By Steve Moskowitz

As someone involved in the purchase decision for commercial roofing systems, you most likely have a variety of other responsibilities. In fact, your roofing system is probably the least of your worries unless you discover a leak that could interrupt productivity, cause an accident, or damage expensive goods or equipment. Once that happens, your leaky roof becomes a major liability that can seriously impact your company and its profits. Besides being a major hassle for you, it begs the question: should you repair or replace that aging roofing system to avoid these headaches?

Before you answer, consider the following guidelines developed by commercial roofing experts. These guidelines will help you to weigh the facts, determine risks, calculate costs and identify the pros and cons of repairing or replacing the roof.

Extent of Roof Damage

Determining the extent of the existing damage is one of the most important factors in your decision-making process. For decision-making purposes, this damage assessment breaks down into two elements.

The first is determining which roof components have been damaged beyond use or functionality. The weatherability of the roofing surface itself is the first item to assess. In single-ply systems, carefully evaluate the roof's surface for signs of significant weathering such as cracking or crazing. In built-up roof systems, look for blistering in the material or signs of alligatoring. The severity and areas affected should be very carefully analyzed. In addition, keep in mind that when weathering and aging mandates a repair, the extent of the damage should be evaluated in the context of repairing isolated areas of the roof vs. a total replacement.

Wet insulation should also be evaluated carefully because many insulation products quickly deteriorate in the presence of moisture. You may realize that wet insulation sacrifices thermal value, but you must also be aware of the structural implications of wet insulation. Insulation is considered to be a structural component in terms of its interaction with the membrane system. If the insulation deteriorates, collapses, swells, warps or loses its compressive strength, it can adversely affect the membrane system performance particularly as it relates to the integrity of the roof material or system's attachment to the deck, and the subsequent wind up-lift performance.

The second part of the damage assessment is to determine - to the extent possible - the future performance of the roofing components that are still functional. Since it is impossible to accurately predict the future, this part of the assessment process is considerably more difficult. Therefore, to assess future product performance, you will be forced to use the "scientific wild guess method."

The scientific portion of this method involves identifying all the roofing components susceptible to moisture damage over the long-term, such as those that can rot or corrode or those that are water-soluble. Once the leaks have been stopped, you need to determine how much water is in the system. Capacitive testing, nuclear scanning, and infrared thermography methods can be used to assess the magnitude of the problem and can also be helpful in finding out where the water is actually located. However, you will still need to perform physical test cuts into the roofing system to determine the extent of the moisture-related damage to the system. The top surface of the deck can also be examined from the openings created by the core or test cuts. If corrosion or deterioration is present, the structural integrity of the deck should also be carefully evaluated.

In the future you may be able to determine specific drying rates better than we can presently do so, as studies are currently under way by organizations such as the Single-Ply Roofing Institute and Oak Ridge National Laboratories to evaluate and determine roof drying rates and how influences such as deck permeability, climatic conditions, and membrane color affect the drying process.

However, until conclusive studies are completed, you'll have to use some guesswork to estimate the drying time and associated damage to the system components. Once you know how much moisture is in the system, you can begin to estimate how long, if ever, it will take the roofing system to dry out - this is the guess portion of the method. To estimate the drying time with some degree of accuracy, you'll have to determine if there are any components in the system that tend to retard moisture migration, such as an impermeable deck, vapor barrier, or an old roofing system that was recovered at an earlier point in time. You should then focus on the air space below the roof deck. Is the area below the deck a controlled, air-conditioned environment, which facilitates drying? What is the average relative humidity below the deck?

You also need to estimate how much, if any, deterioration is likely to occur during this drying out or "transition" period, which could last several years, as well as how much deterioration is acceptable. Will any more moisture be introduced into the system during the transition period? Do you plan to replace decking or other structural components on your next roofing project?

What Is At Risk?

Another important factor to consider is what is at risk if the roof fails. If leaks are strictly an annoyance and do not cause any major work disruptions or safety hazards at your facility, then repairing the existing roofing system may be the best option. However, if the roof leaks are causing potentially serious safety hazards, expensive downtime, and/or irreparable damage to your building, equipment or contents, then it may be wiser and more cost-effective to replace the roof.

Cost of Repairs

If repairs to your roof are being covered by your roofing warranty and are being made promptly and effectively, then it is probably beneficial to continue with the manufacturer's recommended repair procedures. However, if the existing problems are not covered by the roofing system manufacturer's or contractor's warranty, or your roof is not under warranty, and are consuming excessive time and expense, then a new roof may be worthwhile due to the long-term expense and frustration it will save you, not to mention allowing you to again concentrate on the rest of your facility. By limiting the cost of your repairs to the roof system's replacement cost, you may be limiting the potential for major structural damage to occur down the line.

Consider the annual repair costs associated with patching your existing roof. Is the repair cost less than the amortized cost of a new roof? If you wait to replace the membrane system, will the project scope increase from a re-cover application to the much larger job of removing the old roof - including the membrane, insulation and possibly some decking as well? Determining the answers to these questions can help you decide the long-term cost difference between replacing and repairing the roof.

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