Width of a Standard Roofing Liner

Origins

• Local and state building codes define how roofs should be constructed and what roofing materials are needed. These regulations are similar across the U.S. because they are based on the International Residential Code or IRC, which was developed by the International Code Council. This nonprofit member organization streamlined three national codes into the IRC when it was founded in 1994. The IRC enables homeowners, manufacturers and roofers in any part of the country to ensure that structures meet the same standards of durability and function.

Width

• Roofing liner is more commonly known as underlayment, roofing felt or roofing paper. It is made from fiberglass fleece soaked with waterproofing substances such as asphalt or bitumen. Because the fiberglass remains unaffected by moisture, rot or tearing, it holds up well under extremes of weather. Polyester and organic versions are also available. Roofing felt generally comes in 36-inch wide rolls that are laid out on roofing decks, before shingles or roof material are attached. The weight of the felt is their primary distinguishing characteristic, with 15 to 30 lbs. acceptable for housing applications.

Sizes

• Roofing liner is also available in wider versions, which reduces the amount of labor to lay them, and is more suitable for larger roofs such as in commercial applications or on bigger homes. A 48-inch-by-250-feet, 10-square roll, for example, can cover more area than five rolls with a standard width. A square, in roofing terms, is an area equal to 100 square feet. Such wider liners still need to meet the same standards of durability as the 36-inch version. They must be resistant to mold and tearing, impervious to moisture and be able to withstand ultra-violet exposure.

Example

• IRC regulation 905.2.7 is an example of how code specifies the application of roofing liner. For roofing decks with a 17 percent to 33 percent slope, underlayment begins at the eaves with a 19-inch strip parallel to the eaves. It then continues with successive layers of 36-inch-wide liner, overlapping at 19 inches. For roofs with greater than 33-percent slope, the underlayment is applied like shingles, parallel to the eaves and lapped at two inches. In all cases, fasteners are needed to hold the liner in place.