It can be confusing to keep track of your climate zone code requirements due to the fact that the minimum insulation requirements have increased 66 – 100% over the last 9 years. It is important to remember that a building owner only gets one chance to increase the insulation in the roof system approximately every 20 years. When determining the desired R-Value, you should consider future energy requirements and associated energy costs over the entire lifespan of the installed roof system. The current codes reflect the MINIMUM requirements, we recommend when planning for the future to exceed the code by an additional R-10. (Paybacks typically can be seen in 6 – 10 years*)
This guide provides assistance when designing the minimum R-Value in commercial buildings for energy efficiency for thermal insulation above the deck. The respective R-Values are based on the climate for each stated region and only a suggestion. State codes may differ and should be considered. Current code information for each state is available on the websites for the Building Codes Assistance Project and the US Department of Energy Building Energy Codes Program.
Building Codes Assistance Project: http://bcapcodes.org/code-status/state/ US DOE: https://www.energycodes.gov/status-state-energy-code-adoption
The chart below shows the progression of the R-Value changes by climate zones since ASHRAE 90.1 2004.
According to the 2021 International Energy Conservation Code (IECC), under Insulation Requirements, the building thermal envelope shall meet the requirements of Tables C 402.2 based on the climate zones shown below:
Question:
How does this affect R-Values on a Tapered Insulation System?
Answer:
The R-Values shown above are the minimum R-Values required to meet Code requirements. Since a Tapered Insulation system will increase thickness away from the low points, the overall system R-Value will exceed the Prescriptive R-Value requirements.
Question:
Does an Average R-Value that meets the Prescriptive requirement satisfy Code standards?
Answer:
No. The terminology “Average R-Value” for tapered systems is an outdated term and not recognized by the IECC.
Question:
Does building code allow for a change in R-value when using sumps?
Answer:
There is an exception provided that allows the minimum thickness to be up to 1″ less than the prescriptive R-Value (at ¼” per foot slope) as long as the system R-Value meets or exceeds that Prescriptive R-Value.
Example:
Zone 6 requires an R=30 minimum, which is 5.2″ thick. This exception will allow the minimum thickness to be 4.2″ at the low point, or 5.2″, 4′ away from the drain on a ¼” per foot tapered system.
IECC 2021, SEC. C402.2 ROOF ASSEMBLY Exception 2 Allows A 1-Inch Insulation Thickness Variation
– Crickets (aka Saddles or Hogbacks) are a secondary application of insulation – whether over a sloped deck with flat insulation, or over a tapered insulation system. The primary purpose of a cricket is to divert water from a the valley to the roof drain.
– The wider the cricket, the more efficiently the cricket will work. The general rule is for the cricket width of a full diamond cricket to be between 1⁄3 and 1⁄4 of its total length (see PIMA Technical Bulletin #108). If the cricket is less than the primary slope, drainage will be less efficient.
– Typically, the cricket slope is double the primary slope whether a sloped deck or a tapered system. This means that a sloped deck at 1⁄4″ foot will have 1⁄2″ foot sloped crickets. This has been the industry norm and is considered good roofing practice.
– Where the crickets are not in a valley, but may be up the slope (example: drains are 8′ off a parapet wall, and the deck slopes past the drains to the parapet), the crickets need to be double the deck slope to provide positive slope back to the drains. If not, you will essentially flatten the deck slope out creating an 8′ wide area that will pond water.
Multi-layering of Polyiso roof insulation installed with staggered joints offers a number of advantages over a single-layer system.
REDUCED THERMAL LOSS -Multi-layered systems with staggered joints reduce gaps between boards, thereby removing any potential pathway for airflow, heat transmission and condensation or “thermal short.” -Multi-layered systems more easily retain the published R-value compared to single-layer installations.
REDUCED THERMAL BRIDGING -Mechanical fasteners penetrating rigid board insulation may reduce thermal resistance from between 3% to 8% according to a study published in ASTM SPT 959 Roofing Research and Standards Development. Thermal bridging can be significantly reduced by mechanically fastening only the first layer of insulation and using approved adhesive for each subsequent layer.
REDUCED CONDENSATION -Multi-layered systems may help prevent interior building moisture from condensing on the underside of the finished roof surface.
Although a multi-layered system may appear to be more labor intensive to install, many contractors find that working with a thinner, lighter Polyiso base layer makes for a significantly faster overall installation, especially when combined with a specialty composite top layer. These systems may also compensate for inadequate design or improper installation.
For years the benefits of multiple-layer installation of all types of rigid board insulation have been acknowledged by leading industry authorities including the National Roofing Contractors Association (NRCA), Oak Ridge National Labs (ORNL), Canadian Roofing Contractors Association (CRCA) and the Roof Consultants Institute (RCI). Contractors, designers and specification professionals follow this best practice recommendation for the use and installation of multiple insulation layers.
For additional information see PIMA Technical Bulletin #113 or the NRCA Low Slope Roofing Manual.
There are two recognized field test methods for determining uplift resistance of adhered membrane roof systems, both of which can be problematic:
-ASTM E907, “Standard Test Method for Field Testing Uplift Resistance of Adhered Membrane Roofing Systems,” and
-FM Global Loss Prevention Data Sheet 1-52 (FM 1-52), “Field Verification of Roof Wind Uplift Resistance.”
Both test methods provide for affixing a 5′ x 5′ dome-like chamber to the roof’s surface and applying a defined negative (uplift) pressure inside the chamber to the roof system’s exterior-side surface using a vacuum pump, like in the photo below. However, ASTM E907 and FM 1-52 differ notably in their test cycles and maximum test pressures for determining roof system deflections and whether a roof system passes or is “suspect”.
-Using ASTM E907, a roof system is “suspect” if the deflection measured during the test is 25 mm (about 1 inch) or greater. -Using FM 1-52, a roof system is “suspect” if the measured deflection is between ¼ of an inch and 15⁄16 of an inch, depending on the maximum test pressure; 1 inch where a thin cover board is used; or 2 inches where a thin cover board or flexible, mechanically attached insulation is used.
TEST RESULTS’ RELIABILITY The reliability of the results derived from ASTM E907 and FM 1-52 is a concern, especially when the tests are used for quality assurance purposes. A note in ASTM E907 acknowledges its test viability. “Deflection due to negative pressure will potentially vary at different locations because of varying stiffness of the roof system assembly. Stiffness of a roof system assembly, including the deck, is influenced by the location of mechanical fasteners, thickness of insulation, stiffness of deck, and by the type, proximity, and rigidity of connections between the deck and framing system.”
For example, when testing an adhered roof system over a steel roof deck, placement of the test chamber relative to the deck supports (bar joists) can have a significant effect on the test results. If positioned between deck supports, the test chamber’s deflection gauge will measure roof assembly deflection at the deck’s midspan, which is the point of maximum deck deflection. Also, in many instances, field-uplift testing results in steel roof deck overstress and deck deflections far in excess of design values, which can result in roof system failure. These situations can result in false “suspect” determinations of a roof system.
INDUSTRY POSITION/RECOMMENDATIONS Because of the known variability in test results using ASTM E907 and FM 1-52 and the lack of correlation between laboratory uplift-resistance testing and field-uplift testing, the roofing industry considers field uplift testing to be inappropriate for use as a post-installation quality-assurance measure for membrane roof systems.
CONCLUSION FM 1-52 is an FM Global-promulgated evaluation method and not a recognized industry-consensus test standard. The scope of FM 1-52 indicates that it’s only intended to confirm acceptable wind-uplift resistance on completed roof systems in hurricane-prone regions, where a partial blow-off has occurred, or where inferior roof system construction is suspected or known to be present.
FM 1-52 was originally published by FM Global in October 1970. The negative-pressure uplift test was added in August 1980 and has been revised several times. The current edition is dated July 2021 and clarifies the test method can be used to assess existing roof systems for adequate wind resistance but not to determine the cause of wind-uplift damage after a storm event.
The minimum R-value requirements in commercial low-slope roofing have increased over the past decade resulting in thicker roof systems with more insulation. What could an additional ½” of insulation do? Cover boards increase the resiliency of single-ply roofing systems by improving wind uplift performance, protection against hail and resistance to foot traffic. However, not all cover boards are the same. In this article we will compare ½” Hunter Panels H-Shield HD polyiso cover board and ½” gypsum cover board as it pertains to R-value, hail rating, environmental impact and labor savings.
Roofing insulation is driven by minimum R-value requirements defined by the International Energy Conservation Code. While cover boards are typically used to improve the performance of a roofing system, some cover board options have insulating qualities. Hunter’s H-Shield HD polyiso cover board has an R-value of 2.5. Gypsum has an R-value that is negligible at best and most often is not counted towards the total R-value of a roof system. H-Shield HD polyiso can assist in meeting the energy code R-value requirements for a roof system. For example: Two layers of 2.6″ polyiso is equal to R-30. If your system incorporates an HD polyiso cover board like H-Shield HD that has a 2.5 R-value, then you only need R-27.5 with your base layers of polyiso which can be achieved by two layers of 2.4″. In a system with gypsum cover board, you will still need two layers of 2.6″ polyiso. Moving from two layers of 2.6″ to two layers of 2.4″ may not sound like a lot, but it adds up to at least $0.10/sq. ft. Insulating cover boards save money.
One of the biggest differences between Hunter Panels H-Shield HD cover board and gypsum is the compressive strength. HD polyiso has a compressive strength of 109 psi (pounds per square inch), gypsum’s compressive strength is 900 psi or higher. What does the additional 800+ psi accomplish? Factory Mutual’s (FM) severe hail rating test consists of a 1¾” steel ball dropped from 18′. Gypsum boards and H-Shield HD both pass the test with ease. Even though the higher compressive strength might sound like a big deal, the FM rating remains the same. In our research, we have found that an extremely hard surface below the membrane can lead to a higher rate of cutting and splitting when hail hits the single-ply membrane.
In today’s climate, the environmental impact of a product must be weighed before a buying decision is made. A 4′ x 8′, ½ ” gypsum board is about five times heavier than H-Shield HD. As a result, flatbed trucks that carry gypsum to jobsites will “weight-out” before they are full. Transportation for 1,000 squares of gypsum requires six trucks, while only two trucks are needed to transport 1,000 squares of H-Shield HD.
Using an insulation cover board like H-Shield HD means less fuel, reduced emissions and building CO 2 emissions avoidance. Additionally, because of the weight of gypsum it takes about 20 more crane hours to load the roof which increases man hours and emissions into the environment Cover boards are important when it comes to a roofing system, there’s no doubt about it. The clear choice is Hunter Panels H-Shield HD polyiso cover board with higher R-values, lighter weight, and less environmental impact than its gypsum counterpart.
All construction materials, including foam plastics such as polyiso insulation, must provide a suitable margin of fire safety. Polyiso possesses a high level of inherent fire resistance when compared to other foam plastic insulations due to its unique structure of strong isocyanurate chemical bonds. These bonds result in improved high-temperature resistance (up to 390°F [199°C], more than twice that of other building insulation foams) which in turn leads to enhanced fire resistance. In addition, because polyiso does not melt or drip when exposed to flame, but rather forms a protective surface char, its fire resistance is further enhanced, especially in terms of flame spread and flashover potential.
Polyiso passes both the ANSI UL 1256 and FM 4450 fire tests without a thermal barrier. Polyiso, a thermoset material, stays intact during fire exposure in the ASTM E84 or “Tunnel Test.” It forms a protective char layer and remains in place during the test, thereby meeting all building code requirements and contributing to a fire- safe building. For more information on polyiso’s performance in fire tests, visit the PIMA Website where you can find the following papers:
–Technical Bulletin 103: Discusses polyiso insulation as it relates to building codes in construction and fire tests in walls and ceilings, including ASTM E84 and ASTM E119. –Technical Bulletin 104: Provides an overview of polyiso insulation requirements for roof systems and key issues in fire performance, including the importance of the FM 4450 Calorimeter Tests and the UL 1256 Resistance to Interior Spread of Flame test. –Technical Bulletin 105: Provides an in-depth look at fire test procedures for building applications
Changes in season, weather, sunlight, humidity, and temperature can dramatically affect flash-off times of single-ply membrane adhesives and overall performance of adhered single- ply roof systems rely on proper membrane adhesion. ReadyFlash Technology allow contractors to manipulate adhesive flash-off times by choosing between two different- colored facers on every board.
H-Shield CG and H-Shield HD products with ReadyFlash Technology feature a dark-colored coated glass facer (CGF) on one side of the insulation board and a light-colored CGF on the other. Utilizing the sun’s energy, the dark facer accelerates adhesive flash-off; while the light facer slows it down. Contractors can choose between dark and light facers on the same insulation board.
-On a hot, sunny day the adhesive is flashing off prior to the crew completing application. Consider installing the light facer up to slow down adhesive flash-off time.
-On a cold day, the adhesive flash-off is taking longer than desired. Consider installing the dark facer up to speed up adhesive flash-off time and improve productivity.
-The applied membrane bonding adhesive is flashing off quicker than the adhesive applied to the insulation. Consider installing the dark side up so the adhesive on both surfaces can flash-off at the same time when applying bonding adhesive to both the membrane and insulation simultaneously.
Cover boards have the unique ability to enhance the overall performance of commercial roof systems. As a higher compressive strength substrate beneath the single-ply membrane, cover boards enhance wind uplift performance, hail resistance, foot traffic resistance, and even puncture resistance. By enhancing the overall roof system performance, longer duration warranties and/or higher wind gust speeds may be available. Many cover board options exist, including; High-Density Polyiso, Gypsum, OSB, and Recycled boards. Each option provides a host of performance benefits to the roof system. Composite cover board options also exist in which the base insulation is manufactured directly to the cover board above, providing a dual-purpose solution in a single product. Cover board selection considerations:
-Fastening requirements – many products offer reduced fastening schedules -Moisture resistance – options range in their ability to perform in the presence of moisture -Handling and cutting – product weight and ease of cutting -Insulating value – some options provide insulating value, adding additional R-value to the roof system
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