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Re-roofing - alternatives and hazards.

Reroofing - Alternatives and Hazards

Most property managers will not have to decide what type of roof to put on a new building. Their first encounter with the roof system will probably be when HVAC equipment is installed for a new tenant or when a leak develops and the roof must be repaired or replaced. Thus, roofing choices involve repairing an existing roof or placing a new roof on an existing, occupied building. Compared to the original roofing project, reroofing is significantly more expensive, complicated, and risky.

Although reroofing is an opportunity to correct any poor choices made originally, it can also lead to serious damage to the building if done incorrectly. There is always the risk of creating a latent problem which may not become evident until combined with a major storm, leading to a roof collapse. Thus the repair or replacement of a roof warrants more than the cursory referral to a roofing contractor.

When deciding on the installation of a new roof, the primary considerations should include the type of building, its occupants, the projected term of ownership, desire or need for improvement of the property, fire and wind ratings, and any changes in local building codes. The selection of a specific membrane is probably the last decision which must be made. Once all the preliminary problems have been taken care of, the selection of a membrane may become self-evident.


It is essential to determine the condition of the existing roof before calling a contractor. There are three primary considerations.

First, is the roof really in trouble or is the water coming in elsewhere? Replacing a serviceable roof when the HVAC units are leaking is an embarrassing way to waste money.

Next, determine the extent of damage and necessary repairs. A roof moisture survey will define just how much insulation is damaged.

Lastly, consider construction and design advances to correct or maintain the condition of the roof. One should use this construction opportunity to correct anything not done originally and make use of new knowledge.

If the water-damaged areas are small, remove them and repair minor problems. This is usually the least expensive method, but requires good preventive maintenance procedures in which actions are taken before neglect has allowed serious damage to the roof system.

If the water-damaged areas are larger, remove them and put a new membrane over the old - recover. This is less expensive than replacement, but it should be done when only the roof membrane is in poor condition. The insulation must be dry and of adequate thermal resistance, and the drainage must be good. If the whole roof has problems, replacement is appropriate.

If there is asbestos in either the old membrane or sprayed onto structural steel under the roof deck, one may wish to recover now, instead of replacing, to postpone the problem of disposal of the asbestos. It is also not a good idea to install a thick layer of new insulation over an old roof. In this case, tear off to the deck and start fresh.

The condition of the building 10 to 20 years after construction is not the same as when built. Installation of equipment on the roof may have caused deck deflections, which now cause poor drainage. Has foot traffic on the roof changed? Additions to the building may have changed the drainage patterns. Interior occupancy patterns may have changed. The economic condition of the area or owner may have changed creating either more or less demand for the building involved. More significantly, the original construction may have occurred before an applicable building code, and the building now comes under a code as a grandfathered, non-conforming use.

Replacement of a roof is a major task which can seriously interfere with use of the building during the work. Tenant operating requirements must be addressed to define what the construction schedule must be. If relocation of roof-top equipment is involved, when can this be shut down? If parking and storage space around the building is a problem, how can this be arranged for the least inconvenience? If reroofing is planned properly, it should be done during reasonable weather conditions.

Building code requirements

There are also building code requirements with which you must contend, and which may bring about several potential problems. The requirements of the three model code organizations may be more, or less, stringent than a given local or state code. For example, the City of Denver code has more detailed requirements than the Uniform Building Code (UBC), but the North Carolina state code has minimal requirements compared to the UBC.

One must check local requirements before doing anything. The codes represent only minimal requirements for public safety, not for a quality roof.

There are different requirements in different cities for older buildings complying with newer code requirements. The UBC provides for a review by the code official of drainage and other factors to determine what changes must be made. For instance, if a code official requires that non-existent overflow drains be installed, it will likely be in everyone's best interest to do so.

On the other hand, the 1988 UBC requires a minimum roof slope of 1/4 inch per foot for a new roof. If a replacement roof for an originally dead-level roof must comply with this, it may force the closing of doors and windows along adjacent walls, adding drains or raising parapet walls. It is a complicated design decision process to define what is the cost-effective alternative.

The Denver code now has specific requirements for spacing underneath large items on the roof, such as HVAC units and ducts or cooling towers. While these have been common sense recommendations from the National Roofing Contractors Association for about 10 years, many buildings do not comply. Some codes address the wet insulation problem and require its removal, while others ignore the problem. If wet insulation is left, it may be a violation of local statutes or ordinances with possible criminal or civil penalties. Worse yet, it could lead to a structural problem that might incur an insurance claim or litigation.

This may seem trivial since building codes are violated on a daily basis, and persons are rarely caught or prosecuted. The problem is that violation of a criminal law is often taken by the civil courts as irrebuttable presumption of negligence such that only extreme extenuating circumstances can be used as a defense, e.g., the act was committed under threat to life and limb. This could expose the owners and property managers to potential voidance of insurance coverage, not to mention costly, protracted litigation involving multiple parties.

It can be a very expensive and time consuming procedure to have to sue the insurance company to resolve the coverage issues while simultaneously defending a complex multi-litigant counter-suit claiming negligent management.

Selecting an advisor

Whether you choose a designer-consultant, architect, engineer, vendor, or contractor to oversee you reroofing, you should base your decision on what is best for the building owner. Whoever you decide to choose, realize that each has his or her own biases and prejudices.

While the vendor or contractor may cost less, can they truly provide an unbiased evaluation of the situation, particularly non-roofing considerations? Engineers and consultants specialize in roofing problems, whereas most architects must maintain a broad based practice. Preparation of plans and specifications for building construction, including repair, renovation and remodeling, is generally considered to fall within the scope of architecture or engineering.

There is no direct penalty for using someone who is not registered; the difficulty comes if there is a design problem. It is more difficult to make a successful claim for negligence against someone who is registered. Should a major problem develop, use of a consultant who is not legally qualified could be considered negligence by the property manager.

One way to choose the right person is through bids or negotiations. All too often, managers assume that getting bids will save them money, or at least protect them if something goes wrong. Provided that the job description and specifications are very clear and all bidders know they cannot escape the requirements, then taking bids works.

If the bidders are working with a poorly defined project, there is no effective way to compare the bids. Worse, the best contractor probably included money for good workmanship and proper scheduling. The less experienced may have missed these, and the less ethical just left them out.

If you have a contractor whom you trust to do the work just as you would yourself at a fair price, why waste time with bidding - negotiate. If you must take a low bid, consider using full-time construction observation.

Many reroofing projects are conducted based only upon a proposal from a contractor. These proposals do not contain the language regarding schedules, insurance, bonding, warranties, permit requirements, access, clean-up, and so forth, which were in the original building contract.

Work on an occupied building warrants the use of contract documents at least as detailed as the standard American Institute of Architects (AIA) forms. Further, the standard technical sections on roofing in the AIA and the Construction Specifications Institute (CSI) specification systems are oriented toward new buildings. A proper project manual must use sections customized for operations on an occupied building.

Deciding on insulation

The basic problem with wet insulation is that it leads to internal damage of the roof system. This can be structural damage due to rusting, rotting, or spalling of the deck. Damage to screws holding the insulation or membrane in place is also a problem. The long-term impact is that portions of the roof system either can blow off or have a structural failure. These often occur during a major weather event, escalating interior damage far beyond the basic problem.

This insulation cancer can apply to the existing leaking roof or to a new roof system installed over an old roof. While one might be tempted to put a new roof over the old, doing so without knowledge of the roof system's internal conditions borders on negligence. It is not difficult to define the true condition of a roof using modern testing methods - the benefits of which far outweigh the costs.

How much insulation you want or need depends on energy costs, building usage, building construction, climate, building age, and HVAC system capacity. There is less need for good insulation on the roof of a tall building where the wall area dominates; the opposite is true for a large low-rise building. Likewise, a warehouse for tires is much different from one housing expensive machinery or perishable products.

Even if one decides that good insulation is desirable, one must evaluate the structure to define if it can be attained. Some types of buildings, principally concrete, can be difficult to insulate effectively due to lateral heat flow in the concrete. Some of the sheet membrane systems have energy problems that are often overlooked, creating air loss at the edge of the membrane.

The membrane alternatives

The alternatives for a replacement roof membrane are basically the same as for new roofs. The choice is between built-up membranes, elasto-plastic sheet membranes, modified bitumen membranes, liquid applied membranes, metal roof systems, and the various shingle-tile systems. Some of these can be installed in different ways such as loose-laid with rock ballast, mechanically fastened, or fully adhered. There are also many combinations of insulation and vapor retarders for use under the membrane.

Some membranes are easily damaged by chemicals while others resist this. The system that was used originally is not always the best choice when it comes time to replace it. What was easy to install when construction cranes were present may be impossible later.

What is appropriate for one building may be inappropriate for another because of different HVAC equipment or foot traffic on the roof, different interior use of the building, different owner cash-flow and life-cycle conditions, fire codes, and so forth. One building may be appropriate for any of the above roof systems, another may be compatible with only one system.

A major reason for the current popularity of the sheet membrane roofs is that their vendors are giving long-term warranties just at a time when other vendors are pulling back. However, warranties on the membrane material are not always what is expected. Such a warranty is usually not valid for hurricanes, tornados, or gales. A gale is defined as a wind over 35 miles per hour.

The standard vendor or contractor warranties do not cover any consequential damages, either inside the building or even within the roof system, like water-damaged insulation. You do not want to have to claim this on your own insurance policy. Have a roofing architect or engineer include your own warranty, which is more fair. Never buy a roof system just because the warranty looks too good to be true; it probably is.

Rock ballasted systems have been popular due to the low cost of the roof itself. However, they pose real problems for reroofing due to a significant increase in the structural loading. They also have problems with the ballast becoming loose debris.

Mechanically fastened systems create a thermal bridge at each screw. In certain climates, this can lead to condensation on the tips of the screws which creates fastener pullout due to rusting of the metal deck. The membrane can flutter between fasteners so that wind ratings appropriate for the local area must be considered.

A fully adhered membrane may appear to have fewer problems, but its performance is dependent on the performance of the adhesive. The adhesive can be affected easily by weather conditions or workmanship during installation. There is no best choice.

Types of roofs

Asphalt built-up roofs have developed an unfair reputation for problems. Most were killed by poor workmanship or by poor maintenance, which came from ill-advised attempts to cut costs.

It is practical to install a multi-ply built-up roof which will provide 20 year service. It may not be the cheapest system; but for roofs subject to a lot of abuse, it may be the most cost-effective. It does require careful specification of materials and careful attention to details during installation. The multi-ply modified bitumen membrane is often a quality alternative to the classic tar and gravel roof.

Many new buildings are returning to the concept used 50 years ago of steep slopes, even on big buildings. Long, narrow shapes work best for conversion to a steep slope where shingles or tile can be used. The principal problem is what to do with multiple roof-top HVAC units. The reduction in problems with steep roofs for residential properties or small office complexes can be well worth the cost of creating the attic. In cold climates, don't forget possible problems with ice.

Organize the reroofing

Removal of an old roof must be done in daily phases so that the building is never left exposed to water entry overnight. Removal of trash from the old roof and wrappers from new material requires good planning. You must also decide how to deal with dust and debris because metal roof decks do not retard dirt very well. Consider the consequences of finding a damaged roof deck which must be replaced, forcing a major opening of the building.

Insurance and bonds form an important protection for the building owner and tenants. If the new roof is destroyed by a weather event just prior to completion and the contractor is not required to have the proper insurance coverage, he or she may not recover financially. This leaves the manager with a partially completed, ruined roof that is in worse shape than before.

If the contractor is allowed to have claims-made insurance, then changes carriers just after the job and does not buy retroactive coverage for prior acts, he or she will not be covered if a problem develops. Could the manager be held liable for negligent management? It is crucial to use insurance brokers and agents experienced with construction bonding, builder's risk, and so forth to manage the various first- and third-party exposures at risk.


By now you can probably see that during your decision making process, whatever membrane systems are not eliminated are probably equally suitable. The choice can be made on an economic basis. However, do not assume that installation cost is the life cycle cost since different roofs have different life expectancies or maintenance costs. Some roof systems may cost more to remove when worn out.

Roof replacement is not a trivial matter. Do your @omework, as with any other project, to avoid many unpleasant surprises. Once you have successfully installed the new roof, do not put it out of your mind. All roof systems need regular inspection and maintenance for the best performance.

The author would like to thank Steve Thomas, Building Official, City of Glendale, Glendale, Colo; Thomas Chandler, Construction Law, Chandler, Dillion & Allyn, Boise, Idaho; James Goodell, Insurance Broker, The Hartwell Corporation, Boise; and Jeffrey Mercer, Insurance Claims, The Hartford Company, Denver, for their contributions to the article.

H.Z. Don Lewis is the chief principal of ThermoScan Engineering, Inc. of Boise, Idaho. The firm provides consulting engineering services in the areas of maintenance and energy-related matters. He received a B.S.E.E. degree from the University of Arkansas, an M.S.E.E. degree from the University of Illinois, and a Ph. D. degree in engineering from the University of Colorado.

Lewis served as an assistant professor of electrical engineering for the University of Pittsburgh at Johnstown, Pennsylvania, and has background in designing electrical engineering systems, including computer systems, feedback control systems, and communications networks. For the past nine years, he has been involved in the inspection of electrical and other engineering systems. Lewis is a Registered Professional Engineer and is a member of IEEE, NSPE, ASHRAE, ACIL, ICBO, and ACEC.
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Title Annotation:Operating Techniques & Products 394
Author:Lewis, H.Z. Don
Publication:Journal of Property Management
Date:Jan 1, 1989
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