Metal-Over-Metal Retrofitting Trends

by David Flaherty | 9 September 2024 2:37 pm

A metal roof in shop, which will be used in a building retrofit. — Many older buildings across the United States have been retrofitted with new metal roofs.

Innovation is always taking place in the construction industry. New ways to do things, better products, and faster, more accurate data to build our designs around. This is especially true in the retrofit metal roof industry.

Retrofitting of an existing building is becoming increasingly more technical than it was in the early 90s when I began doing retrofits. Uniform loading of the roof design is a thing of the past. We now have corner zone, edge zone, and ridge zone wind load areas. We have unbalanced snow loading, higher ground snow, and wind speed designs.

This is not news to anyone involved in new or retrofit construction. What is changing the retrofit business is the addition of photovoltaic panels installed on older metal roofs.

As the country becomes more and more energy-conscious and the cost of electricity continues to increase, adding photovoltaics after retrofitting with a new roof makes good sense for the following reasons:

Metal roofing is the only roofing material that has a service life exceeding the life of the solar panels.
The cost of the solar panels is often supplemented by local and federal tax credits.
Many utility companies will buy the excess electricity generated by the panels.
The building owner has their utility bill reduced.
The panels can also be installed with specialized roof clamps that eliminate penetration and potential leaks in the new roof panels.
The portion of the retrofitted roof that supports the solar panels may qualify for accelerated depreciation.

So, everything is all good, right? You know it is, except for one small detail, the weight. New solar panels can add 2.72/m² (6 lbs/sf) or more. That is a lot to ask the old metal building purlins, which were never designed to support that load amount.

Now the question becomes how do you deal with this additional dead load? In the past, we would typically have to go inside the existing building and try to add additional purlins to handle the weight. This is a slow, difficult, and expensive process if it is over an office area, meaning the only way to accomplish this is to remove the old roof, add purlins, install additional ones at the needed spacing, and then reroof.

Fortunately for our industry, notched zee, retrofit sub-purlins have been proven to add additional capacity to the existing purlins. Depending on the existing building’s construction, load increases of 2.72-5.44 kg/m² (6-12 lbs/sf) have been accomplished.

A structural analysis will need to be done because not all buildings will enjoy this increase, but most will. This makes retrofitting with the thought of adding solar panels now or in the future a no-brainer. It can also make the cost of the roof retrofit much more affordable.

Ask your panel supplier or retrofit framing supplier about this feature on your next re-roofing project.

Dale Nelson is the president of Roof Hugger, LLC. Tampa, Fla. Founded in 1991, Roof Hugger became a division of the LSI Group, Logansport, Ind. in 2016. Roof Hugger is a nationally recognized manufacturer of retrofit framing systems for existing metal roofed buildings. Dale holds a Class-A Florida Contractors License and a Florida Real Estate Brokers License. He has been in general contracting since 1973.

Source URL: https://www.metalconstructionnews.com/articles/metal-over-metal-retrofitting-trends/