The Evolution of Continuous Insulation

[ Page 4 of 4 ]  previous page Page 1 Page 2 Page 3 Page 4
Sponsored by Owens Corning
By Herbert Slone, R.A.
This test is no longer available for credit

Mineral Wool (MW)

MW used as CI is a semi-rigid board of bonded rock fibers. Its R-value of 4.2-per-inch of thickness when measured at a 75 degrees F mean temperature. The MW fiber does not absorb or bond with water. However, water may temporarily enter the voids in the fiber matrix and displace air, and then drain out as it experiences wetting and drying cycles when placed in a wet cavity wall condition.

MW retains its semi-rigidity and strength through wetting and drying cycles making it suitable for use in wet cavity wall situations when there is adequate space to achieve the necessary R-value. MW is non-combustible and highly fire resistant making it particularly well suited for use in any open joint systems that may be exposed to fire, and in non-masonry systems that provide little fire resistance such as behind ACM/MCM panels.

Due to the high degree of permeability and superior drainage capability, mortar damming is not a concern and the code prescribed 1-inch airspace is suitable. MW is also UV stable so it can tolerate long-term sunlight exposure through open joints. MW can be used behind virtually any type of cladding systems, and is particularly well suited for use where fire and UV exposure may come through open joints and where maximum R-value per-inch of thickness is not critical.

Polyisocyanurate (Iso)

Iso is a rigid board, foam plastic insulation. It is considered “closed cell.” However, cells are irregular in size and often interconnected (See Figure 11) allowing for the possibility of water intrusion.

Figure 11:  Polyisocyanurate Cell Structure.

Figure 11: Polyisocyanurate Cell Structure

The polyisocyanurate molecule is “hydrophillic” meaning that it has a molecular polarity opposite of water molecules. These two characteristics cause the water absorption level of Iso to be higher than XPS, its direct competitor in the foam plastic category.

All Iso is manufactured with a facer as a necessary part of the manufacturing process. Often it is the integrity of the facers that are relied upon to minimize exposure to water in wet cavity wall applications.

Iso derives its R-value from the low-conductivity gas held captive in its cells for the life of the product. Iso has a long-term R-value of 6 to 6.5-per-inch of thickness, depending on the manufacturer, when measured at a 75 degrees F mean temperature. As mean temperature decreases into a more wintery range of 40 degrees F, the R-value of some Iso products decreases to as low as 2 to 4-per-inch, again depending on the specific product and manufacturer.

The decrease in R-value-per-inch is a function of the captive low-conductivity gas in the cells of Iso, and its higher condensation temperature than the gas used to produce XPS. Iso loses its ability to insulate as the gas condenses to liquid inside the cells. As the mean temperature increases, the gas in the cells return to their gaseous state and R-value is recovered until the next dip into cold temperatures.

Some Iso products have an “engineered core” that yields higher fire resistance than that of generic Iso. The fire enhanced Iso products, although they are a foam plastic and are combustible, can be used behind cladding system that provide little to no fire resistance. That makes the “fire enhanced” Iso products suitable for use in open joint systems like terra cotta or precast concrete, and behind ACM/MCM composite metal panel systems. Check with the manufacturer for specific product details to ensure that the product specified has been verified to be NFPA 285 compliant behind the chosen cladding.


CI Construction Details

There are many options available when installing CI, including screws, air/water sealing washers, clips, z-girts and impaling pins. To the extent possible, careful attention should be given to minimizing thermal bridging through the CI layer to avoid negating the performance benefits of continuous insulation. Manufacturers are working on design guides to provide the highest performing, cost-effective and constructible fastening systems. Contact the manufacturers of CI products for the most current recommendations.

Integrating CI into the exterior wall involves changes in standard detailing. Not only will common wall sections be revised by simply including CI where it once was not included, but designers must also address changes in wall thickness and transitions. Other components in the wall such as the air/water barrier layer, and vapor control layer must also be adjusted to accommodate presence of CI and its influence on wall performance. Common details that may require new attention include:

  • Transitions from foundation insulation to wall insulation
  • Masonry ledge thickness
  • Window and door opening thickness
  • Sill pan, head, and jamb detailing (to seal against potential fire intrusion in an NFPA 285 event)
  • Floor line and detailing
  • Steel ledge, shelf angle and detailing
  • Transitions from wall to roof

The choice of the cladding, insulation and the details around openings, are critical in accomplishing an assembly that is NFPA 285 compliant. With CI and NFPA 285 now a “standard method and material” practice, scores of assemblies have been tested or have been accepted through engineering judgments. Check with system manufacturers for design guide for the various product options discussed herein.


Conclusion

Continuous insulation is no longer viewed as appropriate for only the most efficient buildings or a best practice. It is now customary and main stream. As described in this course, multiple advances in research and analysis have proven the benefits of CI to the point that it has been integrated as a standard practice in codes and standards and projects throughout the country. Designers must identify the type of cladding for a building design, and then evaluate the demands that it will place on the selection of a type of continuous insulation product.

Considerations include water resistance, air leakage resistance, appropriate fasteners and assembly fire testing. Designers must review standard details to ensure they are aligned with continuous insulation design principles that are quickly becoming standard practice. As a result of this new best practice, energy consumption, moisture accumulation, and the growth of mold and mildew are all anticipated to be reduced in future buildings throughout America.


Herbert Slone is a registered architect and senior manager of Commercial Building Systems for Owens Corning. He has over 41 years of experience in construction.


“Owens

Owens Corning develops, manufactures and markets insulation, roofing, and fiberglass composites. Global in scope and human in scale, the company’s market-leading businesses use their deep expertise in materials, manufacturing and building science to develop products and systems that save energy and improve comfort in commercial and residential buildings. Through its glass reinforcements business, the company makes thousands of products lighter, stronger and more durable. Ultimately, Owens Corning people and products make the world a better place. Based in Toledo, Ohio, Owens Corning posted 2015 sales of $5.4 billion and employs about 16,000 people in 25 countries. It has been a Fortune 500® company for 61 consecutive years.

Explore and interact with key industry products through our exclusive Interactive Product Spotlight on Owens Corning Enclosure Solutions.

http://www.owenscorning.com.

 

[ Page 4 of 4 ]  previous page Page 1 Page 2 Page 3 Page 4
Originally published in Building Enclosure
Originally published in September 2016


Notice

Academies