Roofs are one of the most critical components of a building’s enclosure. They serve as the first line of defense against water intrusion and are typically the most exposed element of the building. Roofs must manage large volumes of rainwater; withstand significant thermal changes; resist wind loads from storms, hurricanes, tornados; and help regulate interior temperatures — all while performing reliably for 20 years or more. In many ways, the roof is the true workhorse of the building enclosure.

Why then does it seem that roofs often receive the least amount of attention when it comes to evaluating and designing a proper building enclosure system?

The US roofing market is a $25 billion industry, with approximately 70 percent of all roof products sold used in reroofing applications. This translates to approximately $17 billion in roofing work on existing buildings each year. Far too often, design professionals are not engaged in roof replacement projects. If the design or construction of the roof replacement doesn’t go as expected, the resulting litigation can cost tens if not hundreds of thousands of dollars and create continual headaches for the building owner, management team and occupants due to a flawed roofing system.

If a designer is not engaged in the reroofing process, who then is responsible for the design of this building asset? Often the roofing contractor or roofing manufacturer, but at times the owner may (inadvertently and without knowledge) be the responsible party, thereby becoming the designer of record for the project. Owners need to understand if the roofing contractor or roofing manufacturer has the professional registrations, licenses, insurance or credentials to properly serve in this role.

Where to start

When an existing roof has reached the end of its design life, two general options for reroofing exist. The first option is to completely remove all of the existing roofing materials to expose the structural roof deck and install new materials; this process is known as a roof replacement.

The second option is to leave the original roof in place and install a new system (membrane or membrane and insulation) over the existing one; this is known as a roof re-cover. Deciding which of these approaches is right for a building can be a difficult process, driven by many factors. Both approaches require an evaluation of the existing conditions along with a basic understanding of the structure, material compatibility, accepted construction practices and a general knowledge of the building codes. These considerations are necessary to properly design and install a new roof that meets the unique performance requirements for the project.

Determining a plan of action and identifying the right questions to ask frequently involves checking the building codes, the design and installation requirements and understanding the current performance issues, as well as making informed cost considerations. Many different types of roofing products are available and a nearly infinite number of building configurations and conditions exist. When it comes to reroofing, these decisions matter, and certainly one size does not fit all.

Engaging an independent consultant (Registered Roof Consultant, architect or engineer), is generally a prudent approach to beginning a roof replacement or re-cover project. An independent consultant can provide an unbiased professional opinion for design and installation choices without being swayed by personal or corporate financial gain. While contractors may be able to provide options to consider, they may not have the same legal, professional or regulatory responsibility and may not be familiar with the current building code or engineering considerations required to ensure a safe finished product. Engaging a manufacturer’s representative or other entity with a financial interest in the products they sell can create a conflict of interest (or at least the appearance of one) and can make it difficult to truly work in the best interest of the owner.

An independent consultant can prepare reroof design documents to conform to the requirements of the building code and create a basis for establishing equivalencies for all contractors bidding the project. The independent consultant can include products provided by multiple manufacturers for the contractors to consider in preparing their bid. When all contractors are providing estimates based on the same specified criteria, determining which bid provides the best value for the owner is simplified.

When a Registered Roof Consultant or design professional is involved, he or she can help navigate the potential options and solutions and can work with building owners to provide impartial, unbiased, customized professional advice with practical options for reroofing and/or repairs. In the authors’ experiences, the existing conditions are frequently not evaluated adequately by contractors or manufacturers to determine the appropriate reroofing solution for the project.

The roof design

The 2024 International Building Code (IBC), and many of the earlier IBC Codes in Section 107 define “Construction Documents.” To obtain a building permit, construction documents need to be developed and prepared by a “registered design professional.” Section 107.2 describes what should be included within construction documents. Section 107.3.4 also describes additional duties of the design professional in responsible charge.

Chapter 2 of the IBC defines the registered design professional as an individual who is registered or licensed to practice their respective design profession as defined by the statutory requirements of the professional registration laws of the state or jurisdiction in which the project is to be constructed.

In a traditional design-bid-build new construction project, architects, engineers and other professional disciplines, retained by the owner, plan out the new building and ensure compliance with the building code. The owner hires the general contractor. The general contractor hires subcontractors. Subcontractors purchase products from manufacturers and install them. Even if not in a traditional design-bid-build scenario, if there is a construction manager (CM) or it is a design-build arrangement, these entities are involved and the process is similar.

On existing buildings, the design process is different. The building code and various jurisdictions may classify roofing replacement work differently. The model codes have various provisions, with Section 1512 delegated to reroofing. Section 1512.1 states that roof replacement or re-cover shall comply with provisions of Chapter 15. The code also clearly states in Section 1501.1 that Chapter 15 governs the “design,” materials, construction and quality of the roof assembly. However, for reroofing there are some exceptions and specific requirements for reroofing projects that a qualified roof designer will be required to evaluate. These include the following:

  • IIBEC Fig 1Wet insulation – The building code requires that all of the wet materials be removed down to the structural deck during roof replacements. However, a roof re-cover allows for a second roof to be installed over the existing roof. There is an exception where the roof cannot be installed over a “water soaked” roof. There is some debate in the industry as to the definition of “water soaked” but the commentary of the building codes provides some guidance by saying the materials need to dry completely so they do not trap moisture in the roofing layers beneath. As a result, identification and investigation of whether there is wet insulation within a roof assembly needs to be performed and evaluated prior to the roof re-cover (Figure 1).

  • Slope - The building codes require roofs to have a minimum of one-fourth of an inch per foot slope. Older codes provided an exception whereby they allowed for simply having “positive roof drainage” during a reroofing project. However, in the 2024 code cycle this exception was amended to also state that ponding instability of the structure needs to be evaluated per Sections 1608.3 and 1611.2 of the code if only “positive roof drainage” is provided. To avoid complicated engineering analysis on existing structures to evaluate ponding instability, adding the one-fourth inch per foot slope to the roof assembly is an option. However, if this choice is selected the designer needs to consider the impact of adding additional tapered insulation to the roof assembly as existing parapet walls, roof edges, penthouse doors or other rooftop equipment will need to be modified if they are not of sufficient height above the elevation of the new roof membrane.

  • IIBEC Fig 2Overflow drainage – The older model building codes did not require secondary roof drainage in reroofing applications provided the roof had “positive roof drainage.” Many older buildings and some newer improperly designed buildings may not have had secondary drainage provisions, either overflow drains or scuppers (Figure 2). The code allowed this hazardous condition to remain provided “positive roof drainage” occurred. In the 2024 IBC, the exception was amended to also require evaluating ponding instability of the structure per Sections 1608.3 and 1611.2 of the code if only “positive roof drainage” is to be provided. Many existing buildings may not be able to support the required ponding loads. As a result, either strengthening of the structure or the addition of secondary drainage provisions will be required. Regardless of the requirements of the building code, due to the potential for catastrophic damage and injury to the public, the authors recommend overflow drainage provisions be incorporated into a roofing system in every instance where water can accumulate on a roof in the event the primary drainage system becomes blocked (Figure 3).

  • IIBEC Fig 3Insulation - The International Energy Conservation Code (IECC) stipulates the amount of continuous roof insulation to be provided above the roof deck for commercial buildings. Insulation amounts have been slowly increasing over the years. Many existing buildings do not contain the minimum insulation requirement as stated in the IECC; however, the building code requires that roofs be modified to meet this requirement during roofing replacements. This may mean additional insulation is required to comply with the building code. Similar to the slope requirements, the increased thickness of the roof assembly and subsequent impact on the existing roof conditions needs to be adequately considered in the roof design.

  • IIBEC Fig 4Wind uplift resistance – The building code also provides criteria for roofs to withstand pressures associated with blowing winds. The wind uplift resistance and subsequent attachment requirements depend on several factors, including location, height, slope, parapet wall height, surrounding terrain and other characteristics. Each of these factors must be considered to ensure the roofing system remains attached to the structure during design storm events (Figure 4). These requirements can also have a significant impact on the building’s ability to be insured, depending on the insurance carrier.

  • Fire protection – Roof systems are required to satisfy two fire protection criteria: internal protection and external protection. Internal fire protection is intended to protect the building and its structural components from fire spreading upward into or through the roof assembly. Internal fire protection is typically expressed in hourly ratings (1-hr, 2-hr, etc.). External fire protection (classification) is typically a function of the roof covering or membrane and is intended to provide protection to the building from external fire exposure, such as embers, flames or radiant heat from adjacent buildings, wildfires or rooftop ignition sources, such as solar panels. External fire classification for roof coverings is usually expressed as Class A, B or C.

  • Material Selection – The seemingly endless options and possibilities for new roof systems include single-ply thermoplastic membranes, EPDM, sheet metal, multi-ply asphaltic membranes, liquid-applied membranes and others. However, not all roofing materials and systems are appropriate for every building’s performance requirements. In fact, the wrong decision can lead to significant problems and increased costs over the long term. Experienced, independent roof consultants have an in-depth knowledge of the various available roof systems — and the strengths and weaknesses of each — and will work with building owners to understand their goals so that the best solution can be provided.

  • Potential leak sources - Apart from deficient roof conditions, several potential sources of water infiltration can exist that may result in water becoming entrapped in the roof assembly if they are not properly considered and addressed. These may include exterior walls, mechanical equipment, copings and parapets or nonfunctioning drains or scuppers. The roof replacement or re-cover options also need to address these conditions so the new roof system is not compromised by an undiagnosed condition

  • Other elements to consider – Lightning protection systems, fire-protection systems, plumbing issues, specialized rooftop equipment, solar arrays, safety issues, facade access anchors and tie-backs, rooftop access and structural issues with the roof deck are all elements that a consultant or design professional evaluates during a reroofing design.

The roof construction

Depending on where the building is located, some municipalities classify reroofing as a repair and do not specifically require a roofing permit for construction or the permits are prepared by a contractor. In these instances, there are generally no construction documents or they are vague with minimal information, and a proper design may not be performed. If a design professional is not engaged, and an owner contracts with a contractor or manufacturer for the roof replacement, the owner needs to consider: who is the designer? Does that person have the requisite education, training, credentials, licenses and insurance to practice as a design professional? Without the inclusion of a roof consultant or design professional on the project, the answer to this question is most likely, no.

The International Building Code addresses provisions that govern the design, guidelines for materials and construction for roof assemblies and rooftop structures. Experienced design professionals or roof consultants can be engaged to provide unbiased professional opinions on your roofing replacement or repair project. They can help evaluate the existing conditions and propose a suitable and cost-effective roof design that will conform to the building code and provide years of service once installed. During the construction process the design professional can also ensure that the work is being properly performed, ensure that the proper materials are being used and address concealed or unanticipated conditions that often develop during construction. Too often it is how these unanticipated conditions are resolved that can make or break the success of the entire roofing system.

Conclusions

When a design professional is not engaged during the reroofing process, the code requirements discussed above are often overlooked, not understood or not considered. Without a clear and concise set of specifications to outline the requirements of the project, determining equivalency between multiple bids is difficult, and many owners resort to simply selecting the lowest bid with no regard to the difference in approaches considered by the bidders. In the long run, not considering these fundamental design considerations in a reroofing project can result in more money spent by owners on inferior roofing systems, increased heating and cooling costs, water leakage issues and potentially hazardous conditions to interior occupants and the public. Relying solely on contractors or manufacturers to be the designers of the roof during reroofing projects can increase the risk that building owners incur and potentially decrease the overall performance of the roof assembly and the building it is supposed to protect.

If a design professional is needed, the International Institute of Building Enclosure Consultants (IIBEC) is a professional association dedicated to the advancement of the building enclosure. IIBEC provides education and registration programs for Registered Roof Consultants and Registered Roof Observers, in addition to other enclosure registrations and certifications.

For more information about connecting with an IIBEC Registered Roof Consultant in your area, visit www.IIBEC.org or call 800-828-1902.