Reroof or What?

June 4, 2010
The first choice in roofing is usually repair, based on its relatively low cost - at what point, however, is such a measure uneconomical?

Building owners are frequently forced to address roofing problems according to Mother Nature’s schedule – not their own. Because of this, they’re often confronted with having to make roofing decisions when they’re not financially prepared, or when they’re lacking adequate information to reach a sound roofing decision.

Whether the problems are insidious leaks that are staining ceilings, walls, and ruining carpets, problems that interfere with operations within, or catastrophic losses, such as fire, wind blow-off, or a hailstorm, these decisions must be made promptly.

The first choice is usually repair, based on its relatively low cost. At what point, however, is such a measure uneconomical? Every roof eventually reaches the point where it can’t be maintained by inexpensive repairs. (Keep in mind: Many building codes require that, when more than simple repairs are made, the entire roof must be brought up to the current code requirements.)

Once it has been decided that a particular roof is beyond repair, then re-cover, retrofit, and replacement options arise.

  • Re-cover is the superimposition of a new roofing system on top of an existing one.
  • Retrofit may be a superimposition as well, but includes the additional steps of upgrading thermal insulation and perhaps improving drainage at the same time.
  • Replacement means to remove the existing roof and install a new roof system.
  • Repair would be those actions that are taken to postpone the day when re-cover, retrofit, or replacement is necessary.

Roof Reparability

Most low-slope commercial roofing materials can be easily repaired because, during the initial installation, the plies or sheets were joined together in the field. If we know what’s up there, compatible materials can usually be located and applied.

Information that’s needed to decide if a roof is repairable:

Is the deck and structure sound or endangered? Can the roof accommodate thicker layers of insulation or a tapered roof system without a major reconstruction? Codes now call for positive drainage, no matter what roof system is selected. In addition, each roof area requires two independent means of water removal.

Is the insulation wet and non-performing? Is it adequately attached to the substrate?

Bitumen-based materials age in a predictable way. At some point, it will become apparent from the development of recurring leaks that integrity of asphalt-based roofing has been lost and further patching will be fruitless. Although not often seen these days, coal-tar pitch membranes can often be coaxed into lasting longer than asphalt-based roofs.

Since single-ply membranes are factory produced, problems are more likely to be at the field seams or flashings. These are usually simple to fix and will essentially restore the roof’s integrity unless the membrane itself is aged to the point that it has lost its integrity or ability to allow satisfactory attachment.

Sprayed-on foam roofs usually fail first by loss of coating integrity, followed by deterioration of the underlying foam. Each stage can be repaired or restored, but with increasing cost and difficulty.

Metal roofing may fail by loss of seam or lap integrity, usually due to misplaced sealant, poorly installed or misplaced fasteners, or deterioration of the washers used with exposed fasteners. (EPDM washers have much improved durability over the earlier neoprene washers.)

Snow and wind loads or unintended roof traffic can also deform metal panels, overstressing side or end laps. Proper repairs may require removal of damaged panels, which, in many systems, is complex because of the nesting features. While flashing failures and improperly made penetrations will also result in leakage, redesign, or installation of proper “boots” can restore watertight integrity.

Flashings and counterflashings. Flashings, which are defined as an extension of the roof membrane, form terminations and seal penetrations. They’re often the first place on the roof to fail because of the extra stress at transitions. Counterflashings cover the top edge of flashings and frequently consist of metals that are embedded in, or set on, walls, tops of walls, and curbs. If damage is obvious, flashings can frequently be restoredor counterflashings replaced, ideally before much water damage has occurred.

Many roofs have warranties, at least during the early part of the roof’s life. The owner should know where the warranties are and what they cover. In many cases, needed repairs will be covered under the scope of the warranty. On the other hand, no warranty covers abuse or consequential damages to the interior of the building. In addition, often, warranties limit damage by winds in excess of a specified speed.

Owners need to know their obligations to keep warranties in effect, as well as their rights under the warranty. They also need to comply with notification requirements when new penetrations are to be made or in the event of leakage.

Other Factors

Will code or load-carrying ability permit a re-cover? Is the existing roof membrane, flashing, or insulation worth saving? Is poor drainage a factor in the existing system’s difficulties? Does the owner wish to dramatically improve thermal performance? Is there a value to improved aesthetics, high albedo (reflective) coatings, or the installation of photovoltaics? Is a green roof desired or practical? What’s the lowest cost (either first cost or life-cycle cost)?

Still another way to analyze the situation is by evaluating the available systems:

  • Classical hot built-up roof (BUR) with a very long history of performance.
  • High-tech BUR, using polymer-modified bitumens installed hot (by torch) or cold process. Torch-applied systems may not be able to be installed because of local fire codes, and dramatically higher insurance is incurred during installation.
  • High-performance polyester systems, installed hot or cold.
  • Polymeric systems, installed fully adhered, partially fixed, or loose laid and ballasted.
  • Protected membrane systems used with most BUR, single-ply, and liquid membrane systems.
  • Structural standing seam roofs installed over a new sub-structural system that dramatically changes slope and appearance.
  • Sprayed-in-place polyurethane foam systems that offer complete adhesion to the substrate to minimize water migration, low weight, and high thermal efficiency.
  • Structural retrofits with new joists and roof decks supporting steep roofings, such as shingles, metal panels, or tiles.

System Evaluation

When you consider these variables, it’s easy to understand why there is no simple, universal choice.

Some points need to be considered before a roofing decision is made. Is there a need to retard or shed water? Is the roof subjected to rock throwers, bird pecking, or kids on skateboards? Can fire-resistance codes and insurance requirements be met? Will a change of materials affect time-temperature ratings? If PV panels are to be installed, it’s now apparent that this will only make sense if we install a brand new roof system with a high degree of puncture resistance.

A recently identified potential problem occurs when metal deck-penetrating screw fasteners may introduce into the interior of the building fine metal shavings and screw-coating particulate matter that contaminate the interior space and the product being stored or produced within the building.

With so many factors to consider, it’s not unreasonable for the owner to want to choose a system that has worked in the past. The only problem with experience is that situations do change, and many older systems may not offer the same performance they once did.

(The influences of regulatory agencies, such as the EPA, have caused changes to felts, bitumens, blowing agents, fungicides, primers, and solvents in subtle and not-so-subtle ways.) All we can do is exercise our best judgment, try to be conservative, and realize that there will always be some risk involved in roofing activities.

Roof Management

After a repair, re-cover, or replacement, it’s a good time to evaluate the current roof management program. Is there one in place or is it a “management-by-crisis” situation? If no overall program exists, there’s no time like the present to initiate one, especially if a new roofing system was just installed.

The program needs to include a situation analysis, whereby all roofs in inventory are listed and their value and replacement cost estimated. Evaluate rooftop equipment to determine what apparatus is no longer functioning and can be removed from the roof surface. (Every penetration is a potential leak, and sometimes this removal evaluation can best be implemented during the roofing renovation.)

Roof slope and drainage should also be evaluated during the situation analysis; adding drains and improving slope are easily done at the time of retrofit and may be required to comply with the current code.

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