The Advantages of an IMP Roof

A closer look at the thermal performance and sustainability qualities offered by insulated metal panels
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Features and Benefits

It is very common to use IMP roof panels in Europe. They are not used as roofing solutions as much in the United States, but that is changing as architects here become more aware of the benefits of an IMP solution and as the building and energy codes evolve to require greater levels of thermal performance and continuous insulation. Also, IMPs support many sustainable design criteria and so they are often selected on projects that are either pursuing green building certifications or where the owners want the buildings designed to be green conscious.

Photo courtesy of All Weather Insulated Metal Panels

The roof on the Theorum Winery offers the look of traditional standing-seam roof for a stylish appearance as well as the high R-value, energy efficiency, and outstanding fire rating that come with IMPs.

Impressive Thermal Performance

Energy codes are increasingly requiring that building envelopes be designed to deliver higher levels of thermal performance. This means that building envelopes must do a better job of minimizing the movement of thermal energy across the assembly in the form of thermal gains in the summer or thermal losses in the winter.

The metric used to describe a material’s ability to resist heat flow is the R-value. IMP foam cores are is typically tested at 1-inch thickness. The higher the R-value of a material indicates that the material is better at resisting the flow of heat and is a better insulator.

IMPs have a foam core that can provide a thermal performance of R-7 per inch or greater. This R-value is impressive when you look at the typical thermal resistance of other types of insulation. Mineral fiber and cellular glass have a typical R-value of R-3 to 3.5 per inch. Expanded polystyrene typically offers R-4 per inch. Extruded polystyrene another popular insulation solution has an R-value of R-5. Many IMPs are manufactured with a type of polyurethane insulation that can achieve R-values of R-7 or more per inch.

Energy codes today can require the commercial envelope to contain enough insulation to achieve R-values in the 40s. This better-performing insulation can be used to create panels that achieve R-values of up to 45 in dramatically thinner solutions than could be produced with mineral wool or extruded polystyrene. Generally speaking, as the thickness of an IMP wall system increases from 1 to 6 inches, the R-values increase from 7 to 48. The R-value of roof systems also ranges from R-10 to R-48, as the thickness of the panels ranges from 1.5 to 6 inches.

Beyond increasing requisite R-values, the thermal performance of the building envelope can be improved by eliminating any thermal bridges. A thermal bridge refers to a solid connection of higher thermal conductivity between the warm side and the cool side of an assembly that allows heat to flow freely between the sections where the insulation is present.

Research into the science behind the thermal performance of a building has revealed that the effect of thermal bridging plays an important role, even in well-insulated enclosures. The R-value often does not include the impact of specific thermal bridges, so the industry is moving toward designing building enclosures with fewer thermal bridges, and the major motivators behind this movement are the model code bodies.

Photo courtesy of ATAS International, Inc.

IMPs on the walls and roof of this barn-style building provide superior insulating properties, and their outstanding spanning capabilities and one-pass installation makes them quick to install, saving costs compared to other wall assemblies.

Inherent Continuous Insulation

Code language is being modified to emphasize how important it is to avoid thermal bridges and the energy inefficiencies they create in the building envelope by requiring continuous insulation. Continuous insulation, or c.i., is defined by ANSI/ASHRAE/IES Standard 90.1-2019, Energy Efficiency Standard for Buildings Except Low-Rise Residential Buildings (ASHRAE 90.1) as, “Insulation that is uncompressed and continuous across all structural members without thermal bridges other than fasteners and service openings.” It is designed to minimize thermal bridging, primarily of wood- and steel-framed structures, and it can be installed on interior, exterior, or is integral to any opaque surface of the building envelope.

ASHRAE 90.1 shows a clear trend for requiring continuous insulation, specifically in climate zones 5-8. Properly installed, continuous insulation reduces thermal bridging, increases the effective R-value of the wall system, helps control condensation, and air/water infiltration.

IMPs have no compression of insulation and no thermal bridging. The joint geometry of IMP systems addresses thermal bridging in a more robust manner than typical site-built assemblies for walls and roofs, a design asset for maintaining thermal performance.

Sustainability Qualities

Code compliance and efficiency is one thing. Sustainability is another. The concept of sustainability goes deeper and demands more. Products that support sustainable design must do more than make interiors more efficient. They must simultaneously either improve, or at the very least not damage, the quality of the interior environment and the health of its occupants and minimize their environmental footprint. For that reason, green building programs consider criteria like the recycled content or recyclability of a product. They evaluate whether a solution off-gases chemicals that could be toxic to humans or deplete the ozone layer. IMPs support many of the sustainable criteria beyond improving the thermal efficiency of the project.

Recycled Content

Green building programs incentivize the use of products or materials with recycled content to increase the overall demand for building products that incorporate recycled content, reducing impacts on the Earth that result from the extraction and processing of virgin materials.

Recycled content is technically the content of a product or material that has been made from pre- and post-consumer material. Pre-consumer material is diverted waste from manufacturing. Post-consumer material is waste that is redirected from landfills after a consumer has used it and put to use in other forms.

The steel faces in an IMP contain a minimum total recycled content of 30 percent or more. The post-consumer recycled content is approximately 23 percent and pre-consumer recycled content is approximately 7.3 percent.


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Originally published in Architectural Record
Originally published in November 2020