For many decades, asphalt-saturated organic felts went unchallenged as the underlayment material for residential roofing, despite having several weakness and drawbacks. These include not performing well as a secondary water barrier, being prone to degradation from UV exposure, easily tearing and an inability to be left exposed for long periods after installation.
Luckily, in the past twenty years, two completely new categories of roofing underlayments entered the steep-slope roofing marketplace, namely mod bits and synthetics. So what are the factors driving this change? Along with the issues of traditional asphalt-saturated felt, many industry and economic drivers have favored the introduction of new underlayment categories.
Severe storms seasons affected the underlayment marketplace in more ways than one. The extreme hurricane seasons in the middle of the last decade created a demand for labor as well as a shortage in primary roofing materials, such as tiles and shingles, in some markets. Cases were recorded of roofing contractors waiting weeks or months for delivery of primary roof materials.
Underlayment was left exposed for as long as six months and, in some cases, traditional felt material had to be torn off and new felt installed. Asphalt saturated felts do not perform well when left exposed for long periods of time. Exposure limits came into focus as an important benefit of alternatives to traditional felt.
Better Home Designs
New construction and a better understanding of ventilation allowed for the installation of residential roofs with a water-tight secondary water barrier. Much new construction occurred in Southern regions where air-conditioning is more common than heating. These new home designs with modern roof venting systems favor alternative underlayment materials, including premium self-adhering underlayments as well as synthetic underlayments.
For Northern climates, protection against ice dams was addressed through the use of extra protection along the eaves. This extra protection was mandated in various building codes such as the International Building Code (IBC) and the International Residential Code (IRC).
After natural calamities such as the numerous hurricanes that wreaked havoc in Florida in the early 2000s, insurance companies began to encourage the use of secondary water barriers. The extra cost of the secondary water barrier more than offsets potential losses from consequential damages.
As energy prices rose, oil refiners developed new, cost-effective ways to crack the heavier organic molecules found in crude oil to produce gasoline. This dramatically affected the supply of asphalt and resulted in sharp increases in asphalt prices. This new technology continues to place severe pricing pressure on asphalt, making synthetic underlayment, which does not contain asphalt, cost effective compared to asphalt-saturated felt. It should be noted, however, that similar macro-economic conditions also contributed to a spike in the prices of the polymers used in synthetics.
All of the above factors played a role in increasing the awareness of alternatives to traditional felt paper. Despite the bubble burst in the housing market and the subsequent economic recession, premium self-adhering underlayment and synthetics have succeeded in gaining a secure foothold in the underlayment marketplace. In some areas, and in certain applications, double-digit growth per annum was reported for these new product categories.
Yet asphalt-saturated organic felts remain the workhorse for many steep sloped applications, taking a lion’s share of the market in residential roofing.
For more about the history, manufacture and use of the three main types of residential roofing underlayment, see Tarco's white paper “Rethinking Roofing Underlayments."