stresses without rupturing.

The Boldt Company first used the ETA more than four years ago. According to Stroik, the pre-made 90-degree corners adapt to most building needs. Because the transition material is flexible, with “lots of elasticity” as Stroik describes it, not only can it span and seal across irregular window geometries without reduction of performance, but it is also able to shrink and expand according to fluctuating temperatures.

The ETA has a low vapor permeance of 2.59 perms and exhibits the characteristics of an effective vapor retarder. It’s also water-resistant, acting as an effective drainage plane at the window-wall interface. “It’s a great product for any building you want to be energy-efficient,” says Stroik.

Based on a gut feeling, Roth cautiously predicts energy savings of 15% to 20%. “We rarely roll back temperature settings in the hospital,” he says. “Temperature and humidity remain uniform around the clock.”

The construction team turned to Tremco Commercial Sealants & Waterproofing to provide the tie-in between the curtain wall system and adjacent wall assemblies.

The NIST study found that an air barrier system can reduce air leakage by up to 83%, with potential gas savings of over 40% and electrical savings over 25%. In addition to lowering fuel consumption, reducing the amount of heated or cooled air escaping from the building can also reduce wear on the HVAC system due to less usage. Air leakage means the building’s mechanical systems work harder. In fact, a proper building envelope can translate into the ability to use a heating system 20% to 30% smaller with comparable energy usage and costs with a building that has a bigger heating system, but suffers from air leakage. Payback can be as rapid as four to five years when considering reduced energy demands.

Test, One Two
To ensure compatibility and long-term performance of the system, as well as the quality of the installation, Children’s Hospital built and tested a full-scale mockup of the curtain wall and adjacent exterior wall systems. Stroik indicates that 17 different tests were performed at Architectural Testing Inc. laboratories in York, PA, over the course of eight weeks, to determine how well the transition assembly would be able to withstand water penetration, thermal changes, and load deflection, and to measure air infiltration.

“We had to pass all the tests,” he says.

And so they did. To reinforce what they learned, site testing was conducted throughout the installation. Testing protocols included ASTM E1105-00 Standard Test method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform or Cyclic Static Air Pressure Difference; AAMA 501.2-03 Quality Assurance and Diagnostic Water Leakage Field Check of Installed Storefronts, Curtain Walls, and Sloped Glazing Systems; and AAMA 503-03 Voluntary Specification for Field Testing of Storefronts, Curtain Walls, and Sloped Glazing Systems.

“We do four to six tests a day to make sure the installation is done properly,” states Stroik. “The first time, we found a minute leak in one of the five tests. It’s tricky to get every transition right; every building is different. But there’s no room for error—we have to do it right the first time. It’s all about accountability.”

The ETA also underwent independent laboratory testing for air infiltration, water resistance, and structural performance. Even the silicone rubber extrusion was put through testing for vapor permeance.

As construction manager, The Boldt Company implemented an Enclosure Quality Management Program for commissioning of the building envelope that included extensive site testing throughout the installation and regular planning meetings for all contractors involved. “We created the program for all who worked on the building exterior to go through as a review,” says Stroik. “It’s all about accountability.”

Not only were all the lead installers taken to view the offsite mock-ups, but the installation was videoed and photographed for reference. “It touches everybody—the actual installers, everyone, not just project managers,” he says.

In addition to ongoing testing in field trials since 2005, Sebold says Tremco continues to modify Proglaze ETA for new and different window systems. “We work with the top 10 window manufacturers on the design of our system,” he adds.

They’re also taking it a step further by trying to find a thermal specification. “No one has ever tested thermal performance of a joint,” postulates Sebold. “They do walls and windows, but how efficient is rubber? We’re striving for documentation.”

It’s important because the Department of Energy is starting to correlate air loss to energy. The two primary points are window perimeters and roof-to-wall—anywhere two different trades come together. Tremco has done its due diligence, he insists, and it’s paying off—an advantage in the face of increasingly stringent regulations.

Future Applications
Mandates for the environmental separation between interior and exterior environments have increased in recent years, thanks in part to a global concern for reducing energy consumption and the use of non-renewable resources, as well as the costs of energy usage and repair in the case of premature building envelope failure. Materials and construction methods have been improved to coincide with increasingly stringent code requirements, paving the way for acceptance of air barriers, vapor protection, and whole-building envelope systems.

“The Department of Energy introduced the Energy Smart Hospital program in July to reduce energy consumption,” notes Stroik. “This helps achieve that goal.”

Although Roth says it’s too soon for quantitative data, he notes that there has been no moisture buildup during construction. “We know it will help us by making the building much tighter. Energy is important and we expect the performance will help us.”

The pre-fabricated system, combined with installation instructions, produces repeatable, consistent results that make it successful in other applications. Suitable for large expansion joints, it has benefited Exxon in Houston; applicable for seismic drift joints, it is used in California because of its ability to withstand movement. Commercialized in 2001, Sebold reports that Proglaze ETA has found favor with glazers because it’s pre-engineered, with general contractors because it addresses a problem area by trouble sealing corners, and with window manufacturers and waterproofers who “don’t want to do it. We’re the only ones doing this,” he adds.

Tremco believes the technology shouldn’t be limited to window-wall interfaces. With modification, it could be used at junctions between other assemblies within the building envelope where spanning of voids is commonplace, such as roof-to-wall, areas such as control joints or expansion joints, or any location where a degree of movement is anticipated, as well as at any opening or penetration, such as louvers or mechanical openings.

The company has already developed modified versions of the Proglaze ETA that could be adapted for various onsite conditions and curtain wall systems. The Offset Dart Design System is suitable for situations where the window is offset rather than installed flush to the fenestration opening. This style often requires additional corner gusseting, both inside and out, for the membrane to be effectively tied in from the frame to the opaque wall. That, in turn, requires a new offset dart design with offset molded corner, custom shapes, or modifications to the silicone rubber extrusion to perform properly. Typically, this would include expansion joints, extended lap/splice/bridge joints, head receptor, and inside/outside corner conditions.

Tremco’s pressure bar system can be used on curtain wall systems where the connection point for the air barrier onto the curtain wall frame is onto the throat of the curtain wall to the unglazed pocket instead of to the inner part of the curtain wall. Connecting the air barrier to the inner part of the curtain wall extrusion creates potential for breaching the air seal at the junction of the vertical and horizontal members. A silicone rubber extrusion with lock-in dart fits into the curtain wall race and is sealed in place with Spectrem 1 silicone sealant, clamped into place by the pocket filler and pressure plate, and set into the opaque wall air barrier, just as with other ETA systems.

It’s a Wrap
Sebold says there are “no negative trade-offs” with Proglaze ETA. Tremco pledges that it eliminates several factors that can contribute to

A silicone rubber extrusion with lock-in darts fits into the curtain wall raceand is sealed in place with Spectrem 1 silicone sealant.

potential problems, such as reliance on sealants alone for waterproofing, inefficient construction sequencing, multiple contractors, improper or inconsistent detailing, and incompatibility of components. And, it’s “done without added weight,” adds Sebold.

Work at Children’s Hospital has been ongoing since the foundation was poured in 2006, with the expectation of finishing early in 2009. Stroik says the project is going well. “We had some heavy rain and storms in May and June, but that’s about it as far as issues,”
he says.

In fact, Stroik is so pleased with the ETA, he has already recommended it on other projects. “Proglaze ETA is a fantastic product: easy to install, durable, sustainable,” he attests. “It adheres well and will last the life of the building. I like seeing it on other projects; it should be done on every hospital. The industry needs it.”

References

Drysdale, R.G. and G.T. Suter, Exterior Wall Construction in High-Rise Buildings, Canada Mortgage and Housing Corp., 1991

Kubal, Michael T., Waterproofing the Building Envelope, McGraw-Hill Professional, 1992. 

In Ottawa, Canada Building Envelope Is Part of the Package

The Ottawa Hospital (TOH)—considered a premier medical center and staffed with over 1,200 physicians and 11,000 staff—emerged from a difficult financial period in the late 1990s with one particular goal in mind: to sustain long-term fiscal integrity by improving the facility’s infrastructure and managing energy costs. Like the Children’s Hospital, foremost on the minds of the powers that be at TOH was the need to control heating and cooling while managing air quality and humidity levels, all important factors in terms of infection control and the support of a healthy indoor environment.

With an eye towards bringing down energy costs and improving building performance, TOH identified several energy-saving opportunities via internal audits and reviews. After reviewing submissions by several outside vendors, TOH decided to work with Honeywell and the two embarked on a 154-year, $17-million performance project. In the end, TOH hopes to save more than $2.6 million annually in utility costs as a result of the improvements and upgrades. While the building underwent a variety of installations and overhauls—including EBI integrators, upgraded chillers and lighting, and high-efficiency boilers—the plan also involved improvements in the building’s envelope as a way to counteract energy leaks and provide state-of-the-art indoor environmental control for TOH.

The results of the facility upgrade have been stellar: a 40% reduction in gas consumption, 18% reduction in electricity demand, and a reduction of carbon dioxide emissions by almost 12,000 tons annually. In 2005, TOH’s efforts were recognized with the Energy Efficiency Award for Building, awarded by the Ontario Hospital Association’s Green Health Care Awards.

About the Author

Lori Lovely

Winner of several Society of Professional Journalists awards, Lori Lovely writes about topics related to waste management and technology.

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