Metal Roof Terms You Should KnowFeb 15, 2020
Metal roofs offer several distinct advantages over traditional asphalt shingle roofs, but there is a lot that most people don’t know about metal roofs and how they work. If you are considering a roof replacement in the near future and haven’t considered the benefits of upgrading to a metal roof, take a look at the following terms to familiarize yourself with metal roofing systems and think about whether the investment would make sense for your property and future plans.
Not every type of metal roofing is weight bearing. “Architectural roofing” refers to non-weight bearing metal roofs that require placement over solid decking instead of typical battens or purlins. Architectural roofing is also commonly called a “non-structural system.”
Class A, B, or C Fire Rating
A metal roof’s class of fire rating refers to how well the roof will withstand fire. However, this classification only refers to fire protection from flames that originate outside of the home.
Metal roofs require an underlayment, and high-quality metal roofs typically use 30-pound felt. This durable material is made of polyester fleece saturated in tar. Some metal roofing contractors have stopped using 30-pound felt and instead install underlayment made of synthetic materials.
Metal roofs consist of interlocking metal panels. Clips are small fixtures that connect metal roof panels together, and they may also connect metal shingles or standing seams to solid decking.
“Valleys” are the intersections of adjacent roof planes. A closed valley contains an integral cover where the shingles meet. This closed valley will carry water through hidden channels below the roof covering. Unfortunately, this type of system often creates a trap that can collect debris like leaves, twigs, and chunks of ice. If this occurs, water will start to seep under the roofing system.
Metal roofs require some type of coating to not only protect them from rust and corrosion but also to allow for painting and customization. Some of the most common types of metal roof coatings include polyvinylidene (PVDF) paint finish that offers great longevity, stone coating, (which mimics the appearance of asphalt shingles but shares many of the same problems as asphalt shingles), siliconized polyester, and super polyester, (which are both typically suited more to agricultural applications than residential).
Metal roofs are fantastic at absorbing heat from the sun, but this can sometimes create hotspots on the roof that can become problematic. A “cold roof” is one that features “above sheathing ventilation” to prevent both hotspots in the warm weather and ice dams in the winter.
“Cool roofing” may refer to a cold roof or any other type of roof with high reflectivity thanks to lighter coloring or reflective pigmentation in the roof panel material.
A “course” is a row of metal roof shingles that run along the entire length of a roof plane.
A “cricket” is a peaked saddle built into the back of a chimney that prevents snow and ice from accumulating around the chimney. A cricket can also deflect water around the chimney to prevent it from corroding the chimney flashings or seeping below cracked flashing.
Just like most asphalt shingle roofs, many metal roofs require decking, or a solid surface installed over the support structure of the roof to which the underlayment and then the metal roof segments are attached.
The eaves of a metal roof are sometimes vulnerable to water penetration. A drip edge is a piece of metal affixed to the eaves that protects the underlayment and eaves by directing water into the eave trough or gutter.
These fixtures create waterproof perimeters around all a roof’s protrusions, including the chimney and roof vents.
This is a steel alloy made with carbon and a protective alloy coating made mostly of zinc on both sides of the steel. Galvanized steel is available in many different grades, and grade G90 is the preferred type for residential use.
An advanced metal roof option, heat tape is a thin electric cable that runs along the eaves of the roof to encourage faster snow melting. This can be a great option for preventing ice dams.
Unlike a cold roof, a “hot roof” is completely sealed and non-vented attic. Usually, the entire interior space of this type of attic is sprayed with closed cell urethane foam insulating material, but it could also be an air-conditioned space.
When snow melts toward the top of the roof it will trickle down toward the eaves. However, this may take several hours, and, if the temperature changes, the water can refreeze around the eaves and create a bulky buildup. Ice dams can be dangerous, but it’s possible to prevent them with proper ventilation and attic insulation.
The Metal Construction Authority (MCA) is the trade association with professional oversight of the metal construction industry, including metal roofing. MCA certification is essentially a seal of approval awarded to the highest quality metal roofing products.
Affixing starter strips is usually the first phase of installing a metal roof. These strips attach to the eaves of the roof for metal shingle systems and on the leftmost edges of a roof for installing a standing seam metal roof.
This type of metal roofing actually provides additional structural integrity to the building and will not require decking like architectural roofing. This may sound like an advantage, but these systems are not suitable for residential applications due to their tendency to generate high levels of condensation.
UL-2218 Impact Resistance Rating
Metal roofing material manufacturers must conduct quality testing to ensure their materials have appropriate impact resistance. UL-2218 impact resistance rating grades materials from I to IV, and products graded IV offer the highest impact resistance. Choosing a Class IV roof may entitle a homeowner to discounts on homeowners’ insurance.
This is the layer of protective material attached to the roof deck below the metal roofing material. Typically, the underlayment consists of 30-pound felt or synthetic sheeting.
If you have considered upgrading your home with a new metal roof, knowing these terms should help you navigate your options more easily. Be sure to check the credentials and past work of any potential metal roof installation team, and take your time weighing your options to find the metal roof that suits your style, preferences, and plans for the future.