Tile Talk: Roof Underlayments

Understanding the Long-Term Performance of a Roofing Assembly

by Richard K. Olson, president & technical director, Tile Roofing Institute









(Editor’s Note: Richard K. Olson is president and technical director for the Tile Roofing Institute. The association represents industry professionals involved in the manufacturing and installation of concrete and clay tile roofs in the United States and Canada, and works with national, state, and local building officials to develop installation techniques, codes, and standards for better roofing systems. Olson can be reached at rolson@tileroofing.org.)


The decision of when and how to replace a roof’s underlayment is an important aspect to long-term performance of most roofing assemblies. The use of underlayments in steep-slope applications provides a secondary water shedding boundary for most claddings. With cladding materials now providing a longer life cycle, roofing professionals need to determine through regular maintenance any ongoing concerns of the underlayment’s performance.

Over the last decade there has been a rapid expansion in the types of underlayments being offered for steep-slope applications. With synthetic and modified organic materials now available to compete with the traditional organic-based materials, roofing contractors are challenged to understand the actual long-term performance indicators for replacement decisions. Over time, all roof systems will require some form of maintenance to help extend the service life of the full roof assembly. This can include inspection and possible replacement of valleys, eaves, ridges, and roof penetrations. The ability to ensure water is being properly directed onto the roof cladding or off the roof is vital to preventing water intrusion. When damage, repairs, alterations, remodels, or routine maintenance occur, it is an opportunity to visually inspect the underlayment and determine the aging process.

With residential construction demands ticking upward, builders are moving track work forward on more aggressive timelines. In order to coordinate other trades, the roof dry-in process is being done on many projects ahead of the installation of the final roof cladding. This can expose underlayments to UV and weathering conditions for extended periods. Roofing professionals need to determine how this might affect long-term performance of the underlayment. In some areas we see an additional 15 lbs. of materials used as a sacrificial layer for weather exposure during this timeframe. In other areas the upgrade to multiple layers of code required minimums, or even a heavier single layer of underlayments are being installed. Roofing contractors need to review the local codes and underlayment manufacturers’ written requirements to determine the limitations on exposure prior to the cladding being installed.

In areas of high UV impact, the degradation of the underlayment from extended exposure significantly reduces the service life of the materials. The ability of the underlayment to allow breathability while preventing water intrusion is important. The nail ability, resistance to tear, and walkability can be affected by extended UV and weathering prior to the cladding being placed.

Proper selection of code-approved underlayments is another area of concern. With so many new synthetic materials on the market, it is important to identify what local codes allow and what the formal product approvals of the underlayment manufacturers require for the various roof cladding materials. In areas of higher wind applications, the proper attachment to the roof sheathing to meet the full uplift resistance as required by code will need to be determined.

When inspecting roofs that are prone to extreme weather, extra attention should be paid to areas that have higher exposure to natural elements. Eave, hip, and ridge areas can often see wind-driven rain or moisture issues from ventilation of the roof areas. Valley metals that have expansion and contraction elements can also require attention. Looking for evidence of buckling, tearing, or worn areas can help determine if minor spot repairs or a full roof replacement of the underlayment might be in order. Local building codes should be checked for requirements and limitations surrounding repair versus full replacement of roof projects and the need to bring the roof up to current code compliance.

Roof penetrations such as vents, soil pipes, skylights, and chimneys can also create opportunities for water to enter onto the underlayment layers. These penetrations are the number one area for roof leaks to occur and should be inspected on a regular basis to ensure a fully functional roofing assembly. Debris and vegetation can also create water barriers that can pond water upslope, allowing water to penetrate. Roof accessories such as solar, HVAC, and satellite can create additional holes in underlayments that are hard to determine once the roof cladding is installed. These are often installed by non-roofing contractors that do not always repair or seal these penetrations appropriately.

When underlayment replacement is advised, roofing contractors can help assist in the determination of how best to perform the task. Evaluation of the roof cladding should be made, as often times the combination of the two will indicate a full replacement. In some roof claddings, there may be underlayment issues in play and the lift and relay of the cladding might be a viable option to correct the problem. As the secondary barrier, the underlayment may not require the immediate attention for replacement and can often be delayed, meeting the building owner’s needs. This will depend upon the condition of the actual cladding to provide the primary water shedding barrier.

Roofing professionals play an important role in helping to provide the long-term performance of a roofing assembly. The ability to understand the various attributes and limitations of the underlayments combined with the local code requirements, will better prepare us for making informed decisions on proper course of action. The manufacturer of the underlayment should always be consulted to help provide information on limitations, requirements, and possible solutions for better long-term performance.

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