There are three general categories of metal roof systems used for steep-slope roofing applications: architectural metal panel, structural metal panel and metal shingle/shingle panels. Generally, architectural metal panel roof systems are watershedding and are intended for use on steep slope roofs. Structural metal panel roof systems are used on low and steep slope roofs. Structural metal panel roof systems can be used on low slope roofs because of their hydrostatic, or water barrier, characteristics.
Because architectural metal panel roof systems typically are designed to be used on steep slopes that will shed water rapidly over the metal panels' surface, the seams typically are not watertight. Many architectural metal roof systems are well suited for use on roof slopes of 3 inches per foot (14 degrees) or greater. One exception to the general slope guidelines for architectural metal panel roof systems is the traditional flat seamed, soldered or welded metal roof system, such as copper. It may be specified on slopes less than 3 inches per foot (14 degrees). Solid roof sheathing, or decking, is required for architectural metal panel roof systems, and NRCA recommends using underlayment.
Most structural metal panel roof systems are designed to resist the passage of water at laps and other joints, as sealant or anti capillary designs can be used in the seams. Structural metal panel roof systems possess strength characteristics that allow them to span supporting members.
Metal shingles and shingle panels are available in numerous varieties for use as steep-slope roof coverings. Most of the metal shingles are press-formed during the manufacturing process to provide a variety of shapes. These products can take the shape of individual or multiple asphalt, tile, slate or wood shingle configurations.
There are many categories of metal panels. The term often is used as a generic description for a class of metal roof seams. The name is derived from the fact that the seams are joined together above the panel flats. The term also is used to refer to a panel that includes a standing seam: the vertical leg/flat pan and the trapezoidal seam. The trapezoidal standing seam is more commonly associated with structural metal panels. Other panel types are batten, flat, bermuda and shingled.
The original consisted of vertical leg panels placed between wood batten strips and covered with a cap. Today, many batten seam panels are constructed entirely of metal. Because they are designed to shed water, batten seam panels primarily are used in architectural applications.
A is created with individual panels applied in a shingled application. One panel edge is folded back on top of itself; the other panel is folded under, and the two panels are hooked together. Again, because flat panels are considered watershedding, they are more commonly found in architectural installations. Some flat seam panel systems, such as copper, are commonly soldered, which allows them to perform on less steep slopes.
Architectural metal panel roof systems and structural metal panel roof systems are installed over a large variety of substrates. There are two general categories of substrates: continuous or closely spaced decking that provides solid support for the metal roof panel, and the other is composed of spaced structural supports (such as purlins) where the metal panels must span between supports. Most structural metal panels are used over spaced structural supports without being supported by a solid roof deck.
Metal shingles and metal shingle panels should be installed over continuous or closely spaced wood decking, furring strips, or metal or wood purlins using a batten or counter-batten system. These roof coverings typically are considered to be watershedding roof systems, so the roof slope should be 3:12 (14 degrees) or greater.
Underlayment (or "felt paper" as it is frequently called) is installed over the roof deck before the application of a metal roof system. An underlayment performs two primary functions: it provides temporary weather protection until the metal roof system is installed, and it provides a secondary weatherproofing barrier if moisture infiltrates the metal roof panels.
Asphalt saturated, nonperforated organic felts are among the most common underlayments; they commonly are designated as Type 15 and Type 30 or referred to as No. 15 and No. 30, which are reflective of a once used pound per square weight designation. The terms Type I and Type II now are used within the industry in lieu of No. 15 or No. 30, respectively.
For metal panel roof systems, metal shingles and metal shingle panels, NRCA recommends a minimum of one layer of No. 30 asphalt-saturated felt applied horizontally in shingle fashion on roof decks having a slope of 4:12 (18 degrees) or more. For roof decks having slopes of 3:12 (14 degrees) up to 4:12 (18 degrees), a minimum of two layers of No. 30 asphalt-saturated underlayment should be applied horizontally in shingle fashion.
Underlayments typically are not used with structural metal panel roof systems when intermittent supports are used to carry the roof systems. However, if there is a continuous or closely spaced roof deck, NRCA recommends an underlayment be installed.
In locations where the average temperature for January is 30º F or less, NRCA suggests installation of an ice-dam protection membrane. An ice-dam protection membrane generally is a self-adhering polymer-modified bitumen membrane.
NRCA also recommends a slip sheet be installed over the underlayment for metal panel roof systems. A slip sheet is a layer of smooth building paper, such as rosin-sized or unsaturated building paper. Its purpose is to protect the underlayment from damage, as the panels can adhere to and tear the underlayment.
Condensation should be expected to develop on the undersides of metal roof panels. Careful consideration should be paid to vapor retarder, insulation and ventilation issues. Because every building is in some way unique, building owners and designers may need to consult moisture-control specialists.
ASTM E1514, "Standard Specification for Structural Standing Seam Steel Roof Panel Systems"
ASTM E1637, "Standard Specification for Structural Standing Seam Aluminum Roof Panel Systems"
When purchasing a new roof system, there will be two warranties to consider. First, there will be the manufacturer's warranty. In general, these warranties cover defects in the manufacture of the roof membrane, and vary greatly depending up the specific material and products chosen. The Second is the workmanship. At DC Contractors, we provide a 3 year warranty covering all workmanship unless otherwise specified for your particular project.