Like any roofing system, metal roofs can suffer from leaks and failure over time. Applying a coating or sealant may not be the best long-term solution. Fortunately, building owners looking to recover or replace a metal roof have several options available.
Consider the Current Roofing Situation
First, take time to assess the situation at hand and consider numerous factors that may impact your roofing decisions. For instance, what was the cause of the problems with the current roof? How much more weight can the building structure carry? Is additional insulation desirable? What are the insurance or building code requirements of a new system? Answers to these questions can help determine which reroofing or recovering option is best for your needs.
Five Options Available
Building owners considering reroofing or recovering a metal roof have five basic options:
- Metal Roof Replacement involves removing the old metal roof and replacing it with a new metal one. Advantage: An owner can start fresh with a new roof. Disadvantages: Price, disruption to building users during installation, and the possibility the roof will eventually suffer the same problems as the original roofing system.
- Metal Roof Recover is an option if the building structure is strong enough to withstand the weight of an additional metal roof. Advantage: The same durability and other advantages of the original metal roof. Disadvantages: Can be subject to the same problems that made the original roof fail, and can also be a very costly option.
- Coatings or Liquid Applied Systems is the least expensive option initially and good at addressing corrosion and leaks. Advantage: Most coatings are white, and therefore reflect the sun’s rays, resulting in energy savings. Disadvantages: Coatings do not “give” much with expansion and contraction of the metal roof, and are therefore susceptible to cracking at joints and seal areas; performance is also tied to the preparation of existing metal panels and weather conditions at the time of application. Additionally, it is not uncommon to “re-coat” a roof every five years of service life, which can become an expensive proposition over 15 to 20 years.
- Polyurethane Foam Recover is applied directly to the existing metal roof in a manner similar to the way a coating is applied. Advantages: Adds significant
- R-value to the roof, and does not require reinforcing fabric at the laps and fasteners. Disadvantage: Systems tend to be somewhat rigid, and do not accommodate movement well.
- Single-Ply Recover involves installing a single-ply membrane, such as a hot-air weldable TPO, over the existing metal roof. Advantages: Membranes are available in white and light colors, which reflect the sun’s rays and can lower cooling costs; flexible TPO membrane can easily accommodate the movement that is intrinsic in metal roofing, as well as any plane changes in the roof. Cost of additional insulation is already built into the total cost of the roof installation (usually comparable to the cost of applying two coatings). Some single-ply systems installed over metal roofs come with a standard 20-year warranty, while roof coatings typically offer a five- to 10-year maximum warranty period. Lastly, some single-ply systems are also not as sensitive to weather conditions during the installation process as a coating.
Why Metal Roofs Leak
Both types of metal roofing systems – “through-fastened,“ where fasteners are installed through rolled-formed panels into the structure supports (purlins) of the building and at the laps; and “standing seam” roofs, which are also secured to purlins and use hidden clips and machine-roll-locked seams – have several areas where they are vulnerable to leaks. One is at the end laps of the metal panels where the original butyl tape seals age and fail. Another is at the fasteners. An inherent characteristic of metal roofing is that it expands and contracts with temperature changes and, over time, this can enlarge the fastener holes and/or damage any fastener seals. Finally, metal roofs are typically installed with panels that have lapped joints – much like a shingled roof – and the caulking and sealants used at these areas can eventually deteriorate, especially in lower sloped systems.Sam Everett is marketing manager at Stevens Roofing Systems (www.stevensroofing.com), Holyoke, MA.
