Here is a glossary of common roofing terms that may be useful as you select a tiny house roof.
30 lb felt This was the standard underlayment for quality metal roofing systems as well as other roofing materials and is still used but has been replaced in many areas by the newer synthetic underlayments.
Architectural Roofing Refers to metal roofing systems that are non-weightload bearing and must be installed over solid decking rather than battens or purlins. Also called “Non-Structural Systems”.
Architectural Shingles These fiberglass shingles consist of layers laminated together for added definition and texture.
Class A, B and C Fire Ratings Fire-resistance ratings established for roofing per ASTM and UL tests. These indicate the resistance of a roofing system to fires originating from sources outside the building. In many cases, the ratings are given on roof assemblies including underlayments.
Clip A fabricated metal component used to secure metal shingles or standing seam roofing to solid decking or other approved substrate.
Closed Valley A roof valley flashing that has an integral cover over the area where the roofing panels meet at the miter from adjoining roof planes. This valley carries water in hidden channels beneath the roof covering. In many cases, this cover creates a trap for debris such as leaves, ice, and snow to gather and clog the valley system, causing water to overflow underneath the roofing system
Coatings Below are descriptions of the available metal coatings used in the metal roofing industry:
- Kynar 500 and Hylar 5000. Trade names for polyvinylidene (PVDF) paint finishes that provide very strong longevity and durability including fade and chalk resistance that leads the coatings industry. Kynar 500 is produced by Arkema Chemicals, and Hylar 5000 is produced by Solvay Solexis.
- Stone Coating. Similar granules to composition shingles, but on a steel base, usually in a tile or shake profile. Can experience similar problems of streaking, granule loss, and organic growth as traditional composition shingles.
- Polyester. A solvent-based system with polyester resin. Silicone additives are used to increase resin stability and coating flexibility. Standard polyester finishes are commonly used on agricultural metal roofs where price is of greater concern than performance.
- Super Polyester. Siliconized polyester with fade resistant pigmentation. The pigments enhance the performance of traditional polyesters, but the coatings are still prone to chalking as the resin breaks down over time. As the resin breaks down, the pigments also suffer.
- Plastisol. This coating is traditionally used in the siding industry. It is composed of PVC particles embedded in a plasticizer that provides some flexibility and durability. It is not recommended for roofing applications in the United States.
Coil Coating The continuous process in which paint is applied to both sides of a moving strip of metal. The process usually includes cleaning, chemical pre-treatment, primer, and topcoat. The primer and topcoat are both baked on.
Cold Roof A roof incorporating “above sheathing ventilation” in order to help prevent hot spots on the roof (resulting from heat escaping from the living space) and subsequent wintertime ice dams.
Cool Roofing Roofs that have high reflectivity achieved either through light colors or reflective pigments. Cool roofing can also refer to roof systems which have integral ventilation to help carry heat away from the structure and reduce cooling loads.
Condensation This phenomenon occurs at dew point when warm moist air hits a cool surface. This can occur in or on poorly designed roof assemblies. Ventilation, insulation, and vapor barriers are the keys to avoiding condensation in roof systems.
Cor-Ten A type of weathering steel made in heavy gauges by US Steel. It is designed to rust and is not recommended by its manufacturer for roofing applications. There are paint systems made to give a similar look on galvanized or galvalume steel or aluminum.
Course A horizontal row of shingles, slate or tile running the width of the roof.
Cricket A peaked “saddle” constructed on the uphill side of a chimney to prevent accumulation of snow and ice and to deflect water around the chimney.
Decking The surface installed over the supporting framing members of a building to which the roofing is applied.
Dormer A framed protrusion, usually with a window or vent, projecting through the sloping plane of a roof.
Drip Edge A piece of metal placed on the eave of a roof to protect the underlayment and eave of the roof and direct water in the proper direction, often into the gutter or eaves trough. In some instances, a Drip Edge and starter strip are incorporated in the same component.
Eave The bottom (downhill) edge of a roof plane.
Fascia Plumb vertical boards around the perimeter of the gables and eaves of the roof. These are used to hang gutters along the eaves.
Flashings Components, usually fabricated from metal, used to help waterproof the perimeters and protrusions in a roofing system.
Gable The edge of the roof that runs from the eave to the ridge; some within the industry also refer to this as the Rake.
Galvalume Steel Carbon steel with a protective alloy consisting primarily of aluminum on both sides of the steel. AZ50 grade is suggested for painted product while AZ55 is suggested for product with clear acrylic coating.
Galvanized Steel Carbon steel with a protective alloy consisting primarily of zinc on both sides of the steel. Various grades are available based upon the thickness of the coating. G90 is suggested for residential applications.
Heat Tape Electric cable used to help melt snow near the eaves of the roof, as well as sometimes up the valleys, and also in the gutters. This is used to help alleviate ice dam issues.
Hip The inclined external angle formed by the intersection of two sloping roof planes. Runs from the ridge to the eaves. These are usually 90 degree outside corners on the roof but they can be other angles as well.
Hip Roof A type of roof containing sloping planes on each side.
Hot Roof A completely sealed, not vented attic, the entire interior of which is often sprayed with closed cell urethane foam insulation. This can also be a conditioned space. Some roofing materials may not perform as well on hot roofs, because of they way that heat breaks them down. Metal roofs perform very well on these applications.
Ice and Water Shield A self-adhering membrane specifically designed to be used in heavy rain and snow areas where leaks can be a problem. In most cases you would install ice and water shield on the lowest three feet of the roof, or above the wall line. Building codes will require this in certain areas.
Ice Dam When snow melts on an upper section of a roof surface and then refreezes at the eaves where the roof surface is colder. This causes water to back up, causing leaks into the roofing system. Ice damming is controlled through attic insulation and ventilation, and be sealing heat leaks from the living space.
Metal Construction Association (MCA) Certification Program MCA is the authority trade association for metal roofing and other metal construction products. Their Certification Program recognizes products that meet certain quality levels and standards for residential application.
Open Valley A valley design used to transition water and debris off of a roof slope, carrying the water on top of the roofing system. These valley systems are designed to not clog with debris such as tree leaves and needles, ice, or snow.
Pitch The slope of the roof plane, referred to as the height of vertical rise over the length of horizontal run, such as 3:12 which refers to 3” of vertical rise per 12” of horizontal run. Steep slope refers to any pitch great than 3:12 and very low slope refers to any pitch less than 1.5:12. Most metal roofs can be installed on roof pitches of 3:12 or greater though mechanically seamed standing seam systems can be installed on shallower roofs.
Pipe Jacks Also called “pipe flashings,” these refer to metal and/or neoprene flashings used to seal around plumbing pipes, round vents, conduits, and other roof penetrations.
Ridge The very top section of the roof running the length of the roof, where the two roof slopes come together.
Ridge or Hip Caps Accessories used to cover the inclined external angle formed by the intersection of two sloping roof planes, either at the ridge or hip.
Ridge Vent An exhaust vent for attic air that is integrated into the ridge cover. A ridge vent’s proper performance requires adequate intake vents, usually in the eave soffits of the home. For most homes this is the most effective method for siphoning warm air and moisture through and out of the attic.
Roof Framing Styles Gable, hip, and barn style roofs are only a few of the possible shapes and designs a roof can take. For more information and examples please visit: oneprojectcloser.com
Sealant Used most commonly to act as a sealant of joints or cracks to help prevent leaks. The higher grade sealants are usually butyl or polyether chemistry. Sealants should be used for aesthetic reasons as well as for redundant lines of defense against water intrusion. They should never be the sole line of defense. Also, sealants are not designed to be adhesives.
Snow Guards Used in snow country to help break apart snow so it does not leave the roof surface in large pieces and harm people or property. An enhanced variation of these consists of Snow Fences. On standing seam roofs, these items need to be installed in a way that does not impede movement of the roofing system with thermal expansion and contraction.
Square Roofing material adequate to cover 100 square feet of the roof.
Starter Strip Used to begin the attachment of many metal roofing systems. It is used at the eave (bottom) of the roof on many metal shingle systems and on the left hand edge of the roof on many standing seam systems.
Step Flashing A method of flashing commonly used with standard roofing shingles and some other materials to help seal them against brick walls or other surfaces. Step flashing is generally not advised with metal roofing which usually uses continuous lineal flashings for greater life and watertightness.
Structural Roofing Metal roofing that provides structural integrity to the building and does not require decking for installation. Generally these systems are not advised for residential application because a lack of decking can be a contributing factor to condensation issues.
UL-2218 Impact Resistance Rating A test for measuring the impact resistance of roofing materials that rates roofing materials on a scale from I to IV with IV being products that best withstand the impact test. Insurance discounts area available to homeowners in some areas who choose Class IV roofs. Homeowners are advised to investigate any future limitations that accepting the discount may place on their insurance coverage.
Underlayment Asphaltic felt or synthetic sheet installed on the roof deck below the roofing material. This is required by code beneath all metal roofs, even if the old shingles are left in place.
Valley The internal angle formed by the intersection of two sloping roof planes to provide water runoff. Refer to the glossary terms for Closed and Open Valley.
Wall Flashing Where a roof runs alongside a sidewall, a flashing must be used to prevent water intrusion at the juncture.
Need help understanding another roofing term? Ask our own Todd Miller, roofing expert at AskToddMiller.com.