CoolRoofs

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Technical Guidelines Handbook

    The technical guidelines Handbook is based on work carried out in the project but focuses on the work of WP3 - Technical aspects of Cool Roofs.  It addressed three main questions as follows:

    WHAT IS A COOL ROOF AND WHAT CAN IT DO IN EUROPE?

    This chapter gives an introduction/overview of Cool Roofs characteristics and technical aspects including relative merits in comparison to other strategies. It also describes the status of Cool Roofs in the international market. It includes a description of Cool Roofs materials in Europe together with an extensive glossary of terms.

    THE PROOF THAT IT WORKS IN EUROPE

    This chapter presents the results from the pilot actions carried out in this project in five buildings in Greece, Italy, France and the UK.  It also describes the developed tool-kit for Europe which can be used for the assessment of Cool Roofs in the various EU regions.

    HOW CAN IT BE USED MORE?

This chapter presents the results of market research in the EU market and proposals for the incorporation of Cool Roofs benefits and facts into EU policies.

 



Cool Roof Glossary PDF Print E-mail
Technical Guidelines Handbook
  
Monday, 06 April 2009 18:05

Cool Roof Glossary

The objective of the CR glossary is to provide a comprehensive definition and description of all critical CR elements, building blocks, applications and benefits in a holistic way and in vocabulary that is understandable by non-technical people.

Albedo

Albedo is another word for solar reflectivity or solar reflectance of the surface of a material.

Aluminium Roof Coating

It is a cool roof technology. The material is an asphalt-type resin containing "leafing" aluminium flakes, meaning flakes that tend to accumulate at the upper portion of the coating exposed to solar radiation. The aluminium flakes increase the solar reflectance of asphalt from a few percent to above 50%.

Anthropogenic Heat

Anthropogenic heat is man-made heat generated by buildings, people, or machinery. It is considered as a climate change contributor by almost the whole scientific community.

ASHRAE

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers. ASHRAE produces energy efficiency standards for buildings, which include cool roof requirements or performance criteria, with respect to the overall energy performance of the building envelope.

Asphalt Cement Concrete

Usually called asphalt, it is a construction material used for paving roads but sometimes roofs as well. It is a hardened mixture mainly composed of an asphalt binder (material produced by petroleum refineries that glues loose material together and accounts for less than 8% of the total pavement weight) and aggregate (mixture of various sized stones, dust and sand, accounting for not less than 92% of the total pavement weight). Cool roof materials and technologies improve the thermal performance of asphalt-made roofs under solar radiation.

Asphalt Chip Seals

It is a cool material technology. Asphalt chip sealing is a paving treatment in which a thin layer of asphalt binder is applied and immediately covered with a layer of light-coloured aggregate. Afterwards, the aggregate is pressed into the binder using a heavy roller. Using a light-coloured aggregate increases the solar reflectance of the roof's paved surface.

ASTM

The American Society for Testing and Materials. The society provides international technical standards. See CEN and EN for the European equivalent bodies. The ASTM publishes reference standards for solar and thermal testing of cool roof materials.

Building Envelope

It is the separation between the interior and the exterior environments of a building. The exterior can be the outdoor environment as well as another built environment. The main components of the building envelope include: the ground construction, roof, walls, doors and windows. The building envelope serves as the outer shell to protect the indoor environment and should ensure comfortable conditions with minimum energy consumption.

Built-Up Roof

A product widely used for flat roofs. It is a membrane consisting of layers of asphalt, which serve as a waterproofing component, alternating with felt fabrics. Cool roof materials and technologies improve the thermal performance of built-up roofs under solar radiation.

Canopy (Layer)

It is a "mattress-type" layer of air just above the ground in cities, extending up to the average height of buildings. Above the urban canopy layer lies the urban boundary layer, whose thickness varies from a few hundred meters up to one kilometre. The urban heat island often refers to both layers, but usually the urban heat island effect refers the layer to below the canopy.

CEN

CEN is the European Committee for Standardization and contributes to the objectives of the European Union and European Economic Area with voluntary technical standards which promote free trade, the safety of workers and consumers, interoperability of networks, environmental protection, exploitation of research and development programmes, and public procurement.

Climate Change

Climate change is sometimes used to refer to all forms of climatic inconsistency. But because the Earth's climate is never static, the term is properly used to imply a significant change from one climatic condition (human driven or natural) to another.

Climate Zone

Portion of the earth's surface within which the climate is generally homogeneous in some respect. The performance of cool roof materials and technology is related to the climatic characteristics of the site. The hotter the climate is, the greater the benefits will be in terms of energy savings and thermal comfort.

Coatings

Products that can be applied with a brush, roller or spray equipment, over a roofing system for several purposes (like protection from moisture, water, hail, UV rays, physical damage). Elastomeric coatings have elastic properties (in the summertime heat and then return to their original shape without damage) and are widely used in roof applications.

Concrete

Construction material often used in roof and road pavements. Concrete is a hardened mixture of Portland cement, sand, and coarse aggregate. Waste materials like fly ash, slag and plastic fibres can also be used in concrete mixture. Cool roof materials and technologies improve the thermal performance of concrete roofs under solar radiation.

Cool Roofs

Roofs with reflective and emissive properties that help improve the energy efficiency of the building and/or mitigate the urban heat island effect.

Cool Roof Rating Council (CRRC)

The Cool Roof Rating Council is the US supervising entity for standards and testing of roofing products, and is responsible for administering the certification program relating to reflectivity and emissivity ratings for those roofing products. No similar body exists in Europe.

Degree Days

Cooling and heating degree days (CDD/HDD) are often used to estimate how hot the climate is and how much energy may be needed to keep buildings at a comfortable temperature.

CDD are calculated by subtracting a reference indoor temperature from the mean daily temperature, and summing only positive values over an entire year.

HDD are calculated by subtracting the mean daily temperature from a reference indoor temperature, and summing up only positive values over an entire year.

The reference temperature is generally the comfort temperature and varies according to regulations or standards. CDD and HDD are climatic indicators, useful for assessing the energy performance of cool roof technology in different climatic zones. CDH or cooling degree hours rely on the same methodology (as does heating degree hours or HDH), with hours not days.

As an example the HDD in Rome and Brussels are 2092 and 3758, at a reference indoor temperature of 20°C; the CDD in Rome and Brussels are 346 and 23, at a reference indoor temperature of 20°C. To be noted that these are not official, they were determined by homemade calculation starting from a typical reference year and are presented simply to demonstrate the concept.

Emittance

The infrared emittance (emissivity) of a material refers to its ability to release absorbed heat, expressed with a number between 0 and 1 (or 0% and 100%). Metallic surfaces have a low infrared emissivity. Most construction materials have high emittance. High infrared emissivity helps keep surfaces cool, even if a high solar reflectance is needed as well.

EN

Abbreviation of European technical standards produced by CEN

Energy Consumption

The amount of energy consumed in a process or a system. In buildings it refers to the energy consumed by the energy systems to ensure comfortable indoor conditions. Energy consumption can also refer to a single energy system, for example: heating, cooling, ventilation, or artificial lighting. More efficient buildings use less energy ensuring the same comfort conditions. Cool roof technology applications can reduce the cooling and the overall energy consumption of a building and improve its efficiency.

Energy Star

A voluntary labelling program designed to identify and promote energy-efficient products, including roofing products, developed by the Environmental Protection Agency of the USA. Several energy efficient products for buildings are labelled, including: heating and cooling systems, lighting, windows, insulation and so on. Including cool roof products into the Energy Star Program recognises the importance of the technology to achieve significant energy savings. Also the EU has launched an Energy Star Program dedicated to energy efficient equipment.

Global Warming

Global warming is the gradual rise of the earth's surface temperature. Global warming is believed to be caused by the greenhouse effect and is responsible for changes in global climate patterns and an increase in the near-surface temperature of the earth.

Green Roofs

Green roofs are rooftops planted with vegetation. Intensive green roofs have thick layers of soil that can support a broad variety of plant or tree species. Extensive roofs are simpler green roofs with a soil layer to support turf, grass, or other thin ground cover. Green roofs can be considered as an alternative to cool roofs because they keep the surface cool, reduce the cooling demand of the building and, in addition to cool roofs, provide thermal insulation. Green roofs have higher construction and maintenance costs in respect to cool roofs.

Greenhouse Gas

A greenhouse gas is any gas that absorbs infrared radiation in the atmosphere. Most well known greenhouse gases are: carbon dioxide, methane, nitrous oxide, halogenated fluorocarbons, ozone, per-fluorinated carbons and hydro- fluorocarbons; however water vapour is also included. By reducing energy consumption in buildings, cool roofs reduce  greenhouse gas emissions in the atmosphere.

Heat transfer

Heat transfer is the transition of thermal energy from a heated item to a cooler item. Classical transfer of thermal energy occurs only through conduction, convection, radiation or any combination of these.

ISO

International Organization for Standardization is an international standard setting body composed of representatives from various national standards organizations. The organization promulgates worldwide proprietary industrial and commercial standards. ISO standards are often implemented in the EU as EN standards.

Membranes

These are roof products, fabricated from strong, flexible, and waterproof materials. They can be applied in multiple layers or consist of a single-ply membrane. Membranes usually contain a fabric made from felt, fibreglass, or polyester for strength, which is laminated or impregnated with a flexible polymeric material. Cool roof materials and technologies improve the thermal performance of built-up roofs under solar radiation.

Reflectance (Solar)

Solar reflectance (or reflectivity) is the fraction of the solar energy that is reflected by the roof's surface back to the sky, expressed with a number between 0 and 1 (or 0% and 100%). White surfaces have the highest solar reflectivity, while black have the lowest.

Reflectivity

Another word for albedo or reflectance.

Roof (Slope)

The roof slope (inclination) determines the roofs' classification and consequently the choice of CR technology on a given roof. There are ASTM standards that define the criteria for roof classification.

Flat roofs generally have a small slope so that water will run off to a drain system and not collect.

Low-slope roofs have a surface with a maximum slope of 5 centimetres rise for 30 centimetres run, corresponding to somewhat less than a 10 degree inclination, as defined in ASTM Standard E 1918-97.

Steep-slope roofs, or sloped roofs, are surfaces with a minimum slope of 5 centimetres rise for 30 centimetres run, corresponding to more than a 10 degree inclination, as defined in ASTM Standard E 1918-97.

Shingles (Asphalt)

Shingles are cool roof materials composed of asphalt saturated mats made from organic felts or fibreglass. The asphalt is protected from the sun ultraviolet light by roofing granules pressed into the shingle while it is hot (and soft). The roofing granules are 1 millimetre-sized stones, which are coated with an inorganic silicate material. The coating contains microscopic pigment particles, similar to those used in paint, to provide colour. They can be used for both roof and road pavements.

Shingles (Roof)

Roofing technology consisting of individual overlapping elements. These elements are normally flat rectangular shapes that are laid in rows. Shingles are laid from the bottom edge of the roof up, with the bottom edge of each row overlapping the previous row by about one third its length. Cool roof materials and technologies improve the thermal performance of roof shingles under solar radiation.

Single-Ply Roof

Single-ply roofing is a flexible or semi-flexible pre-manufactured membrane typically made of rubber or plastic materials. Single-ply roofing comes in large rolls and must be glued or mechanically fastened to a roof, and sealed at all seams. Cool roof materials and technologies improve the thermal performance of single-ply roofs under solar radiation.

Solar Reflective Index (SRI)

The Solar Reflective Index is a measure of the constructed surface's ability to reflect solar heat, as shown by a small temperature rise. This indicator was developed by the Heat Island Project within Berkeley Laboratory's Environmental Energy Technologies. It is defined so that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. SRI combines reflectance and emittance into one number.

Temperature rise

The maximum rise of the roof surface temperature above the outdoor air temperature. This indicator was developed by the Heat Island Project within Berkeley Laboratory's Environmental Energy Technologies. The maximum roof surface temperature is calculated adding the maximum air temperature to the temperature rise. Cool materials have very small temperature rise, while traditional construction materials reach temperature rises of 20-25°C or even higher.

Thermal comfort

Thermal comfort is a condition of mind that expresses satisfaction with the thermal environment. The most commonly used indicator of thermal comfort is air temperature. But air temperature alone is neither a valid nor an accurate indicator of thermal comfort, as it must be considered in relation to other main environmental and personal factors. Cool roofs help maintain thermal comfort conditions in the built environment, by lowering the indoor air temperature and radiant temperature (responsible for the radiant thermal exchange between the human body and the temperature of the surface around the built environment).

Tiles

Roofing tiles can be ceramic (e.g., clay fired at a high temperature) or fabricated from cement concrete or other stone types. Some of the lighter tile types use fibres (e.g. cellulose) added for strength. Cool roof materials and technologies improve the thermal performance of tiles under solar radiation. The light colour of a tile may be dispersed throughout, or it may be applied in the form of a coating.

Urban Heat Island Effect

It is the increased air temperatures in urban areas in contrast to cooler surrounding rural areas. The main cause of urban heat island is modification of the land surface in the urban development, where vegetation is replaced by built surfaces characterised by low solar reflectance, high impermeability and favourable thermal properties for energy storage and heat release. Many studies show that the urban heat island effect is higher at night. The urban heat island depends on several factors, but is typically between 2 and 4°C.  Yet intensities up to 12°C have been measured.

White and Tinted Roof Coatings

White cool roof coatings contain transparent polymeric materials, such as acrylic, and a white pigment, to make them opaque and reflective. These coatings typically reflect 70 to 90 % of the sun's energy. Despite the white appearance, these coatings absorb the 5 % or so of the sun's energy (apart from the white cement-based coatings which can reflect up to 60%) which falls in the ultraviolet. In this way, the pigments help protect the polymer material and the substrate underneath from UV damage.  The solar reflectance of coloured coatings is in general lower than white coatings, but still can reach reflectance as high as 85%, particularly the lightly coloured ones. Additionally organic coatings can be produced, using natural products such as milk and vinegar.