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The Building Futures glossary provides definitions of over 400 terms used within sustainable design and construction, urban design and planning.


In the natural environment, the effect of mechanical erosion of rock, especially a river bed, by rock fragments scratching and scraping it; wearing down.

The ability of people to move round an area and to reach places and facilities, including elderly and disabled people, those with young children and those encumbered with luggage or shopping.

ACH - Air changes per hour
An air leakage rate, expressed as multiples of the house volume per hour at a pressure differential of 50 Pascals.

Action planning
Participation techniques, including community planning weekends and Urban Design Action Teams (UDATs), which enable local people and invited teams of professionals to explore design ideas for particular areas over one or several days.

Active frontage or Live edge
Provided by a building or other feature whose use is directly accessible from the street or space which it faces; the opposite effect to a blank wall.

Activity spine
Street or streets along which activity is concentrated.

Activity node
Concentration of activity at a particular point.

Improving our ability to deal with the impacts of a changing climate, now and in the future.

The capacity of a building or space to be changed so as to respond to changing social, technological and economic conditions.

Simple plants ranging from single cells to large plants.

The quality of being pleasant or attractive; agreeableness. A feature that increases attractiveness or value, especially of a piece of real estate or a geographic location

AONB - Areas of Outstanding Natural Beauty
An area designated by the appropriate government bodies as requiring protection to conserve and enhance its natural beauty

APR - Air Permeability Rate
Expressed as m3 of air flow per hour per m2 of dwelling envelope area at a pressure differential of 50 Pascals, m3/h/m2 @ 50Pa. Sometimes expressed) as an air leakage rate in ACH @50Pa.

AQMAs - Air Quality Management Areas
Local areas in which national air quality objectives are not likely to be achieved. Accompanied by Local Air Quality Action Plans which are jointly produced by the District or Borough Council for that area

An underground body of water used to supply drinking water.

Architecture and Planning Centre
An institution which provides a focus for a range of activities and services (such as discussions, information, exhibitions, collaboration and professional services) relating to architecture and planning.

Area appraisal
An assessment of an area’s land uses, built and natural environment, and social and physical characteristics.

Surplus product or leftover salvageable material

Article 4(1) direction
The Secretary of State or a local planning authority has the power to take away all or some of the permitted development rights given by Schedule 2 of the General Permitted Development Order for a specified area. They are typically used to restrict particular types of development or specific changes to the architecture and appearance of buildings and their curtilage.

Arts & Crafts
A vernacular architectural style common on inter-war and early post-war period housing.

ASHP - Air Source Heat Pumps
An electric heating system which converts low grade thermal energy from the air outside to higher grade energy that can be used for space heating indoors.

To weaken or reduce in size, effect, intensity or value

Reduction of peak flow and increased duration of a flow event.


Balancing pond A pond designed to attenuate flows by storing runoff during the storm and releasing it at a controlled rate during and after the storm. The pond always contains water. 

BAPs - Biodiversity Action Plans The Hertfordshire BAP sets out a 50 year vision for the wildlife and natural habitats of Hertfordshire and reviews UK priority habitats and species within the local context. The Hertfordshire BAP identifies 5 Species Action Plans and 8 Habitat Action Plans that guide work on protecting, restoring and re-creating a sustainable level of biodiversity in the county. 

Baseflow Flow in a channel sustained by ground-water discharge in the absence of direct runoff. The typical flow rate for a given stream at a particular time of year. 

Basin A ground depression acting as a flow control or water treatment structure that is normally dry and has a proper outfall, but is designed to detain stormwater temporarily. 

Berm A mound of earth formed to control the flow of surface water. 

Biodegradation Decomposition of organic matter by micro-organisms and other living things. 

Biodiversity The variety of living organisms. It includes the genetic diversity within individual species, the variety of different species, and the range of plant and animal communities within a specific ecosystem or area. 

Biomass  A renewable energy source from living or recently living biological material. 

Bioretention The process in which contaminants and sediments are removed from stormwater runoff. 

Bioretention area A depressed landscape area that is allowed to collect runoff so it percolates through the soil below the area into an underdrain, thereby promoting the removal of pollutants. 

Black water Untreated waste water from sources such as toilets and kitchen sinks which requires considerable treatment before it can be reused, for example to irrigate gardens. 

Block paving Pre-cast concrete or clay brick sized flexible modular paving system. 

Blue infrastructure or Bluespace Refers to a strategic network or individual examples of water features and water based habitats. These habitats provide a wide range of ecosystem services including flood water storage, sustainable drainage, urban cooling as well as cultural benefits such as leisure and amenity space. 

BREEAM The Building Research Establishment Environmental Assessment Method used for measuring the environmental performance of non-domestic buildings and large multi-use development, including Courts, Data Centres, Education buildings, Healthcare buildings, Industrial buildings, Multi-residential buildings, Offices, Prisons and Retail buildings. 

Brief Refers to site-specific guidance or plans including design briefs, planning briefs and development frameworks 

Brownfield land Referring to site, an area of land that has previously been developed by building upon. Also referred to as Previously Developed Land (PDL). 

Building elements Doors, windows, cornices and other features which contribute to the overall design of a building. 

Building envelope guidelines Diagram(s) with dimensions showing the possible site and massing of a building. 

Built form Can refer to an individual building, group of buildings or a wider urban area. A description of the combination of the layout (structure and urban grain), density, scale (height and massing), appearance (materials and details) and the landscape of the development or area. 

Building line The line formed by the frontages of buildings along a street. The building line can be shown on a plan or section. 

Bulk The combined effect of the arrangement, volume and shape of a building or group of buildings. Also called massing. 

Bund A barrier, dam, or mound usually formed from earthworks material and used to contain or exclude water (or other liquids) from an area of the site. 

Burgage plot A mediaeval term meaning tenure of land in a town held in return for service or annual rent, but more commonly used within master plans to refer to the basic plots of land that make up residential sites.


Capping layer In a typical Road pavement construction, the capping layer caps the substrate (original undug soil) and is before the sub base - the lowest course of the road construction structure. 

Carbon footprint  The combined quantity of carbon dioxide emitted by a process or activity, for example the carbon emitted during the construction and operation of a building, which would include emissions arising from the change of land use, the manufacture and transport of the building's materials and fittings, use of energy to physically build the structure, and the heating, cooling, lighting and other services associated with the building’s operation. 

Catchment The area contributing surface water flow to a point on a drainage or river system. Can be divided into sub-catchments. 

CERT – Carbon Emissions Reduction Target A former central government policy to reduce emissions from existing homes to approaching zero by 2050. Under the CERT 2008-2011, obligated suppliers were set a carbon emissions reduction target. This has now been superseded by the Green Deal and Energy Company Obligation (ECO). 

CESP - Community Energy Saving Programme A former central government policy requiring gas and electricity suppliers and electricity generators to deliver energy saving measures to domestic consumers in specific low income areas of Great Britain. Like CERT (see above), this has now been superseded by the Green Deal and Energy Company Obligation (ECO). 

Character assessment An appraisal identifying the distinguishing physical features and historical and cultural associations within a specified area, for example a street, town quarter or landscape. 

Charrette An event (ranging from a couple of hours to several days) which brings together a range of people to discuss design issues. A charrette may or may not use techniques of collaborative design. Also known as a design workshop.

CHP - Combined Heat and Power Gas or biomass fuelled engine that simultaneously generates both electricity and heat. The heat is often used to provide heating and hot water, and the electricity is usually fed into the National Grid, generating an income Through FiTS. 

CIRIA - Construction Industry Research and Information Association

Climate Refers to the average weather experienced in a region over a long period, typically at least 30 years. This includes temperature, wind and precipitation patterns. 

Climate change  Refers to any change in climate over time, whether due to natural variability or as a result of human activity. 

Climate Change Adaptation In the context of the built environment, this is a risk based approach to considering a. how a changing climate will impact upon a building, product, service, activity or infrastructure, b. how important the function it provides is and whether it can continue to provide that function in the context of a changing climate, and c. what actions or measures can and should be taken to ensure that it still provides that function despite a changing climate, or if that function can be provided in another way.

Climate proofing The measures that are taken to ensure that a building, product, service, activity or infrastructure is able to continue to function as required in the face of a changing climate. 

Climate projections  Projections give climate information for the UK and its regions up to the end of this century. They are provided by the Meteorological Office (latest projection being those within UKCP09),. They are based on simulations from climate models. 

Code for Sustainable Homes Also referred to as CfSH or the Code, this is an environmental assessment method for rating and certifying the performance of new homes in areas such as energy, carbon and water 

Connectivity Principle of designing places to ensure they are easy to get to and well integrated both physically and visually with their surroundings so people can move around without effort. 

Conservation Areas  Locally designated areas of special architectural or historical interest, the character or appearance of which it is desirable to preserve or enhance. Planning restrictions and design requirements are, in general, more stringent within Conservation Areas. 

Conservation area character appraisal A published document defining the special architectural or historic interest which warranted the area being designated. 

CDM - Construction (Design & Management) Regulations 2007 Construction (Design and Management) Regulations 2007, which emphasise the importance of addressing construction health and safety issues at the design phase of a construction project. 

CQA - Construction Quality Assurance A documented management system designed to provide adequate confidence that items or services meet contractual requirements and will perform adequately in service. CQA usually includes inspection and testing of installed components, and recording the results. 

Contaminants  A biological, chemical or physical or radiological concentration to affect living organisms. 

Context The setting of a site or area, including factors such as traffic, activities and land uses as well as landscape and built form. 

Context appraisal A detailed analysis of the features of a site or area, including land uses, built and natural environment, and social and physical characteristics. This can serve as the basis for an urban design framework, development brief, design guide or other policy or guidance. 

Continuity (or Enclosure) The use of buildings and their design to create a visually defined street frontage or enclosed external space. 

Conventional drainage   The traditional method of draining surface water using subsurface pipes and storage tanks. 

Conveyance Movement of water from one location to another. 

Corrosion   A process in which a solid, especially a metal, is eaten away and changed by a chemical action, as in the oxidation of iron in the presence of water by an electrolytic process. 

Crime Pattern Analysis Carried out by the Police and is available through liaison with the Architectural Liaison Officer/Crime Prevention Design Adviser. It comprises four components: crime series identification, trend identification, ‘hot-spot’ analysis and general profile analysis. This last aspect includes an examination of demographic and social change and its impact on criminality and law enforcement. 

Culvert A covered channel, watercourse or drain enabling it to pass under a road, embankment etc. 

Curtilage The area of land within the boundary of a property. 


DCLG UK Government’s Department for Communities and local Government.

DECC Department for Energy and Climate Change .

Defensible space A space that is surveyed, demarcated or maintained by private or public owners. Derived from Oscar Newman’s 1973 study of the same name, and an important concept in securing public safety in urban areas, defensible space is also dependent upon the existence of escape routes and the level of anonymity which can be anticipated by the users of the space.

DEFRA UK Government’s Department for Environment, Food and Rural Areas.

Density The floor space of a building, number of buildings or other unit of measure in relation to a given area of land. Built density can be expressed in terms of plot ratio (for commercial development); number of units or habitable rooms per hectare (for residential development); site coverage plus the number of floors or a maximum building height; or a combination of these.

Deposition Laying down of matter via a natural process.

Design assessment An independent assessment of a design usually carried out for a local authority by consultants, another local authority or some other agency.

Design code A set of prescribed urban design and architectural rules of thumb or principles that create an increased level of control and assurance over the quality of the resultant development. 

Design criteria   A set of standards agreed by the developer, planners, and regulators that a proposed development or system should satisfy. 

Design principle An expression of one of the basic design ideas at the heart of an urban design framework, design guide, development brief or a specific development.

Design standards Specific, usually quantifiable measures of amenity and safety in residential areas.

Desire line An imaginary line linking facilities or places which people would find it convenient to travel between easily. 

Development brief A document, prepared by a local planning authority, a developer, or jointly, providing guidance on how a site of significant size or sensitivity should be developed. Site-specific briefs are sometimes known as planning briefs, design briefs or development frameworks. 

Dewatering The removal of groundwater/surface water to lower the water table. 

DEC - Display Energy Certificate Rating system and certificate required under the EU’s Energy Performance of Buildings Directive. The certificate provides an A to G rating for non-domestic buildings of their actual energy use and efficiency, incorporating all energy uses in the building. A certificate must be on display and visible to the public. 

DECC UK Government’s Department of Energy and Climate Change. 

DER - Dwelling emission rate The calculated CO2 emissions of a dwelling in kilograms per m2 of floor area per annum, kg/m2/yr. 

Dip slope A slope of the surface of the land determined by and conforming approximately to the dip of the underlying rocks. Also known as back slope. 

Dissolution The action or process of dissolving or being dissolved 

District Heating A communal system whereby buildings are supplied with space heating (and often hot water) from a centralised shared heat generator via a network of insulated pipes. 

Downdip Pertaining to a position parallel to or in the direction of the dip of a stratum or bed. 

Downpipes A vertical pipe for carrying water down from a rain gutter to ground level. 

Drought A period of abnormally low rainfall normally adversely affecting habitats and biodiversity.  

Dry Free of water under dry weather flow conditions. 

Dry bench First stage of entry to a wetland habitat from its surroundings, sloping down from the outside.


Ecosystem An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving, physical components of the environment with which the organisms interact, such as air, soil, water, and sunlight. 

Ecosystem services The outputs and products generated naturally by an ecosystem that are of benefit to humans, for example the filtration of water and air, recycling of organic compounds within the soil, and pollination of crops by insects.

Elevation The facade of a building, or an architectural drawing of a façade.

Emissions The release of substances into the external environment, for example pollutants such as carbon dioxide or nitrogen dioxide.

Enclosure (or Continuity) The use of buildings and their design to create a visually defined street frontage or enclosed external space. 

ECO - Energy Company Obligation A Government scheme run in conjunction with the Green Deal that is designed to enable the take up of energy efficiency measures by the poorest and most vulnerable households and within certain types of property (e.g. hard to treat) which cannot achieve the potential financial savings on offer through the Green Deal without additional support. ECO financial assistance is provided by energy companies, in place of the previous CERT and CESP schemes. 

Energy efficiency Using less energy to generate the same output or outcome, or the same amount of energy to generate a greater output or outcome (e.g. to heat and light a building).

Enquiry by Design A planning and visioning tool that uses workshops to bring together key stakeholders and local community to develop a vision and plan for an area, place or community.

EPC – Energy Performance Certificate Rating system and certificate required under the EU’s Energy Performance of Buildings Directive. The certificate provides an A to G rating for homes and commercial building non-domestic public buildings of their actual energy use and efficiency, incorporating all energy uses in the building. 

Erosion The group of natural processes, including weathering, dissolution, abrasion, corrosion, and transportation, by which material is worn away from the earth's surface.

ESCO - Energy Services Company Typically operates a CHP or District Heating system to provide heat and/or power on a commercial basis to residents and businesses within a given area. 

Evaporation   To convert or change into a vapour.

Evapotranspiration The combined processes of evaporation, sublimation, and transpiration of the water from the earth's surface into the atmosphere.  The total amount of water transferred from the earth to the atmosphere.

Exceedance The amount by which something, especially a pollutant, exceeds a standard or permitted level.

Exceedance flow route   Design of above ground areas that act as pathways permitting water to run safely over land to minimise the adverse effect of flooding. This is required when the design capacity of the drainage system has been exceeded.

Extensive green roof  Tend to include mosses, herbs or grasses and that usually require minimal watering and maintenance. They are generally lighter, shallower and cheaper than an intensive green roof. 


FEES - Fabric Energy Efficiency Standard The maximum allowed space heating and cooling demand for a zero carbon home, expressed in kilowatt hours per unit floor area per year, kWh/m2/yr. 

Fenestration The style and arrangement of windows on a facade. 

Figure and ground (or Nolli) diagram A plan showing the relationship between built form and publicly accessible space (including streets) by presenting the former in black and the latter as a white background (or the other way round). May be represented in 3D form showing building blocks. 

Filter drain A linear drain consisting of a trench filled with a permeable material, often with a perforated pipe in the base of the trench to assist drainage. 

Filter strip A vegetated area of gently sloping ground designed to drain water evenly off impermeable areas and to filter out silt and other particulates. 

Filtration The act of removing sediment or other particles from a fluid by passing it through a filter. 

FiTS – Feed in Tariffs A Government scheme which pays you for electricity generated from a renewable or low-carbon source such as solar PV or wind turbine. You can be paid for the electricity you generate, even if you use it yourself, and for any surplus electricity you export to the grid. 

Flood zone A classification used by the Environment Agency to describe the risk of river (or fluvial) flooding (flood zone 1-3) for a given area of land. Areas classed as flood zone 1 having the least risk of flooding and areas class as flood zone 3 having the greatest risk. Areas without a flood zone classification are not at risk of river (or fluvial) flooding. 

Flow conditions   Conditions under which a fluid passes along a conduit, including pressure, density, velocity, volume, direction, temperature, etc. 

Flow control   The control of flow through a means of conducting a fluid (through a pipe, channel, etc.) by means of valves, weirs, orifice holes, etc. 

Flow control device   A device used for the control of surface water from an attenuation facility, e.g. a weir. 

Fluvial Produced by the action of a river or stream. 

Fluvial flooding Flooding caused by overflowing rivers or streams. 

Feasibility study An assessment of the potential for a particular type of development to take place in a particular area in light of the policy and physical context that applies to it. For example, is there sufficient infrastructure, are the ground conditions suitable for a particular building or land use, or are there any planning restrictions in place for a particular type or scale of development. 

Forebay A small basin or pond upstream of the main drainage component with the function of trapping sediment. 

Form The layout (structure and urban grain), density, scale (height and massing), appearance (materials and details) and landscape of development. 

Formation level Surface of an excavation prepared to support a pavement 

FRA - Flood Risk Assessment Required when a planning application is made, in accordance with the requirements set out in Government’s policy on development and flood risk as stated in the NPPF. The assessment considers the scale of the proposed development in relation to the flood zone it is located within and the vulnerability to flood. The FRA is considered by the Environment Agency as a consultee to the planning application. See also SFRA. 

Freeboard Distance between the design water level and the top of a structure provided as a precautionary safety measure against early system failure. 

Fruin analysis A US method of analysing pedestrian movement devised by Bernard Fruin which defines and appraises capacity and speeds of movement in various forms of corridors, pavements and other pedestrian routes. 

Future Search A participation technique enabling groups of people to identify common interests, discuss ideas and share information and experience. ‘Open space’ is a similar technique.


Garden City  
Concept of urban design and planning developed by Ebenezer Howard and his contemporaries that sought to create settlements that combined the positive aspects of both the town and countryside

Like a garden; having the appearance or free symmetrical style of a garden, in which the form of beds may be varied from formal geometrical outlines. Applied to the laying out of grounds

GPDO - General Permitted Development Order
Government regulations that set out the types of development, subject to various conditions, that can be carried out without the need for planning permission.

A plastic box structure used in the ground, often to attenuate runoff. 

Soil reinforcing fabric using jute.

An impermeable plastic sheet, typically manufactured from polypropylene, high density polyethylene or other geosynthetic material.

The study of the physical features of the surface of the earth and their relation to its geological structures.

A plastic fabric that is permeable.

Glaciofluvial deposits  
Material moved by glaciers and subsequently sorted and deposited by streams formed by the melting ice.

Glaciolacustrine deposits
Material ranging from fine clay to sand derived from glaciers and deposited in glacial lakes by water originating mainly from the melting of glacial ice;

See ‘urban grain’.

Green Belt
A certain area around a metropolis or settlement that has certain controls against development in place. Green Belt boundaries are laid out in local planning policy. Areas of green belt within Hertfordshire are part of the wider Metropolitan Green Belt which surrounds London.

Green Deal
Government scheme designed to support the increased take up of energy efficiency measures by homeowners, landlords and commercial property owners to improve the energy efficiency and use of renewable energy in their homes and buildings. The Green Deal uses market based approach and loan agreements, as opposed to earlier schemes such as Warm Front and CERT which provided free or subsidised energy efficiency measures. See also ‘ECO’

Greenfield runoffrate
The surface water runoff rate and regime for an area of land before it is (re)developed.

Greenhouse gases
Greenhouse gases reflect heat from the Earth and stop it being lost into space, causing the atmosphere to warm up. See also ‘GWP - Global Warming Potential’ below.

Green infrastructure
A strategic network of green spaces and features or an individual feature thereof. Green Infrastructure can provide a wide range of environmental benefits and ecosystem services in both rural and urban areas including flood water storage, sustainable drainage, urban cooling and local access to shaded outdoor space.

Green roof  
A roof with vegetation growing on its surface, which contributes to local biodiversity, provides a degree of retention, attenuation and treatment of rainwater, and promotes evapotranspiration. See ‘Extensive green roof’ and ‘Intensive green roof’

Green space 
Often used to refer to the spaces that separate or surround built up areas and are maintained for recreation or similar enjoyment, such as parks, woods, playing fields, allotments and private gardens, but can also refer to smaller features such as and green roofs and walls.

Untreated waste water from wash basins, showers and baths. Waste water from kitchen sinks and toilets is considered ‘Black water’.

Water that is below the surface of ground in the saturation zone.

Groundwater discharge
Total groundwater discharge, as reported through a specified area, is similarly expressed as:

Q is the total groundwater discharge ([L3•T−1]; m3/s),
K is the hydraulic conductivity of the aquifer ([L•T−1]; m/s), dh/dl is the hydraulic gradient ([L•L−1]; unitless), and
A is the area which the groundwater is flowing through ([L2]; m2)

For example, this can be used to determine the flow rate of water flowing along a plane with known geometry.

GSHP - Ground Source Heat Pump
A heat pump that converts low grade thermal energy from the ground into a higher grade energy that can be used for space heating. They are best used in conjunction with underfloor heating. The heat pump can be reversed to provide cooling in summer months. Not to be confused with geothermal heating systems which utilise a deeper and higher grade of source of heat.

GWP - Global Warming Potential
Refers to the relative potential of air borne compounds (commonly know as greenhouse gases) to trap heat in the atmosphere contributing toward global warming. The potential of each compound is measured relative to that of Carbon Dioxide, which has a GWP of 1. For example, Methane has a GWP of 21 and so has 21 times the potential of carbon dioxide to trap heat in the atmosphere.


The area or environment where an organism or ecological community normally lives or occurs

A paved or stabilized area where vehicles are parked. Open ground area having a prepared surface and used for the storage of materiel.

Concrete bedding to a pipe.

The upward movement of the ground which is supporting a building and its foundations. This is commonly caused by dry? clay soil which suddenly absorbs a lot of moisture, causing it to swell.

HECA – Home Energy Conservation Act
The Home Energy Conservation Act was enacted in 1995. Its purpose is to make provision for the drawing up of local energy conservation reports in relation to residential accommodation and to give the Secretary of State functions in connection with this purpose. The Department for Energy and Climate Change issued revised guidance in 2012 to require HECA authorities to draw up HECA reports by 31st March 2013, with updates to follow every two years.

HECA Authority
Any English local authority with housing responsibilities.

HECA Report
A report to the Secretary of State for Energy and Climate Change setting out the local energy conservation measures that the HECA authority – or group of authorities – consider practical, cost-effective, and likely to significantly improve the energy efficiency of residential accommodation in its area.

The height of a building can be expressed in terms of a maximum number of floors; a maximum height of parapet or ridge; a maximum overall height; any of these maximum heights in combination with a maximum number of floors; a ratio of building height to street or space width; height relative to particular landmarks or background buildings; or strategic views.

HLC - Historic Landscape Character
A process which classifies the landscape into different historic types related to age, origin, and land use

HIU - Heat Interface Unit
A heat exchanger in place of a boiler.

Horizontal complexity  
With regard to SuDS habitats, the greatest biodiversity across an area rather than with depth.

Human scale
Design of elements within a new development (primarily buildings and streets) to relate well in size and scale to an individual human being and their assembly in a way which makes people feel comfortable rather than overwhelmed.

A metal flow controller for stormwater designed to limit the flow past it to a controlled amount without requiring a power supply.

The area of geology that deals with the distribution and movement of groundwater in the soil and rocks of the earth’s crust.

The scientific study of the properties, distribution, and effects of water on the earth's surface, in the soil and underlying rocks, and in the atmosphere.


In-curtilage parking 
Parking within a building’s site boundary, rather than on a public street or space.

Independent design audit
An assessment of a design, carried out for a local authority by consultants, another local authority or some other agency.

Indicative sketch
A drawing of building forms and spaces which is intended to convey the basic elements of a possible design.

Will not allow water to pass through it.

Impermeable surface  
An artificial non-porous surface that generates a surface water runoff after rainfall.

Infiltration (to the ground)  
The passage of surface water into the ground.

Infiltration basin  
A dry basin designed to promote infiltration of surface water to the ground.

Infiltration device  
A device specifically designed to aid infiltration of surface water into the ground.

Infiltration trench   A trench, usually filled with permeable granular material, designed to promote infiltration of surface water to the ground.

A computer programme designed to predict the environmental impact of a rainfall event on a stormwater system, including open channels, pipework and all connecting structures. It can show the effects of localised sewer or similar flooding on above ground terrain, including an animated 3D view.

Intensive green roof 
An intensive green roof tends to be deeper and may require more watering and other maintenance. It may be accessible by building users and may be a herb garden, vegetable plot, lawn or ornamental garden, for example.

Interception storage  
The capture and infiltration of small rainfall events up to about 5mm.

IDB - Internal Drainage Board
Where an area known as an internal drainage district is in place, the IDB has a role in managing the risk of flooding from ordinary watercourses within that area. Bedford and Ivel is the only IDB within Hertfordshire, situated to the North West of Hitchin.

The artificial application of water to land and soil, most commonly for growing crops, but also for public spaces, landscaping and private gardens.


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Kilowatt peak - the maximum output of an electrical generation system.


A building or structure that stands out from its background by virtue of height, size, architecture or some other aspect of design.

An area, as perceived by people, whose character, including its shape, form, ecology, natural features, colours and elements, is the result of the action and interaction of natural and/or human factors. Landscape character can be expressed through landscape appraisal, and maps or plans. In towns ‘townscape’ describes the same concept.

The way buildings, routes and open spaces are placed in relation to each other.

Layout structure
The framework or hierarchy of routes that connect within a development, the local area or at wider scales.

LLFA - Lead Local Flood Authority
In England, this means the unitary authority for the area, or if there is no unitary authority, then the county council for the area. The LLFA has a role in managing the risk of flooding from surface water, ground water and ordinary watercourses within their area.

The degree to which a place can be easily understood and travelled through.
Term used to indicate the probability of an something, for example a flood, taking place

Life costing 
Total cost during the lifetime of the product or building in order to assess the lowest cost of ownership and potential pay back time

Lifecycle Assessment/Analysis
A holistic assessment of all the inputs and outputs associated with the production, transportation and consumption of goods and services, from the ‘cradle to the grave’. Typically, inputs relate to environmental resources, such as energy, water and raw materials, with outputs relating to externalities such as pollution and waste (by)products. A recent shift to the concept of ‘cradle to cradle’ has occurred, recognising the potential benefits associated with up-cycling and recycling of goods being manufactured and their by-products. See also ‘Ecological footprint’

Listed Buildings
A building of special architectural or historic interest. Buildings are listed for a number of different reasons, including for their architectural interest, historic interest, unusual construction methods, and value as part of a group of buildings.

Live edge or Active frontage
Provided by a building or other feature whose use is directly accessible from the street or space which it faces; the opposite to a blank wall. Also used to describe the vibrant interaction of buildings with the street, e.g. outdoor rooms and pavement cafes, and pedestrian movement/shoppers.

Local distinctiveness
The positive features of a place and its communities which contribute to its special character and sense of place.

London Clay 
This is a soil type present in some parts of South East and East England. Due to its reduced ability to filter water quickly it tends to be prone to shrink-swell.

Lynchian analysis
The widely used method of context appraisal devised by the urban designer Kevin Lynch. It focuses on gateways to an area, nodes, landmarks, views and vistas, and edges and barriers.


Main river
Typically larger streams and rivers that have be classified as Main Rivers by DEFRA. The Environment Agency and riparian owners are responsible for managing and maintaining main rivers.

Where a solution for reducing one area of climate change risk could negatively affect another area of risk, or be unsustainable in other ways. Such solutions should be avoided to ensure that they do not compromise the overall capacity to adapt.

Management train  
The management of runoff in stages as it drains from a site.

The combined effect of the height, bulk and form of a building or group of buildings

Master planning
A process of considering and producing a detailed vision or plan for a specific area or development

Most commonly understood in the context of climate change mitigation, which refers to curbing the emissions of greenhouse gases such as carbon dioxide in order to slow or stop global climate change. However, the term can used to refer to reducing the incidence or creation of other negative phenomena, such as river pollution or loss of biodiversity.

Mixed use
A mix of uses within a building, site or specified area. ‘Horizontal’ mixed uses are side by side, usually in different buildings. ‘Vertical’ mixed uses are on different floors of the same building or complex.

Modal shift
Changing people’s travel behaviours so that they use public transport, cycling and walking instead of cars and other forms of private automotive transport.

Modal split
How the total number of journeys in an area or to a destination is split between different means of transport, such as train, bus, car, walking and cycling.

Movement hierarchy
Prioritising certain modes of travel through the design and layout of developments, typically in the priority order of pedestrians, cyclists, public transport users, specialist service vehicles, and other (private) motorised traffic.

Movement network
People and vehicles going to and passing through buildings, places and spaces. The movement network can be shown on plans by space syntax analysis, highway designations, figure and ground diagrams, data on origins and destinations or pedestrian flows, desire lines, details of public transport services, walk bands and details of cycle routes.

The ability to perform many functions in one area or space

MVHR - Mechanical Ventilation with Heat Recovery
A whole-house, ducted, fan-driven ventilation system which recovers a proportion of the heat from the extract air and re-circulates this heat back into the house.


NPPF - National Planning Policy Framework
Government guidance on general and specific aspects of planning policy to be taken into account in formulating development plan policies and in making planning decisions.

Natural or Passive surveillance
The discouragement to wrong-doing by the presence of passers-by or the ability of people to be seen out of surrounding windows.

A place where activity and routes are concentrated often used as a synonym for junction.

Nolli diagram (or Figure and ground diagram)
A plan showing the relationship between built form and publicly accessible space (including streets) by presenting the former in black and the latter as a white background (or the other way round).

Nitrogen oxides produced by endothermic reactions during combustion. NOx contribute toward air pollution, and NO and NO2 may react to form smog and acid rain.


ODP - Ozone Depleting Potential
Refers to the relative amount of degradation to the ozone layer an air borne compound can cause, where CFC – 11 is the base unit of measure with an ODP of 1.0.

Open water  
Clear water surface i.e. free from submerged or floating aquatic vegetation.

Ordinary watercourse
An ordinary watercourse is every river, stream ditch, drain, cut, dyke sluice, sewer (other than public) and passages through which water flows, but which does not form part of a main river. Internal Drainage Boards, the Lead Local Flood Authority and riparian owners share responsibility and powers for the management and maintenance of ordinary watercourse.

Outdoor rooms
Open space adjoining buildings (either public or private, e.g. cafe terrace), typically in the form of courtyards or intimate pedestrian zones, that acts as places for civic engagement and social activity.

The downstream end of a river, sewer, drain, etc., from which it discharges.

Sowing seeds where plants are already growing without first clearing and cultivating the ground.


Passive or Natural surveillance
The discouragement to wrong-doing by the presence of passers-by or the ability of people to be seen out of surrounding windows.

The road or car park surface and underlying structure, usually asphalt, concrete, or blockpaving. Conversely, the path next to the road for pedestrians (colloquially referred to as the Pavement in the UK) is technically referred to as the Footway.

To cause a fluid to pass through a permeable substance or through small holes.

Performance criterion
A means of assessing the extent to which a development achieves a particular functional requirement (such as maintaining privacy). This contrasts with a standard, which specifies how a development is to be designed (by setting out minimum distances between buildings, for example).

The degree to which an area allows for through movement of people via pleasant, convenient and safe routes.

That can be penetrated or permeated by liquids or gasses.

Permeable pavement/highway 
A permeable surface that is paved and drains through voids between solid parts of the pavement

Permeable surface  
A surface that is formed of material that is itself impervious to water but, by virtue of voids formed through the surface, allows infiltration of water to the sub-base through the pattern of voids, for example concrete block paving 

Pervious surface
A surface that allows inflow of rainwater into the underlying construction or soil.

Illustration showing the view from a particular point as it would be seen by the
human eye.

Piped system  
Conduits generally located below ground to conduct water to a suitable location for treatment and/or disposal.

PFRA - Preliminary Flood Risk Assessment
An assessment carried out by the Lead Local Flood Authority in accordance with EU Floods Directive. The assessment includes a summary of information on significant historic floods; information on future flood risks based on datasets; and information for reporting to the European Commission.

A type of urban design audit advocated by the Urban Design Alliance, based on the Connected City approach. A local collaborative alliance or partnership uses checklists to investigate the connections in the built environment, in its movement network and among the people who shape it. The Placecheck becomes the first step in a continuing collaborative process of urban design.

Place making/shaping
Designing public places and large developments in such a way as to reflect a wide variety of social, cultural, environmental, economic and aesthetic factors in the creation of a high quality place for people to live, work and take pleasure in.

Planning brief
A site-specific plan or set of guidance setting out a framework for its future development. Other terms, including development briefs, design briefs and development frameworks are also used in this context.

Planning for Real
A participation technique pioneered by the Neighbourhood Initiatives Foundation that involves residents and others with an interest coming together to make a model of their area and using it to help them determine their priorities for the future.

Plot ratio
A measurement of density generally expressed as gross floor area divided by the net site area.

Characterized by, or due to the action of rain

Pluvial flooding
Flooding caused by excess surface water runoff. Most common in urban areas.

Air borne particulates under 10µm in size, predominantly arising from road traffic, which can cause respiratory and other health problems

A change in the physical, chemical, radiological, or biological quality of a resource (air, water or land) caused by man or man’s activities that is injurious to existing, intended, or potential use of the resource.

Permanently wet depression designed to retain stormwater above the permanent pool and permit settlement of suspended solids and biological removal of pollutants

Porous paving
A permeable surface that drains  through voids that are integral to the pavement.

Porous surface
A surface that infiltrates water to the sub-base across the entire surface of the material forming the surface, for example grass and gravel surfaces, porous concrete and porous asphalt.

Collective term for rain, hail, sleet or snow.

Proactive development control
Any process by which a local authority works with potential planning applicants to improve the quality of development proposals as early as possible before a planning application is submitted.

Public art
Permanent or temporary physical works of art visible to the general public, whether part of the building or free-standing.

Public/private interface
The point at which public areas and buildings meet private spaces and buildings.

Public open space (or Public realm)
The parts of a village, town or city that are available and accessible, without charge, for everyone to use or see, including streets, squares and parks.

PV - Photovoltaic
Photovoltaics convert solar energy into electricity and are available in a variety of forms, such as panels, tiles and laminate


Quality audit
A review of the management of the design and planning process by a local authority or other organisation.


Protected nature sites. The protection of Wetlands of International importance dating from a convention in Ramsar, Iran, 1971 later adopting an international treaty in 1975

Processing of waste products and materials to produce the same or similar product or material, for example recycled paper.

Registered Parks and Gardens 
A register (administered by English Heritage) of designated parks and gardens that make a contribution to the richness of the English landscape and cross references listed buildings associated with them

The ability to continue to function as required when faced with stress or change.

Carrying out works to an existing building to improve the performance of the building as a whole or in one particular aspect, for example energy or water efficiency.

RHI – Renewable Heat Incentive
A Government scheme of financial incentives set up to encourage the uptake of renewable heat technologies such as heat pumps and biomass boilers in homes and other buildings.

An open surface water channel with hard edges, used to collect and convey runoff. They can also be planted to provide a cleaning function.

The probability of an adverse or hazardous event taking place combined with the consequences or impact (extent and severity) of that event. Determined by carrying out a risk assessment. Differs from an impact assessment, which does not consider the probability of the event taking place.

Risk management  
An iterative process of assessing and classifying the probability of a hazard or event and the consequences of it in order to rank those risks from high to low, and to inform the prioritisation of actions that should be taken in response.

Capable of being cleared by the use of a drain rod.

The integrated soil moisture content from which the plant is extracting moisture from the soil. The rootzone is used to calculate the amount of water in mm which is required to be applied to the crop to maintain optimum productivity.

Water flow over the ground surface to the drainage system. This occurs if the ground is impermeable, is saturated or rainfall is particularly intense


SAB - SuDS Approval Body
Responsible for the approval of SuDS schemes which form part of new development.Typically the same body responsible for the adoption and maintenance of the completed SuDS scheme.

SAP - Standard Assessment Procedure
The Building Regulations methodology for calculating CO2 emissions for dwellings.

Saturation zone   
A subsurface zone in which water fills the interstices and is under pressure greater than atmospheric pressure.

The impression of a building when seen in relation to its surroundings, or the size of parts of a building or its details, particularly as experienced in relation to the size of a person. Sometimes it is the total dimensions of a building which give it its sense of scale: at other times it is the size of the elements and the way they are combined. See also Massing.

Section drawing
Showing a slice through a building or site.

Sediments are the layers of particles that cover the bottom of water-bodies such as lakes, ponds, rivers, and reservoirs.

Settlement pattern
The distinctive way that the roads, paths and buildings are laid out in a particular place, or the pattern of and relationships between distinctive settlements over a larger area.

The extent and magnitude of a negative impact.

A pipe or channel taking domestic foul and/or surface water from buildings and associated paths and hardstandings from two or more curtilages and having a proper outfall.

SFRA – Strategic Flood Risk Assessment
Assessments carried out by the local planning authority to inform the preparation of appropriate policies for flood risk management at the local level

The extent to which soil will expand when wet and contract when dry.

Sick Building Syndrome 
A condition in which occupants of a building experience headaches, fatigue, skin irritations, and respiratory problems thought to be caused by indoor pollutants, micro-organisms, or poor ventilation

Sight line
The line of sight from a travelling vehicle or person. Sight lines will help to determine how fast vehicles are likely to move and how safe other road users are likely to be.

The generic term for waterborne particles with a grain size of 4-63 µm, i.e. between clay and sand.

Siltation is the pollution of water by fine soil, with a particle size dominated by silt or clay.

SIPS - Structural insulated panel system
A modern method of construction where the prefabricated structural elements are also factory-insulated.

Site / regional control  
In the context of SuDS, management of runoff drained from a sub-catchment or several sub-catchments. The controls deal with runoff at a catchment scale rather than at source.

Space syntax analysis
A technique for analysing movement through urban space and predicting the amount of activity likely to result from that movement

Spatial scale 
The relative size of an area. For example, a building is a much smaller spatial scale than a group of buildings, a Masterplan or a river catchment.

In the context of planning and urban design, the street or streets along which activity (typically commercial and movement activity) is concentrated

Strategic view
The line of sight from a particular point to an important landmark or skyline.

Street furniture
Structures in and adjacent to the highway which contribute to the street scene, such as bus shelters, litter bins, seating, lighting, railings and signs.

Street scene
Composition and character of an existing or proposed street, created by the nature and relationship of various elements, including but not limited to architecture, pattern and grain of built development, landscaping, highway design and topography.

Sulphur Dioxide, a pollutant and volatile compound of sulphur and oxygen

A sub-surface structure into which surface water is conveyed, designed to promote infiltration.

The terrestrial medium on which many organisms depend, which is a mixture of minerals (produced by chemical, physical and biological weathering of rocks), organic matter, and water. It often has high populations of bacteria, fungi, and animals such as earthworms.

Source control  
In the context of SuDS, the control of runoff at or near its source

Site of Special Scientific Interest

A layer of material on the subgrade that provides a foundation for a pavement surface.

Part of a catchment, which is an area contributing surface water flow to a point on a drainage or river system.

Material, usually natural in situ, but may include Capping layer, below Formation level of a Pavement.

Occurs when the ground subsides, or sinks to a lower level. In buildings, this might affect the foundations and it is commonly caused by clay soils that have been prone to shrink-swell.

A substance or layer that underlies something, or on which some process occurs, in particular. 

Success factor
One of the characteristics of a place (or places in general) that tends to make
it attractive to live in, work in, or visit. Success factors can be expressed as design principles.

SuDS - Sustainable Drainage Systems  
A man made drainage system for a given area of land that consists of a sequence of management practices and control structures designed to mimic the natural drainage regime that was present prior to its development. SuDS can also be designed to treat runoff, attenuate and conserve water, and provide benefits such as habitat creation and outdoor amenity space

SuDS features
These are features of sustainable drainage systems, designed to mimic the natural method of disposal of surface water, infiltrating into the ground and/or flowing into natural watercourses, to alleviate the risk of flooding arising from a building development. Examples include ditches, drains, culverts, swales, detention ponds, and filter strips

A pit that may be lined or unlined and is used to collect water and sediments before being pumped out.

Superficial deposits  
Deposits related to or near to the surface.

Surface water  
Water that appears on the land surface, e.g. lakes, rivers, streams, standing water, and ponds.

The discouragement to wrong-doing by the presence of passers-by or the ability of people to be seen from surrounding windows.

A shallow vegetated channel designed to conduct and retain water, but may also permit infiltration. The vegetation filters particulate matter.


Thermal mass
The capacity for materials used in construction to passively absorb, store and later release heat.

Tissue study
In the context of urban design, the comparison of scale and layout of different settlements. This technique makes use of overprinting or tracing maps of successful places over the proposed development site or area, at the same scale. Its gives the designer a clue to the capacity of a place and how it may be structured.

A description or representation of artificial or natural elevation features on or of the ground.

Transect diagram
Diagram which helps urban designers to develop an urban-to-rural ‘transect hierarchy’ through a development illustrating appropriate densities, building and street types for each area along the transect.

The act or process of transpiring water vapour, especially through the stomata of plant tissue.

Having sediment or foreign particles stirred up or suspended; muddy:

Classification according to a general type


UKCIP – UK Climate Impacts Programme
Provides a range of tools and guidance to help organisations identify how they might be affected by climate change and what they can do to minimise their risks to or exploit the opportunities of climate change.

Converting or renewing waste or redundant products/materials into new goods and products that are typically used for purposes very different to what the ‘parent’ product or material was used for.

A drain buried below agricultural land.

Urban design 
Entails the design of buildings, groups of buildings, spaces and landscapes to create sustainable and liveable places. It also involves the establishment of frameworks and processes which facilitate sustainable and successful development.

Urban design framework
A document which informs the preparation of development plan policies, or sets out in detail how they are to be implemented in a particular area where there is a need to control, guide and promote change. Also referred to by other names, including urban design strategy, area development framework, spatial masterplan, or planning framework

Urban grain
The pattern, arrangement and size of buildings and their plots in a settlement; and the degree to which an area’s pattern of street-blocks and street junctions are respectively small and frequent, or large and infrequent

Urban Heat Island 
A phenomenon whereby urban temperatures are higher than the surrounding rural areas due to heat being stored and released by the fabric of buildings and roads. The result is that urban centres can be a lot warmer than the surrounding countryside, especially at night when buildings and roads release heat energy that has accumulated during the day.

A value, measured in Watts per metre squared at a given temperature (Wm2K), assigned to a material or a building component such as roofs, floors, windows and walls. It indicates how well it prevents heat from escaping to the external environment. The lower the value the less heat energy is lost through the material or element.


No entries


Walk band
A line on a map or plan showing the furthest distance that can be walked from a particular point at an average pace in a certain time (usually five or ten minutes).

Warm Front
A central government funded scheme that provided grants to improve the heating and/or insulation in the homes of people on certain benefits. The scheme formally ended in January 2013.

Water butt  
Small scale garden water storage device which collects rainwater from the roof via the drainpipe.

Water table  
The level below which the ground is completely saturated with water

Water treatment  
Typically refers to the purification of water to make it suitable for drinking or other defined uses, but can more generally refer to improving the quality of water by physical, chemical and/or biological means.

A significantly sized body of water, e.g. pond, lake, river, stream, sea.

A term including all rivers, streams, ditches, drains, cuts, culverts, dykes, sluices, and passages through which water flows.

The natural flooding and over-irrigation that brings water at underground levels to the surface.

An area of grassland subject to controlled irrigation to increase agricultural productivity.

Weather is the day to day condition of the atmosphere. This includes temperature, precipitation and wind.

Any of the chemical or mechanical processes by which rocks or other materials exposed to the weather undergo changes in character and break down.

Wet bench  
Second stage of entry to a wetland habitat from its surroundings, i.e. adjacent to the wetland. 

Flooded area in which the water is shallow enough to enable the growth of bottom-rooted plants.

WHO - World Health Organisation

WWF - World Wildlife Fund for Nature


No entries


The overall dwelling heat loss due to thermal bridging at junctions, expressed in Watts per m2 of exposed dwelling area per degree, W/m2/K.


Zero Carbon
Activities, processes or objects (such as buildings) that do not  produce carbon emissions. Commonly used in the context of a policy objective for all new buildings to be ‘zero carbon’ by 2019, meaning no carbon emissions arising from heating, lighting and cooling a building. However, the exact definition in this policy context remains unclear.








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