Metal Roofing Over Metal Roofing

When the large warehouse and industrial metal building roofs of the 1950’s and 1960’s started to fail, including one of his own, one of the true pioneers in the metal building industry, “Red” McConnohie, recognized a problem needing attention. “Red” set out to develop a system that allowed a new metal roof to be installed without the cost and liability of removing the existing roof. He knew others had used hat sections attached to the major ribs, but that approach depended on the new roof loads being transferred into the existing structure through only the old skin of the existing metal roof. Engineering reviews of that method proved it to be inadequate for wind load transfer.

A structurally sound, long term solution for metal roofs was needed. Whoever knows “Red” also knows that he is not one to give up when there is no obvious answer to a question and soon enough he determined that a “Notched Zee” was going to be the best solution. This modified purlin would span over the ribs and rest firmly on the flat portion of the existing roof panel allowing the fasteners to go directly through the base flange of the zee and old panel, and into the existing structure. Thus was born the Roof Hugger system which has been in use since 1991.

As we all know, what can be devised in plan does not always work in the “real world”. This method of reroofing an existing metal roof with a new metal roof, without having to remove the existing roof, however, is one of those plans that work. The obvious benefits are as follows:

1. No need to remove the existing roof panels, exposing the interior to the outside elements.
2. No interior space contamination from air borne particles such as dust, dirt, rust, etc. caused by the roof removal.
3. No need to remove existing roof insulation. Additional insulation can be added between the old and new roof, improving existing energy performance.
4. Edge and corner conditions, per ASCE 7, require higher wind uplift resistance than was originally designed. The Roof Hugger system can be designed to meet these new code requirements. This design work must be performed by a licensed professional engineer in the state where the system is to be installed. The professional will identify the loads per the applicable code, review the panel system capacities and check the framing system to insure each element will adequately perform its’ structural task.
5. Roof Huggers can significantly increase the existing sub-structural support system, as well as structural rigidity.
6. Many of the old metal roofs that need replacing were attached by “through fastening” directly into the metal panel surface. Over many years of expansion and contraction, these fasteners were either loosened or created an elongated hole in the surface of the metal panel. Conditions that allowed water to infiltrate the weathering surface. Part of the retrofit process is to choose a new metal roof panel system. Today’s standing seam roof systems are attached by concealed clips and provide uplift resistance while being able to slide up and/or down slope as the panel expands and contracts, eliminating this panel trauma.
7. Many first generation paint systems on the original metal roof allowed the finished surface to chalk, fade, or peel excessively. Today’s roofs can be permanently replaced by a new roof panels with Kynar or equal based paint systems field proven to last 35 years and more.

Examples of how the Roof Hugger system has been used throughout the USA are as varied as their locations. Three (3) such case studies, showing the benefits of how this system can yield a new modern metal roof system, are as follows:

Printing press facility – Mobile, Alabama
a. It was determined that the panel clip spacing for a metal roof installed about 2000 was deficient. After serious consideration of options how to correct this problem, including the possibility of removing the existing roof and replacing it with another metal roof, it was determined to use a Roof Hugger system and install a new metal roof system. The owner’s architect was concerned about the cavity between the roofs being conducive to condensation formation, which was solved by filling this cavity completely with un-faced fiberglass insulation. In addition, because the clip spacings were so random, many of the edge and corner conditions had insufficient attachment points and/or incorrect attachment spacings. With the use of the roof Hugger system, these conditions were corrected by locating the new sub-structural members where needed to yield the proper spacings. All work was done without adversely affecting the continual printing processes inside the building.
b. The contractor for this project was Keith Moseley Construction, Saraland, Alabama.

Fish hatchery building – Coastal Maryland
a. This project entailed an old metal building roof constructed in the mid 1970’s. The existing roof system was attached to the building purlins by “through fastening” the panels at the purlin locations. These fasteners, over the years, had loosened in some places and caused elongated holes at the eaves.
b. The high humidity inside the building had, over the many years, permeated the interior vinyl vapor barrier enough to allow back-side condensation on the original panels. Several of the panels were deteriorating from the inside-out. Attempting to remove this insulation and metal panels would have resulted in a large amount of particulates falling into the fishery tanks below. The existing roof purlins were tested to determine that no appreciable deterioration of the top leg, necessary for proper fastener pull-out resistance, had occurred. Leaving these materials intact, and installing an exterior Roof Hugger system and a new metal panel system, allowed the project to proceed without negatively affecting the building’s interior operations.
c. The contractor for this project was Brothers Services Company, Hampstead, MD.

Middle School in central North Carolina
a. While this school system initially wanted to remove the sloped metal roof systems due to faulty paint, they opted to allow the existing roof panels to remain while a Roof Hugger system was installed, along with a new “concealed fastener” metal roof system. Since the original metal roof was not insulated, allowing condensation on the interior surface, new un-faced insulation was added in the cavity. The resultant new composite envelope had an R value that exceeded 20 as opposed to less than 2 prior to the retrofit. Of course, the new metal panels came with a 20 year guaranteed Kynar based paint system.
b. The contractor for this project was LaFave’s Construction, Landis, NC.
“Red” definitely knew what he was doing when he developed his engineered Roof Hugger system. It has proven to be an extremely effective solution to reroofing the millions of SF of warehouse and industrial metal building roofs as well as allowing for a method to rectify faulty installations of current metal roofs. This method has a proven track record, with over 60 million SF of product in place, and should be considered whenever an existing metal roof requires retrofitting.

The author of this article, Chuck Howard, PE, was privileged to be involved with the case studies mentioned. He can be contacted at chuck@metalroofconsultants.net with any questions.