The Quest for the 20 Year Roof


Karen Warseck

I s a roof that lasts 20-years the Holy Grail of the industry? Is it, like that cup of legend and romance, the ideal to be striven for yet not attained? Or is it a real goal that can be grasped and displayed as a monument to virtue and hard work? It may come as a surprise to those of you who have seen the demise of roofing systems after two or three years in service, but a roof lasting 20 or more years is not only attainable, but reasonable.

The main challenge is not lack of good roofing materials. The technology exists and has existed for a hundred years. The problem is the way materials are selected, installed and used. Proper design, installation and maintenance are key to achieving a "20-year roof. "

Material Selection Why do some roofs last 20-years or more while others fail in only a few years? The problem isn't technology; it's the way materials are selected, installed and used.

The quest begins long before the roof is installed with the design of the roofing system. That doesn't mean getting on the phone to a couple of contractors and asking for proposals - a course of action that can spell disaster. Contractors, although many are reputable and reliable, do not make a living if they do not sell a job. Consequently, they are forced into a position where they must bid on lowest denominator materials if they wish to compete against other not-so- scrupulous contractors in a highly competitive market. Consequently, the first and most understandable priority for a contractor is to sell a job at the lowest price but best profit. Longevity of the system rarely makes a difference. So the first step to attaining a 20-year roof is to be sure that you are willing to pay for one. Quality is not cheap in the short run.

When A Roof Must Be Replaced

The design of a long-lasting replacement roof begins with an analysis of the condition of your existing roof. A careful survey of why the existing roof failed offers valuable clues as to what characteristics should be sought in the new roof.

Two important things to look at are signs of standing water, and wrinkles and splits in flashings or membrane. Standing water means that more slope is needed or extra drains should be installed. Standing water causes most types of roofing systems to deteriorate prematurely and aggravates problems even in those it does not. Even a tiny pin hole in an area of standing water will be a major leak, since water runs to the lowest point. Wrinkles and splits are symptoms of movement in the substrate or structural system that needs to be accommodated for a long service life.

Once a failure analysis has been completed, determine the characteristics of the roofing materials that most closely fit the characteristics of your building and any detrimental results of the failure analysis. Carefully consider the following:

  • Slope and drainage. If there is no slope or minimal slope, it should be added or drains should be installed to remove standing water. If neither is possible, a roof system that is minimally affected by ponding, such as coal tar, should be chosen.

  • Movement of structure. Some roofing materials will accept movement within the substrate better than others. If movement is a problem, an elastic membrane is a more appropriate choice than a built-up membrane. If other conditions dictate a multiply system, the roof should be designed with control joints to minimize the amount of movement transferred to the roof membrane.

  • Climate. Although most roofing systems can be successfully used in most climates, it makes sense to choose those most suitable to the weather in your area. Elastomeric flexible sheet membrane are particularly suited to cold climates as they can be installed at lower temperatures with less likelihood of failure. They also have the ability to take the extremes of thermal movement over the yearly cycle from summer to winter. However, heat and humidity make them less desirable in hot, wet climates. Light-colored membranes can be a cooler choice in hot climates. Thermoplastic and elastomeric membranes formulated in several light shades and coatings can cool off the surface of most multi-ply systems.

  • Code and insurance requirements. The local building code may affect the choice of roofing materials and how they are installed. Fire safety requirements may restrict kettles on roofs or disallow torch applications. Underwriters Laboratories (UL) Class A fire-rated roofs may be required by code or local jurisdictions. Wind loading may restrict roofing systems to certain types of installation methods or may ban some types altogether. Insurance requirements may affect choice of decks, fastener spacing and types of fasteners used. Fire ratings may dictate the total system design. Limitations on volatile organic compounds (VOCs) may affect the installation of EPDM membranes.

  • Deck type. Different deck types require different methods of attaching the insulation or membrane. Mechanical fastening to a structural concrete deck is not generally a good idea; on the other hand, mechanical fastening on a lightweight concrete deck is recommended. Wood decks require different fasteners than lightweight concrete which uses different fasteners than cementitious wood fiber which uses different fasteners than steel. Fastener choice may also be affected by the code and insurance requirements.

  • Energy requirements. There is no question that adding insulation to an underinsulated building will affect the building's operational efficiency. The growing concern with renewable resources can also affect the choice of materials.
Building Codes
Building codes and insurance requirements can affect both
choice of roofing materials and method of installation.

  • Accessibility. The need to bring roofing materials to the roof or to access small interior or isolated areas could argue against choices of wide or heavy rolls of materials. Repairs to electrically heat welded seams may become a major effort if electrical outlets are not readily available and a generator is needed every time a small leak develops.

  • Building size, shape and configuration. Wide, open spaces are best served by wide rolls with few seams. Small, narrow spaces are not. Lots of penetrations need an easily flashed system.

  • Current roof materials. Logic says that compatibility between existing materials and those to be installed helps assure longevity.

  • Abuse potential. Some roofing materials stand up to abuse due to vandalism and foot traffic better than others. Multiply redundancy generally is more tolerant of abuse than single ply membranes.

  • Tear Off. Attaining a 20-year roof means tearing off the existing roof and replacing it, since building a new house on a deteriorated foundation does not improve its chances for longevity. Roofing materials manufacturers seem to believe this also. The best warranty issued by a manufacturer for a recovered roof is no more than one half the length of the best tear off and replacement warranty. Manufacturers don't think that a recover will last. Why should you?
Once the determination has been made as to the materials and installation method best suited to your building, prepare drawings and specifications that show in detail the requirements for the reroofing project. The words "in detail" are especially important. Too often, the manufacturer's recommendations are referenced as the sole design criteria for installing the roofing system.

There are two problems with this:

First, manufacturers' literature states that they are manufacturers, not architects or engineers, and as such claim no liability for the use of their recommendations in the design of the roofing system. What they are basically saying is that if you want a roof designed, get a design professional to do it.

Second, manufacturers' specifications and details (especially details) are generic and are not suited to all applications, nor are they complete enough to define the individual situations that exist on each roof. So, by merely referencing manufacturers literature, you are asking for a one size fits all roof. And, as we all know, one size fits all usually means that one size doesn't really fit anybody.

A competent architect or engineer should specify and design the roof to suit your individual building, complete with all flashing details that exist on the building. Special conditions such as expansion joint terminations or unusual penetrations should be designed before the roof goes out to bid.

Installation Concerns

The best materials will not last anything close to a normal life span if they are not installed properly. The first step toward that end is to choose a competent contractor. This is difficult, because even the best contractors occasionally install a poor roof. Roofing is not a science, but rather a mixture of attention to detail, craftsmanship, common sense, pride and luck. However, the chances of finding a reasonable contractor increases if some simple steps are taken.

Proper Installation
The best materials will not last a normal life
span if they are not installed properly.

First and foremost, check to see if the contractor is licensed in the jurisdiction in which he or she will be installing the roof. If there is a consumer complaints commission in your state, check to see if there have been any complaints lodged against the contractor's license. Second, be sure the contractor maintains proper insurance by requesting an insurance certificate prior to beginning the work. Especially check for worker's compensation insurance. Fly-by-night contractors rarely carry worker's compensation insurance because they do not intend to be around long enough to have any claims on it.

The design of a
long-lasting replacement
roof begins with an
analysis of the condition
of your existing roof.

Ask for the manufacturer's approved applicator list for contractors who can install the roof and obtain a no-dollar-limit warranty. Even if you don't intend to request a warranty, this assures that the contractor you choose will at least be familiar with the product to be installed. Check their ability to obtain bonding. Bonding limits will give you an idea of the size of the project the contractor can handle.

See if the contractor is a member of local, state or national roofing contractors associations. While this does not guarantee a good contractor, it does show at least a minimum commitment to the industry. Ask the contractor to give you a list of contacts for roofs he has installed at least three years ago, and call the people on this list. Most installation related problems will have shown up within the first three years.

Once the background check has been completed, have someone who understands roofing observe the installation. Contractors are less likely to cheat on installations, cut comers or install unauthorized substitute materials if they know they are being monitored.

Contractor Background Check
Even the best contractors occasionally install a poor roof; however, the chances of finding a good contractor increase if the facility executive takes a close look at the business backgrounds of competing firms.

Hidden conditions that cannot reasonably be foreseen can be handled quickly and with less aggravation if someone representing the owner is available when the condition is exposed. The project representative can catch any errors in installation that might be covered by subsequent roofing installation such as improper fastener installation, wrinkles, voids in adhesives, etc., and get them corrected before they become a problem. Having a fulltime project representative on the roof during installation is the best assurance of the contractor's compliance with the contract documents.

Once the roof is installed, this does not mean the grail is in your hands. The third point on the 20-year roof triangle is roof maintenance. This should be an ongoing operation that begins the day the roof is finished. It begins with the compilation of a roof history file. This file should contain the following items:

  • Names, addresses, phone numbers and contact names of everyone involved in the roofing project, including the design professional, the contractor, the membrane manufacturer's representative, the HVAC or electrical contractor if used and any others involved.

  • A copy of the manufacturer's warranty, if you have requested one. A warranty does not ensure the roof will last its specified design lifetime. However, a reputable manufacturer will stand behind its product and provide the remedies listed in the warranty. Note that you must notify the manufacturer of the roofing membrane in writing within 30 days of a leak to keep the warranty in force. The manufacturer must also be notified of changes in ownership, use and the installation or removal of mechanical equipment.

  • A roof plan drawn to scale. This will help locate leaks and problem areas.

  • A log book of who was on the roof, when and why they were there. This helps assign responsibility if a leak occurs after a visit by an air-conditioning contractor, window washing contractor, sign installer or other rooftop visitor.
Keeping The Roof In Good Shape

Once the new roof is installed, it should be inspected twice a year. Flashings should be checked for punctures, cracks, slippage, open laps and other problems. Drains should be checked and debris removed from the roof. If the drains do not remove water from the roof, any small leak becomes a big problem, the warranty can be voided and the roofing membrane will prematurely deteriorate.

Be sure that no grease or oil vents onto your roof. Except for Hypalon based and special polymer formulations, most roofing materials are sensitive to hydrocarbons and will break down if exposed to them. Pay attention to tenant installations. Additions of ventilators, air-conditioning; units, satellite dishes, etc., often are not flashed by an approved roofing contractor and many times are not flashed at all. This simple inspection and prompt repairs are keys to keeping the roof serviceable for the full 20-years.

Proper Maintenance
Even a well designed roof with good materials expertly installed
will not last if the roof is not properly maintained

Finally, keep traffic off your new roof. People, carts, window washing rigs and other such traffic across your roof can crush insulation, puncture flashings, tear membranes and wreak havoc with your investment. Roof traffic is one of the worst enemies of roof longevity.

The 20-year Commitment

Any quality roofing system can provide a 20-year service life. But as you can see, the quest for a 20-year roof is not a quick and dirty process. It begins long before the roof is installed and ends only with the replacement roof 20 or more years later. Skimping on design, materials, installation or maintenance will severely shorten the service life of any roofing system. Good installation will not help if the roof is not properly designed, and the correct materials and installation methods chosen. The best design will not matter if the installation is haphazard. A competent installation of good materials well designed will not last if the roof is not maintained. Regular maintenance cannot compensate for poor design and lack of care in installation. Attaining a roof that will last 20-years requires a commitment to provide support for quality from the initial design through the roof service life and, in that, can be done by anyone.

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Karen Warseck, AIA. CSI, is president of Building Diagnostics® Associates, a Hollywood. Fla., firm that specializes in the analysis of roofing and waterproofing problems.

This article was reprinted from the February 1996 issue of Building Operating Management Magazine. For other great articles, log on to Facilities Net at

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