Planned Maintenance for Roofing Systems

Roof Performance Requirements

It can be safely stated that the roof receives more abuse than any other building component. It is no accident that although a typical roof represents about 10% of a building’s cost, it involves nearly 90% of the litigation dollars associated with the construction industry. A roof has three major functions:

  1. First and foremost, it must serve as a water barrier to keep the building interior and its contents dry.
  2. It also performs as an insulating element to restrict the flow of heat into and out of the building.
  3. Additionally, it must, in combination with the decking system, bear the weight or permanent and temporary loads.

Along with the above, roofs are also employed for undersigned uses such as material and equipment storage, recreation and additional area for plant or building operations. Roofs are subjected to temperature extremes, accumulations of chemicals, traffic when equipment is being installed or serviced, vandalism and scores of other natural and man-made abuses. There is certainly ample opportunity for the performance capabilities of any roofing system to be severely tested.

History of Performance

The life expectancy of quality, well-constructed built-up roofing membranes is projected to be 20 years. The newer membranes, such as the thermoplastic and elastomeric single plies and modified bitumens, have not had the history of use of traditional tar and asphalt roofs. Thus, the projected longevity of these more recent systems is based on limited actual long-term experience. There is, however, a developing inventory of single-ply products with a service period of 10 years and longer.

In a recent survey, contractors and architects were asked to identify and architects were asked to identify the most common causes of roof failures. Most prominent on their list were poor workmanship, flashing details, seam failure, interply voids and poor bitumen adhesion. Failure of the membrane itself was ranked very low as a reason for roofing problems. In this survey, the respondents were to consider all roofing systems. Therefore, items such as seam failure would be clearly related to the single-ply products, while poor bitumen adhesion is associated more with built-up roofs.

When surveys of this type were made in the 1970's, the responses were obviously based on built-up systems – the dominant roofing of the time. Then, problems such as blistering, splitting and ridging, as well as flashing details were the leading causes of roof failure.

The point that becomes apparent when analyzing this data is that roofs seldom, if ever, fail catastrophically. They fail gradually because of day-to-day deterioration of system components as a result of improper workmanship, poor design or badly performing accessory materials. This step-by-step loss of performance can be detected through experience. The potentially critical areas can be addressed and upgraded before a serious problem occurs.

Value of Roofs

A roofing system is by no means an inexpensive investment. The value of your roof in today’s dollars is probably well over $3.00/square foot. Replacement costs involving tear-off of the old roof will likely be even higher. If your present roof contains asbestos, as many older built-up roofs do, there is a further complication and cost factor Disposal and removal of asbestos-containing roofs is now being strictly regulated by many states and municipalities. Costs of $0.50/foot and more are being added to the removal charges for these types of roofs.

Planned maintenance can identify small problems before they become very costly to correct. A single-ply seam that is showing signs of opening is easier to patch or repair than having to replace water-saturated insulation boards. Built-up roofing membranes are especially maintainable because of their redundant ply configurations. The critical period of roof performance is in the first few years after application. If a roof performs well through this early period, it is likely to continue performing for many more years. Once a roof has proven its performance capabilities, sound judgment and good economics tell us that is should be maintained to extend its performance life as long as possible.

Panned Maintenance Programs

A Planned Maintenance Program (PMP) is very simply a regular schedule of roof inspections and the performance of the necessary corrective actions. The elements involved in a program of this type are many and we can only highlight a very few of them here.

Although best begun immediately after installation, a PMP can be initiated at any point in the roof’s service life. As a part of the program, a file should be developed on each separate roof or roof section. This file should contain as much information as possible including such items as:

  • As built specifications and any changes that have been made to roof after installation.
  • Roof drawings showing all rooftop equipment and penetrations (vents, drains, etc.).
  • All guarantee or bond information.
  • Results of previous inspections including any problems that were found and how they were corrected.
  • All correspondence related to the roof such as letters from contractors, consultants and manufacturers, internal memos, etc.

All this information is key when any roof modifications or inspections are performed and in determining the types of corrective steps that should be taken when problems arise.

The inspection can be performed in a variety of ways, but it is imperative that it be conducted by someone knowledgeable in the technical aspects of roofing. Sometimes conditions such as blisters, splits and ridges may not be immediately obvious to an untrained eye. Single-ply seams that are showing signs of opening must be closely examined by a person experienced in recognizing the early stages of these problems. Just a few of the key points that should be checked in an inspection are:

  • Masonry – Porous masonry and improperly sealed joints account for many of the leaks that are initially blamed on the roof membrane. The location of the leak on the building exterior may not be at the point where the water enters the interior. Water can run across the flutes of the roof deck or some other hidden subcomponents of the building.
  • Flashings and edges – The points where the field of the roof is tied into the building perimeter and projections are probably the major source of leaks in a building. Some claim that flashings account for as much as 90% of the leaks in roof systems. Cracks, breaks, open seams and poor attachment are just a few of the problems that can appear at the edged and flashings.
  • Built-up roofs – These should be examined for exposed felts, open seams, blisters, splits and ridges. Surfacing such as gravel or granules serves several functions. One very important one is to protect the bitumen from the deteriorating rays of the sun. If left uncovered, the tar or asphalt top pour will degrade at an accelerated rate. Thus, the surface cover should be replenished or redistributed if it is not adequately protecting the roof. On smooth-surfaced asphalt roofs, a coating of some type is used as the protective layer. If this material has eroded, steps should be taken to recoat the roof.
  • Single-ply membranes – As mentioned earlier, the opening of seams has been the leading cause of problems with these systems. One technique used for examination is to project compressed air at the seam edges to check for loss of adhesion. Other types of potential problems associated with single plies are punctures and tears. These must be repaired with patching kits available from the manufacturer.
  • Drains and water ponding – The accumulation of water on roofs is undesirable for several reasons:
  1. It adds weight, which may result in compression of the insulation and, in drastic situations, may cause collapse of the roof.
  2. It creates a reservoir for continued leakage into the building if the ponding occurs over failure points on the roof.
  3. It accelerates the deterioration of the roofing system, especially in combination with UV radiation. This, unfortunately, serves to ensure that the leak points will occur in the areas of ponding.

Drains should be inspected and cleaned regularly. If the drains are not doing the job adequately, there are accessory siphon systems that can be used to remove the water. The best solution to the problem, however, is to build slope into the system by means of tapered insulation, the installation of roof crickets, etc.

Inspection Techniques

The industry has made significant progress in the methods available for routine inspection of roofing systems. In the past, roofs were evaluated simply by visual examination. The quality of the inspection was directly related to the ability and experience of the examiner. Good surveys could be made but they involved some guesswork and were based on what could be seen and felt.

The first instrumental technique used in roof inspection was the moisture meter. This is an electronic device that operates on the basis of current passing between electrodes inserted into the roofing membrane. Two rod-like electrodes are driven through the membrane and into the roof insulation. A voltage is developed between these two rods and, if the insulation is wet or damp, a current will flow. This will be registered on a dial on the moisture meter. The small holes made in the membrane are immediately repaired with the proper materials. The areas of wet insulation are outlined by taking moisture readings until dry insulation is detected.

Methods have developed that involve instrumentation much more sophisticated than the moisture meter. These newer techniques do not require penetration into the roof membrane and can examine the continuous roof area rather than isolated points. Only a few roof cores need to be taken to verify or standardize the measurements made. There are three general types of nondestructive methods in common use:

  • Electrical capacitance techniques detect moisture by imposing an electrical field on the roof system. The presence of water causes a change or distortion in the field and this is instrumentally measured as a current or power loss. There is a threshold level of moisture detection for these methods. In use, a grid pattern is laid out on the roof at 5 to 10 foot spacings with measurements taken at the intersection points. Instrumentation of this type was already in common use in the paper, textile and wallboard industries before being adapted to roofing.
  • Nuclear backscatter methods actually detect moisture by counting the hydrogen atoms in roof systems. Water, of course, contains hydrogen and the intensity of the reading is proportional to the moisture present in the roofing system. A complication with the nuclear technique is that other roofing materials (bitumen, insulation, etc.) also contain hydrogen so this “background” must be considered in interpreting the results. A grid pattern is also employed when making a survey with nuclear equipment. These instruments are portable, but one negative is that a small radioactive source is contained in the unit. Although safe, they carry some shipping restrictions and operators are best advised to carry radiation badges.
  • Infrared thermography is probably the most widely used technique. It operates by measuring temperature differentials on the roof’s surface. Since moisture decreases the effectiveness of insulation, more heat will be lost through wet roof sections and these areas will appear warmer to the infrared detector compared to the dry areas. Experience has shown that this technique is very accurate when properly interpreted. A further advantage is that 100% of the roof surface is examined. There is no need to grid the roof as with the electrical capacitance and nuclear backscatter methods which, in practice, examine about 5-10% of the roof area. It is very important with all three nondestructive inspection methods that an individual knowledgeable in roofing be involved in the data interpretation.

Advantages of Non-Destructive Techniques

Roof replacement is not only very costly, it is also very wasteful. Many roofs have been completely removed when only 10 to 20% of their area was no longer functional. Prior to the non-destructive techniques, a roof walkover, along with a few roof cores or moisture meter readings, were all that was available. Since the cores and moisture probes were taken randomly, a roof could be presumed to be completely water-saturated when, in fact, only a portion was wet. Also, by the old methods, there was not easy means of determining which portions of the roof should be removed.

It is very apparent that if a major portion of a roof can be saved and maintained, the cost savings can be highly attractive. Some building owners have nondestructive surveys performed on an annual bases. They are used as a tool to follow the condition of their roofs and as a complement to the recommended spring and fall visual inspections.

Maintenance Options

Built-up roofs present the greatest number of maintenance alternatives to the building owner. Bituminous built-up roofs can be either asphalt or coal tar. The type of bitumen can be readily identified by using a simple solubility test in a particular organic solvent. Once the type of bitumen is known, the proper materials can be selected for maintenance procedures.

  • Primers – These come in asphalt and tar form and are used to pretreat dusty (not dirty) surfaces to ensure good adhesion for additional material applications. They are often used prior to application of emulsion (water-based) coatings. Primers are sometimes used to seal porous surfaces such as masonry or absorbent insulation boards.
  • Coatings – The wide choices of coatings available in the marketplace is staggering. Coatings can be tar or asphalt, asbestos or non-asbestos, rubberized or non-rubberized, etc. The selection of coating material is, of course, dependent on the end-use. A detailed discussion on coatings is beyond the scope of this article but some general guidelines are:
  1. Fibrated coatings give a greater film build or application thickness than non-fibered products and consequently greater waterproofing. They are also used on sloped surfaces and flashings because of their greater sag resistance. There are now a number of manufacturers no longer willing to supply the asbestos-containing products because of potential liability and insurance problems.
  2. Aluminized or white-pigmented products are used for their aesthetics and reflectivity. They protect smooth-surfaced roofs as well as flashings from harmful ultraviolet rays. They also save air-conditioning costs in warmer climates.
  3. Resaturant coatings have oils in their formulations. These materials soften the top pour bitumen of aged roofs, add waterproofing to the roof’s surface and “resaturate” exposed, dried-out roofing felts. Resaturants are used in a several-step maintenance procedure in which the gravel surfacing of a roof is removed and the roof is carefully examined. All problem areas are then repaired, the restaurant coating is applied and the roof is regravelled.
  4. Bituminous emulsions are used for their excellent weathering resistance. These materials weather by erosion or chalking just like a good quality house paint. They are used to surface or resurface smooth asphalt roofs and on flashings. Sometimes they are coated with aluminized products to even further improve their weathering performance.
  • Mastics – These are general purpose, heavy-bodied materials used for patching, bedding felts and metal trim, utility repairs and a multitude of other applications. They come in tar and asphalt form and contain a significant amount of fiber for strength and sag resistance. The rubberized versions (elastomerics) are used where there is a good deal of expected movement (such as at metal joints) because of their elongation and fatigue resistance properties. Mastics are often used with reinforcing membranes and the combination produces a longer lasting application because of improved strength and fatigue properties. Some of the common reinforcing materials are glass, polyester, cotton and jute.

Modified Bitumen Maintenance

Maintenance of these products is relatively straightforward. All the general procedures such as cleaning of drains, inspection of flashings and roof metal, etc. should, or course, be performed. The torch-applied membranes may be repaired with material of the same type using a hand-held propane torch. Mastics, preferably rubberized types and recommended by the membrane manufacturer, are used for general procedures. Be sure that all surfaces are thoroughly cleaned before attempting to adhere materials.

Many suppliers of modified bitumens suggest that they be coated for improved weather-resistance and reflectivity. After a time, the coating will deteriorate and new application will be required. When this is done, be sure that proper surface preparation is accomplished before recoating. Loose, old coating should be brushed off or a high pressure water jet should be used to prepare the roof. There are commercial cleaning services available that can perform this latter operation. Be sure that the membrane surface is dry before recoating with solvent-based products. Emulsion products may be applied on slightly damp (not wet!) surfaces. Membranes that have granule surfacing can be touched-up with new granules applied in liquid adhesive. Some of the modified products must be surfaced to ensure good, long-term performance. It is critical that the surfacing be maintained on these products.

Elastomeric and Thermoplastic Single-Plies

Maintenance of the products includes close inspection for tears and punctures and, most important, the opening or seams. The seam adhesives and sealants recommended by the single-ply manufacturer should be used and patches should be made with the same membrane materials. Again, thorough cleaning and sometimes even abrading are required. Some of the single-plies cure after being installed on the roof. This produces a surface that can be difficult to bond. This cured layer may have to be scoured to ensure good adhesion. Mastics may sometimes be used on single-ply products, but it is key that the manufacturer be consulted or the guarantee may be jeopardized.

Emergency/Wet Conditions Repairs

Leaks, obviously, show up when there is water on the roof. These, naturally, are the worst possible conditions for making a repair. The leak must first be located and this may be a difficult task in itself.

Safety must be the first priority. Sending workmen on a roof in an electrical storm is not a desirable situation. High winds can blow down power lines across the roof or topple equipment. If it is unsafe to send someone on the roof, live with the leak until it is safe. Divert the leak with plastic sheets, catch the water in pails – do whatever is necessary to make conditions in the building at least tolerable.

 

When patching, one technique is to build a dam around the leak area using small boards embedded in mastic. Dry the area as well as possible and make the repair. There are also products such as expanding bentonite clay which can be poured into the leak for temporary repair. Tar mastics perform well under wet conditions because of their density (heavier than water) and the unique chemistry of tar. Asphalt mastics can also be sued for emergency repairs if properly formulated. If asphaltic materials are formulated with special surfactants, the water at the leak site will be displaced allowing for a good bond.

All emergency repairs should be inspected when conditions allow. If necessary, they should be removed and redone under dry conditions.

The Value of Planned Maintenance Programs

The roof of your building is a corporate asset. Just like the equipment in your plant, it allows your company to stay in business and manufacture your products or carry out your services. It is interesting that many companies have regular maintenance schedules or their equipment to avoid breakdowns, but ignore their roof until a serious problem occurs. Just like plant equipment, your roof will cost you a certain number of dollars over its lifetime. The choice is whether you want to control those dollars in a planned program and avoid problems or spend them all at once with substantial disruptions in your building. It’s much like maintaining your automobile. Do you want many miles of trouble-free service through regular maintenance? Or, do you want a serious and costly breakdown that may require that you buy a replacement automobile on short notice?

Below are some very general guidelines that can be used as a measure of your present roofing expenditures.

  • $0.06 per square foot per year:  If you are spending at this rate, your roofs are in very good condition or you are not maintaining them at a proper level. At this cost level, there could be some serious problems requiring major dollars in the future.
  • $0.08-0.12 per square foot per year:  This is a reasonable maintenance cost and will enable you to do good yearly maintenance along with quality restoration programs on a 10-year cycle. Needed repairs could be made to flashings and details as well as isolated roof membrane problem areas and a complete surface renewal could be accomplished. Spending at this rate would allow you to avoid costly replacement of major roof areas.

Over $0.15 per square foot per year:  Spending at this rate means you have unusual problems with your roof. You are probably maintaining a roof that may have to be replaced. You may have avoided maintenance in the past and are now paying the price. There are probably leaks occurring on a regular basis causing inconvenience and disruptions in the building.

Next Steps

Now is the time to determine the adequacy of your present roof maintenance programs. The goal, of course, is to keep roofs watertight at the lowest possible costs and with the fewest problems. Regular maintenance is the best way to accomplish this and allows you to take control of your roofing budget. A regular inspection schedule should be implemented to prevent potential problems. Your roofs should be ranked as to age and condition and corrective actions should be taken on a planned basis. The roofs in most serious need or repair and maintenance should be given priority. A knowledge of your problems and priorities allows you to have the work done at your convenience and eliminates the need of reacting to crisis situations. Your plant or building crews may be able to do much of the work with good scheduling.

The technology and management of roofing is not simple. A roof is a complex component of a building, but can be understood and controlled with the proper information and planning. Budgets can be developed that will bring your roofs into excellent condition and keep them that way. This allow you to manage your roofing inventory instead of it managing you.

Originally published in Plant Services Magazine, April 1989