Tag Archives: insulation

Using Temperature to Control Condensation in Cold Climates

Photo © BigStockPhoto/Pavel Losevsky

Photo © BigStockPhoto/Pavel Losevsky

by Daniel Tempas

Designers have been concerned about condensation in walls for decades. Since the mid-1970s, the greater amounts of insulation specified in the building envelope has increased the likelihood for condensation somewhere in the assembly. Many articles have been written over the years describing the physics of the problem and, for the vast majority of the time, there has been a laser-like focus on one solution.

Initially, water vapor diffusion was seen as the likely culprit for condensation problems and designers and consultants spent hours running and analyzing wall assemblies using the ‘profile’ (or ‘dewpoint’) method (Figure 1). With such analyses came the concept the wall system should be tuned for maximum condensation resistance by altering or selecting the appropriate permeability of the wall components.

The rule of thumb became to place low-permeability materials/retarders on the wall’s warm side, and higher permeability materials on the cold side (Figure 2). In this fashion, the designer strove to make it difficult for water vapor to enter the wall (lessening water’s ability to condense in the wall) and easy for water vapor to leave the wall (drying out any water that still managed to get inside). Manufacturers began to introduce high-permeability air barriers, water barriers, and sheathings along with ‘smart’ vapor retarders for the warm side of the wall.

This low-perm/high-perm strategy reveals two goals in wall design: the efforts to decrease condensation potential and increase drying potential. Reducing condensation potential is fairly well-understood but increasing drying potential is a less commonly sought after goal. Both are important for robust wall design.

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Problems with permeability
While all this sounds good, it was not necessarily preventing condensation problems. There are some basic facts about permeability designers need to understand to get a better grasp on not only controlling condensation, but general wall design.

Fact 1: If a material’s temperature gets low enough, water vapor will condense on or in it, regardless of how high its permeability.
This is something to keep in mind in cold climates. This author has seen both fiberglass batts and high-perm air barriers with ice encrusted on their surfaces. When a material gets cold, its effective permeability dramatically drops. High permeability is useless at low temperatures. In other words, condensation is a temperature-related phenomenon.

Fact 2: Cold water dries slower than warm water, no matter how permeable the shell surrounding it.
Increasing a wall assembly’s drying potential is an important and valuable goal. However, water at lower temperatures will take a long time to dry because the related evaporation rate is slow. Simply put, robust drying potential cannot be achieved in the layers of a wall assembly that are at low temperatures.

For example, one can consider a puddle on a sidewalk (Figure 3). How long does it take that puddle to dry? If the ambient temperature is 32 C (90 F), it will not take long at all, perhaps only several minutes. However, when the ambient temperature is only 4 C (40 F), the puddle might take hours or even days to evaporate. This is an example of the profound effect temperature has on evaporation rate.

Fact 3: Air movement transports far more water vapor than diffusion.
This is something that has been understood by building scientists for quite some time, and has been filtering into the design community for decades. However, the subtle ramifications of this knowledge are just now finding their way into the world at large. The fact air movement is so dominant in water vapor transport (and subsequent condensation) means any vapor retarder must work either as, or in conjunction with, a near perfect air barrier.

Any installation flaw or penetration in the air/vapor barrier on the higher temperature side will result in an amount of air leakage that will overwhelm any planned benefit from that barrier’s diffusion characteristics. This will result in a much greater potential for condensation in or on any layer that is at a low enough temperature for condensation to occur. Additionally, this means diffusion-based analyses of the wall system are rendered moot.

Fact 4: Water vapor does not move from areas of higher temperature to lower temperature.
Thinking this is the only direction water vapor flows is incorrect. Water vapor moves from areas of high concentration to low concentration, regardless of the direction of heat flow. This is an important concept when it comes to understanding drying verses condensation.

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Temperature to the rescue
After considering these four facts regarding water physics, it would seem there is a great deal of confusion and trouble regarding wall design. The manipulation of material water vapor permeabilities in a wall design cannot achieve a truly robust assembly. What can be done?

‘Temperature’ is the common thread running through the facts regarding water vapor condensation in wall assemblies. A wall assembly’s temperature profile plays a critical role in the ability to resist condensation and promote drying. This is not an unknown concept, of course—a quick search of building science literature will yield the occasional article mentioning the importance of the temperature profile. The problem is temperature profile manipulation is far down the list of the wall designer’s methods for creating a more robust wall. It is seen as unimportant when in reality, it is the opposite.

As much of the wall insulation as possible should be placed on the outbound side of the assembly (Figure 3). This is easy to do whether the base wall is metal stud, concrete masonry unit (CMU), or poured concrete. In cold-weather conditions, this will warm the entire interior wall, changing the temperature profile with far-reaching consequences (Figure 4).

For example, designing a wall assembly so more of the components will be in the higher temperature portion of the wall profile significantly reduces the potential for condensation. Not every part of a wall is equally sensitive to exposure to moisture. A standard rainscreen veneer wall assembly (Figure 5) is not sensitive to water, as it must be exposed to the elements on a constant basis. The support elements for the veneer are also not sensitive to water—they are in the drainage space behind the veneer and quite a bit of water reaches that space. As for the insulation layer on which the supports rest, it too must be moisture-resistant for the same reason. If condensation can be forced to happen only around components immune to water, then the wall design is completely robust in its resistance.

Designing a wall assembly so more of the components will be in the higher temperature portion of the wall temperature profile also significantly increases the drying potential for any water that does find its way into the wall. Referring back to the puddle example, higher temperatures means much higher drying rates. Combine the greater drying temperature with the longer drying time and one has a wall with a drying potential increased by an order of magnitude or more.

The importance of temperature modification to improve walls systems can be better understood when considering that both condensation and drying are two-step processes (Figure 6):

  • movement of water vapor to or from the point of condensation or drying; and
  • actual phase change of water from the vapor phase to the liquid phase (condensation), or vice versa (drying).

No matter how rapidly water vapor is transported to a given location in a wall assembly, either by the slow process of diffusion or the rapid process of air infiltration, condensation will not take place if the temperature of that location is high enough. This is also true in the drying process. No matter how easy it is for water vapor to exit a given location in a wall assembly, either by the slow process of diffusion or the rapid process of air infiltration, drying will not take place when the temperature of that location is too low. Again, temperature plays a critical role in the condensation and drying processes in a wall assembly. Altering the temperature profile of a wall assembly through judicious placement of materials is an effective method to control these processes.

The aforementioned Fact 4 about the true nature of the movement of water vapor makes it clear even when the exterior sheathing/insulation is completely impermeable, the drying potential of this wall is much greater than the previous design and the condensation potential is much lower. Since it is at a temperature near to that of the interior, any water in the stud cavity will have a much higher evaporation rate, which means a much higher drying rate. Also, it will easily dry to the building interior.

Proper placement of the right insulation negates the need for a vapor retarder. Why worry about water vapor getting into the wall when most of it is at a temperature far too high for condensation to take place? If the insulation has been well-chosen, any condensation taking place toward the exterior of the building will be minute and meaningless. Besides, the stud cavity needs to dry to the interior, and an interior vapor retarder will only get in the way.

The overall robustness one gains from placing most wall components in the highest temperature part of the temperature profile overwhelms almost every other condensation/drying consideration in the wall design.

Using the temperature profile of a wall as part of the design process leads to a wall that is easier to build. Relying on permeability (to alter water vapor diffusion rates) in the design process for a wall assembly results in a dependency not only on material properties, but also on the quality of installation.

A critical part of any vapor retarder (or air barrier) is its continuity. Any flaw in the installation process of that air/vapor retarder that results in breaches of its continuity heavily compromises its ability to reduce condensation potential. This would include unrepaired construction damage or poorly sealed seams. Even normal penetrations in the wall assembly, like outlets and switches, present opportunities for discontinuity in the air barrier/vapor retarder.

On the other hand, manipulation of the temperature profile of a wall assembly is only about positioning the right amount of insulation in the right location in the wall. A board of insulation is far more robust that film of plastic, making insulation continuity far easier to achieve. Also, the outside of the wall typically has far fewer penetrations, making them far easier to handle.

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Conclusion
Designing wall assemblies by adding or altering the permeabilities of the wall components is an artifact of the limited analysis tools relying on investigation of water vapor movement via diffusion. Such walls gain only mild improvements in condensation resistance and, more importantly, drying potential. To create a truly robust wall system with the greatest condensation resistance and drying potential, designers must look at altering the temperature profile of the wall assembly by moving insulation as far as possible to the wall’s exterior.

This does not mean one should no longer think about, or design with, the permeability of materials in mind, of course. Rather, it means the water permeability analysis/profile part of design efforts should be relegated to the proper place in the design consideration hierarchy: behind the wall temperature profile design effort.

Daniel Tempas is a building envelope technical service representative for Dow Building Solutions; he has held technical and engineering positions at the Dow Chemical Company for almost 30 years. Tempas is a (HERS) rater, a Leadership in Energy and Environmental Design (LEED) Green Associate, and a member of the RESNET Training Committee. He has also been a member of ASTM, Exterior Insulation and Finishing Systems Industry Members Association (EIMA), and Building Thermal Envelope Coordinating Council (BTECC). Tempas can be reached atdtemp@dow.com.

Concern regarding long-term insulation data

The December 2013 issue of The Construction Specifier included the article, “Out of Sight, Not Out of Mind,by Ram Mayilvahanan. The feature focused on expanded polystyrene (EPS) and included reference to a particular industry study. In response to the piece, we recently received the following e-mail from John Ferraro, executive director of the Extruded Polystyrene Foam Association (XPSA):

This article included conclusions on the long-term thermal performance of XPS in below-grade applications contrary to more broadly evaluated and accepted industry data. It references a 2009 evaluation published by the EPS Industry Alliance (IA) industry trade organization, then known as EPSMA, and since republished in many forms by EPS-IA members.

In our opinion, the results of this EPS evaluation, which in essence rely on one data point, are not well-supported and are inconsistent with previous significant research conducted in this field. This EPS evaluation also was not independently peer-reviewed within the industry. The data used was reportedly the result of tests conducted by the same test lab and at the same test site, which were apparently employed in two prior studies: Society of the Plastics Industry’s (SPI’s) 1994 report, “Expanded Polystyrene Thermal Insulation Performance in a Below-grade Application” (Twin City Testing Corp.) and AFM Corp.’s 1996 report, “Thermal Transmission and Moisture Content Analyses Conducted on Buried EPS Perform Guard Insulation” (Maxim Technologies/Twin City Testing). There are unanswered questions surrounding the data reliability from these previous analyses that may also carry forward into the EPS evaluation.

The long-term thermal performance of below-grade foundation insulation is an important building design consideration that directly impacts building comfort and energy conservation. We want to draw your attention to a more comprehensive and objective review of the long-term thermal performance of polystyrene foam insulation in below-grade applications that was conducted by the American Society of Civil Engineers (ASCE) 32 Committee during its revisions to ASCE 32-01, Design and Construction of Frost-protected Shallow Foundations.

This committee’s work was documented in the technical paper, “Below-ground Performance of Rigid Polystyrene Foam Insulation: Review of Effective Thermal Resistivity Values Used in ASCE Standard 32-01, Design and Construction of Frost-Protected Shallow Foundations,” which was published in the Journal of Cold Regions Engineering in June 2010.

Based on this critical review of frost-protected shallow foundation designs, the ASCE committee recommends for below-grade vertical orientation (i.e. exterior of walls) using effective in-service design R-value equal to:
● 90 percent of the ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, R-value for XPS; or
● 80 percent of the ASTM C578 R-value for EPS because of the potential for water absorption.

The ASCE committee also recommends for below-grade horizontal orientation (i.e. under concrete slabs) using effective in-serve design R-values equal to:
● 80 percent of the ASTM C578 R-value for XPS; or
● 65 to 67 percent of the ASTM C578 R-value for EPS because of the potential for water absorption.

We believe it is very important to provide your readership and the industry with objective and accurate information to support and facilitate informed choices in building design. By reporting data from a single, non-peer-reviewed, narrow-scope study and ignoring the vast amount of research and experience, this article does not serve the best interest of the industry.

Designing Plaza Hardscapes: Considerations from insulation and waterproofing to structural support

All images courtesy Raths, Raths & Johnson

All images courtesy Raths, Raths & Johnson

By Kurt R. Hoigard, PE, SECB, FASTM, and Brian T. Lammert, SE, PE, CDT

Outdoor plazas provide open spaces that break up the massing of neighboring buildings and provide a respite from busy schedules. In urban environments, they are frequently constructed over underlying occupied spaces used for parking, storage, conference rooms, and classrooms. Landscape treatments typically include planters, trees, and paving of various types for pedestrian and/or vehicular traffic. The resulting construction is a complex sandwich of materials ranging from the landscape and hardscape components visible at the surface to the structural elements keeping the plaza from falling into the occupied space below.

The materials and components used in plaza construction over occupied space are needed to provide thermal resistance, water management, structural capacity, a durable wearing surface, and an attractive finished appearance. Designers select product characteristics to fulfill these functions, typically relying on technical data and recommendations from product manufacturers.

An example of split-slab construction including components to distribute surface loads, provide thermal insulation, manage water, and protect interior space from water ingress.

An example of split-slab construction including components to distribute surface loads, provide thermal insulation, manage water, and protect interior space from water ingress.

The authors have found the available published manufacturer technical data is inadequate for designing plazas to which heavy loads will be applied. When not properly accounted for in the plaza design, the interaction of the various materials and components can result in unplanned movement and damage to the exposed hardscape materials. Plaza damage investigated by the authors attributed to hardscape/substrate stiffness interaction include concrete topping slab cracking, paver cracking, paver edge raveling, and paver joint deterioration.

Supporting actors in compression
Figure 1 depicts some of the products frequently used in plaza construction. These include:

  • extruded polystyrene (XPS) foam board insulation for thermal resistance or adjusting finished elevations;
  • waterproofing membrane and protection course applied to an underlying concrete structural slab to keep water out of the occupied space below;
  • composite drainage and air layers providing flow channels for water drainage; and
  • hardscape paving materials such as concrete topping slabs and unitized pavers of brick, concrete, or stone.

There is a common misconception that plaza hardscape materials, whether monolithic (e.g. cast-in-place concrete) or modular (e.g. concrete, stone, or brick pavers), simply ‘sit’ on the underlying materials and do not ‘move.’ However, in reality, most supporting materials can compress somewhat. Loads applied at the hardscape surface are transmitted into the supporting materials, creating compressive stresses that in turn cause the material to locally shorten like a spring.

Anyone who has ever stood on a bed has encountered this phenomenon—feet sink down as the mattress springs compress, as shown in Figure 2. The heavier the person, the deeper his or her feet sink into the mattress since the springs compress more. In plaza hardscape construction, compressible materials that can behave like the springs in the mattress analogy include the XPS, waterproofing membrane, drainage mat, and protection course. Each of these materials can be defined by, among other things, a unique ‘springiness,’ more technically known as compressive stiffness.

The downward displacement of a mattress resulting from a person’s weight is related to the mattress springiness—more technically known as compressive stiffness. This weight is distributed to only a few springs because the mattress does not include a stiff surface element to laterally distribute the weight.

The downward displacement of a mattress resulting from a person’s weight is related to the mattress springiness—more technically known as compressive stiffness. This weight is distributed to only a few springs because the mattress does not include a stiff surface element to laterally distribute the weight.

The addition of a 6.4-mm (¼-in.) thick plywood sheet on the top surface of a mattress laterally distributes the person’s weight. The plywood sheet and mattress are analogous to a plaza hardscape material such as a concrete topping slab and the underlying support.

The addition of a 6.4-mm (¼-in.) thick plywood sheet on the top surface of a mattress laterally distributes the person’s weight. The plywood sheet and mattress are analogous to a plaza hardscape material such as a concrete topping slab and the underlying support.

 

 

 

 

 

 

 

 

 

 

Returning to the ‘standing on the bed’ analogy, the surface of the mattress that sinks down the most is directly under the feet, since those springs directly beneath are the ones carrying the person’s weight. Most of the mattress surface was unchanged, though, because the fabric enclosing the top of the mattress is flexible and cannot help spread the weight out onto other adjacent springs.

If this experiment was modified by first placing a sheet of 6.4-mm (1/4-in.) plywood on the bed, and then the subject stood on the plywood, the behavior would be changed. The mattress springs directly under the person’s feet would still be compressed the most, but some of the adjacent springs would also be compressed and the plywood would bend as it spread the load to the adjacent springs (Figure 3).

Depending on the weight of the person standing on the bed, the plywood might or might not crack due to the induced bending stresses. Cracking would depend on whether the bending stress exceeded the plywood’s flexural strength. In this case, the plywood is analogous to plaza hardscape materials such as concrete topping slabs and mortar setting beds for unitized pavers. The ability of a material to spread load out to supporting materials not directly under the load application point is related to flexural stiffness, which is, in turn, related to the material configuration, including thickness and the position, type, and size of any reinforcement present.

Multiple materials and manufacturers
The various components used below the hardscape surface of a plaza are in many cases manufactured by multiple entities, each with published product-specific properties. For example, XPS insulation types are described in ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, which includes product requirements such as minimum compressive strength and density.

Graph showing results of compression testing performed on a dimple-type drainage composite, 50-mm (2-in.) thick extruded polystyrene (XPS) insulation, and assembly incorporating both components. The slope of each graph line is equal to the compressive stiffness. The assembly test (red line) compressive stiffness is significantly less than the dimple-type drainage composite (blue line) or XPS insulation (green line) individual component compressive stiffness.

Graph showing results of compression testing performed on a dimple-type drainage composite, 50-mm (2-in.) thick extruded polystyrene (XPS) insulation, and assembly incorporating both components. The slope of each graph line is equal to the compressive stiffness. The assembly test (red line) compressive stiffness is significantly less than the dimple-type drainage composite (blue line) or XPS insulation (green line) individual component compressive stiffness.

XPS insulation used in plaza construction includes, but is not limited to, Types VI, VII, and V, with minimum compressive strengths of 275, 415, and 690 kPa (40, 60, and 100 psi), respectively. The compressive strength is based on material uniformly loaded according to the procedure in ASTM D1621, Standard Test Method for Compressive Properties of Rigid Cellular Plastics. Similar to the XPS insulation, drainage composites will have a compressive strength value included on a manufacturer data sheet based upon uniform load testing according to the procedure in ASTM D1621. These compressive strength values represent individual material properties.

Compressive stiffness values for XPS insulation are also typically available through the manufacturer and, similar to the compressive strength, are based on uniform loading. Stiffness values are typically larger for higher compressive strength material (i.e. Type V XPS is stiffer than Type VI XPS) and decrease as the material thickness is increased (i.e. 25-mm [1-in.] thick XPS is stiffer than 50-mm [2-in.] thick material). Limited data is available on the stiffness of the other components previously described, including drainage/air composites, waterproofing membranes, and protection courses.

Designing for durability
The success or failure of a plaza hardscape installation hinges on many things, one of which is the durability of the finish materials. Cracking, spalling, and joint deterioration mar the plaza appearance and are generally considered unacceptable outcomes.

The authors have found hardscape/substrate interactions governed by compressive and flexural stiffness are often at the root of these types of problems. Avoiding them requires understanding the behavior of not only the individual component materials, but also the resultant assembly. The authors have found the industry literature lacking in this regard. To fill in some of the data gaps, the authors undertook a laboratory test program to evaluate representative plaza materials and assemblies for compressive strength and stiffness.

The authors tested hot-applied rubberized asphalt waterproofing membrane applied to concrete slabs, the membrane manufacturer’s approved protection course, weave-type and dimple-type drainage composites, and Type VII 50-mm (2-in.) XPS insulation board. Each material was subjected to compression testing, with load and deflections recorded using a computerized data acquisition system. Assemblies constructed from the tested materials were then subjected to the same tests, allowing material versus assembly behavior comparisons. Some of the resulting comparisons were quite surprising, with the measured strength and stiffness of the assemblies much lower than would be predicted by the individual material tests.

An example of compressive stiffness and strength reduction due to component interaction is demonstrated by tests performed on dimple-type drainage composite and Type VII 50-mm thick XPS insulation board. The following compressive stiffness values were determined for these components when loaded individually:

  • 676 kPa/mm (2490 pounds per cubic inch [pci]) for the drainage layer; and
  • 638 kPa/mm (2350 pci) for the XPS board.

These stiffness values represent a ratio of the uniform surface load in kPa to the vertical compression displacement in millimeters. Stacking the insulation and drainage layer, as would be expected in a plaza system, is similar to placing two springs end-to-end, assuming the load is distributed uniformly between components. The stiffness of these two components when stacked together as an assembly can be theoretically calculated to be 328 kPa/mm (1210 pci). However, testing performed on drainage composite and insulation assemblies resulted, on average, in a compressive stiffness of only 128 kPa/mm (470 pci)—a 61 percent reduction from the theoretical value.

The relationship between load and displacement for this test series is shown in Figure 4, where the slope of each line on the graph is equal to the compressive stiffness. The stiffness reduction between theoretical and tested is caused by partial contact between the insulation and drainage composite, resulting in increased localized stresses in the insulation. Testing of other assemblies confirmed this same concept applied at the interface between other plaza system components, such as drainage composites and waterproofing membrane with or without a protection course.

XPS board insulation after compression testing of an assembly incorporating dimple-type (left) and weave-type (right) drainage composite. The insulation surface indentations demonstrate the uneven distribution of load at this interface.

XPS board insulation after compression testing of an assembly incorporating dimple-type (left) and weave-type (right) drainage composite. The insulation surface indentations demonstrate the uneven distribution of load at this interface.

The tests also revealed localized crushing failure of the XPS board at load levels well below the advertised material compressive strength. The reduced contact area at the high points of the drainage mat change the behavior of the assembly from the uniform bearing condition assumed by ASTM D1621 to a series of smaller load points with open space in between—at least initially.

With increased load, the drainage mat high points pushed into the XPS until it conformed to the drainage mat surface undulations, as shown in Figure 5. Beyond the obvious effect on assembly compressive stiffness, crushing of insulation can result in a reduction of drainage/air composite capacity due to intrusion into the flow channels.

Assessing configurations
All the foregoing discussion about plaza component and assembly behavior under compression loading provides the background on which realistic design-phase assessment of proposed configurations can be performed. This is particularly important when heavy loads will be present either early (i.e. during construction and landscaping activities) or later (i.e. from planned vehicular traffic, maintenance equipment, or emergency response vehicles).

Overestimating the strength and stiffness of a plaza assembly can have serious consequences. Insufficient supporting material compressive stiffness can cause concrete topping slabs, pavers, and paver setting beds to crack due to larger than anticipated flexural stresses, as shown in Figure 6, and paver edge raveling and mortar joint crushing, as shown in Figure 7. These problems can be avoided by evaluating the entire plaza assembly, and not just focusing on the properties of individual components.

Flexural stress levels in concrete topping slabs, pavers, and paver setting beds that may be subjected to heavy loads should be evaluated taking into consideration not only the strength and stiffness characteristics of the hardscape materials to which the loads will be directly applied, but also those of the supporting materials. Without accurate component and assembly strength and load/deflection performance data available to incorporate into plaza design calculations, project-specific testing should be considered.

Designers can use the test results to evaluate the anticipated behavior of a proposed plaza design using analytical techniques such as finite element modeling to quantify anticipated displacements and associated stress levels. If unacceptable levels of cracking are analytically predicted, the design should be revised.

Exaggerated deflection of topping slab subjected to vehicular loading with flexible plaza assembly represented by blue layer with springs. If not properly evaluated, the interaction between the concrete topping slab and supporting assembly can result in unsightly topping slab flexural cracks, shown in red.

Exaggerated deflection of topping slab subjected to vehicular loading with flexible plaza assembly represented by blue layer with springs. If not properly evaluated, the interaction between the concrete topping slab and supporting assembly can result in unsightly topping slab flexural cracks, shown in red.

Exaggerated deflection of pavers subjected to vehicular loading with plaza flexible assembly represented by blue layer with springs. If not correctly evaluated, the interaction between each paver and supporting assembly can result in paver edge raveling (shown above), paver flexural cracking, or mortar crushing.

Exaggerated deflection of pavers subjected to vehicular loading with plaza flexible assembly represented by blue layer with springs. If not correctly evaluated, the interaction between each paver and supporting assembly can result in paver edge raveling (shown above), paver flexural cracking, or mortar crushing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Possible design modifications include:

  1. Increase topping slab, mortar bed, and paver thickness when project constraints allow, thereby spreading surface loads over a wider area and increasing the flexural resistance. A trade-off exists with this approach in that the underlying structure, which may be a parking garage or the basement level of a building, may not be capable of supporting added dead load from thicker materials.
  2. Add reinforcement to topping slabs and mortar beds to control cracking. Care must be taken with this approach since reinforcement can control, but not eliminate, cracking.
  3. Modify component selections below the hardscape materials to increase the support stiffness, such as selecting a different insulation board material with a higher compressive stiffness.
  4. Consider adding bollards to preclude vehicular access to particularly problematic areas.

Conclusion
As is true with any design exercise, the key to avoiding plaza hardscape/substrate interaction problems is to be able to answer four key questions:

  1. What are the loads that are likely to be applied to the plaza?
  2. What path will the loads follow from the point of application to the underlying structural support?
  3. What materials will be incorporated into the design?
  4. What are the strength and load/deformation behaviors of the proposed hardscape and underlying support, drainage, and waterproofing materials?

Answering these questions will go a long way toward developing a successful plaza hardscape design.

Kurt R. Hoigard, PE, SECB, FASTM, specializes in evaluation and repair of distressed buildings and structures. Since joining Raths, Raths & Johnson in 1985, his experience has encompassed preconstruction consulting, implementation of construction-phase quality assurance programs, investigation of water leakage, deterioration and complete collapse, and repair design. Hoigard has received numerous awards from the American Institute of Steel Construction (AISC), International Masonry Institute (IMI), and ASTM International. His memberships include the American Architectural Manufacturers Association (AAMA), American Concrete Institute (ACI), International Code Council (ICC), and Structural Engineering Institute (SEI). Hoigard can be reached at krhoigard@rrj.com.

Brian T. Lammert, SE, PE, CDT, specializes in field investigation, lab and field testing, structural analysis, collapse investigation, peer review of new construction, and repair design and implementation. Since joining Raths, Raths & Johnson in 2005, he has directed load tests to evaluate distressed structures, component suitability for new construction, and failure causation. Lammert’s structural analysis experience includes development of computer models used for failure analysis, structural design peer review, existing structure evaluation, and repair design. He can be contacted via e-mail at btlammert@rrj.com.

 

 

Making Sense of Sprayed Polyurethane Foam

All photos courtesy Spray Foam Coalition

All photos courtesy Spray Foam Coalition

 

by Peter Davis

For decades, the U.S. design and construction industry has turned to sprayed polyurethane foam (SPF) to insulate and air seal buildings. SPF can help provide temperature control in various climates, reduce sounds transmitted through the air, and lower construction costs.

When employed as a roofing material, SPF’s monolithic nature allows for a seamless, self-flashing application that can keep out water. It can also improve energy efficiency through its superior insulating and air barrier qualities, helping building owners and general contractors comply with energy codes and meet performance requirements for green building programs and certifications.

As the use of SPF grows, the industry is working to provide answers so architects, engineers, and construction professionals can be confident when specifying SPF insulation or roofing to achieve energy-saving or sound-dampening.

Types of SPF
SPF insulation can be categorized into three main types:

  • low-density, open-cell;
  • medium-density, closed-cell; and
  • high-density, closed-cell.

The molecular structure of the polyurethane cells in the foam produced determines whether SPF is classified as open- or closed-cell. Each type has certain characteristics determining the applications for which it is most appropriate.

Open-cell SPF
Also known as 1/2-pound SPF, which refers to the density of one cubic foot of the product, open-cell SPF is best suited for applications such as ceilings, interior walls, floors, and the underside of roof decks. As a low-density product, this type uses water as the blowing agent. When the foam forms, the water reacts with other chemicals to produce carbon dioxide (CO2), which expands the cells to form semi-rigid porous polymer foam. The CO2 leaves the cells and is replaced with air, hardening the foam.

Spray polyurethane foam (SPF) is a spray-applied material widely used to insulate buildings.

Spray polyurethane foam (SPF) is widely used to insulate buildings.

Closed-cell SPF
Closed-cell SPF, also known as 2-pound foam, is formed by using a blowing agent instead of water. The agent is retained in the closed cells, making the foam rigid and providing exceptional compressive strength. Closed-cell SPF can be further classified into two types: medium- and high-density. The former can be used to insulate:

  • exterior and interior walls;
  • ceilings;
  • floors;
  • slabs and foundation; and
  • the underside of roof decks.

High-density foam is used primarily in flat or low-slope roofing applications, since its density and rigidity lends itself best to this purpose.

Quality installation
One of the most important considerations for architects and builders is selecting a professional contractor to install SPF. Each manufacturer has its own model specification to help architects and specifiers choose the proper product. A contractor should be able to educate architects and builders about the product, its applications, and installation process, including any mechanical ventilation needs during the installation and afterwards.

Qualified contractors can also explain best safety practices, such as the type of protective equipment workers wear and how they keep others out of the space during installation and curing. The latter is especially important, because other trades and building occupants should not be in the area when SPF is being applied and curing. Re-entry time can vary depending on air temperature, humidity level, and the type of SPF applied. Once the product cures, it is considered to be essentially inert, according to the U.S. Environmental Protection Agency (EPA), meaning the chemicals have stopped reacting. (The SPF contractor can advise when it is safe to re-enter the space.)

General contractors and specifiers should consider using an SPF company that employs individuals who have completed the Center for the Polyurethane Industry’s (CPI’s) SPF Chemical Health and Safety Training, and who have been certified by the Spray Polyurethane Foam Alliance’s (SPFA’s) new Professional Certification Program for SPF applicators. The comprehensive certification program, developed in compliance with American National Standards Institute/International Organization for Standardization (ANSI/ISO) 17024, Accreditation Program for Personnel Certification Bodies, focuses on safety, quality installation, and professionalism.

Air, sound, and vapor barrier

SPF’s monolithic installation allows it to be used around irregular shapes and penetrations.

SPF’s monolithic installation allows it to be used around irregular shapes and penetrations.

A reliable air barrier and a continuous seal are essential elements in creating an energy-efficient, comfortable space. Both types of SPF meet the requirements of an air barrier material at a typically installed thickness of 25 mm (1 in.). When installed with other materials in a building assembly, SPF can provide an effective continuous air barrier.

By acting as both insulation and an air barrier, it could even help lower construction costs, because less air sealing materials would be required to meet local and state building energy codes for air leakage mandates.

Since SPF adheres to the substrate, it allows for easy monolithic installation around irregular shapes and penetrations. The material is applied as a liquid and then expands into foam in any nook and cranny in the enclosure to provide a seal. This offers energy performance and occupant comfort.

Open-cell SPF, typically associated with residential applications, is commonly used to fill cavities in interior spaces or to insulate unvented attics. This type is moisture vapor-permeable, and usually requires a properly designed and installed vapor retarder. Generally, open-cell foam has an R-value between R-3 and R-4 per 25 mm (1 in.) of thickness.

Open-cell SPF has also been used on the underside of roof decks in multiple climate zones for years. As with the usage of all building products, the building science of the structure needs to be understood. Potentially, a vapor barrier may be needed with open-cell SPF. Open-cell is vapor permeable, so depending on the structure, design, and climate zone, a determination of whether a vapor barrier needs to be added should be made. If a roof leaks when open-cell SPF is used on the underside of the roof deck, the water will likely gradually move its way through the open-cell SPF. Since it is an open-cellular matrix, the water, in a relatively short period of time if in sufficient quantity, will pass through the foam, and the leak can be identified and then repaired.

Closed-cell is the dominant SPF material for commercial construction, especially when used as an air barrier and thermal insulation system applied on the building’s exterior, or as foundation and slab insulation. This type of SPF has a higher R-value than open-cell—typically between R-6 and R-7 per 25 mm of thickness. Its relatively low moisture permeability means it rarely requires an additional vapor retarder. An exception may apply in areas, such as bathrooms, with high relative humidity (RH).

Regardless of the project type, understanding SPF and its influence on a building’s energy performance is critical. During the design process, architects and general contractors need to take these impacts into account so they can take advantage of SPF’s energy-saving properties. For example, buildings using SPF as the insulation of choice typically require the use of smaller HVAC systems because less air escapes the building, reducing the heating and cooling loads.

SPF insulation seals gaps to reduce air leaks.

SPF insulation seals gaps to reduce air leaks.

SPF benefits
While SPF is most often associated with energy-saving properties, it has numerous other benefits, including soundproofing. In commercial and residential buildings, open-cell foam is typically used in interior partitions for sound control. Since SPF seals the cracks and crevices in a building, and adds another layer between the interior and exterior, it helps dampen noises that travel through the air, such as the sound of an airplane overhead or a phone conversation in the adjoining office.

Given SPF’s ability to air seal, it is necessary to design proper air distribution systems to control moisture and air flow within the finished building. While a continuous seal is desired, interior spaces require a certain amount of outside ventilation to maintain air quality. Similarly, moisture created by cooking and bathing must be able to dissipate safely within the building.

Structural integrity
Ultimately, all construction projects are judged on their integrity—how long they can withstand the tests of the elements and time. SPF, especially closed-cell foam, enhances a building’s strength and stability because of its rigid structure.

Many of the properties making SPF effective as a stabilizer also make it attractive for flat roofing applications. SPF roofing, a high-density closed-cell foam, can form a continuous insulation (ci) barrier on the top of a roof deck. Since SPF roofing has no seams or joints and is rigid, it forms an impermeable surface. Since it is fully adhered to the substrate, the rigid foam provides exceptional uplift resistance during severe storms producing high winds.

About 10 months after Hurricane Katrina, the National Institute of Standards and Technology (NIST) issued, “Performance of Physical Structures in Hurricane Katrina and Hurricane Rita: A Reconnaissance Report”1 on damage to buildings in the Pascagoula, Mississippi area. It found all but one of the buildings with SPF roofs made it through the storm “extremely well without blow-off of the SPF or damage to flashings.” For the building that was the lone exception—just one percent of its roof area had failed.

An SPF roof properly maintained with regular recoats of the exterior membrane can last for decades. According to SPFA, some SPF roofs have lasted for more than 30 years. Closed-cell SPF also enhances a structure’s resistance to water damage. By acting as a barrier to water and condensation in the building envelope, SPF can help a building resist the growth of mold and mildew. Its ability to adhere to and around surfaces ensures every nook and cranny is filled, so there are no spots for these to grow. Its water-proofing abilities extend to increased floodwater protection as well.

Closed-cell SPF is a material that meets Federal Emergency Management Agency (FEMA) requirements for a Class 5 flood-resistant material—the highest class of materials that can resist damage from floods, according to a FEMA technical bulletin, “Flood Damage-resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in accordance with the National Flood Insurance Program.” This class of material can submerged for 72 hours, and can easily be dried and cleaned following a flood.

SPF’s monolithic nature allows for a seamless, self-flashing roofing application to protect against moisture.

SPF’s monolithic nature allows for a seamless, self-flashing roofing application to protect against moisture.

Green building benefits
As green building practice and techniques become the norm, many building owners, designers, and general contractors want to reduce the environmental impact of buildings. Due to its superior insulating qualities, SPF allows the building community to achieve a balance between energy efficiency, building durability, and comfort. It can also help them meet the requirements of programs such as EnergyStar and the Leadership in Energy and Environmental Design (LEED) rating program. Additionally, a study by SPFA, “Life Cycle Assessment of Spray Polyurethane Foam Insulation for Residential & Commercial Building Applications,” found energy and environmental benefits of using SPF for retrofits of non-residential roofs and residential applications outweigh the amount of energy and environmental impacts associated across the product’s lifecycle.2

Conclusion
With several types of SPF available and numerous application possibilities, it is worthwhile for architects, specifiers, and builders to gain a deeper understanding of this product. SPF allows for more creative design, filling in cavities and covering surfaces that could otherwise pose challenges. It helps reduce air infiltration, eliminating intrusions from dust and pollen and making buildings more comfortable. As a roofing material and exterior insulator, SPF can strengthen a structure by increasing its water resistance and durability.

Notes
1 To read this report, visit www.nist.gov/customcf/get_pdf.cfm?pub_id=908281. (back to top)
2 The “Life Cycle Assessment of Spray Polyurethane Foam Insulation for Residential & Commercial Building Applications” report can be viewed at www.sprayfoam.org/files/docs/SPFA%20LCA%20Long%20Summary%20New.pdf. (back to top)

Peter Davis is chairman and CEO of Gaco Western, chairman of the Spray Foam Coalition at the Center for the Polyurethanes Industry, and serves on the executive committee of the Spray Polyurethane Foam Alliance (SPFA). He can be reached via e-mail at pdavis@gaco.com.

Updating values for polyiso

The January issue of The Construction Specifier included the article, “Impact of Advancements in Model Energy Codes,” by Jared O. Blum. We received the following letter to the editor from Tim Merchant of the EPS Industry Alliance, an organization representing those in the expanded polystyrene community.

The EPS Industry Alliance has always supported informative articles that advance the knowledge, proper use, and application of foam insulation. That said, the article makes some inaccurate claims regarding R-value of polyisocyanurate (polyiso) insulation that we would like to address.
The chart on page 68 lists the R-values of several foam insulations, including polyiso, which it says has an R-value of 6. This is in alignment with ASTM C1289-13, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board, and Underwriters Laboratories of Canada (CAN/ULC) S770-09, Standard Test Method for Determination of Long-term Thermal Resistance of Closed-cell Thermal Insulating Foams as of your publication. However, new testing methods developed in 2013 have shown the R-value of 25 mm (1 in.) of polyiso is 5.6—seven percent less than the measure of previous standards.
Last June, the Polyisocyanurate Insulation Manufacturers Association (PIMA) announced it would be updating its QualityMark-certified R-value program to reflect the new data, which was determined using a new test method for finding long-term thermal resistance (LTTR). The new 5.6 R-value rating was to be incorporated in Canadian and U.S. standards as of January 1, 2014. Please keep this in mind for future articles related to the R-value of polyiso insulation.

We asked the article’s author to respond:

ASTM C1289-13 was updated last year, and features important improvements regarding the prediction of long-term thermal resistance value (i.e. R-value) for various polyiso insulation boards. The article published in this issue of The Construction Specifier was originally written before PIMA and its members began reporting LTTR values in accordance with the standard on January 1, 2014 as part the PIMA’s QualityMark program.
To participate in PIMA’s QualityMark certification program, a Class 1 roof is suggested to have a design R-value of 5.7 per inch. It should be noted polyiso is unique in the R-value increases with the thickness of the foam, so 76 mm (3 in.) of polyiso has a higher R-value per inch than 50 mm (2 in.).
Since its founding, PIMA has been active in the harmonization of relevant standards to provide greater continuity in the reporting of polyiso roof insulation thermal values throughout North America. This is why the association implemented the industry-wide QualityMark certified R-value program for rigid polyiso roof insulation in 2004. The update to this standard provides more data to aid in the prediction of long-term thermal performance of North America’s most popular rigid roof insulation.