Common IMP Roof Installation Mistakes

Insulated metal panel (IMP) roofs provide a number of benefits, including ensuring a tight envelope and a high R-value. However, those benefits won’t be realized if mistakes are made during the installation process. Here are five mistakes to avoid when installing an IMP roof.

Information on five mistakes to avoid when installing a metal roof

By Al Detmer

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Not Starting with a Level Surface

Before laying the first panel, it is imperative to make sure the steel structure is in line. Failing to do so can result in a poorly finished product. Installers need to check to make sure the purlins are level and square. This can be done by pulling a dry line across the steel or using a laser level. Most IMP manufacturers will specify the amount of tolerances they allow.

Installing IMP roof panels on a frame that is out of spec will cause two problems. The first is it will be difficult to lock the panels together. The second is that when the sun shines on the roof, it will have an oil canning effect and show the ripples in the roof. Oil canning is also known as elastic buckling or stress wrinkling.

Poor Caulking and Taping

All IMP roof installations involve the use of butyl caulk and butyl tape. The interior joints get caulked and provide a vapor barrier. It is crucial that installers use a heavy, even bead of caulk. Butyl tape is typically used on the exterior seams, and is applied to the male leg, which has a 90-degree angle. Neither is difficult to apply, so mistakes are typically due to sloppy workmanship—the results of which may not be noticed until the rainy season or when cold weather and warm interior temperatures meet, causing condensation.

Loose Foam-to-Foam Connections

On an IMP roof, the foam panel provides the R-value. It’s probably one of the main reasons that IMPs are specified. If the foam-to-foam joints are not tight, the envelope will be compromised by vapor leaks. Repairing gaps in those joints is a major endeavor due to the height of most buildings.

Bad Seaming

Most IMP roof installations will involve the use of an electric seamer. The seamer rolls and forms the final bend when panels are joined. Prior to seaming, clips (concealed fasteners) are used along the outside edges of each panel to keep them in place. A hand crimper is used to pull the clips together tight. If the clips are not properly installed, the electric seamer will bounce off and leave a gap that will allow air and water in.

Poor Lap Joints

Lap joints are where two panels butt together. Failing to make sure the joint is tight will produce a vapor leak, compromising the integrity of the envelope. What would cause these problems when installing an IMP roof? One reason would be a lack of experience on the part of the installer.

Experience in other types of roofing does not mean a company or crew has the skills needed to properly install an IMP roof. Another reason is poor workmanship. Installation problems should be avoided at all costs when using IMP roofs because removing panels after the work has been completed to fix problems is very difficult, costly and time consuming.

Most IMP manufacturers provide classes and seminars on proper installation procedures. Contractors can contact manufacturers for recommendations on finding qualified installers.

Al Detmer is field technical services manager for Kingspan Insulated Panels North America, Deland, Fla. For more information, visit

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