The U-factor or "U-value", is the overall heat transfer coefficient that describes how well a building element conducts heat or the rate of transfer of heat (in watts) through one square metre of a structure divided by the difference in temperature across the structure. The elements are commonly assemblies of many layers of components such as those that make up walls/floors/roofs etc. It measures the rate of heat transfer through a building element over a given area under standardised conditions. The usual standard is at a temperature gradient of 24 °C (75 °F), at 50% humidity with no wind (a smaller U-factor is better at reducing heat transfer). It is expressed in watts per metres squared kelvin, or W/m²K. This means that the higher the U value the worse the thermal performance of the building envelope. A low U value usually indicates high levels of insulation. They are useful as it is a way of predicting the composite behaviour of an entire building element rather than relying on the properties of individual materials.

Unidirectional Externality

 These are externalities in which the external costs or benefits of the resource use are 'one way'.

Urban Airshed Model (UAM):

 Urban Airshed Model (UAM): A three-dimensional grid-based photochemical computer model of the production of ozone from precursors (VOCs and NOx) and the dispersion of air pollution in a specific geographic area over a period of one or two days.

Urban biodiversity

Urban biodiversity is the variety and richness of living things, including genetic, species and habitat diversity found in and on the edge of cities.

Urban compaction

The process that aims to increase built area and residential population densities; to intensify urban economic, social and cultural activities and to manipulate urban size, form and structure and settlement systems in search of the environmental, social and global sustainability benefits that can be derived from concentration of urban functions.

Urban Fabric

 Urban fabric is the physical structure of an urban area.

Urban Fabric

This refers to the manner in which urban tissues, either uniform or diverse in nature are knitted together with the urban structure to form an entity.

Urban Form

It is the collective three dimensional expression of an urban area as represented by their relationship to each other. The term built would refer to buildings, city wall, vertical towers, flyovers etc, while open spaces would include streets, courtyards, roads, parks, tot-lots, river beds etc. Size shape, grain and texture of an area are some of the characteristics which determine the nature of urban form.

Urban Form

 Urban Form means the physical form of an urban area consisting of street patterns, building sizes and shapes, architecture, and density.

Urban Heat Island

 Urban areas being warmer then the surrounding rural area. Ordinarily a nocturnal phenomenon.

Urban Heat Island Effect

 The Urban Heat Island Effect is a measurable increase in ambient urban air temperatures resulting from the replacement of vegetation with buildings, roads and other heat absorbing infrastructure. The heat Island effect can result in significant temperature differences between urban and rural areas.  

Urban Morphology

The three dimensional form of a group of building and the spaces they create. 

Urban Open Spaces

Open spaces in urban areas used for performing different outdoor activities like movement, recreation, relaxation, play etc. 

Urban renewal plan

A measure of the balance between shear stress and shear strength in a slope; a state of limiting equilibrium exits when shearing forces equal resisting forces in a slope and F=1


Urban resilience

A city’s ability to cope with, and adapt to, natural disasters and changing circumstances.

Urban Street Canyon

 The space delimited by the street and the facades of the building outdoor activities along the street.


A process of migration of people that results in population increase in cities with increased urban area and population density. 



Urban and Regional Development Plans Formulation and Implementation (URDPFI)