Glossary of Terms

Cool Metal Roofing Glossary / Terms

AISI – American Iron and Steel Institute

MBMA – Metal Building Manufacturers Association

MCA – Metal Construction Association

CMRC – Cool Metal Roofing Coalition

CRRC – Cool Roof Rating Council

NCCA – National Coil Coating Association

Coil Coating - The application of a finish to a coil of metal sheet using a continuous mechanical coating process.

CDD – Cooling Degree Day - The difference in temperature between the outdoor mean temperature over a 24-hour period and a given base temperature. For example, using a base temperature of 65°F a day with 85°F mean temperature has 20 CDD (85-65=20). The annual Cooling Degree Days are the sum of the degree days over a calendar year.

Cool Roof Color - The color coating on or self color of the roofing material that gives it a high solar reflectance and a high thermal emittance.

Energy Cost - The total estimated annual cost for purchased energy for the building, including any demand charges, fuel adjustment factors and delivery charges applicable to the building.

Galvalume - A proprietary trade name for a coating, used over sheet steel, that is composed of an aluminum-zinc alloy for corrosion protection.

Galvanized - Steel coated with zinc for corrosion resistance.

Gauge – The thickness of sheet metal.

HDD – Heating Degree Day - The difference in temperature between the outdoor mean temperature over a 24-hour period and a given base temperature. For example, using a base temperature of 65°F a day with 50°F mean temperature has 15 HDD (65-50=15). The annual Heating Degree Days are the sum of the degree days over a calendar year.

IECC – International Energy Conservation Code

Insulation – Any material used in building construction to reduce heat transfer.

Metal Building System - An integrated set of components and assemblies, including but not limited to frames that are built-up structural steel members, secondary members that are cold-formed steel or steel joists, and cladding components, specifically designed to support and transfer loads and provide a complete or partial building shell. These components and assemblies are manufactured in a manner that permits plant and/or field inspection prior to assembly or erection.

Pittsburgh Lock Seam - A method of interlocking metal sheets where each of two sheets are folded with two 180° bends.

Pre-painted Coil – Coil of metal that has received a factory applied paint coating.

R-value - The reciprocal of the U-factor (thermal transmittance). Units of R and h.ft2/Btu. Higher R-values indicate a material's ability to resist more heat flow.

Ribbed Panel - A panel that has ribs with sloping sides and forms a trapezoidal shaped void at the side lap.

Rigid Board Insulation - Typically, a rigid polyisocyanurate or polystyrene foam insulation.

Roof Covering – The exposed exterior surface consisting of metal panels.

Sandwich Panel - A panel used as covering consisting of an insulating core material with inner and outer metal skins.

SI - The International System of Units. Also known as the metric system.

Single Slope - A sloping roof in one plane. The slope is from one wall to the opposite wall.

Solar Reflectance - The ratio of the reflected solar flux to the incident solar flux.

Solar Spectrum - Radiation originating from the sun, including ultraviolet, visible, and near-infrared radiation. Approximately 99% of solar energy lies between wavelengths of 0.3 to 3.5 micrometers. 1) Ultraviolet (UV) 3% of total energy (responsible for sunburn) 2) Visible (VIS) 40% of total energy (visible light) 3) Infrared (IR) 57% of total energy (felt as heat).

Standing Seam - Side joints of roof panels that are arranged in a vertical position above the drainage plane of the panels or flashings.

Standing Seam Roof System - A standing seam roof system is one in which the longitudinal (side) joints between the roof panels are arranged in a vertical position above the roof line. The roof panel system is secured to the roof substructure by means of concealed hold down clips attached with screws to the substructure, except that through fasteners may be used at limited locations where simple lap joints occur, such as at ends of panels and at roof penetrations.

Sustainability - "Meeting the needs of present generations without compromising the ability of future generations to meet their needs." — The World Commission on Environment and Development, 1987 (U.N. Brundtland Report).

Thermal Block - A thermal insulating material that is placed between the metal building roof and the compressed insulation over the purlins. Also known as a "thermal spacer block."

Thermal Conductance (C-Factor) - The time rate of heat flow through unit area of a body induced by unit temperature difference between the body surfaces. Units are Btu / (hour x ft2 x °F) [Imperial system] or Watts / (m2 x °C) [SI system]. See "Thermal resistance."

Thermal Conductivity (K-factor) - The time rate of heat flow through unit thickness of a flat slab of a homogeneous material in the perpendicular direction to the slab surfaces induced by unit temperature gradient. Units for k are (Btu x in) / (hour x ft2 x °F) or Btu / (hour x ft x °F) [Imperial system] and Watts / (m x °C) [SI system]. See "Thermal resistivity."

Thermal Emittance - The ratio of the radiant heat flux emitted by a sample to that emitted by a blackbody radiator at the same temperature. (Total Thermal Emittance). Values are expressed from 0 to 1.0, with 1.0 being the maximum emittance possible.

Thermal Movement - The expansion and contraction that occurs in materials due to temperature change.

Through-Fastened Roof System - A through-fastened roof system is one in which the roof panels are attached directly to the roof substructure with fasteners which penetrate through the roof sheets and into the substructure.

Trapezoidal Panel - A panel configuration whose edge profile forms an open geometric form, roughly in the shape of a trapezoid.

U-Factor (U-Value) - Heat transmission in unit time through unit area of a material or construction and the boundary air films, induced by unit temperature difference between the environments on each side. Units of U and Btu/h.ft2. A lower U-value, means less heat flow that occurs through an assembly from the warm side to the cooler side.

Underlayment - A secondary waterproofing sheet material installed between the substrate and the roof panels, usually used in hydrokinetic roof construction. Some types may be self-adhering.

Urban Heat Island - A built environment wherein the large proportion of dark surfaces such as asphalt paving and dark roofs absorb solar radiation and radiate the heat back into the atmosphere causing higher ambient temperatures and higher pollution levels.

Variegated Roof Surface - A surface marked with patches, spots or areas of different colors. In contrast to a surface having either one color or a regular pattern or texture, a variegated surface has a varied design of several colors and/or textures.

Water Barrier Roof System - Metal panel systems that are designed to withstand being submersed in water for a short period of time. Water Barrier roof details typically rely on sealant to keep water from infiltrating the joints and seams. Water Barrier roof details can be used at almost any roof slope (1/4:12 minimum). These roof systems are also known as Hydrostatic Roof Systems.

Water Shedding Roof System - Metal panel systems that are designed to "shed water" because of their configuration and profile, construction details and installation techniques. Water Shedding roof details are typically devoid of sealant and rely on water to freely flow over and past the joints. These roof systems are also known as Hydrokinetic Roof Systems.