Installation Archives - Hunter Panels

Determining Minimum R-Values on Tapered Insulation Systems

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No. The terminology “Average R-Value” for tapered systems is an outdated term and not recognized by the IECC.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

Cricket Design Guidelines for Tapered H-Shield Products

– 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-Layered Polyiso Roofing Insulation Recommendations

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.