| damp proof course | an impervious membrane laid about two brick courses above ground level to prevent damp from rising. |
| daylight | a natural source of light, daylight consists of sunlight, cloud diffused sunlight, both reflected by the ground and adjoining surfaces. |
| daylight transmittance | the ratio of the amount of light transmitted through a window divided by the amount of light incident on its outside surface. |
| daylighting design | the use of controlled natural lighting methods indoors, through the use of skylights, windows and reflected light. |
| decent homes | a government established standard to ensure that all social housing meets a set decency standard by 2010. by definition: a decent home is one which is wind and weather tight, warm and has modern facilities?(odpm 2002). to meet this definition, homes must meet the current statutory minimum standard for housing, be in a reasonable state of repair, have reasonably modern facilities and services, and provide a reasonable degree of thermal comfort. |
| degree days | the difference between the average daily temperature and the cibse degree day baseline temperature. this measure is used to estimate building energy needs. it is also a quick way to compare the severity and character of a climate. a heating degree day is counted for each degree below 15.5o reached by the average daily outside temperatures. for example, if, on a given day, the daily average temperature outdoors is 12 oc, then there are 3.5 degrees below the 15.5 oc. thus, there are 3.5 heating degree days for that day. reverse this process (degrees above 15.5 oc) to calculate cooling degree days. |
| demand side management | the planning, implementation, and monitoring of utility activities designed to encourage consumers to modify patterns of electricity usage, including the timing and level of electricity demand. it refers only to energy and load-shape modifying activities that are undertaken in response to utility-administered programs. |
| de-regulation | the process of removing or reducing regulation. it is often employed in connection with the liberalisation process for privatised industries. the term is sometimes used erroneously to describe the movement of publicly owned companies and industries in to the private sector. |
| design criteria | a set of standards agreed by the developer, planners and regulators that the proposed system should satisfy. |
| detention basin | a vegetated depression which is normally dry, except after storm events, constructed to store water temporarily to attenuate flows; may allow infiltration of water to the ground. |
| dew point | a calculated temperature at which water vapour will condense |
| dioxins | a general term that describes a large group of chemicals that are highly persistent in the environment. the most toxic compound is 2,3,7,8-tetrachlorodibenzo-p-dioxin or tcdd. dioxins are generally formed as unintentional by-products of industrial processes involving chlorine (such as waste incineration, chemical and pesticide manufacturing and pulp and paper bleaching), but also during the combustion of biomass, such in wood stoves. |
| district energy or heating | heating provided from a central boiler, or a number of heat stations, to serve a network of pipes that supply heat to a number of buildings. such schemes may be fuelled by a range of sources, both fossil and renewable and some schemes are multi-fuelled. the buildings served may be a mix of housing, public and commercial buildings. |
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