A metal roof system can be through-fastened or standing seam, referring to the method used to attach it to a building. With a through-fastened roof, fasteners are installed through the metal panels, holding them to the structural supports and the laps. With a standing-seam roof, concealed clips and roll-locked seams are used to secure the panels.
Periodic inspection and maintenance of your roofing system is the key to maximizing its service life and preventing early failure. Depending on your location, inspections should be conducted between two and four times per year and after any major storm. Important inspection points include:
Supporting Structures:Look for water stains on the building exterior, which may suggest problems with flashings or walls. Check the underside of the roof assembly for water stains on insulation, ceilings, piping, ducts and structural members to identify potential leaks. Also check the underside of the deck if exposed. Noting problem areas on a diagram will help you identify corresponding defective areas on the roof.
Fastener Condition:Check for missing, loose or deteriorated neoprene fasteners. Expansion and contraction of the metal panels due to temperature changes or wind-induced movement can enlarge the fastener holes. In through-fastened systems, this movement often causes the holes to become slotted, compromising the roofs watertight seal.
Sealant Condition:Sealant exposed at terminations and flashings will eventually crack or shrink and need replacement. Unanticipated component movement, especially in older systems, can also result in sealant failure.
Corrosion of Panels:Contaminant exhaust, ponding water and condensation drainage from HVAC units can corrode metal panels. Debris accumulating on the roof, especially metal shavings, can accelerate corrosion and should be removed regularly. Note: Be especially careful when walking over a metal roof that has been coated, as corrosion can sometimes hide beneath the coating, creating a safety hazard.
Interior Gutters:Gutters installed where two sloping roof sections come together are referred to as interior gutters (as opposed to gutters on the exterior perimeter of a building). Unless interior gutters are constructed of stainless steel with welded seams or fully lined with heat-welded thermoplastic membranes, leaks can be a continuing headache. Differential movement of two roof sections tends to break soldered or caulked seams. Again, accumulation of debris can cause problems by plugging drains and causing the gutter to overflow. Undersized gutters or an inadequate number of drains can also contribute to overflow.
Wind Damage:Look for damaged or missing metal flashings at the roof perimeter. After major storms, walk the perimeter areas to ensure roof panels are secure, checking for deformed or uplifted panels. Failure of fasteners or concealed clips can cause roof sections to float even though seams still appear to be intact.
Roof Penetrations: Rooftop penetrations will be a source of leaks if not properly flashed. Improper flashing installation may be the result of using unskilled contractors or taking budget short-cuts. Drainage and structural movement must be considered when flashing is installed.
Damage to Panels:Foot traffic can damage the watertight integrity of laps and seals at fastener locations. In some cases, it can even crack the light-gauge metal, allowing moisture infiltration. Workers should avoid the raised portion of the panels and walk on the flat surfaces, preferably close to or over structural members. If there is significant roof traffic, consider installing a walkway system. Elevated metal walkway assemblies are available to eliminate panel deflection.
Deflection:Another issue of which to be aware is the practice of attaching equipment to the purlins below the roof. If design loads are not taken into account, the purlins can deflect, causing the roof panels to redirect. This will result in broken seals at seams and laps as well as ponding water. If design loads are significantly exceeded, catastrophic structural failure could occur.
If your roof is at the end of its service life or repairs are no longer cost-effective, its time to decide between a new roof and a retrofit application. You are faced with the task of identifying possible solutions from scores of manufacturers that provide metal roofing, single-ply coating and spray-on foam systems. Here are some questions to help you narrow the options:
- For what is the building used? How does its current or projected use impact the roof system?
- What was the cause of original roof systems failure?
- What is the extent and nature of previous roof repairs?
- What are the building code and insurance requirements of a new system?
- Is additional insulation required or desirable?
- Is a vapor barrier required?
- What weight/structural limitations apply?
- What are the buildings service-life expectations or requirements? For example, if the building will be demolished or replaced in five years, it doesnt make sense to install a 20-year roof system.
- Will new rooftop units or other penetrations be added, and how will that affect the requirements for roof traffic?
- Is resistance to chemical emissions or contaminants a requirement of the new system?
- Is the existing drainage system adequate?
- What budget or scheduling constraints affect the project?
Coatings or Liquid-Applied Systems.Coating systems will address surface corrosion and improve the appearance of the roof. The reflectivity of a white coating can help reduce thermal heat gain, resulting in lower interior temperatures. If the existing roof is sound, there is minimal panel movement (or the movement can be controlled), and loose fasteners can be tightened or replaced, a liquid-applied system can correct leaks at laps and fasteners.
There is a variety of coating systems with different properties and costs. The most common systems use elastomeric coatings. The application process starts with a thorough cleaning. Rusted panels are treated with a primer and damaged panels are replaced. Special flashing materials, such as self-adhering tapes and reinforcing fabrics, are applied at laps and flashings, and exposed fasteners are sealed. The coating is then applied in a number of coats to achieve the required thickness. Many coating manufacturers offer limited warranties up to 10 years, depending on system details and coating thickness.
Polyurethane Foam Re-Cover.This system is not typically used over architectural roof systems. Sprayed Polyurethane Foam (SPUF) can be applied over an existing system if the roof is of sufficient gauge and otherwise meets the manufacturers requirements. Since the SPUF system is somewhat rigid, it doesnt accommodate movement very well, but it has the distinct advantage of adding significant R-value.
This virtually eliminates damage from expansion and contraction of the roofing surface, since the metal panels are insulated from daily temperature changes. In addition, its not necessary to apply reinforcing fabric over the laps and fasteners.
The application process is similar to that of coatings. Damaged panels must be replaced. Surface corrosion must be treated or primed to ensure good adhesion of the foam. The foam is then spray-applied, generally in several passes, to the desired thickness (at least 1 inch). Finally, a coating is required to protect the SPUF from ultraviolet damage. If desired, granules can be set in the coating before it dries to improve resistance to foot traffic and provide additional traction.
Single-Ply Re-Cover.Single-ply systems are frequently used to recover metal roofs. You begin by replacing damaged roof panels, then insulation is cut to size and installed on the flat-panel areas to match the height of the raised panel ribs. A second layer of rigid board insulation (preferably a moisture-resistant insulation such as polyisocyanurate) is mechanically attached over the entire roof surface. The insulation provides additional R-value and a stable substrate.
Finally, a single-ply roofing system is fully adhered or mechanically attached. Manufacturers offer specifications for installing their systems over metal roofing. As most systems consist of light-gauge metal panels, its imperative the correct type and frequency of fasteners is used. Factory Mutual Global, a commercial-property insurance and risk-management company, recommends that roof fasteners actually engage the underlying structural members. If aesthetics are an issue, some manufacturers offer a ribbed system that is similar in appearance to architectural metal roofs.
Metal Re-Cover.A new metal roof can be installed over an existing low-slope, metal roof. In this case, the existing building must be sufficient to withstand the added weight. Corroded panels and fasteners from the existing system do not generally require replacement, though its a good idea to install fiberglass blanket insulation between the two systems. This option can provide an excellent new roof while minimizing the labor associated with removal or repair of the existing one. Disruption of building operations is also reduced. Systems with roll-locked seams are preferred, as they create fewer problems associated with exposed fasteners and neoprene gaskets.
Replacement With a New Metal System.In some cases, its necessary to replace the existing roof with an entirely new system. Perhaps the existing structural supports are corroded, many new roof penetrations are needed, or other conditions exist that make it expensive or undesirable to leave the existing roof in place.
Choosing a Contractor
When deciding which re-roofing option is best for you, there are many factors to consider. One of the most important is the selection of a roofing contractor. The following questions may help you choose:
- Has the contractor spent time on your roof, examining and verifying existing conditions?
- Has the contractor asked questions to understand how a roofing project might impact your business?
- Does the contractor have the training, knowledge and experience to make recommendations appropriate for the existing structure?
- Does the contractors crew have the supervision, training, skills and knowledge to safely and effectively complete the project?
- Does the contractor have a safety plan that identifies potential risks to you, your employees and your facility, and includes countermeasures to reduce them?
- Will the contractor leave your facility and grounds in the same condition in which they were found?
- Does the contractor have a clearly defined process for making sure the project goes smoothly, i.e., holding preconstruction meetings, addressing issues, identifying potential risks, developing a schedule, identifying staging/access areas, and establishing a clear line of communication?
- Is the contractor responsible and trustworthy? Will he be there in the future to assist with the long-term care of your roof?
These are questions only you and your company can answer. If you already have a relationship with a roofing contractor you trust, you are well on your way to roofing peace of mind.
Greg Thirnbeck is the vice president of contract administration for D. C. Taylor Co., a Cedar Rapids, Iowa-based company with more than 50 years of commercial and industrial roofing experience. Mr. Thirnbeck is responsible for reviewing contract terms and conditions and assisting with risk-management issues. In addition, he helps national clients make informed roofing-related decisions, including preventive maintenance to roof-management programs. He is a Registered Roof Consultant and a member of the Roof Consultants Institute, National Roofing Legal Resource Center and Grain Elevator and Processing Association. D.C. Taylor delivers expert roofing and OmegaSTARR roof-retention services to keep facilities protected and secure. It has more than 60 service and roofing crews and five service areas: Atlanta; Cedar Rapids, Iowa; Chicago; Concord, Calif.; and Phoenix. The company has been ranked among the nations largest industrial roofing contractors for more than 20 years. For more information, visit www.dctaylorco.com.
Roof Maintenance Made Easy
By Teresa Sedmak, President, Everbrite Inc.
Your roof gets more abuse from the elements than any other part of your facility. Preventive maintenance will help you save money by giving your roof a longer service life. Here are some simple maintenance tips:
- Regularly clean all debris from the surface of the roof. This includes refuse that has gathered behind HVAC units, pipes and pitch pans, and any other roof penetrations.
- Replace broken or bent gutters, metal trim or downspouts. This will not only enhance the look of the facility but increase the life of the roof.
- Excess debris has a tendency to hold water, and broken gutters can also trap water. Do not allow water to pool on your roof under any circumstances. Not only does it increase the weight load on the roof, it contributes to deterioration and other problems, such as leaks.