Put in the simplest terms, a roof is required to provide shelter from the outside elements. It is a barrier that is constructed to prevent the intrusion of the environment into the space beneath it. Since primitive times, roofs were designed solely to protect man from the elements. Today, roofs are not only expected to provide shelter from the elements - they must also satisfy numerous other functions. A roof must control the flow of heat and the passage of air and water vapor, and it must resist noise, dust, fire and airborne pollutants as well. A roof must also have adequate drainage, high thermal insulation, compatible materials and efficient flashings. It should also be costeffective and provide a long waterproofing service life.

Satisfying these functions is difficult enough bearing in mind all the negative elements that affect a roof on a constant basis. A roof is consistently exposed to sunlight, rain and the forces of wind. All of these elements can degrade a roof system. In addition to weather elements, a roof system is subject to deformations in the structural frame, seismic forces, and wear and tear from traffic over the surface. Furthermore, unbalanced loads that are caused by the accumulation of snow and ice could also be detrimental.

While roof systems have changed considerably since primitive times, the mind-set regarding their purpose has remained the same. As long as the roof remains watertight, little attention is paid to it. The roof is normally the least maintained subsystem of the building, when in reality it should be continually maintained. In some respects, the roofing system is like an automobile; it needs constant maintenance to provide a long service life. Just as an automobile degrades when it is not serviced properly, a roof will slowly deteriorate to the point of failure if it is not maintained.

Avoiding Common Roof Problems

Proper roof design and annual maintenance are two of the most important aspects of a successful roof. These two attributes, coupled with good workmanship, will result in a roof system that provides a long waterproofing service life. That is why it’s important to briefly describe each of these areas and their relationship to roof deterioration before the roof repair analysis is discussed. It is the experience of most building owners and property managers that roofs of commercial facilities, particularly in temperate climates and those having a low slope, are a chronic problem. Nationwide statistics and historical reviews of building systems’ performance offer plentiful testimony to this condition. For the purpose of more thorough understanding of the situation, we should point out that the chronic problems with roofing systems generally stem from two conditions:

1. Of the major generic building systems - structures, mechanical systems and protective systems - it is the protective systems that are subject to the most intensive distress.

2. Roofs, while the most critical of the protective systems, are difficult to effectively maintain because of:

• Their massive size.
• Their system complexity.
• The intensity of their exposure to weather effects.
• The complexity of problem diagnosis and the uncertainty of the effectiveness of the treatments.
• The typical administrative process employed to deal with them.

These factors do not preclude the obvious problems. The American Institute of Architects states that over 50 percent of all building construction litigation involves roofing. This is the single leading building subsystem involved in this area. This is an astonishing rate when it is taken into consideration that the roof system only accounts for approximately 10 percent of the entire building cost. Most of the litigation involves moisture intrusion and premature failures. It is estimated that 4 percent to 5 percent of all roofs completed annually experience premature failure. A premature failure could be defined as a roof system that fails to provide waterproofing service for a 10- to 15-year period. Most failures occur within five years after their application. The expenses of litigation, and the repair and replacement of the roof system, cost building owners millions of dollars each year. In most of these cases, the costs could have been avoided had the roof system been properly installed.

A roof is actually a system that relies on several components that must interact and be fully compatible. The integration of this system is comprised of three equally important stages: design, application and maintenance. All three of these stages serve an exact function that contributes to the success of the roof as a system. A lapse in any one of these areas often will result in a premature failure.

The Roof Design Decision

The roof design decision is the most important decision in the roofing process. It encompasses a number of important issues that can only be determined at this stage of a roof’s progression. The assurance of proper roof performance is the main issue with roof design. Consideration must be taken in determining proper design, material and application techniques.

Proper roof design is the basis from which the roof system is assembled. It is at this point where all aspects of the roof system are devised. The roof assembly generally falls into two component groups: substrate and roofing. The substrate consists of all components that are protected from the environment. This group would include the roof deck, any vapor retarders and the insulation. Roofing is considered to be all of the components that provide protection for the substrate. This group includes the membrane, flashings, exposed trim, drains and all other items required for a complete roof installation. The type of roof that is designed is normally limited by several factors. The pitch or slope of the roof will largely designate the type of system that can be applied. Roof slopes that are less than three inches in twelve (3:12) are considered to be low-slope roofs. Low-slope roofs will accommodate the majority of nonresidential systems available and will be the focus of all further discussion. The roof’s slope is a key consideration when determining the type of bituminous material that is applied on a built-up roof. Roofs with a slope of ½ :12 or less, which are referred to as dead level, should use coal tar pitch. Coal tar pitch is highly resistant to water penetration, but it has a low sloping point. If it is applied on roofs that are sloped over ½ :12, there is a possibility that it may release in high temperatures, causing membrane slippage.

Asphalt is applied on sloped surfaces in accordance with their softening points. Type I asphalt, which has a low softening point, is recommended for a roof slope of 1:12 or less. This type of asphalt has a better resistance to water absorption and protection, but because of the low softening point, membrane slippage can occur at high temperatures. The Type III asphalt has a higher softening point and is recommended for roof slopes above 1:12. The shape of the roof also limits the roof designers’ choices when it comes to the roof system. Certain types of systems can be altered to more complex or warped roof designs; others are more restrictive. The number of roof penetrations, such as those required to accommodate HVAC units and skylights, will also limit the type of systems that can be applied. This is important in today, as it seems more building areas are designed with rooftop HVAC equipment to utilize more space inside of the building.

The selection of the roof system is not complete until the roof designer has carefully analyzed the past performance of the system chosen. The performance characteristics or requirements to be considered when analyzing a roof system should include durability, cost, aesthetics and the system’s compatibility to other roof and building components.