Lowering the Risks of Reroofing

SUCCESS IN REDOING ROOFS OFTEN MEANS
CONTENDING WITH RUSTING FANS,
ABANDONED CONDUITS, CLOGGED DRAINS,
AND MISTAKES MADE BY OTHERS.

by Barbara A. Nadel, AIA

Continuing Education

Learning Objective:
After reading this article, you will be able to:

1. Identify at least 15 factors in structure analysis, owner requirements, and building use to consider in programming, designing, and specifying reroofing projects.

2. Cite authoritative sources and references for roofing information and research.

3. Write specification solutions for environmental problems that affect roofs and offer detailing/ specification tips to avoid preinstallation communication problems.

Much of the time, reroofing is a contractor's job. But an architect may be called in when a roof presents persistent problems or when reroofing becomes part of a larger renovation project. After a flurry of new membrane types were introduced in the 1980s, technological change has settled down, and most roofing technologies in common use now have a track record. This does not mean roofs are problem-free. They remain vulnerable to poor design, poor installation practice, and poor maintenance. More claims are filed each year regarding roof and wall systems than any other part of a building, according to a recent survey by liability insurer DPIC.

Retrofit roofs are not the same as roofs designed for new buildings. Undocumented existing conditions (such as a rooftop addition) may have been in place for a while and may be contributing to deterioration. Unforeseen environ- mental factors (perhaps grease from an added fan) and lack of maintenance may also shorten roof life.

Why did the old roof fail?
Most of the time, however, an architect is called in when the old roof leaks. A split or hole in the membrane may be an obvious cause, but for many roofs, finding the source of leakage is a tricky yet essential step toward getting the designed performance out of the new roof.

When faced with a roofing retrofit project, the two most important reroofing questions an architect should ask are why the original roof failed and why the building leaked. "Roofing professionals recognize that most failures occur at penetrations, substrate and material transitions, base flashings, and termination details,'' says Ken Bensimon, AIA, principal of KMB Architects in Olympia, Washington. "Incompatible materials may cause a reaction adversely affecting waterproof capabilities,'' he continues, such as a metal flashing to which a thermoplastic membrane won't adhere. He also explains that roofing commonly fails where penetrations are not detailed to account for building movement. A building may expand and contract or even permanently "grow'' due to changing temperatures and positive air pressure.

Jan Kalas, AIA, an associate at LZA Technology in New York City, frequently examines defective roofing systems for the forensic-investigations arm of LZA, a large engineering firm, to determine whether to restore, repair, or replace them. An existing-conditions assessment should not only evaluate the condition of the membrane but also identify any trapped wet materials and the source of leaks. Signs to look for include blistering and delamination of the roofing membrane, leaks, moisture and stains in spaces below the roof (such as on ceiling tiles), rips and holes in roofing or flashing, ponding water, and moss or other plant growth. If a spongy, uneven surface or water bubbling out of the membrane is encountered while walking on the roof, more detailed analysis is needed.

"Roofing is only as good as what's underneath it—the deck, substrate, and attachments between the roofing and the structural system,'' says Kalas. "Roofing leaks can damage the substrate and structure. Moisture infiltration can lead to indoor air quality problems caused by mold, bacteria, stagnant air, and standing water.''

Kalas usually follows visual observation with testing. Non-destructive testing includes infrared photography or nuclear scanning for moisture content. If such testing or observation suggests that roofing or substrate materials are wet, destructive testing may be needed. Destructive testing requires cutting into the roof and taking a piece out for analysis. This core sampling indicates the condition of the roofing, insulation, and subsurface deck.

For example, if a roof with a steel deck, perlite insulation, and a membrane over it has leaked and the insulation is wet, the insulation must be removed. This is critical because the deck will continue to rust, the metal fasteners for the replacement roof will corrode, and the new membrane will probably blister. The roof may not rest on a firm substrate, making it subject to premature wear or puncture.

One of the key decisions the designer must make is whether a new roof can be applied over the old roof or whether conditions warrant a "tear-off.'' The structural condition of the underlying roof deck to a great extent determines the answer, says Jack Robinson, the technical services deputy director of the National Roofing Contractors Association in Rosemont, Illinois. New roofs add weight that might not have been anticipated in design, for example. "Inspect the underside of the roof deck to see if the existing structure is damaged,'' says Robinson. "Look for signs of rust in steel decks, rot in wood, or spalling in concrete. If there is damage, you need to repair or replace the decking first, which can mean a tear-off rather than a re-cover.'' He also advises making sure no conduit runs above or below the roof deck in channels to avoid penetrating the conduit with new roofing fasteners.

A reroofing may involve improving earlier, unfortunate design decisions. When dealing with retrofits, says Kevin Cash, associate at Simpson Gumpertz & Heger, Inc., in Arlington, Massachusetts, a consulting firm that specializes in building-envelope design, check the existing roof-drain system, especially in buildings more than 15 years old that may not have been sized to modern standards. If the existing system and roof drains are undersize, it may be necessary to substantially upgrade or replace the entire drainage system to current codes. In such instances, coordination with local building officials may be required. Drains may also have been placed too close to walls and parapets, where water can be trapped or where there is insufficient space for the roofer to flash them properly.

"Skylights are often placed over the interior construction and not where the roof wants them,'' Cash explains. Skylights and other interruptions in roof slope require crickets on the up-slope side to divert runoff. An older building may have accumulated a junkyard of conduits, pipes, and mechanical equipment, all of which can cause leaks and make reroofing nigASParish. Part of the reroofing analysis includes considering which of these items can be removed or relocated.

Recently, roof-mounted antennae for cellular phones have proliferated. Although cellular antennae are said to generate harmful micro- waves and extensive exposure may pose a health risk, more owners are adding them to roofs and facades because they generate income. "These antennae must be placed at a roof high point, where water is unlikely to collect, not at a low point, where water will inevitably find its way into the building,'' cautions Peter Blaufeux, AIA, principal of Peter Blaufeux AIA Architects in New York City, who specializes in building exteriors and institutional work. Installing any rooftop items after roof completion and inspection may also void a warranty.

The National Roofing Contractors Association (NRCA) offers a great deal of guidance on various commercial roofing systems (the association can be reached at 847/299-9070). The NRCA fields more than 4,000 calls annually from architects, engineers, attorneys, contractors, and homeowners asking for roofing advice and contractor referrals. It publishes a roofing manual, roofing-material guides, and the Handbook of Accepted Roofing Knowledge (HARK). The NRCA also publishes more than 300 detail drawings on low-slope roofing on CD-ROM and for CAD systems, and maintains Project Pinpoint, a program identifying roofing problems and solutions using new technology.

Selecting a reroofing system

Kalas decides on a reroofing approach by balancing installation and life- cycle costs, energy-conservation performance, and the degree of protection the owner wants to maintain. He develops strategies with options for roofing systems and cost estimates for each alternative.

When choosing roofing systems, architects should consider the building use and the client's financial circumstances. [See "Simplifying Single-Ply Roofs,'' RECORD, February 1995, pages 38-29, for an overview of standard roofing types.] Developers generally want low first cost, even if maintenance levels may be higher or replacement will loom sooner. Institutional clients can often pay incrementally more for a roof if there is a return in longevity and lower maintenance. (Metal-roofing manufacturers have successfully made a low-maintenance case for retrofitting metal roofs on a sloped purlin system over older roof systems with nearly flat built-up or single-ply roofs.) Many large owners choose a roof system because it has a proven track record for them and because it is easier to maintain a great number of buildings that have the same roof.

A competent roof designer will design a system suited to environmental and site-specific conditions—such as rooftop exposure to chemicals, falling debris, interior exposure to fumes, extreme winds, or a marine climate—and will evaluate potential or existing roof problems that may go beyond the scope of roofing itself. These might include structural modifications, thermal-insulation improvements, improved thermal-movement or seismic-movement control, and better handling of roof or attic ventilation, as well as upgrades to bring the structure up to code and design to reduce needed maintenance.

Building use also affects roof selection. "Buildings housing electronics, computers, and telephone equipment are highly susceptible to water damage,'' advises Roland Frerking, AIA, vice president at HNTB Corp. Facilities Consulting in Kansas City, Missouri, who specializes in roofing design. In such cases, the roof must offer absolute protection. A less expensive, low-maintenance roof might be fine for a warehouse storing farm implements, however.

Some building types present unexpected issues. Dormitory roofs covered in synthetic-rubber membranes can suffer deterioration due to kitchen-exhaust grease or oils used by sunbathing students. Buildings under an airport landing path may be subjected to soot and exhaust fumes that can interact chemically with some membrane types. Loose-laid membrane systems and poorly detailed metal roofs have proven particularly susceptible to gales, and slates or tiles torn off in high winds have become dangerous projectiles. In waterfront areas, seagulls may be attracted to polyurethane-foam roofing and have been known to peck at and build nests on sprayed-urethane decks. Preventive coatings are available.

Many products appear on the market for new and retrofit applications. Using new technology can pose a risk, because problematic field conditions may not appear immediately. "A roof is no place to experiment,'' advises Blaufeux. "I'll wait for the glitches to be worked out. I want a proven track record.''

Design and detailing issues

Reroofings should be designed, not merely specified, Bensimon asserts. "A roofing contractor may recommend a system they are authorized to install, rather than one that may be more cost-efficient, such as a system with the proper material and wind-uplift requirements,'' he says. Details are a sore point for many contractors, NRCA's Robinson says. "Most contractors see drawings that are inadequately detailed and contain too many 'RFOs' (roofer figure out) and such blanket responsibility-shifting phrases as 'Shall conform to the recommendations of the NRCA Roofing and Waterproofing Manual.''' The manual is 1,900 pages, Robinson explains. "Can't they narrow it down to one chapter?''

"It's refreshing to get a call from an architect asking about a detail for an expansion joint running into a wall. That's a classic RFO,'' Robinson adds. "Architects basically tell contractors, 'Don't do it right' or 'Do it over at your cost.' We'll comment and mark up an architect's sketch and provide related information.''

"Manufacturers' details are good but generic,'' LZA's Kalas adds. "Standard details should be made project-specific. Roofing design errors also occur when the designer fails to understand the roof as an entire system consisting of membrane, flashing and terminations, insulation, vapor barrier (if needed), decking, and the roof-support structure.''

Contractor selection
Since improper installations are much more common than material failures, the selection of the roofing installer is a critical decision. The contractor's roofing experience should be verified and the company should be a member of the NRCA. "The NRCA list is a good place to start,'' says Simpson Gumpertz & Heger's Cash. He also advises,

"Choose roofers from among those certified by the roofing manufacturer for installation, not just the ones who buy the materials.'' As you narrow the list, ask for references and check them, says Cash, and check the roofer's financial state (its Dun & Bradstreet rating) and its safety programs. Then call the contractor and make sure they can handle your specific installation. "Ask who their best competitors are,'' says Cash. "Put them on the bid list.'' Cash continues, "It's good to know a contractor's specialty. Certain roofing systems are more common in some parts of the country and will be more competitively priced by the contractor.''

Solving problems before construction
Blaufeux is among those who stress the value of a preconstruction conference. "Drawings are no guarantee you'll get what you designed,'' he explains. Meeting attendees should include at least representatives from the owner, architect, roofing contractor, and roofing-system manufacturer. Other affected subcontractors or consultants (environmental and structural, for example) should be included. The meeting gives parties a chance to resolve questions about documents and existing conditions rather than having to solve them on the roof while bitumen kettles are bubbling, rain is threatening, or seams are curing.

Assuring installation quality
Much can go wrong with a roofing installation, and experts identify some common problem areas.

Existing conditions. Before new materials go on, it is important to inspect areas that will be hidden when roofing is complete, says Blaufeux. "Architects should discuss the possibilities with their clients in advance of construction. Let them know that some conditions needing further attention can't be determined in advance, such as clogged drains.''

Materials storage. "A wet blanket doesn't insulate very well,'' Blaufeux observes. "Roofing materials must be stored dry.''

Timing and crew changes. How the partially completed roof is protected at the end of the day or when a sudden storm threatens is key to performance. Protection not only has to enclose the new material, it has to keep water out of the exposed or unrepaired old roof. A crew change can result in a lapse of quality control, Frerking says, if the contractor is not paying close attention or a designer or inspector is not present.

Craftsmanship. Single-ply roofing materials, including EPDM, PVC and PVC blends, CSPE, and TPO, depend on essentially perfect field seams, which are lapped and glued or solvent-welded. The multiple plies of built-up roofs offer some redundancy if craftsmanship is not up to par.

Because quality control and workmanship are so important to modern roof systems, Frerking recommends that his clients retain an on-site observer during roofing installation. It's an expense many clients don't want to bear and an inconvenience for contractors, but the consequences of premature roof failure may be worse. Manufacturers are supposed to inspect the work of their certified installers before signing off on a warranty, but Blaufeux contends that the inspection often doesn't occur until the installation is completed, when it is too late.

An independent inspector is most important in observing the installation of materials and components that will ultimately be hidden, such as insulation, flashing, or vapor barriers. Inspectors may not be empowered to stop the work (it's a job often outsourced to an experienced third party), but they can put the roofer and general contractor on notice that apparently nonconforming procedures may compromise the roof, and get the designer and roofer together in a timely way to resolve unexpected problems. Observers pay for themselves when they help prevent the roofer from removing improper work and doing it over again. Cash has developed an extensive checklist, used for training, with more than 24 items and reminders for roofing installation and quality control.

Blaufeux recommends requiring the roofing contractor to inspect the roof twice under the one-year guarantee usually called for in general-construction contracts and to issue a written report documenting observed conditions. The architect should inspect the roof a few months prior to expiration of the contractor's agreement to determine if any defective work needs to be corrected under the guarantee. Documen-tation should include written records and dated photos of flashing, seams, and other key areas.

Are warranties worth it?
As manufacturers have offered longer and longer warranties, owners have come to think of them as taking care of any problem. "They don't preclude the need for maintenance,'' explains Robinson; in fact, many are voided if prescribed maintenance is not performed. Warranties usually come in two types: materials only, which covers only defects in the membrane and related materials, and a system warranty, which covers defects in the material and installation of the roof membrane and related items supplied by the roofing manufacturer. Such warranties are useful because deficiencies are not always immediately obvious, explains Blaufeux. "The glue doesn't always hold. Adhesives and sealants may blister and form bubbles, but you may not see them until the sun beats down in spring and summer.''

"A maintenance agreement provides a better value,'' says Robinson. "Most people are better off without a warranty.''Some companies issuing 10-year warranties haven't been around for 10 years or lack the assets to back them up, for example.

"A warranty is a piece of paper that doesn't keep water out,'' says Cash. "The typical manufacturer's warranty is not written to serve the owner but to limit the exposure of the manufacturer,'' adds Robinson. "Warranties rarely cover related damage,'' he says, such as damage to insulation or roof decks. Some manufacturers' warranties limit liability to cost of material replacement only, excluding labor and related materials, or to costs at the time of initial installation, without allowing for inflation. If owners do not choose a warranty, they may have to sue for relief, if, for instance, a loss of business occurs due to a faulty membrane leaking into the interior. HNTB's Frerking observes: "A warranty is like an insurance policy; you should design a roof so you never have to use it. Most warranties help sell a product and aren't worth it.''

Maintenance agreements represent an ongoing cost, but the owner is assured of timely recognition of problems. According to the NRCA's Robinson, a maintenance agreement should include a twice-yearly roof inspection, roof maintenance work, and a schedule of what is to be inspected. Typical maintenance should include cleaning out drains, gutters, and scuppers; checking for proper roof drainage; repairing any minor flashing damage; replacing gravel or ballast where it has scoured; renewing coatings on flashings; checking for damage by other trades, such as repairs to rooftop HVAC systems; and checking flashing near roof penetrations, where leaks often first appear.

Manufacturers have increasingly stressed regular roof inspections and attention to maintenance, but most owners still don't visit the roof unless there is a problem, experts agree. But they also say a preventive-maintenance program is the best way to ensure roofing longevity. Once- or twice-yearly inspections are sufficient for most buildings, but more frequent checks are warranted when there are major storms, vandalism, or foot traffic. In rainy areas of the Pacific Northwest, notes Bensimon, plants—even trees—promptly germinate on roofs where natural debris has been allowed to accumulate.

He recommends the following roof-maintenance strategies: limit roof access to key personnel, and hold them accountable for maintenance; provide access-control systems to keep track of who is going onto the roof; standardize roof systems and materials within a campus to facilitate training in maintenance, repairs, and quality assurance; supply maintenance personnel with repair kits and complete information, and train them to observe and document roof conditions; implement a seasonal maintenance strategy to allow for winter preparation, spring cleanup, and documentation of items for summer maintenance and repair.

Questions:

1. The penthouse suite of the Cosmos Building, a popular hotel erected in 1972, has developed roofing leaks. A quick visual inspection of the roof shows that two skylights, a multilevel terrace with a partitioned lower deck housing a cellular communications tower, building-intergrated photovoltaics, and rooftop HVAC equipment. Describe what to consider in reroofing analysis for this facility.

2. Describe the resources available for commercial roofing from the National Roofing Contractors Association.

3. Summarize the suggested approaches for working with owners when selecting reroofing systems.

4. List five possible potential or existing design problems that go beyond the scope of roofing itself

5. Give two examples of building uses that affect roof selection and the degree of protection required.

6. Suggest solutions for the following environmental conditions that may damage roofs: a) high winds; b) a marine climate; c) chemical interactions.

7. Explain what architects can to do prevent "roofer figure out" design and detailing errors.