Steep Slope Roof: Part 1
By: Kevin Duffy
As you may recall, Sullivan Engineering recently ran several articles pertaining to low slope, or flat roofs. Now, a new series will shed light on steep slope roofing systems. Steep slope roofs differ from low slope roofs in the fact that they are, as the name implies, steeper. They are defined by the National Roofing Contractors Association as having slopes exceeding 3:12 or 14 degrees. Also, unlike low slope roofs, theyare not inherently water impermeable; they are designed to shed water, not retain it. Similar to low slope roof systems, there are many types of steep-slope roofing systems that can be classified into 3 main categories. Shingles, tile and metal roof systems are the 3 most common types of steep slope roofing systems available. The first article in our three part series on steep slope roofing will concentrate on shingles.
Shingles are the single most common material used in steep slope roofing in the United Stated. There are several types of shingles. While popular in Scandinavian countries until the 1950s, wood shingles are mostly used on historic sites. Asphalt is the most prevalent type of shingle currently used. Asphalt shingles have been around since the early 1900as and have become by far the most popular roof for residential homes. The granular surface on these shingles helps protect the asphalt from UV degradation.
Due to the water shedding nature of shingles, it is important to install an impermeable underlayment. This usually comes in the form of Number 15 or Number 30 felt paper, so named because, traditionally there was either 15 or 30 pounds of material per 100 square feet, or Roofing Square. There are, however, other underlayment options such as self adhered, self sealing polymer-modified bitumen membrane. These membranes can be used over the entire roof, as long as itas vented properly at the top. However, they are most typically used as a 2a to 3a border around a roof to create added protection against ice daming. Ice daming occurs when snow and ice build-up prevents water from entering into gutters. This adds increased loads to the roof, which could lead to a partial or full-scale roof collapse.
As with any roofing system, the flashings are the most important component. Typical flashings on an asphalt roof are made of 16 oz copper; however, Sullivan Engineering recommends a more durable 20 oz copper. Flashings are necessary at certain areas of the roof including valleys, penetrations and vertical surfaces such as chimneys and parapet walls.
As with any new roof system, warranties are often a consumeras top priority. Many asphalt shingle manufacturers offer 20-year warranties. Recently, some manufactures have started offering 50-year warranties if certain stringent installation requirements are met. With any warranty, it is important to remember the wise words of Carl G. Cash in his book, appropriately titled, Roofing Failures aA warranty usually covers about 8 A1/2a x 11a and is not very waterproofa. In other words, pick the right shingle roof system for your building based on the manufactureas reputation for providing quality products, not necessarily the warranty.