Insulated Metal Panels Used for Low-Slope Roof Projects

For years, insulated metal panels (IMPs) have been used for non-load bearing exterior wall, partition and roof panels for projects that required claddings to meet standard design loads, including wind and deflection resistance. However, the very nature of combining components—in this case a semi-rigid urethane core and light-gauge steel facings—into a composite creates a much stronger building module.

Roofing IMPs are a strong building module with value

By William Lowery

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In this case, the sum of the components far exceeds the limited physical properties of each. Many traditional low-slope roof deck assemblies require products to meet not only resistance to wind and deflection standards, but diaphragm shear resistance values as well.

Over the last few years, several leading IMP manufacturers, through their research and development teams, embarked on physical testing to see what diaphragm shear resistance levels could be achieved, and then compare the results to typical steel deck assemblies.

Not surprisingly, the results of initial testing showed IMPs performed extremely well. Subsequent testing at higher loads and with various external gauges of steel and fastening combinations established the data needed to publish diaphragm resistance tables for roof decking.

When it came to practical use, earlier efforts to push IMPs into the U.S. low-slope roof market gained little traction because they included complete assemblies. That is, the roof deck arrived at the job site with the membrane pre-adhered.

In concept it might have made a lot of sense, but without the ability to use exterior fasteners through the composite deck, there was no way to achieve diaphragm shear resistance. Furthermore, the width limits on the panels required too many seams, prompting concerns about leakage.

Nonetheless, an IMP roof deck combined with a membrane remained rich in obvious benefits over traditional steel deck-based assemblies. Initial installations of IMP roof deck panels and a field-applied membrane have revealed these advantages:

Installation: IMP roof deck installations eliminate the layering, staggering and then fastening of roof insulation fiberboards to the B deck, a time-consuming, costly step. Also, an IMP roof deck can be installed in rain and serves as a far superior substrate.

Strength: Not only is an IMP roof deck highly resistant to damage during and after installation, but the deflection resistance (transverse load) is also superior to traditional assemblies.

Better insulation: Because the semi-rigid urethane core is encapsulated with impermeable steel facings, it provides R values of approximately 8 per inch of thickness at 40 F mean temperature. This means a thinner monolithic roof assembly requiring less roof edge trim.

Versatile substrate: Wind uplift testing has been completed for both mechanically attached and field-adhered Thermoplastic Polyolefin (TPO) and Polyvinyl Chloride (PVC) single-ply membranes. The former attach into the exterior primed steel substrate only and not through the entire composite panel, preventing leakage.

White interior finish: IMP roof decks are supplied as a standard with a nominal 1.0-ml embossed white polyester factory-applied, high-heat paint finish that will lower interior lighting requirements.

Fewer fasteners: For assemblies requiring diaphragm shear resistance, IMP deck panels are attached to the secondary steel supports using low-profile, deck-style fasteners similar to those used to attach both the roof insulation board layers and the single-ply membrane, with far fewer fasteners. For assemblies not requiring diaphragm shear resistance, IMP deck panels can be attached via hidden joint fastening. In either case, the primed steel substrate is ready for installation of the single-ply membrane. Also, the Induction Welding Technology with the All Weather Insulated Panels’ OneDek system will provide further installation efficiencies.

Membrane: Membranes tested and approved in combination with IMP roof decks include 60-ml white TPO and PVC, the white being preferred for lower carbon footprint.

Speed: IMP roof deck panel assembly should allow for a building to be dried in much faster than traditional field-assembled roof assemblies, and can easily be applied in sections, allowing for greater flexibility in construction scheduling.

Easy to reroof: At some point, when the single-ply membrane needs to be replaced, IMP roof deck panels will continue to perform as the insulated substrate. The roof remains intact during repair. If an original membrane has been fully adhered, a new mechanically attached membrane can be installed over it. If the old membrane was mechanically attached, it can easily be removed and replaced. These significant savings cannot be assumed by owners of buildings with traditional roof assemblies.

Warranty: Because the complete roof assembly, inclusive of the deck, is tested and available under single brands, a 20-year “top-to-bottom” warranty is available from the manufacturer.

The savings achieved during installation add to the value of roofing with IMP products. But there’s something even more important to contractors and building owners. IMPs bring peace of mind by increasing the chances of a project coming in on time and on budget.

William Lowery is president of All Weather Insulated Panels, Vacaville, Calif. To learn more about IMP roof deck products, go to www.awipanels. com/onedek-list or email

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