Tag Archives: 07 21 00−Thermal 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.

Passive Fire Protection and Interior Wall Assemblies

All images courtesy ClarkDietrich Building Systems

All images courtesy ClarkDietrich Building Systems

by Gregg Stahl

Integral to commercial building design, passive fire protection is a method for containing a blaze at its source, preventing the spread of flames and smoke throughout a building for a specified time so occupants can evacuate the structure.

Unlike active fire protection devices, such as sprinkler systems, fire alarms, and fire extinguishers, these passive fire protection systems utilize fire-resistant materials embedded in interior building assemblies, lying dormant and hidden from public view until a fire ‘calls’ them into action.

One of the most important areas of concentration for these passive fire protection design strategies is the wall assembly. To ensure optimal fire protection, the building codes require these assemblies to be evaluated by industry standards to determine their fire performance. This article provides examples of fire-rated wall assemblies and passive firestop systems. It also describes the testing they must go through to achieve their fire ratings while covering best practices for their specification and installation.

Fire-rated wall assemblies
Total passive fire protection cannot be achieved through the use of one product—it requires an assembly of several different fire-resistant materials that work together systematically to slow the passage of flames, smoke, and toxic gases. For example, most exterior and interior commercial wall assemblies feature light-gauge steel studs, fiberglass insulation, and gypsum wallboard, which are all materials possessing naturally high fire resistance. The three materials perform well together in wall assemblies and are used in various combinations of thickness and numbers of layers to increase fire resistance.

The fire resistance of wall assemblies is evaluated by two industry standards—ASTM E603, Standard Guide for Room Fire Experiments, and ASTM E119, Fire Tests of Building Construction and Materials. These standards rate the assemblies based on how many hours they prevent the passage of fire, heat, smoke, and gases.

The integration of intumescent firestop materials onto steel framing members is one of the most recent high-performance innovations in passive protection. Such products eliminate both overage and underage often associated with messy caulks and sprays.

The integration of intumescent firestop materials onto steel framing members is one of the most recent high-performance innovations in passive protection. Such products eliminate both overage and underage often associated with messy caulks and sprays.

ASTM E603 measures temperatures, smoke generation, ignition to flashover time, combustion gas, and total energy release as a fire moves from one room to the next. Referred to as the ‘room corner test,’ it involves a corner of a room constructed in an accredited testing facility, using standard building materials. Materials to be tested are mounted on the walls and ceiling of the room corner. A fire source, usually a wood crib or a diffusion burner, is placed in the corner and ignited. The test mimics a wastebasket-sized fire that spreads to something nearby. To achieve a satisfactory performance rating, the tested assembly must not allow the spread of smoke and fire or generate excessive amounts of smoke.

ASTM E119, on the other hand, establishes a wall assembly’s effectiveness to act as a fire barrier. In this case, a wall is tested for structural integrity and the ability to contain a fire for a quantified period. The assembly is mounted to a specially constructed furnace and gas burners are lit as thermocouples record temperatures and the flames mimic heat from an adjacent fire. Observations are made through viewing windows in the furnace and with instrumentation. Temperatures and the length of time before the system fails are recorded.

This test method uses a furnace-heating schedule, or timed increase of temperature, which brings the furnace up to 538 C (1000 F) in five minutes, up to 927 C (1700 F) in one hour, and to 1010 C (1850 F) in two hours. Assemblies must survive these temperatures to be successfully fire-rated by the standard. A hose stream test follows to measure the assembly’s resistance to water pressure after the burn.

Fire-resistant wall assembly examples
Non-combustible, non-load-bearing wall assemblies must be constructed from fire-resistant materials. All combinations of assemblies are tested to establish hourly fire ratings. In the following paragraphs, this article examines three common variations of such assemblies.

Typical one-hour-rated assembly, UL Design V450—non-combustible, non-loadbearing1
One layer of 15.9-mm (5/8-in.) Type X gypsum board2 is applied horizontally or vertically to either side of minimum 92-mm (3 5/8-in.) steel drywall framing spaced on 600-mm (24-in.) centers. Gypsum board is fastened to the steel studs using 25-mm (1-in.) Type S bugle-head steel screws at 200 mm (8 in.) on center (oc) perimeter and field for horizontal applications, or 200 mm oc perimeter and 300 mm (12 in.) oc field for vertical applications. Joints must be offset. For extra fire resistance, thermal resistance and acoustic control, add 89 mm (3 1/2 in.) of fiberglass batt insulation to the wall cavity.

Typical two-hour rated assembly, UL Design V450—non-combustible, non-loadbearing
Two layers of 15.9-mm (5/8-in.) Type X gypsum board is applied horizontally or vertically in accordance to the fire assembly to either side of minimum 63.5-mm (2 1/2-in.) steel drywall framings spaced on 600-mm (24-in.) centers. The base layer of gypsum board is fastened to the steel studs using 25-mm (1-in.) Type S bugle-head steel screws spaced 400 mm (16 in.) oc perimeter and field.

Track members having the intumescent material already integrated can provide up to 76 mm (3 in.) of total movement and up to three-hour fire-rated protection.

Track members having the intumescent material already integrated can provide up to 76 mm (3 in.) of total movement and up to three-hour fire-rated protection.

The same screw placement and use of a 130-mm (5 1/8-in.) screw apply to the face layer as well. Joints must be offset on the opposite sides of the wall and between layers. For extra fire resistance, thermal resistance, and acoustic control, 64 mm (2 1/2 in.) of fiberglass batt insulation can be added to the wall cavity.

Area separation firewalls
Another important assembly demanding fire resistance performance is the area separation firewall. These walls are required between adjacent apartments or townhouses, and in some cases, they are required in commercial and institutional buildings.3

The area separation wall is designed to allow for collapse of the construction on the fire-exposed side, without collapse of the entire wall. To do this, aluminum breakaway clips attach the separation wall to the adjacent framing. When one side of the separation wall is exposed to fire, the clips are designed to soften and break away. This allows the structure on the fire side of the separation wall to collapse, while the clips on the unexposed side of the separation wall continue to support the separation wall.

A typical area separation firewall assembly consists of two layers of 25 x 610-mm (1 x 24-in.) gypsum shaftliner panels inserted between floor and ceiling runners with steel H-studs installed between adjacent panels. A 19-mm (3/4-in.) air space must be maintained between steel components and adjacent framing. An 89-mm (3 1/2-in.) layer of fiberglass batt insulation in the wall cavity is also recommended.

Proper installation of a fire-rated assembly is important. Good construction practices—executed in accordance with manufacturers’ recommendations and the fire-rated assembly’s requirements—are needed to ensure the assembly built in the field is representative of the one tested. However, an additional passive firestop system is needed for these assemblies to seal off the passage of flames, smoke, and toxic gases through the joints and penetrations of a wall assembly.

Passive firestop systems
Penetrations are often made through fire-rated wall assemblies for switches, electrical boxes, power outlets, or the passage of pipes, cables, or HVAC ductwork. At these locations, as well as wherever there are wall perimeter joints, it is necessary to seal the openings off with firestop materials. There is no one universal product that will work for every firestop application. Traditionally, specified materials include:

  • sealants;
  • intumescent materials;
  • sprays (i.e. spray-applied compounds, usually latex or silicone-based, that provide firestopping through penetrations, voids, and construction joints of the wall assembly, framing, and ductwork); and
  • foam blocks or pillows (i.e. self-contained, intumescent firestop products for through-penetration, such as where ductwork or support beams pass through wall assemblies—on exposure to flames, they intumesce to form a hard char that tightly seals penetrations against flame spread, smoke, and toxic gases).

It is important to select products that have been appropriately tested to meet applicable fire safety standards.

Using a cured factory-metered dosage intumescent material, this profile provides firestopping and sound-dampening effective immediately as framing composite is installed.

Using a cured factory-metered dosage intumescent material, this profile provides firestopping and sound-dampening effective immediately as framing composite is installed.

Sealants
Sealants are the most recognized group of firestop products due to their versatility, as caulk can have various uses on construction projects, such as sealing penetrations and construction joints. These products are available in various forms and chemical formulations. Firestop sealants in caulk, self-leveling, and spray grade are readily available in silicone, latex, and solvent-based products. They often require the addition of a backing material (e.g. polyethylene backer rod) in the system for support.

Often, the effectiveness of their application is governed by the ambient temperature. Consequently, in unheated spaces during construction, this may be an issue.4 Additionally, any overlapping work from other subcontractors—such as previously installed mechanical ductwork or piping—can interfere with the sealants’ application and inspection.

Intumescent materials
Intumescent materials are firestop products that expand in volume when exposed to heat or flames exceeding a specified temperature. They are one of the primary groups of products employed in applications where one of the assembly components deteriorates or burns away during fire exposure or where surfaces are uneven and a tight fit is impossible.

The expansion of the material closes the void that is created when the item melts or burns away, maintaining the fire-rated assembly’s integrity. Intumescent firestop materials come in various forms, from caulks to metallic collars with intumescent strip linings, with each product being designed for a specific purpose.

Integrated firestop systems
The integration of intumescent firestop materials onto steel framing members is one of the most recent high-performance firestop innovations. In many commercial and institutional projects, architects and specifiers are now using steel tracks manufactured with a factory-metered dosage of intumescent material applied in a controlled environment to the track flanges. These products help architects specify product and assembly solutions for both hidden and exposed aesthetic conditions where fire, smoke, and sound resistance ratings are required.

Single-source construction of wall assemblies and installation of joint protection can now be achieved by drywall contractors, eliminating any trade overlap issues common to installing traditional firestop materials. Track members having the intumescent material already integrated can provide up to 76 mm (3 in.) of total movement and up to three-hour fire-rated protection.

These integrated firestop products are easier to install than traditional firestop materials. Contractors simply install the track member, which includes the intumescent tape, at the top, bottom, or sides of the wall. This eliminates the need to return and install intumescent caulking at a later time, eliminating multiple labor and material operations.

Passive firestop system evaluation

Integrated passive fireproofing systems, such as this one, provide several design advantages, including earlier and easier inspection as the system is installed and inspected as ‘joint framing’ (before obstructions).

Integrated passive fireproofing systems, such as this one, provide several design advantages, including earlier and easier inspection as the system is installed and inspected as ‘joint framing’ (before obstructions).

Like wall assemblies, the fire performance of passive firestop systems must also be evaluated by various industry standards. ASTM E1966, Standard Test Method for Fire-resistive Joint Systems, is one standard that covers sealants, coatings, and materials used in joints. ASTM E814, Fire Tests of Through Penetration Firestops, is the complementary test to ASTM E119 that evaluates penetrations through a tested, fire-resistive (i.e. ASTM E 119-tested) wall or floor assembly.

The test involves a standard time-temperature curve and a hose stream test; it assigns ratings based on ‘T’ (temperature rise) and ‘F’ (flame occurrence through the firestop/penetration). The objective of specifying this type of system is to return the floor or wall to the compartment’s original fire rating. An ‘L’ (air leakage) rating can also be assigned. Air leakage simulates smoke movement through a penetration, measured in cubic feet per minute.

Conclusion
Fire-rated wall assemblies and passive firestop systems are crucial elements in the design of all commercial buildings. They help increase occupant safety and allow project teams to meet building code requirements.

By following the guidelines for fire-rated wall assemblies and passive firestop systems, building and design professionals can produce interior walls that will help protect building occupants against flames and smoke for a specified time. Combined with active fire protection methods and occupant education, these passive fire protection techniques provide a safer, more balanced strategy for protecting a building and those inside.

Notes
1 Underwriters Laboratories refers to this design as BXUV.V450. For more, visit bit.ly/1e5sKvR. (back to top)
2 Type X is standard fire-resistant gypsum board. Type C offers stronger resistance. (back to top)
3 In general, the purpose of area separation walls is to provide extra fire resistance between adjoining residential or commercial building units. They impede sound transmission, as well as the spread of fire from one unit to the next. Not all commercial or institutional buildings are going to have multiple tenants. (back to top)
4 In the cooler seasons, installers may have to employ the use of temporary, portable heaters to reach the proper temperature to ensure sealant adhesion. However, contractors should be keenly aware of the safety concerns when using these instruments in the work environment. (back to top)

Gregg Stahl is the director of product development at ClarkDietrich Building Systems, a manufacturer of steel framing and finishing products for the commercial construction industry. With more than 25 years of industry experience, he has served in multiple capacities at ClarkDietrich, including vice president of its subsidiary Vinyl Corp. Stahl has also held various roles within sales and product management. He can be reached at gregg.stahl@clarkdietrich.com.

 

 

Impact of Advancements in Model Energy Codes: The Value of Energy Conservation

There are several statistics, trends, and implications related to energy consumption and conservation that can be quite eye-opening.*

Economic impact

  • annual national energy bill for buildings is more than $415 billion;
  • average household spends $1900 a year on energy;
  • improving energy efficiency by 50 percent has an annual value of $950 for the average household; and
  • during the nominal 75-year lifespan of a typical home, $950 a year in energy savings has a ‘present worth’ value of $18,500.

Resource impact

  • commercial and residential buildings account for 41 percent of U.S. energy consumption—a number higher than for industry or transportation;
  • most energy consumed in buildings is produced by fossil fuels (i.e. non-renewables like coal, oil, and natural gas), which can compete with a national security interest to conserve these resources and reduce dependency on foreign sources; and
  • if all U.S. households were to apply even a modest R-3 of continuous insulation (ci) to walls, the estimated energy savings is equivalent to 70 large oil tankers per year, the total energy produced at five large nuclear power plants per year, or removing 7 million vehicles from use (which equates to 2.5 billion gallons of gasoline not consumed each year).

Environmental impacts

  • burning of fuels to produce energy releases air pollutants including sulfur dioxide, nitrogen oxides, carbon monoxide, and particulates having consequences including smog, acid rain, respiratory disease, and many other negative human health and ecological effects;
  • energy consumption or losses from buildings generate 1.2 billion tons of carbon dioxide (a greenhouse gas [GHG]) into the atmosphere; and
  • if all U.S. households were to apply the aforementioned R-3 of ci, air pollutants could be reduced by 30 million tons per year (or 2.5 percent of the total).

* This information comes from the U.S. Energy Information Administration’s (EIA’s) 2009 annual energy review, a New York State Energy Research and Development Authority (NYSERDA) report, Comparison of Current and Future Technologies,” and a 2000 Franklin Associates paper, “Plastics Energy and Greenhouse Gas Savings Using Rigid Foam Sheathing Applied to Walls of Single Family Residential Housing in the U.S. and Canada.”

To read the full article, click here.

Impact of Advancements in Model Energy Codes: What’s the effect on insulation?

Images courtesy PIMA

Images courtesy PIMA

by Jared O. Blum

In response to a national interest in, and policies for, conservation of energy, model energy codes are striving to advance the way commercial and residential building envelopes are insulated. The effect on how design professionals specify materials for thermal management will be substantial.

The International Code Council’s (ICC’s) 2012 International Energy Conservation Code (IECC) calls for a 30 percent increase in building energy savings as compared to the 2006 code. This represents the single largest efficiency increase in the history of the model energy code.

For walls, a continuous insulation (ci) system is featured as a solution in recent model energy codes because it effectively addresses these challenges. When it comes to commercial roofs, significant savings can be attained by upgrading insulation to provide an R-value meeting current code standards and practice.

Light frame and mass wall systems with continuous polyisocyanurate (polyiso) insulation for code-compliant commercial building construction.

Light frame and mass wall systems with continuous polyisocyanurate (polyiso) insulation for code-compliant commercial building construction.

Continuous insulation in walls
In American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2007, Energy Standard for Buildings Except Low-rise Residential Buildings, ci is defined as:

insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior, exterior, or is integral to any opaque surface of the building envelope.

Of course, this insulation approach is not new—it has been commonly used for many years on various types of low-slope roofing assemblies. Since 20th century construction practices were developed during periods of ample and cheap energy, its use on both residential and commercial building walls has lagged behind its energy-saving potential. This situation is changing through the emphasis of higher-performing wall assemblies in newer model energy codes. Like any construction material, continuous insulation must be properly specified to ensure its intended performance and appropriate use.

Materials: function and versatility
As shown in Figure 1, ci can be used with various wall structural systems and cladding materials such as:

  • cement board;
  • portland cement stucco;
  • wood lap;
  • brick veneer;
  • stone; and
  • vinyl siding.

In these applications, the primary function of continuous insulation is to provide code-compliant or better energy conservation performance. Additionally, properly qualified and installed ci products can serve other important functions for exterior wall assemblies, including air barriers and water-resistive barriers (WRBs). When laminated to structural materials, ci can even provide structural functions such as wall bracing. (The designer should refer to the manufacturer’s data for code-approved capabilities.)

R-value is the measure of resistance to heat flow through a given thickness of material; the higher the R-value, the greater that resistance.

R-value is the measure of resistance to heat flow through a given thickness of material; the higher the R-value, the greater that resistance.

Various code-compliant foam plastic insulating sheathings and other types of materials are available to address ci applications on walls. The most common foam plastic insulating sheathing products are manufactured and specified in accordance with ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation, or ASTM C1289, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board.

Material types include polyisocyanurate (polyiso) foam, expanded polystyrene (EPS), and extruded polystyrene (XPS). Each product type has different thermal properties (which affect required thickness), costs, and capabilities (Figure 2). Model building code requirements for foam plastics are found in Chapter 26 of the International Building Code (IBC).

Modern energy and building code requirements
Continuous insulation provides one of the most thermally efficient ways of complying with modern energy codes. It mitigates avoidable heat loss due to thermal bridging in walls and roofs not continuously insulated (Figure 3). Modern energy code requirements for walls feature the use of continuous insulation as shown in Figure 4.

When using continuous insulation to meet or exceed the applicable energy code, certain matters of building code compliance should also be considered.

WRBs
Many ci products can be used as a water-resistive barrier behind cladding, offering water protection and thermal performance in one product. (Design professionals should refer to manufacturer installation instructions and code-compliance data.) Alternatively, WRBs can be separately applied to walls with continuous insulation.

Continuous insulation minimizes thermal bridging and provides favorable economic and performance benefits over use of cavity insulation alone in exterior walls.

Continuous insulation minimizes thermal bridging and provides favorable economic and performance benefits over use of cavity insulation alone in exterior walls.

Wind pressure resistance
For code compliance guidance on wind pressure resistance of foam sheathing materials, one should refer to the American Chemistry Council’s (ACC’s) Foam Sheathing Committee Technical Evaluation Report (TER) 1006-01, Prescriptive Wind Pressure Performance of Foam Plastic Insulation used as Insulating Sheathing in Exterior Wall Covering Assemblies,1 along with the manufacturer’s installation instructions and design data.

It is important to verify the wind pressure resistance of other wall assembly components—including framing and siding—because testing has shown they may not be as strong as the foam sheathing material itself under wind pressure loading.

Cladding (siding) attachment
Various proprietary and standard fasteners and connection strategies can be used for attachment and support of cladding materials when installed over continuous insulation. For guidance, refer to the Foam Sheathing Committee’s Tech Matters, “Guide to Attaching Exterior Wall Coverings through Foam Sheathing to Wood or Steel Wall Framing.”

This document features solutions for direct attachment of cladding through foam sheathing and use of furring placed over and attached through foam sheathing. Both these practices minimize thermal bridging through ci due to cladding connections. Design professionals should also refer to the cladding manufacturer’s installation requirements. For example, such documentation will list minimum siding fastener size, how penetration into framing should be maintained, and whether longer fasteners are required.

For this table, wall R-values are shown as cavity insulation alone or as XX + X where the first number is the cavity insulation R-value and the second is for continuous insulation. (Continuous insulation R-values are shown in red.) The commercial Wall R-values are based on all commercial building use groups, except R (residential) which may require additional continuous insulation depending on climate zone.

For this table, wall R-values are shown as cavity insulation alone or as XX + X where the first number is the cavity insulation R-value and the second is for continuous insulation. (Continuous insulation R-values are shown in red.) The commercial Wall R-values are based on all commercial building use groups, except R (residential) which may require additional continuous insulation depending on climate zone.

Fire performance
Foam plastics are held to a comprehensive set of fire performance requirements that include various types of tests and criteria to address flame spread, smoke development, and ignition protection. By far the most significant code requirement that applies to walls with continuous insulation (foam plastics) is the National Fire Protection Association (NFPA) 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-load-bearing Wall Assemblies Containing Combustible Components. This flame spread test uses full-scale, multi-story wall assemblies.2 In general, compliance with NFPA 285 is not required for buildings meeting limitations for Type V construction or one- and two-family dwelling construction.

Moisture vapor retarders
It is important to ensure ci is specified together with moisture vapor retarders in such a way that moisture vapor is properly managed. Recent building code improvements (i.e. 2009 IBC Section 1405.3, Vapor Retarders) ensure adequate R-value is provided in different climates to prevent condensation by keeping walls warm (i.e. above dewpoint) and to ensure vapor retarders are used in a manner that promotes seasonal drying capability.

Energy codes and the roof
One of the best and simplest ways to achieve a high degree of energy efficiency is by increasing the levels of insulation on the roof. In fact, for long-term energy savings, the commercial roofing market provides a significant multiplier effect to accelerate energy efficiency efforts. For every new roof installed on a building, approximately three additional ones are installed on existing buildings to replace older, less energy-efficient assemblies.

More than 370 million m2 (4 billion sf) of flat roofs are retrofit annually, with untold other existing roofs waiting for their turn.3 If all these commercial roofs were upgraded to meet the requirements of the 2012 IECC, energy savings would be significant.

Published by Polyisocyanurate Insulation Manufacturers Association (PIMA) and the Center for Environmental Innovation in Roofing, Roof and Wall Thermal Design Guide provides information regarding the prescriptive thermal value tables in the 2012 IECC and the references to these tables in the 2012 International Green Construction Code (IgCC). The guide translates this information into simple and straightforward roof and wall R-value tables covering the most common forms of commercial opaque roof and wall construction.

For example, R-values for the 2012 IgCC and IECC for “roofs with insulation entirely above deck” are determined by reducing the overall roof assembly U-factor by 10 percent, and converting the assembly U-factor to the corresponding insulation R-value. Resultant R-values in the table (Figure 5) are rounded to the nearest 0.5 R-value.

In 2013, both ICC and ASHRAE adopted language making it clear once and for all the R-value required for new building construction also applies where “the sheathing or insulation is exposed” during reroofing. For attics and other roofs, the rated R-value of insulation “is for insulation installed both inside and outside the roof or entirely inside the roof cavity.” This information can be found in Figure 6.4

R-values for roofs with insulation entirely above deck, as set out by the building codes.

R-values for roofs with insulation entirely above deck, as set out by the building codes.

R-values for insulation installed inside and outside the roof, or entirely inside the roof cavity.

R-values for insulation installed inside and outside the roof, or entirely inside the roof cavity.

Construction detailing
It is important to provide workable and complete construction details for walls and roofs with ci to ensure a constructible and functional assembly relating to many of the topics discussed in this article. Construction details to consider include:

  • envelope component attachments;
  • integration of flashing and WRB;
  • integration of furring (if used) around wall penetrations and flashing;
  • attachment of cladding to wall framing through ci or to furring;
  • details for cladding attachments through ci at inside and outside corners; and
  • installation detailing per NFPA 285 tested assembly when required. Some useful detailing resources or concepts can found from various sources. Proprietary cladding systems may also include details for accommodation of continuous insulation.

The advancement of model energy codes represents another step forward in ensuring a reduction in energy consumption, which in turn helps stabilize or even decrease utility costs.

Whether for new construction or energy-efficient retrofits, new ways of thinking about insulation are leading to improved products, refined assemblies, and better outcomes. Photo © BigStockPhoto/Gina Sanders

Whether for new construction or energy-efficient retrofits, new ways of thinking about insulation are leading to improved products, refined assemblies, and better outcomes. Photo © BigStockPhoto/Gina Sanders

Notes
1 The group’s membership includes numerous foam sheathing manufacturers, along with the ACC’s Center for the Polyurethanes Industry (CPI), EPS Molders Association (EPSMA), Extruded Polystyrene Foam Association (XPSA), and Polyisocyanurate Insulation Manufacturers Association (PIMA). For more information, visit www.foamsheathing.org. (back to top)
2 For more information, refer to the Foam Sheathing Committee’s Tech Matters, “NFPA 285 Tested Assemblies Using Foam Sheathing,” and the specified manufacturer’s fire test data. (back to top)
3 This comes from a 2012 report, “Twenty-five Years of Polyiso: The Energy and Environmental Contribution of the Polyiso Insulation Industry 1987−2011” prepared by Tegnos Research for PIMA. (back to top)
4 Additional details on these wall and roof types, as well as others, can be found in the Roof and Wall Thermal Design Guide. Visit c.ymcdn.com/sites/www.polyiso.org/resource/resmgr/latest_news/icodesguide2012_snglpgs.pdf. (back to top)

Jared O. Blum is the president of the Polyisocyanurate Insulation Manufacturers Association (PIMA), the Washington-based North American trade association representing manufacturers of polyiso foam insulation. He can be reached via e-mail at joblum@pima.org.

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Investigating Sheathing Durability: Recommended IR Camera Specifications

Several factors should be considered before investing in an infrared thermography (IRT) camera.* Issues such as ergonomics and easy user interface play a vital role in enabling efficient use of equipment. From a technical standpoint, the following minimum requirements are usually recommended:

  • thermal sensitivity of 0.1 C (100 mK) at 30 C (86 F)—a critical factor in obtaining clear images (greater sensitivity provides the opportunity to conduct IRT surveys during more challenging conditions);
  • wide-angle lens for a greater field of view that greatly reduces survey times—20×20 is recommended; and
  • spatial resolution of 320×240 for the detector array size.

Other camera specifications often considered while making purchasing decisions include LCD display quality, battery life, accompanying software package for image editing and report preparation, visual image quality and palette options, and frame rate for real-time monitoring. Basic economics of the investment should also be considered, as some professional thermographers choose to rent, rather than buy, equipment.

* This information comes from John Snell and Matt Schwoegler’s “The Use of Infrared Thermal Imaging for Home Weatherization” (www.thesnellgroup.com/ReceiveWhitePapers.aspx) and a phone interview with Greg Stockton, founder of Stockton Infrared Thermographic Services.

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