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Residential and Light Commercial Roofing Practices
Roofing is often overlooked, and very misunderstood. It is taken for granted but, how
does it work? The first thing to remember is that a roof is a “system”, not an individual
component. Roofing systems can be broadly categorized as steep slope or low slope. However,
there is one thing all roofs have in common; it takes several layers working in unison to function
properly. Each layer from the base to the outer membrane must be present, and intact to ensure
the roof functions as designed, protecting the structure from the elements.
When looking at residential roofs the vast majority are what would be considered “steep
slope”, meaning they have a pitch of at least 4”. Which leads to the next question, what is pitch?
The slope of a roof is referred to as the pitch. The slope, or pitch, of the roof, is determined by
the vertical rise in inches for every horizontal twelve-inch length, called the run. A roof with x
rise/12 run slope means that for every 12 inches horizontally, it rises x inches (Steep Slope
Roofing, 2015).
Residential roof technology has evolved over the centuries, in fact, one of the first widely
used mediums was bundles of straw attached to rafters, known as “thatch”. Although primitive,
and highly combustible thatch is unexpectedly watertight. The installation, however, is very
labor intensive and installing a “thatched” roof could take weeks or even months. As civilization
progressed, and technology advanced, new mediums became available. Slate laid in overlapping
courses, wood shake (primarily cedar), and curved clay tiles became the materials of choice.
Surprisingly, depending on where you reside these materials are still widely in use, remain
hearty, and serviceable. Regardless of the material selected all steep slope systems rely on an
overlay pattern to repel water and counter wind uplift.
However, the undisputed king of the residential roof is the fiberglass reinforced, asphalt
shingle. Installation begins with sheets of plywood, or planks (1×8-dimensional lumber) being
attached to the joists creating what is called a deck. Next a water resistant membrane, known as
felt is installed, and often sheet metal flashing is used in areas prone to leakage. The asphalt
shingles are then laid in either a staggered (which is the most common) or stacked pattern. The
shingles are attached to one another, then secured to the deck utilizing a variety of fasteners, and
nailing patterns dependent on local code. To ensure a moisture resistant seal, modern asphalt
shingles are self-sealing, which accomplished by the manufacturer applying heat activated
adhesive strips.
Primarily reserved for commercial applications, a low slope roof is one that has a pitch of
