Re-covering the Roof: Right and Wrong

Building codes, insulation needs and age are just a few considerations to take into account

By Loren Snyder  

Whether it’s because many facilities do not have periodic roof inspection practices in place, or simply because a roof is usually out of sight – and consequently out of mind – the need for reroofing can come as a costly and unwelcome surprise.

Exactly how costly is reroofing? That depends, say roofing consultants. Building owners essentially have two options: re-covering the existing roof or tearing it off and replacing it.

Re-covering can postpone more expensive roof replacement projects, but if a re-cover is performed without due consideration, the new membrane can exacerbate existing problems within the roof. On the other hand, a new roof is a better way to guarantee protection, but it comes at a cost.

Whether a re-cover or replacement project is best depends on many factors. Insurance considerations, building codes or other regulations might prevent re-covering a roof. For example, the International Building Code prevents more than two systems on a roof deck. A need to replace insulation or portions of the deck are among the other factors that can force replacement.

But roof replacement can be a dirty, noisy, dusty endeavor. If sensitive materials or technologies, such as those found in surgical suites, or expensive, sensitive electronic equipment exist beneath the roof, building owners might want to consider re-covering the roof to mitigate business disruption.

Essential Points

The first step in determining whether to re-cover the roof is to conduct a thorough evaluation of the existing system. The deck structure must be able to support the extra weight of another roof. What’s more, the re-cover should be applied to an existing roof that is well attached to the substrate. And it’s crucial that roofing insulation beneath the existing membrane be dry and in good condition. Re-covering wet insulation will likely shorten the life of the re-cover system. Energy loss also increases when roof insulation is wet.

Local regulations must also be taken into consideration. Because his company is based in northeastern Illinois, Tom Hutchinson, RRC, AIA, of Hutchinson Design Group often works on projects that must adhere to the energy code adopted by Chicago several years ago. Among other things, the code requires that, if a project on an existing building exposes the roof deck, the roof must meet energy standards that often require additional insulation and the use of roofing materials with greater solar reflectivity.

In other words, building owners who re-cover their roof instead of performing a tear-off are exempted from Chicago’s energy code insulation and reflectivity regulations. “The catch to that exception is that building owners need to check their deck and insulation carefully and should still consider a tear-off if necessary,” says Hutchinson.

Building owners also need to consider changes in building use. “In rural Illinois, there’s this beautiful facility,” Hutchinson says. “Just gorgeous. But it changed hands recently and is being made into a water park — an indoor water park.” According to Hutchinson, the facility’s new owners wanted to know how the change from an office structure to indoor water park would affect the roof. The answer: Interior humidity levels would surge, requiring vapor retarders and extra attention to curb the build-up of moisture in the roofing system.

Although re-covering a roof might not be the perfect solution, Hutchinson says, there is one often overlooked benefit: It allows facility executives to budget for a new roof and to build the case with senior management for replacement.

But roofing is an expensive process, and deferring a tear-off might be a kind of shell game in which costs are shifted to other aspects of the roofing process. As Curt Liscum, RRC, of Benchmark Inc. points out, deferring tear-off costs until later is a risk because it might prove more expensive to dispose of roofing materials.

Weighing Benefits

When it comes to re-covering roofs, the primary benefit is the reduction in cost. According to Gary Cattel, RRC, PE, president of Roof Engineering Inc., labor costs on a replacement project typically range from 75 cents to $1.50 per square foot to remove material from the existing system. And then there are the labor costs of application and potential disposal costs.

Researchers at the Oak Ridge National Laboratory estimate that for low-slope roofs, the tear-off and roof replacement costs are approximately $9 per square foot. Adding to the expense is the cost of landfill disposal of old roofing materials, including asphalt, foam and asbestos.

Re-covering does require some labor to prepare the existing roof for new material. Contractors will need to slit or shave off blisters to allow the area beneath to dry. And depending upon the roof type, at least a partial tear-off might be required to remove wet materials or remove aggregate and create an optimum slope. Conventional wisdom and many building codes say that a 25 percent removal of existing materials is the limit. After 25 percent removal, the cost of re-covering begins to approach that of a complete tear-off.

Another benefit of re-covering a roof is using the insulation already in place as part of the existing roof. Existing insulation can be considered when determining the necessary R value.

Construction time with re-covering roofs also is minimized, which can, in turn, minimize interior disturbances or liabilities from having a facility exposed to the elements.

But re-covering a roof has its share of risks. The short list of risks includes water in the existing roof, code violations and an existing roof that is not compatible with materials used in the re-cover, which can lead to a lack of adhesion to the substrate or a compromised deck structure.

But there are other issues to consider. For example, there is the risk that the re-covered roof membrane will act as a vapor retarder and trap condensation beneath the recover.

Other items to be aware of include: structural deficiencies; flashings that cover existing weep holes, causing water to run directly behind the flashings and compromise the re-cover; and mechanically fastened re-covers that penetrate the existing roof and create a thermal bridge.

Staying on Track

Assuming that all the conditions are right and the choice has been made to re-cover the roof, facility executives must take steps to keep the project on budget and on schedule.

Both Cattel and Hutchinson advise owners who are re-covering their roof to proceed with caution. “Property managers who stipulate project requirements may be assuming a designer’s role,” says Cattel. “The person in that role needs to be fully aware of code requirements and long-term performance considerations.”

Because projects are usually bid upon, facility executives should choose a contractor carefully. Don’t simply hire the company with the lowest bid; look for a company that has an established reputation.

Hutchinson advises reviewing items of repair at a preconstruction meeting and says repairs should be itemized in a contract before construction begins. And what about a warranty?

“Whenever the existing roof system is left in place, it adds more elements to the equation of performance and longevity,” says Cattel. “These additional elements tend to affect performance negatively.”

As a result, roofing manufacturers tend to be wary about giving long warranties.

“In some cases, you may not be able to get a warranty at all,” says Hutchinson. “Manufacturers aren’t going to know what kind of system the re-cover is attached to, and so in providing warranties, they might have to do it on a case-by-case basis.”

The decision to re-cover a roof is ultimately about saving money. If all the conditions are right, a re-cover can save facility owners money and avoid the business disruption that a complete tear-off might create. Focus on RCI The Roof Consultants Institute (RCI) is an international, nonprofit association of professional roof consultants, architects and engineers who specialize in the specification and design of roof systems.

RCI’s professional ranks include three principle categories: registered roof consultants, quality assurance observers and registered roof observers.

The consultants are experts on specific roof types and materials. Professional members operate without a conflict of interest and are not affiliated with any manufacturer or product.

The RCI’s 1,800 members include professional, industry and facility manager members.

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  posted on 12/1/2003   Article Use Policy

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