The Role of Insulation in Mission-Critical Design  

There is a growing demand for the design of mission-critical facilities in the United States. A mission-critical facility is broadly defined as a building with any activity, device, service, or system that cannot fail or be disrupted. There are a wide variety of facilities that may be designated as mission critical: financial facilities, trading floors, casinos, hospital complexes, laboratories, military facilities, data centers, public safety centers, airport control towers, call centers, utility command centers, governmental structures critical to the national infrastructure, and even municipal buildings that must function as working shelters in a worst-case scenario.

All images courtesy of Owens Corning

Selecting the right insulation is a critical aspect of creating a building envelope that delivers the superior moisture control and fire performance demanded by mission-critical projects.

In today’s era of connectedness, keeping a building operational means that the systems remain online and people inside can continue to connect to the outside. It also requires that the interior environment remain comfortable, healthy, and safe for occupants 24/7. Achieving these design objectives demands an incredible level of consideration and contingency planning as it relates to security (both physical and cyber), connectivity, cooling systems, power systems, information and communication technology, and extensive analysis to identify and eliminate single points of failure.

Here is an example of one way in which the design of a mission-critical building differs from a typical commercial project. Mission-critical buildings must ensure the reliability of the mechanical and electrical infrastructure. While an average power availability of 99.98 percent may be acceptable for a standard commercial building, the potential 2 hours of downtime per year is unacceptable for some types of facilities. Mission-critical facilities are often designed to achieve a six sigma of power availability (99.9999 percent), reducing their potential annual downtime to less than 30 minutes. A FacilitiesNet article titled “Mission-Critical Facilities: The Next Generation” written by Raj Gupta describes how these systems are structured to avoid interruption: “The typical electrical infrastructure for mission-critical facilities will contain two separate feeds from the electric utility, which are backed up by several diesel generators. The generators are commonly found in a parallel, redundant configuration where one extra module is provided to allow for planned maintenance and prevent a single point of failure in the system.”

While much of the discussion of mission-critical facilities seems to revolve around the robust nature of the IT, electrical, and mechanical systems inside the building, the structural envelope that houses all of these critical systems is also a crucial line of defense that keeps occupants safe and enables systems to continue running smoothly. Designing a building envelope to help withstand extreme weather and prevent the spread of fire and combustion across the exterior further protects the mission-critical functionality of the interior from many of the natural and manmade threats knocking at the door.

This course will explore the importance of selecting the most appropriate insulation for the envelope of a mission-critical building. When chosen correctly, insulation can offer an additional protective layer in the exterior wall assembly or the roof. It can provide redundancy to help protect interiors from the ingress of moisture, effectively contain fires, or prevent the propagation of fire up the exterior wall. Choosing the right insulation for a mission-critical project can not only save lives and minimize property damage, but it can also help to protect the designers and owners of the building from costly litigation that may result from claims that may occur if the building was targeted by an act of terrorism.

The Importance of Insulation in The Building Envelope

The building envelope is comprised of the foundation, roof, walls, doors, windows, necessary air and water barriers, and insulation. In its simplest definition, the building envelope physically separates the conditioned interior from the environmental elements around it. But a simple definition hardly seems to do justice to the complexity and importance of this architectural element. The building envelope is responsible for moisture control as well as temperature control and regulating airflow. In a mission-critical facility, it must be designed to offer the highest level of protection against the most extreme outdoor elements. The omnipresence of insulation as its wrapped around the building, on the roof, and in soffits make this component a powerful ally in creating an envelope that can perform as needed.

While the traditional role of insulation in an envelope is tied to the temperature control or thermal performance of the building, certain insulating materials can be used to enhance features of the envelope important to projects that have been deemed mission critical. The right insulation can improve the way that the building resists or manages moisture intrusion in the roof and walls. It can create effective perimeter fire containment to minimize the progression of and damage caused by fires, and the right insulation choice in the building envelope can even limit potential liability if a building is the target of an act of terrorism. Let’s dive a little deeper into each one of these benefits to more fully explore how an insulating material can impact the design of a mission-critical project.

Cellular glass insulation is vapor impermeable, watertight, and can be used to create an additional layer of moisture protection in mission-critical roofs.

Provide Redundant Moisture Control in the Roof

The roof of a mission-critical building cannot leak, regardless of the weather. Rain, snow, hail, hurricanes or tornadoes must not breach the water membrane in the roof designed to keep moisture at bay. The costs associated with a roof leaking into a mission-critical interior and potentially compromising the functionality of the space can be exorbitant, which explains why architects on these projects often look to create a redundancy in the roof, in the same way that redundancies in electrical and mechanical systems are incorporated into the overall design of the building. Watertight insulation can be used to provide that additional layer of moisture protection.

As an additional benefit of this extra protective layer, certain insulation materials can outlast the material used as the regular roofing membrane, allowing facilities teams and building owners to extend the life of the roof without risking water exposure. This can be incredibly valuable in areas where the logistics around renovating and reroofing a structure are prohibitive. In congested urban areas, for example, there can be severe restrictions on accessing the pathways and work-staging areas necessary to complete this type of project, which also can increase the cost of the renovation.

Improve Fire Performance of the Building Envelope

There is a dramatic difference in the way that different types of insulation respond to an exposure to fire. Some types of insulation melt. Some ignite, and some remain intact after hours of burning at temperatures over 2,000 degrees Fahrenheit. When a fire propagates vertically and laterally across the exterior of a building, the type of insulation in the exterior wall assembly can play an important role in determining how successfully the envelope resists the spread of fire. Selecting an insulating material that can withstand the incredible heat that these fires produce can protect the other combustible materials in the exterior wall assembly and help minimize the damage that results from the fire, allowing more time for people to escape.

In multistory projects, the fire-containment material that is placed in the space between the floor slab and the curtain wall is referred to as safing. Mineral wool safing (shown here) can dramatically improve the fire performance of the envelope.

Reduce Liability from Acts of Terrorism

In 2002, Congress enacted the Support Anti-Terrorism by Fostering Effective Technologies Act, better known as the Safety Act, which provides broad protections from liability to the manufacturers, sellers, subcontractors, suppliers, and purchasers of products designated by the Department of Homeland Security (DHS) as “qualified antiterrorism technology” if they fail to prevent injuries or damage caused by a terrorist attack.

The Support Anti-Terrorism by Fostering Effective Technologies Act, or the Safety Act, provides broad protections from liability when products are used that have been designated by the Department of Homeland Security (DHS) as “qualified antiterrorism technology.”

Initially, the purpose of this legislation was to encourage the innovation of technology that could be used to help the post-9/11 United States in its antiterrorism efforts by removing the threat of enterprise-crushing liability that could result in the fallout of another terrorist attack. Since then, the application of the law has expanded to offer liability coverage to entities making decisions about how to deploy antiterror technologies that have earned the Safety Act designation. Airports, for instance, are getting coverage on the decision-making process they use to determine which type of antiterrorism measures are warranted and the way in which they are used. Stadiums are getting Safety Act coverage on the safety procedures they employ during games and other large events. Coverage is also being provided to building owners and design firms to protect the architectural teams making design decisions about the level, extent, and type of security deployed and embedded in a facility.

Ray Biagini, a partner at Covington & Burling, conceived of and wrote core provisions for the Safety Act. He explains how Safety Act coverage can support the AEC teams working on the design and construction of mission-critical or potentially high-risk targets: “The purpose of the Safety Act is to limit the risk to people and entities who are making decisions about the type of security that should be deployed against possible terror attacks. This is relevant to the design community because there is potential liability that exists if a building that is either under construction or occupied is attacked. A potential plaintiff may say that there was inadequate security designed into the structure or question the vulnerability of the building, and this train of thought has validity today, as terrorist attacks are now considered foreseeable events by many courts. Architects could obtain Safety Act coverage for the processes, procedures, and protocols they use to determine or recommend the nature and extent of security to be embedded in a facility’s architectural design to insure the way in which they chose the safety and security features to incorporate into a project.”

“With the highest form of Safety Act coverage known as ‘Certification’ coverage, protected parties have the presumption of immunity in a situation deemed a terrorist attack by the DHS. This means that if there is an attack on a building and the design team is sued, the plaintiff will have to prove that the design team acted with fraud or willful disregard in submitting its Safety Act application to DHS. If they cannot do that, the lawsuit will be dismissed, which eliminates the need for insurance companies to respond, prevents a drawn-out litigation process, and saves a considerable amount of time and money.”

Designers can also protect themselves, to some extent, by specifying products that have been deemed by the government to be a qualified antiterrorism technology under the Safety Act. As of August 2019, there were more than 1,000 products and services that had earned the Safety Act designation, including some types of perimeter fire-containment insulation and safing, the fire-stop material placed in the space between the floor slab and curtain wall in a multistory construction. Specifying Safety Act-designated products can also provide some liability protection to the architectural design team in the event of an act of terrorism.

A mineral wool perimeter fire-containment solution (shown here) is available as a Safety Act designated product.

Types of Insulation

There are several types of insulation. However, for this course, we will focus on the benefits of using mineral wool and cellular glass insulation in mission-critical facilities.

Mineral Wool

Mineral wool, also known as stone wool, rock wool, and slag wool, is created by combining basalt rock and slag. Slag is a byproduct of the steel industry that is then repurposed into mineral wool instead of being discarded. The slag content in mineral wool typically ranges from 70–75 percent, resulting in high pre-consumer recycled content. The rock and slag are heated into a lava-like material, spun into fibers, cooled, and cut into rigid board, semi-rigid batts, or loose fill final product. Notably absent from this manufacturing process are blowing agents such as hydrofluorocarbons or HFCs.

The mineral wool manufacturing process melts rock and slag, creating fibers that are cured to form batts, rolls, boards, or loose-fill insulation products.

Energy codes, such as the 2018 International Energy Conservation Code (IECC) or ASHRAE 90.1, define minimum thermal resistance or R-value requirements for the opaque thermal envelope to improve the HVAC efficiency and prevent condensation in buildings constructed today. The R-value of mineral wool is typically around R-4.3 per inch.

The use of mineral wool also supports various tenets of sustainable design. Beyond the impressive amount of recycled content it contains, life-cycle analysis demonstrates that after only one month of use, 1 pound of mineral wool insulation saves the same amount of energy used in its manufacture.

Mineral wool batts or rigid boards can be easily cut with saws or serrated knives to fit snuggly into openings, preventing the passage of fire, or secured to the exterior wall as rigid board continuous insulation.

Cellular Glass

Cellular glass insulation is a lightweight, rigid insulation that is known for its durability, moisture resistance, and the non-toxic elements it contains. The primary ingredients in cellular glass are recycled glass, sand, and other glass batch ingredients, which are combined and then melted. This mixture is ground and mixed with a cellulating agent, then heated again. CO2 is used as the blowing agent, which creates the cellular structure in the material that makes it an insulator.

Cellular glass has a closed-cell structure, which means that the material is filled with cells that are self-contained within their own walls and maintain their own shape. A closed-cell structure offers greater insulation value and better moisture resistance than the alternative open-cell structure, allowing this material to be air and watertight.

Recent innovations in manufacturing have allowed cellular glass to reach an R-value of R-4 per inch, giving it an insulating power that is on par with many of the rigid foam plastic insulations while delivering a superior moisture resistance and compressive strength.

One of the reasons cellular glass offers such an incredible resistance to moisture is the way it is installed. Cellular glass is usually installed by embedding and sealing in a liquid adhesive, such as hot rubberized asphalt, and is then covered with the roof membrane such as a built-up roof (BUR) assembly. Beyond the roof, design teams today are specifying cellular glass into the walls, floors, perimeter, and under slab in a wide variety of commercial and industrial projects.

Cellular glass also supports sustainable design goals in many important ways. It is manufactured using more than 60 percent recycled glass. Beyond the impressive amount of recycled content contained within cellular glass, this inorganic material contains no ozone-depleting propellants, flame retardants, or binders and is free of volatile organic compounds (VOCs). Another green aspect of cellular glass is that zero waste is sent to the landfill during the manufacture of this material.

Matching Insulation Solutions with Mission-Critical Needs

Mission-critical buildings have special needs. They are structures that cannot fail. They have operations that cannot be interrupted. The right insulation can offer the optimal mix of performance characteristics to help safeguard the interior from extreme events, and the typical ones like aging components, leaking, and use. For example, roofs with heavy overburden can benefit from insulation with a high compressive strength, water impermeability, and durability. Insulation selected for exterior walls behind combustible claddings should exhibit superior fire performance and be resistant to incidental moisture in the wall cavity. Let’s take a closer look at the various needs of a mission-critical envelope and the insulating materials that are best equipped to meet them.

High-profile buildings such as One World Trade Center have been constructed using mineral wool perimeter fire-containment system products that are Safety Act designated.

Moisture Resistance

Unfortunately, building materials located within the building envelope will at some point encounter water in the form of either rain, snow, or ice. While some materials are only briefly exposed during construction, others are left to encounter intermittent moisture throughout the life of the building, as is the case for continuous insulation in the exterior wall cavity. Other materials are exposed to more moisture pressure when placed on a horizontal roof surface or below grade.

According to a study of Zurich insurance companies, the number-one insurance claim filed for construction defects is water intrusion. Common moisture management weaknesses in the envelope include rain or groundwater leaking through the roof, walls, windows, or foundation; the infiltration of water vapor through the building envelope during warm, humid weather; or the exfiltration of humidified air from the interior to the exterior in dry winter climates.

These moisture problems can have significant and negative effects on the efficiency, safety, and health of the interior environment. Moisture can degrade the performance of the thermal insulation and even damage the insulation material. It can cause the deterioration and failure of roofing and flooring adhesives and damage wood, brick, concrete, and metal building materials. Damp conditions can also result in the proliferation of molds, mildews, and bacteria, which can threaten the indoor air quality of the interior space. All of these issues can be especially problematic in a mission-critical building that cannot be contaminated or afford the exposure or the downtime to correct them. Selecting an insulation with greater degrees of moisture resistance can help to equip the envelope to perform as needed in these sensitive interiors.

Mineral wool continuous insulation has been engineered to be hydrophobic, which means that it is highly resistant to liquid water absorbing into the surface. However, should the material ever absorb moisture, its resiliency is demonstrated by how quickly it drains and reliably returns to its previous thermal properties.

For environments with heavier moisture exposure such as low-slope roofs, cellular glass is impervious to liquid water due to its closed-cell structure. Because it is watertight, cellular glass, when combined with watertight adhesives, may be installed with the actual roofing membrane to introduce multiple waterproofing layers into the assembly. One advantage to this design redundancy is that when the roof membrane reaches the end of its life or needs to be repaired, the cellular glass insulation, if incorporated into an assembly designed for removal and replacement of the roof membrane, may be left intact and prevent disruption to the critical functions of the building during repair or replacement.

A Note about Vapor Permeability

Vapor permeability describes a material’s ability to allow water vapor to pass through it and it is measured in perms. Perms, roughly, quantifies a rate of vapor diffusion, an amount of moisture that can pass through a barrier in a certain amount of time. The lower the perm value, the better a material is at restricting the movement of water vapor. Materials with very low perm values are considered vapor barriers. The International Building Code (IBC) uses ASTM E96 Method A to categorize materials as vapor retarders. For example, according to the 2018 IBC:

Vapor-Retarder Classification
Class I: 0.1 perm or less
Class II: 0.1 < perm ≤ 1.0 perm
Class III: 1.0 < perm ≤ 10 perm

Vapor-permeable materials are identified as having a minimum permeability of 5 perms per IBC. Materials with a perm rating greater than 10 are considered a permeable material, which means that liquids and vapors easily pass through. Mineral wool continuous insulation is tested around 50 perms depending upon the specific product, indicating that the material has a high vapor permeability and allows a considerable amount of water vapor to pass through it. This creates the opportunity for quite a bit of design flexibility. A vapor barrier could be included on the interior of the wall and mineral wool continuous insulation in the exterior wall cavity would not stop other vapor from escaping; or a vapor barrier could be placed on the exterior sheathing (as the air barrier) and mineral wool would not negatively impact vapor diffusion; or lastly, the entire wall could be constructed without a vapor barrier and mineral wool, with its high vapor permeability, would continue to contribute to vapor diffusion. This ability to fit into multiple wall designs allows for design flexibility when mission-critical buildings need to be adapted for use without concern of trapping vapor.

Because mineral wool does not act as the vapor retarder, a designer has the flexibility of integrating a vapor retarder on the interior wall, exterior wall, or not at all.

On the other hand, cellular glass has a high vapor impermeability, which means it limits the movement of vapor well. Tested at 0 perms per ASTM E96, cellular glass is a Class I solution and an optimal match for applications where there are components that are highly susceptible to moisture damage. Cellular glass can also be used to control humidity levels, which can lead to the downsizing of heating and air-conditioning (HAC) units, as less humidity would need to be removed from (or added to) the indoor air to reach the same comfort levels. This vapor-impermeable quality can create a strong, redundant barrier to moisture vapor in roofs. It also serves as a protective barrier for some vapors aside from just water—although anticipated fumes or other irritants should be analyzed on a case-by case basis to identify a vapor retarder’s ability to prevent their intrusion.

Compressive Strength

The compressive strength of an insulation is the ability to resist an applied load without a specified deflection. Deflection is measured along a graphed curve of deformation of the product related to increase in load and is often reported in percentage of deformation of the total product compared to the load applied. While deflection may occur without failure, the higher the compressive strength, the greater the resistance to a load with less deformation. This resistance to compressive loads is critical in multiple applications throughout the mission-critical building envelope from foundations to walls to roofs.

Many roofs and their components are required to resist surprisingly high loads, including dead loads, live loads, wind loads, soil loads, snow loads, rain loads, flood loads, and even earthquake loads. Dead load is defined by the IBC as the weight of materials of construction incorporated into the building, including but not limited to walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items, and the weight of fixed service equipment, such as cranes, plumbing stacks and electrical feeders, heating, ventilating and air-conditioning systems, and automatic sprinkler systems. Per IBC, a live load is the load produced by the use and occupancy of the building or other structure that does not include construction or environmental loads, such as wind load, snow load, rain load, earthquake load, flood load, or dead load. On roofs, a live load is a load produced:

• during maintenance by workers, equipment, or materials;
• during the life of the structure by movable objects such as planters or other similar small decorative appurtenances that are not occupancy related; or
• by the use and occupancy of the roof, such as for roof gardens or assembly areas.

All of these loads exerted on the roof assembly must be safely resisted and may be more extreme for mission-critical buildings, such as in the case of heavy rooftop units for medical facilities, increased wind loads in hurricane-prone regions, and snow loads for extreme northern climates.

Vegetative and paver roofs have historically been a strategy for long-term roof protection. In these protected membrane assemblies (PRMAs), the waterproofing membrane is buried beneath layers of insulation, drainage assemblies, pavers, and growing media, which serves as protection from sun, freeze-thaw cycling, foot traffic, and water. This requires the insulation, placed above the membrane to be highly moisture resistant while retaining thermal value and exhibiting high compressive strength, as the overburden is often very heavy to combat wind-uplift forces.

XPS insulation is placed above the waterproofing membrane in a protected roof membrane assembly, such as the vegetative roof shown here. This product is required to resist moisture and the loads of overburden.

A traditional and highly successful solution for this application has been extruded polystyrene insulation (XPS), which has the highest compressive strength and resistance to moisture absorption of foam plastic board insulations. Polystyrene insulation is categorized into types based on physical properties such as compressive strength according to ASTM C578: Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation. Type V insulation has the highest compressive strength with a minimum of 100 psi. Generally, this meets or exceeds the needs of basic vegetative roof or paver roof assemblies.

But what if a mission-critical building needs more? Where foam plastics leave off, cellular glass picks up with higher compressive strength and even more moisture resistance as previously discussed. For roofs anticipating even greater weights from vehicular traffic, such as fire-rescue equipment or specialized machinery, cellular glass reaches compressive strengths exceeding 100 psi. Similar to the various types of polystyrene insulations defined by ASTM C578, cellular glass products are classified into grades according to ASTM C552: Standard Specification for Cellular Glass Thermal Insulation. (It should be noted that while the current ASTM C552 standard is used, a new standard is being proposed to differentiate cellular glass used for industrial applications as described in ASTM C552 and for construction applications in the new proposed standard.) Products are organized into grades based upon performance properties. Grade 24 requires the highest tested compressive strength at a minimum of 240 psi. It should be noted that the compressive strength of the product is tested with the waterproofing membrane applied or “capped” on top of the surface for a more accurate representation of the compressive performance.

Its compressive strength allows cellular glass to be used to provide insulation where there was previously no solution, like at the foundation of exterior walls where the insulation is in contact with the continuous below-grade insulation along the foundation or slab edge.

Because cellular glass can withstand loads that crush other materials, this product may be used to provide insulation where there was previously no solution for continuous insulation. An example of this is at the foundation of exterior walls where exterior continuous insulation on the wall would ideally be placed in contact with continuous below-grade insulation along the foundation or slab edge. Unfortunately, the heavy stone or masonry veneer would bear on a masonry ledge and at that location, traditional exterior continuous insulations could not withstand such high compressive loads. However, as mentioned above, cellular glass insulation provides a solution to this conflict between continuous load path and continuous insulation path, eliminating the nagging thermal bridge at many exterior foundations. For mission-critical walls, this potentially ensures more energy efficiency and less risk of moisture or condensation at this thermal-bridge location.

Compressive strength can also provide a very different opportunity for mission-critical buildings when used for exterior wall applications. The IBC defines continuous insulation as an insulating material that is continuous across all structural members without thermal bridges other than fasteners and service openings installed on the interior or exterior, or as integral to any opaque surface of the building envelope. Over the past decade, ASHRAE 90.1 and the IECC have begun to require continuous insulation across most building envelopes. As more rigid insulation was placed into the exterior wall cavity where continuity was easier to achieve with less structural and other building component obstacles, more focus has been placed on cladding attachment systems that continue to reduce the penetrations, or thermal bridging, through the continuous insulation.

This has evolved into applications whereby the cladding attachment system is fastened outside of the continuous insulation, completely in the exterior wall cavity, with only screws or fasteners penetrating the actual continuous insulation to return back to the structural stud system. This application, however, relies upon insulation materials that exhibit high compressive strength. Some mineral wool continuous insulation products have been engineered to retain such high compressive strength as to support this type of cladding attachment while retaining the other attributes and benefits of mineral wool. The fire properties of mineral wool allow combustible claddings to be adhered to mission-critical buildings.

Fire Performance

Be it a mission-critical or average building, fire is one of the most planned for threats to a building. A three-pronged approach is usually employed to offer occupants the greatest opportunity to get to safety and minimize potential fire damage. These strategies include a detection system, an active suppression system, and passive fire-containment measures. The detection system alerts occupants and authorities to the presence of a fire and helps facilitate an urgent, safe evacuation. An active suppression system is also triggered by the presence of fire or smoke. Sprinklers are a common example of an active suppression system.

As an important redundancy, buildings also incorporate passive fire-containment measures that do not require a trigger to activate in the instance of a fire. If the passive fire systems are designed and installed properly, fire and smoke may be contained or slowed, allowing occupants crucial time for escape. Some insulation products work with other components to create passive fire containment assemblies.

Mineral wool insulation can be used as part of the curtain-wall assembly to create perimeter fire containment at floor line and roof locations. One of the most complex and least understood areas where a fire can propagate is at the exterior of the building, where a non-rated curtain wall bypasses a rated floor assembly. If a void exists between the non-rated exterior wall and the rated floor assembly, the IBC requires that designers extend the rating of the floor slab out to that exterior wall. This is accomplished by putting a system in the joint that has been tested to ASTM E2307: Standard Test Method for Determining Fire Resistance of Perimeter Fire Barrier Systems and rated to stay in place for the same length of time as the floor assembly. The reliable fire performance of specially engineered mineral wool is a leading material to create these perimeter fire-containment systems that will prevent or retard the spread of fire and hot gases through the opening.

The time versus temperature curve found in ASTM E119 indicates the response of multiple materials to fire exposure over time based upon years of testing and research.

ASTM E2307 is just one of several fire-assembly tests to indicate performance in the presence of fire. For mission-critical buildings, several factors like occupancy, building contents, or location increase the likelihood of fire-rated exterior walls or roofs being required. ASTM E119: Standard Test Methods for Fire Tests of Building Construction and Materials is referenced by IBC to meet these requirements. The test exposes a wall or roof assembly specimen to a standard controlled burner that achieves specified temperatures throughout a specified time period and evaluates the duration for which an assembly can contain the fire and retain its structural integrity. Results are plotted along a time/temperature curve.

Through decades of testing and fire science, the ASTM E119 time and temperature curve has become well-known as an indicator of fire behavior in materials. Of note is that a significant proportion of standard building materials present in wall and roof assemblies are compromised within the first hour of fire exposure. This includes common materials like foam plastics, glass fiber, zinc, aluminum, and glass. Yet these materials can be included in hourly rated systems. This is an example of where the system is greater than the individual parts. It is how these materials work together that matters most.

This highlights the need for taking a deeper look at the details. For example, gypsum sheathing is introduced into many wall assemblies as a means of providing a thermal barrier for more combustible products. Mineral wool insulation has also been identified as a thermal barrier for these applications and can be a particular problem solver for mission-critical buildings where other materials are not desirable or reasonable. Notice on the previously mentioned curve, mineral wool can potentially withstand fire exposure for hours.

Unfortunately, designing the envelope of a building to limit the spread and growth of fire is more complicated than simply choosing an insulation with good fire performance. In fact, it is not even as simple as meeting a single fire-assembly test requirement. The IBC requires buildings of Types I–IV construction (mission-critical buildings often falling into Types I or II) to have noncombustible construction. However, exterior walls subsequently are wrapped in multiple combustible materials, such as air and water barriers, combustible claddings, and possibly insulations.

The NFPA 285 testing procedure exposes a wall assembly to fire on a lower level and measures vertical and lateral propagation of the fire across the wall.

In order to help designers create building envelopes that control the spread of fire, a standard was developed to test the fire propagation of exterior wall assemblies. This standard is the National Fire Protection Agency (NFPA) 285: Standard Fire Test method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies Containing Combustible Components. NFPA 285 measures what happens during a fire when a noncombustible building is wrapped in combustible materials. In order to pass NFPA 285, the wall assembly must resist flame propagation over the exterior face of the system, the combustible core or components in the panel must resist vertical flame from one story to the next, the interior (room side) surface of the panels must resist the vertical spread of flame from one story to the next, and the assembly must resist the lateral spread of flame from the compartment of fire origin to adjacent spaces.

Based on decades of research, similar to ASTM E119, general conclusions have been drawn about combining common materials to pass NFPA 285. For example, noncombustible claddings such as masonry veneer, stone veneer, and concrete may be combined with combustible insulations like most foam plastic continuous insulation as well as noncombustible insulations like mineral wool continuous insulation. However, when the cladding is combustible, such as aluminum composite material panels, hollow terra cotta panels, high-pressure laminate panels, or other metal composite material panels, designers must select a noncombustible insulation or very carefully design with specially engineered materials to provide thermal protection.

A Qualified Antiterrorism Technology

Many mission-critical facilities are considered higher-risk targets for acts of terrorism. Designers working on these types of projects can garner valuable liability protection for themselves and building owners by selecting products and delivering services that have earned the Safety Act designation from the DHS.

Due in part to the extraordinary fire performance demonstrated by some mineral wool products, this material has earned the Safety Act designation from the DHS. This means that incorporating the mineral wool products that have been deemed a “qualified antiterrorism technology” will extend a level of protection to the design team and building owners from claims implicating these products resulting from an act of terrorism.

There are a number of considerations incorporated into the review of a potential Safety Act product. One is demonstrated use and efficacy through sales or use by commercial or government customers. Four of the five tallest buildings in North America incorporated specific mineral wool products for fire protection into their envelope, and the fire performance of the material has been exhaustively tested in stand-alone and exterior assembly applications.

Additionally, the liability protections granted by earning the Safety Act designation can be retroactive, meaning design teams or building owners using these mineral wool products may have a level of protection on projects they worked on in the past if their security procedures/products are substantially similar to those covered under the SAFETY Act.

It is important to note that the Safety Act designation is product specific, not material specific. For more information about the specific types of mineral wool that have been recognized by the DHS as a qualified antiterrorism technology and offer this broad liability protection, please refer to www.safetyact.gov or contact the manufacturers of mineral wool directly.

Conclusion

In conclusion, insulation plays a powerful role in creating a design that meets the nuanced performance needs of a mission-critical project. Selecting materials that protect against moisture ingress and enhance the fire-containment abilities of the envelope equips these facilities to continue their important work without interruption, even when the extreme happens. Of the many types of insulation currently on the market, cellular glass can offer design teams an extra waterproof layer to create the redundancy that is commonplace inside a mission-critical building in the roof and compressive strength available that cannot be matched by other rigid board boards. Mineral wool offers an unparalleled performance when exposed to fire and allows designers the freedom to use the types of combustible cladding that have been gaining popularity, without sacrificing code compliance or safety. In short, selecting the right insulation for a project can help to fortify the envelope of a building against environmental elements, which is especially important when the mission inside the envelope is critical.

Jeanette Fitzgerald Pitts has written nearly 100 continuing education courses exploring the benefits of incorporating new building products, systems, and processes into project design and development.