Air infiltration - Another term for air leakage / permeability

Air permeability - Determined by Part L of the Building Regulations as the uncontrolled air leakage through the building envelope including the roof, walls and ground floor. Air permeability is defined by BS EN 13829. Units are in m3/m2hr at 50 Pascals or m/h @ 50 Pa.

Airtightness - Part L of the Building Regulations specifies maximum values for the air permeability of dwellings, commercial and public buildings. (see also: Refurbishment: Airtightness)

Airtightness layer - Essential to the energy performance of a building, the airtightness layer is the method by which the flow of air through the building structure is controlled. The layer represents an unbroken / un-penetrated envelope encompassing the interior of the building which prevents warm air ‘leaking’ to the exterior. In timber frame buildings the airtightness layer usually comprises of a membrane integrated into the structural element (located more often on the ‘warm’ side of the insulation), whereas in masonry construction plaster usually acts as an effective barrier.

Airtightness line - A design technique that defines the location of the airtightness layer, usually represented by a line on the drawing. Having defined the line, details can be developed to ensure the continuity of the airtightness layer around junctions / connections / penetrations within the structure.

Airtightness test - A requirement of Building Regulations, the test establishes the effectiveness of a building’s airtightness through measuring the extent to which air is lost through leaks in the building, in units of air changes per / hour at a test pressure of 50 pa. The current regulations require a maximum of 10 whereas the more demanding Passivhaus standard requires 0.6. The most common method of testing is through use of a ‘Blower Door Test’ which uses a fan to ‘blow’ air into the building in order to achieve the necessary indoor air pressure.

Alpha (a) - value - The overall thermal performance of the entire building envelope, taking into account the positive effect of the U-value of all plane elements (roof, rooflights, walls, etc) and the negative 'heat draining' thermal bridging effect of junctions, details and interfaces, which act as direct heat conductors from the inside to the outside of the building. To achieve compliance under Part L of the Building Regulations, two a-values must be calculated, one for a notional building and one for an actual building. The objective is to establish that the a-value of the actual building is lower than the notional building.

Abiotic components - The non-living components of the biosphere. Chemical and geological factors, such as rocks and minerals, and physical factors, such as temperature and weather, are referred to as abiotic components. THIS GLOSSARY AND THE INFORMATION CONTAINED IN IT WAS SUPPLIED BY GREENSPEC

Abiotic depletion - Refers to the exhaustion of natural (non-living) resources such as iron ore, copper and fossil fuels.

ACH (Air Changes per Hour) - Measures ventilation as the number of times per hour that the air inside a building is changed. Units m3 hr/ m3.

Acid Rain - See Acidification.

Acidification - The result of acidifying pollutants emissions, such as SO2 or NOx, to the air. These emissions have negative impacts on soil, groundwater, surface waters, biological organisms, ecosystems and materials

AECB - The sustainable building association (see also: )

Aerobic digestion - The bacterial process of decomposition or rotting occurring in the presence of oxygen - aka composting.

Afforestation - The planting of trees in areas that have not previously held forests.

Air barrier / airtightness membrane - Membranes that prevent the flow of air from the inside to the outside of a building (see ‘airtightness layer’ below). They are available in different materials according to their function. In its basic form, an air barrier / airtightness membrane is nothing more sophisticated than polythene sheeting that can also double as a vapour barrier; A more sophisticated membrane is one that permits the flow of moisture through the material which is allowed to diffuse through the structure to the exterior (‘breathing wall’). Air / vapour barriers can also include materials such as OSB and plasterboard. (see also: Airtightness membranes)

Air film resistance - Results from convection currents at the surface of a material. As the surface heats up or cools down, it affects the temperature of the air immediately adjacent. This then starts to rise or fall depending on whether it is hotter or colder. This has the same effect as increasing the resistance of the material to the flow of heat.


Blackwater - Wastewater containing faecal matter and urine. It is also known as brown water, foul water, or sewage. It is distinct from greywater, the residues of washing processes.

BRE (Building Research Establishment) - BRE is an independent and impartial, research-based consultancy, testing and training organisation that help clients create better, safer and more sustainable products, buildings, communities and businesses.

Breathable sheathing - A board which is vapour permeable enough to allow it to be used externally in timber frame construction.

Breather membrane - A membrane which allows vapour to escape whilst preventing water from entering the construction. Breathing wall

Breathing wall - ‘Breathing’ walls allow a significant amount of water vapour (and other gases) to be absorbed and released quickly to the outside, thereby regulating the room climate and hence indoor air quality. Much debate continues over the value and physics involved.

BREEAM - BRE Environmental Assessment Method (BREEAM) is a voluntary measurement rating for assessing the environmental impact of buildings. It comes in a variety of flavours according to the function of the building.

Brown roof - Local soil and rubble forms a substrate on a low-pitched or flat roof, which is allowed to colonise naturally.

Building envelope - The outer shell that separates the interior and the exterior environments

Balance point - The outdoor temperature at which a building's heat loss to the environment is equal to internal heat gains from people, lights, and equipment.

Balancing pond - A pond designed to attenuate flows by storing Runoff during the peak flow and releasing it at a controlled rate during and after the peak flow has passed.

BFRC Rating - A measure of the overall performance of a window, rated from A-G.

Bio-accumulation - The increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment.

Biocide - A chemical additive which prevents growth of bacteria or fungi. More often found in paints and floor coverings. Biocides are dangerous in large concentrations.

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

Biofuel - Ethanol and diesel made from crops including corn, sugarcane and rapeseed.

Biological wastewater treatment - The use of bacteria to eat the organic material present in wastewater.

Biomass - A renewable energy source, commonly used to refer to plant matter grown to generate heat or electricity.

Bioretention area - A shallow, landscaped depression that receives runoff from impervious surfaces.


Cold spots - Areas either on the inside or outside of the building envelope, whose temperatures are significantly lower than the surrounding area. Usually only apparent through infrared thermographic survey they can have a number of causes including areas that have simply been shaded from the sun or, more importantly, areas of differential heat loss occurring through the building fabric. Often a cold spot on an internal surface will be matched by a ‘hot spot’ on the exterior – representing a thermal bridge where opposite, or air leakage by a more complex path through the structure when not opposite.

Combined Heat and Power (CHP) - Works based on the principle that electricity generation produces heat as a bi-product. CHP was developed as a way of capturing and using the ‘waste’ heat. CHP plants have been successfully established at a variety of locations and scales in recent years, but recent research has been concentrated on developing CHP units for domestic use. (See also: Micro CHP)

Composting toilet - A self-contained unit that treats waste using aerobic decomposition (composting). The output compost is best used for fruit trees and bushes rather than vegetables.

Cradle-to- - Life Cycle Analysis (LCA) is often broken down into phases of lesser ambition. Where recyclable / reusable products are the subject, the entire analysis is referred to as ‘cradle-to-cradle’. For non-recyclable materials that are destined to be disposed of, the complete analysis is referred to as ‘cradle-to-grave’. Expressions such as ‘cradle-to-gate’ or ‘cradle-to-site’ refer to production from extraction of raw material and factory production; and extraction, factory production and delivery to site, respectively – though these LCAs are useful and more common, they tend not to tell the whole story.

Cross-laminated timber (CLT) panels - Pre-fabricated load bearing timber panels that are used in timber structures. Originally developed in Switzerland in the 1970s, products are now beginning to be imported from central Europe and Scandanavia. The panels are produced from softwood strips (eg spruce) that are stacked crosswise on top of each other and glued to each other to create a distinctly strong structural element. Fabricated off-site and quick to erect, the resulting panels can be used to form complete floors, walls and roofs.

CSH (Code for Sustainable Homes) - An environmental assessment system for rating new build dwellings. A CSH assessment is mandatory for Housing Association dwellings.

CAPEM - An EC funded project, currently underway, to develop a harmonized assessment procedure for building materials based using a simplified LCA-based methodology.

Carbon neutral - Conceptually, a state whereby the CO2 generated by a process is exactly balanced by the amount of CO2 either offset or sequestered by the process. A carbon neutral building is one that either uses no fuel that generates CO2 or where its consumption of CO2-generating fuel is equally balanced by exported renewable energy. The definition continues to be debated as to the extent of direct / indirect CO2 that is included in the equation – eg CO2 generated in the construction of the building. See also ‘Zero Carbon’

Carbon sequestration - The deliberate removal or storage of carbon in a place (a sink) where it will remain. Carbon Sequestration in construction usually refers to building products derived from plant materials such as wood and hemp, where CO2 is absorbed as part of the growing process. The carbon remains 'locked' in the material for the lifetime of the building.

CarbonLite Programme - The AECB's Carbon Literate Design and Construction Programme (see also: CarbonLite Programme)

Chloroflourocarbon (CFC) - A chemical compound made up of carbon, fluorine, and chlorine. CFCs were until recently used as blowing agents in the production of insulation (as well as in refridgerators). Their use has been phased out because of their contribution to depletion of the Ozone layer.

Closed loop-recycling - A system by which a given mass of material is remanufactured into the same product.

Co-generation - The use of a heat engine to generate both electricity and heat simultaneously. (See also: CHP below)

Code for Sustainable Homes - Is an environmental impact rating system for housing in England. The Code replaces Ecohomes and sets new standards for energy efficiency above those in current building regulations and sustainability.

Coefficient of performance (COP) - COP is usually referred to in measuring the efficiency of heat pumps. It is the ratio of the heat energy output of heat pump versus the amount of electrical energy input.

Cold bridging - A discontinued term for thermal bridging.


Desertification - Is the degradation of land in arid and dry sub-humid areas, resulting primarily from man-made activities and influenced by climatic variations.

Design for Deconstruction (DfD) - Anticipating the end-of-life of a building at the design stage can help optimise the reuse and recycling of components in the event of its deconstruction. (see also: Designing for dismantling)

Diffuse pollution - Is the release of potential pollutants from a range of activities that individually may have no effect on the water environment, but at the scale of a catchment can have a significant impact (ie reduction in water quality, decrease in wildlife, etc.).

Diffusion Open - Usually applicable to timber frame construction - a membrane / layer that permits the passage of vapour – normally the ‘breather membrane’ is included in the outer layers of the construction.

Diffusion Tight - Usually applicable to timber frame construction - a membrane / layer that inhibits the passage of vapour – usually the ‘vapour control layer’ is applied to the warm side of the insulation layer.

Distributed generation - Is the generation of energy at smaller scales, usually close to where it is used, than that of traditional power stations. Amongst other advantages, distributed generation reduces the amount of energy lost through transmission. (See also: Distributed generation)

District heating - Is the use of a centralised boiler installation to provide heat for a number of buildings. This can use heat from only a boiler, or the heat from a combined heat and power (CHP) plant.

Diurnal heat flow - The heat that flows in and out of a building from daytime to night-time.

Diurnal temperature variation - The daily temperature shift that occurs from daytime to night-time.

Downcycle - A material that loses its original function / value through recycling, but continues to be used in its downgraded format.

Daylight transmittance - The ratio of the amount of light transmitted through a window divided by the amount of light incident on its outside surface.

Deconstruction - Sometimes referred to as ‘construction in reverse’, deconstruction is the selective dismantling of a building for re-use, recycling and waste management. The technique is in contrast to ‘demolition’ which is where a building is removed from a site by the most expedient means.

Decrement delay - Refers to the time it takes for heat generated by the sun, to transfer from the outside to the inside of the building envelope and affect the internal conditions. Materials affording higher rates of decrement delay will have a low lambda (thermal conductivity or k-value) value, high specific heat capacity and high density. Insulation materials offering a high decrement ‘factor’ include cellulose fibre (7.3 hr), wood fibre insulation board (11.3 hr); whereas materials with a low decrement factor would include low-density mineral fibre (3.7 hr) and polyurethane/polystyrene. Decrement delay can be useful in the design of timber frame buildings. Insulation with a high decrement factor can be used to limit solar over-heating in particularly warm climate conditions. For example, installing cellulose as a roofing insulation will likely slow-down the heat transfer from a sun-heated roof surface, through to the inside by around 7 hours – or by evening time.

Decrement factor - The time taken (measured in hours) for heat to transfer between opposite surfaces of a material. (see above)

Deforestation - Is the clearance of naturally occurring forests by the processes of logging and/or burning of trees in a forested area.

Degree days - Is the rate of heat loss from a building, (related to the building fabric) and the temperature difference between the inside and outside of a building - the greater the temperature difference the more heat will be lost. A heating degree day is counted for each degree below 15.5oC reached by the average daily outside temperatures.

Delivered energy - The amount of energy which is supplied to final users, e.g., households, office buildings, schools and factories.


Environmental profile - The ouput of an environmental profiling process (see below). Profiling can be of a generic nature using general industry data or it can be of a proprietary nature using product-specific data – for example as part of the BRE’s ‘Environmental Profiles Certification Scheme’. Generic profiles form the basis of the BRE’s ‘Green Guide to Specification’.

Environmental profiling - The ‘identifying and assessing the environmental effects associated with building materials’ (BRE) – usually using a standardised methodology. The identification and assessment of the environmental effects associated with building materials, usually using a standardised methodology. The UK profiling market is dominated by the BRE, but other methodologies are currently being developed – for example through the EC-funded CAP’EM project.

EPC (Energy Performance Certificate) - Contains information about a property’s energy use, typical energy costs and gives recommendations about how to reduce energy use and save money. EPC’s are mandatory when selling or renting a property.

Eutrophication - The process by which a body of water accumulates high levels of macronutrients, particularly nitrates and phosphates.

Evaporative cooling - A means of temperature reduction which operates on the principle that water absorbs latent heat from the surrounding air when it evaporates.

EWI (External Wall Insulation) - A thermally insulated, protective, decorative exterior cladding system designed to improve the thermal efficiency of a building and to reduce energy consumption.

Earth construction - Construction incorporating earth as a material.

ECO (Energy Companies Obligation) - A financial scheme to fund energy efficiency improvements to people living in fuel poverty and those living in hard-to-treat properties.

Eco-design - Is an approach to design of a product with special consideration for the environmental impacts of the product during its lifecycle.

Eco-label - An ‘eco-label’ indicates that a product has a reduced environmental impact compared with other products in the same product group. A number of ‘eco label’ commercially-sponsored schemes exist, but the most important is the European Ecolabel backed by the European Commission. The leading UK building eco-label is the BRE Environmental Profile Standard.

Embodied energy - All the energy required to grow, harvest, extract, manufacture, refine, process, package, transport, install and dispose of a particular product or building material. (see also: Embodied energy)

Energy efficiency - Using less energy to provide the same level of energy service. Along with renewable energy, energy efficiency is own of the twin pillars of sustainable energy.

Engineered wood - Also called composite wood, engineered wood includes a range of derivative wood products which are manufactured by binding together the strands, particles, fibres, or veneers of wood, together with adhesives, to form composite materials. eg plywood.


FiTs (Feed-in Tariffs) - A scheme in which homeowners can be paid for electricity generated through an electricity-generating technology from a renewable or low-carbon source, such as Solar PV.

Flood routing - Refers to designing to channel water over land in a controlled fashion in the event of flooding and when the capacity of a drainage system has been exceeded.

Flow control device - Is one which controls the rate at which water is discharged to a surface water drain or watercourse.

Fly ash (PFA - Pulverised Fuel Ash) - Known as Pulverised Fuel Ash (PFA) in the UK, is a by-product from burning coal for the production of electricity. PFA is used as a cement substitute in the manufacture of concrete. (see also: Cement substituttes )

Fossil fuel - Coal, oil and gas.

f-factor - Indicates the risk of surface condensation, the lower the value, the greater the risk. The risk depends mainly on the surface energy balance and on the moisture content of the ambient air. Part C of the Building Regulations determines the minimum f-factor in a number of applications.

Fan Pressurisation Test - A fan or series of fans is connected to an external doorway which pressurises / de-pressurises the building. The test establishes the effectiveness of a building’s airtightness through measuring the extent to which air is lost through leaks in the building, in units of air changes per / hour at a test pressure of 50 pa. The current regulations require a maximum of 10 whereas the more demanding Passivhaus standard requires 0.6.

Filter drain - A filter drain is a device that has a volume of permeable material below ground to store surface water. ‘Runoff’ flows to this storage area via a permeable surface.

Filtration - The act of removing sediment or other particles from a fluid by passing it through a filter. Water filtration can be achieved in several ways including using Carbon filters, Ultraviolet (UV) filters, distillation, sand filters and ‘reverse osmosis’.


Green Guide to Specification - Now published online, the BRE’s ‘Green Guide to Specification’ rates a large directory of construction elements according to their environmental impact. The ratings are based on Life Cycle Assessments using the BRE’s ‘Environmental Profiles’ methodology. The ‘Green Guide’ is closely integrated into the BREEM and Code for Sustainable Homes assessment tools. Some of the ratings are much derided by many in the design community. (

Green Register - The Green Register is an independent organisation promoting sustainable building through training and events. (

Green roof - A roof of a building that is partially or completely covered with vegetation and soil, or a growing medium, planted over a waterproofing membrane. (see also: Green Roofs Pt 1 & Green Roofs Pt 2)

Greenhouse gases - Gases in the earth’s atmosphere that absorb and emit radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The main greenhouse gases in the atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone.

Greenwash - A term used to describe the practice of companies disingenuously spinning their products and policies as environmentally friendly.

Greywater - Greywater Wastewater generated by domestic processes such as washing and bathing.

Ground source heat pump (GSHP) - A system that extracts heat from the ground, upgrades it to a higher temperature and releases it where required for space and water heating.

G-value - Measures the degree to which glazing blocks heat from sunlight. The G-value is the fraction of the heat from the sun that enters through a window. G-value is expressed as a number between 0 and 1. The lower a glazing’s G-value, the less solar heat it transmits.

Gasification - Gasification A waste treatment process where waste is heated to produce a combustible gas that can be burned in excess air to generate heat.

Geotextile - Permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain.

Geothermal energy - Is heat derived from the earth. See also ‘Ground Source Heat Pumps’

Global Warming Potential (GWP) - A measure of how much a given mass of greenhouse gas is estimated to contribute to global warming. It is a relative scale which compares the gas in question to that of the same mass of carbon dioxide (whose GWP is by definition 1). For example, methane, nitrous oxide and sulfur hexafluoride have GWPs many times that of CO2, although CO2 is being emitted into the atmosphere in much larger quantities.

Green Deal - The Green Deal is a Government-backed initiative to help privately fund energy efficient measures to domestic and business premises, at no up-front cost to the property owner.

Green Deal Home Improvement Fund - The Green Deal Home Improvement Fund is a new Governmental incentive that gives householders, landlord and tenants up to £7, 500 cash-back towards energy efficiency improvements under the Green Deal.


Human toxicity - The impact on human health of toxic substances emitted to the environment..

Humidity - The amount of water vapour in the air. Relative humidity is defined as the ratio of the partial pressure of water vapour in a parcel of air to the saturated vapour pressure of water vapour at a prescribed temperature.

Hydrocarbons - Hydrocarbons are the simplest organic compounds that contain only carbon an hydrogen. Examples include benzene and methane..

Hydrochlorofluorocarbon (HCFC) - Man-made compound containing hydrogen, chlorine, fluorine and carbon. HCFCs have become popular following the phasing-out of the use of CFCs, which were used in the construction industry as blowing-agents in the production of insulation. Although HCFCs pose a much smaller risk to the ozone layer, they are also potent greenhouse gases.

Hydrofluorocarbon (HFC) - Man-made compound containing hydrogen, fluorine and carbon. HFCs have become popular following the phasing-out of the use of CFCs, which were used in the construction industry as blowing-agents in the production of insulation. Although HFCs pose no risk to the ozone layer, they are potent greenhouse gases.

Hygroscopic material - One which attracts moisture from the atmosphere. Hygroscopic materials are key to the concept of ‘moisture buffering’.

Hazardous waste - Waste that poses substantial or potential threats to public health or the environment. For the purposes of disposal, the Environment Agency provides information that categorises types of hazardous waste.

Heat capacity - More commonly known as ‘thermal mass’, it is the measure of how much heat a material can 'store’ heat in units of J/K.

Heat Exchanger - A device built for the efficient transfer of heat from one medium to another.

Heat island - Heat island An urban area which is significantly warmer than its surroundings.’

Heat Loss Parameter (HLP) - The building's specific heat loss (in units of W/K) divided by the building's floor area (measured internally – i.e. within the thermal envelope). Units W/K.m2

Heat pump - A device that moves heat from a low temperature heat source to a higher temperature heat sink. Examples include ground source heat pumps, air to air heat pumps, refrigerators and air conditioners. (see also: Refurbishment: Heat pumps )

Heat recovery - Captures waste heat energy and reuses it by returning it to systems or processes. This can include heating space and water.

Heat transfer - The transition of thermal energy from a hotter object to a cooler object.

Hot spots - Areas either on the outside of the building envelope, whose temperatures are significantly higher than the surrounding area. Usually only apparent through infrared thermographic survey they can have a number of causes including areas that have simply been heated by the sun or, more importantly, areas of differential heat loss occurring through the building fabric through means of leakage or thermal bridging.


Internal heat gains - Internal heat gains Uncontrolled space heating from, usually, people, electrical applicances and lighting.

Interstitial condensation - Occurs when relatively warm moisture-laden air diffuses into a vapour-permeable material or structure such as fibrous insulation or a porous brick wall. If it is relatively warm on one side and below the dew point temperature on the other; this can result in the moisture-laden air reaching ‘dew point’ within the material and depositing liquid water at this point. Interstitial condensation presents a problem when it remains undetected, threatening structural damage such as timber decay, or degrading the effectiveness of insulation.

IWI (Internal Wall Insulation) - A thermally insulated cladding system used to treat solid walls where cavity wall insulation and External Wall Insulation (EWI) are not possible due to planning restrictions or it may affect appearance of property.

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

Indoor air quality (IAQ) - Indoor air quality (IAQ) The air quality within a building as it relates to the health and comfort of the occupants. IAQ can be affected by contaminants or gases. Chossing matierials , finishes, fixings and furniture that do not off-gas is the best route to ensuring air quality followed by adequate ventilation.

Insulating concrete formwork (ICF) - Hollow lightweight block components that lock together without intermediate bedding materials, such as mortar, to provide a formwork system into which concrete is poured.

Intelligent building - The concept of a building that remotely monitors and controls its own systems including lighting, heating, IT and security.


Life cycle cost analysis (LCCA) - Life cycle cost analysis (LCCA) A method for assessing the total cost of facility ownership. It takes into account all costs of acquiring, owning, and disposing of a building or building system.

Lifetime Homes - A design standard that encompasses 16 design features that ensure that a new house or flat will meet the current and future needs of most households.

Light shelf - A horizontal overhanging element located above eye-level and having a reflective upper surface. Daylight is reflected from the upper surface onto the ceiling and deeper into the space.

Locally sourced materials - By sourcing materials in close proximity to a building, embodied energy is saved through reducing transport miles.

Low-grade heat - Normally used to mean heat at a temperature of ≤ 100°C

LABC (Local Authority Building Control) - LABC is the member organisation representing LABC departments in England and Wales. They promote the design and construction of buildings that are safe, accessible and environmentally efficient to comply with the Building Regulations.

Laminated veneer lumber (LVL) - Laminated veneer lumber (LVL) An engineered wood product that uses multiple layers of thin wood assembled with adhesives. It offers several advantages over normal wood: it is stronger, straighter, and more uniform. It is much less likely than conventional lumber to warp, twist, bow, or shrink due to its composite nature.

Latent heat - Latent heat The heat released or absorbed by a material during a change of state without change of temperature. For example ice to water or water to steam.

Leaking wet systems - Leaking wet systems Can be identified using infrared thermography. The method is particularly useful where pipework is concealed within walls, ceilings or floors.

Lean Construction - A project management system that maximises value and minimises waste.

Life cycle analysis/assessment (LCA) - A technique that allows the comparison of the environmental impacts of materials and products. LCA analyses the movement of materials and energy from the point of extraction of raw materials, through the manufacture, use in a building, demolition and final disposal. The analysis provides quantitative data to identify the potential environmental impacts of the material or product on the environment. Ideally LCAs encompass the entire life cycle of a material, but it is common for assessments to be made of more limited periods eg ‘cradle-to-gate’.


Moisture buffering - Moisture absorption and desorption of materials in contact with indoor air of buildings is believed to be a possible way to moderate indoor humidity passively. Research is being undertaken to explore the potential of moisture buffering as a means of improving indoor air quality as well as saving energy.

Moisture content - The quantity of water contained in a material. The MC of wood is expressed as a percentage ratio of the amount of water in a piece of wood compared to the oven-dry weight of the wood.

Moisture resistance - A moisture resistant material is one that slows down the penetration of water, but is not in itself waterproof eg lime render / mortar

Moisture vapour transfer / transmission rate (MVTR) - A measure of the passage of water vapour through a material. The term is usually used in connection with ‘breathing wall’ construction. (see also: Airtightness membranes )

MVHR - Mechanical Ventilation with Heat Recovery - a system of ventilating buildings, in which heat is recovered from the exhaust air stream to preheat the fresh air intake. (see also: Refurbishment: Whole house ventilation )

Marine aquatic ecotoxicology - The impact of toxic substances emitted to marine aquatic ecosystems.

MCS (Microgeneration Certification Scheme) - An internationally recognised quality assurance scheme, supported by Department of Energy and Climate Change (DECC). MCS certifies microgeneration technologies used to produce electricity and heat from renewable sources.

Methane (CH4) - A flammable, non-toxic but highly potent greenhouse gas.

Microclimate - A local atmospheric zone where the climate differs from the surrounding area.

Microgeneration - The generation of zero or low-carbon heat and power by individuals, small businesses and communities to meet their own needs. (see also: Low-carbon energy technologies and also: Energy-efficient housing refurbishment )

Microporous finish - A wood finish that allows wood to breathe thereby preventing rapid contraction and expansion, the primary cause of buckling and cracking.

Minimum ventilation requirement - The amount of ventilation required in maintaining acceptable levels of indoor environmental conditions such as temperature, relative humidity and airborne pollutant concentrations.


Nitrogen oxides (NOx) - Nitrogen Oxide and Nitrogen Dioxide are collectively know as Nitrogen Oxides. Nitrogen Oxides are primarily produced as a result of the combustion process, typically from motor vehicles and power stations. They are one of the precursors for photochemical ozone formation as well as being injurious to human health.

Non-potable water - Non-potable water is water that is not treated to drinking water standards and is not meant for human consumption.

Non-renewable resource - A natural resource that cannot be produced, re-grown, regenerated, or reused on a scale which can sustain its consumption rate.

Natural (passive) ventilation - The supply and removal of air inside a building through natural means. There are two types of natural ventilation occurring in buildings: wind driven ventilation and stack ventilation.

Natureplus - A German-based environmental labelling system for building products.

Night-time ventilation - Involves cooling the building structure overnight in order to provide a heat sink during the daytime when air temperatures peak.


Ozone depletion potential (ODP) - The relative amount of degradation a chemical compound can cause to the ozone layer.

Off-gassing - The release of chemicals from various substances under normal conditions of temperature and pressure. Off-gassing can take a variety of forms, and is an issue of concern for some people, since some of the chemicals released during the off-gassing process are potentially harmful.

Ozone (O3) - An unstable (reactive), and water soluble gas having chlorine-like odour, and formed in the upper atmosphere by the action of solar radiation on oxygen. Its presence as a layer in stratosphere serves as a screen (called the ‘ozone layer’) to block harmful ultraviolet radiation from reaching the earth's surface. At ground level it is formed by the combination of hydrocarbons and nitrogen oxides in the presence of sunlight and is the main ingredient of smog.


PFA (pulverised fuel ash) - Is a by-product from burning coal for the production of electricity. PFA is used as a cement substitute in the manufacture of concrete. (see also: Cement substitutes)

Phase Change Material (PCM) - A substance with a high heat of fusion (or ‘specific melting heat’) which by melting and solidifying at certain temperatures, stores and releases heat. Where integrated with a construction element component (eg gypsum board), a PCM provides a very effective form of thermal mass.

Phenols - Hydrocarbons used to make resins and glues. Very toxic and may outgas.

Photochemical oxidation - The formation of reactive chemical compounds, such as ozone, by the action of sunlight on certain primary air pollutants. These compounds may be injurious to human health, ecosystems, materials and crops.

Photovoltaic (PV)(solar) cell - A module incorporating a semiconductor that generates electricity when exposed to sunlight. (see also: Photo Voltaic (PV) cells )

Plenum - An air compartment connected to a series of ducts. For example, a ceiling plenum is the space above the suspended ceiling and below the floor above that is used as part of the air distribution system.

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.

Post occupancy evaluation (POE) - The evaluation of opinion about buildings in use, from the perspective of the people who use them. whereas other definitions would include off-site generation to various degrees and remoteness of source. No official definitions currently include the Carbon generated in the construction of a building.

Post-consumer recycled content (%) - An end product that has completed its life cycle as a consumer item and would otherwise have been disposed of as a solid waste.

Pozzolan - Vitreous siliceous materials which react with calcium hydroxide to form calcium silicates that have cementitious properties. Use of pozzolans can permit a decrease in the use of Portland cement when producing concrete eg pulverised fuel ash (PFA)

Pre-consumer recycled content (%) - A product that contains materials recovered from the waste stream of a manufacturing process. The recovered materials are not normally those reused by the original process.

Primary energy - The amount of energy mined or extracted at source; e.g., from coal, oil, natural gas, uranium or wood. Includes losses within processes such as electricity generation and transmission.

Purge ventilation - Rapid ventilation achieved by opening windows and doors in order to remove moisture and odours. Can also refer to overnight ventilation of hot internal air.

**Parging - A thin coat of plaster applied to masonry to seal the surface. Often used to ensure airtightness.

**Particulate - The tiny particles of solid or liquid suspended in a gas or liquid.

**PAS 2030 - A standard that all installers need to meet in order to be an approved installer of Green Deal or ECO measures. There are courses available which help installers through the process of meeting this standard.

**Passive cooling - Technologies or design features used to cool buildings without power consumption.

**Passive solar design (PSD) - A design strategy that optimises a building's form, fabric and orientation to maximise solar gain from autumn to spring, whilst minimising it during the warmer part of the summer. At the same time, daylighting is maximised at all times. Passive solar design has long been the key element in developing low-energy building solutions in the UK – often characterised by large integrated conservatories. The alternative Passivhaus approach, with its emphasis on energy conservation, will likely interrupt this particular evolutionary design branch.

**Passive solar technology - Devices and design methodologies that use sunlight for useful energy without use of active mechanical systems. Passive solar technologies include direct and indirect solar gain for space heating, solar water heating systems, use of thermal mass and phase-change materials for slowing indoor air temperature swings, and solar chimneys for enhancing natural ventilation. (see also: Low-carbon energy technologies )

Passive stack ventilation (PSV) - Ventilation systems based on the 'Stack Effect'. This is the movement of planned air paths through the dwelling as a result of internal and external temperature differences and wind induced pressure differences.

Passivhaus Planning Package (PHPP) - A modelling and accreditation software tool developed and updated by the Passivhaus Institut.

Payback period - The number of years it takes to recoup an initial investment.

Permeability - A measure of the ability of a material to transmit fluids or gases.

Permeable paving - Provides a structural pavement whilst allowing water to pass straight into the pavement construction for temporary storage and dispersal into the ground or for collection. It is one of the main techniques for Sustainable Drainage Systems (SUDS).

Persistant organic pollutants - Organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of this, they have been observed to persist in the environment, to be capable of long-range transport, bioaccumulate in human and animal tissue, biomagnify in food chains, and to have potential significant impacts on human health and the environment.

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


Relative humidity - The amount of water vapour that exists in a gaseous mixture of air and water. Relative humidity is normally expressed as a percentage.

Remediation - The removal of pollution or contaminants from soil, groundwater, sediment, or surface water for the general protection of human health and the environment.

Renewable energy - The energy generated from natural resources—such as sunlight, wind, rain, tides, and geothermal heat—which are renewable (naturally replenished).

Renewable resource - A natural resource that has the capacity to be naturally replenished despite being harvested (eg forests, sheep). Limits to renewable resources are determined by flow rate and such resources can provide a sustained yield.

Resource depletion - Resource depletion occurs when all of the natural resources in an area, both renewable and non-renewable have been exhausted.

Retention pond - A type of constructed wetland that is designed to contain storm water or rain run-off from a small surrounding drainage area that would otherwise flow into other areas.

RHI (Renewable Heat Incentive) - UK Government scheme set up to encourage uptake of renewable heat technologies among householders, communities and businesses through the provision of financial incentives. The RHI is split into two streams, domestic and non-domestic.

RHPP (Renewable Heat Premium Payment) - A one-off grant designed to help towards meeting the costs of installing renewable technologies in your home and has been made available until the RHI is introduced for domestic customers.

Runoff - The water flow which occurs when soil is infiltrated to full capacity and excess water, from rain, snowmelt, or other sources flows over the land.

R-value - The capacity of a material to resist the transmission of heat. The R-value is calculated by combining the lamda value (thermal conductivity) and the thickness of the material. Hence R=t/λ, where 't' is the thickness. Units are measured in m2W/K. Used in connection with insulation, the higher the R-value, the more effective the insulation. The R-value is also used to calculate the U-value (thermal transmittance) where U = 1/R

Radon - Radon is a colourless, odorless, tasteless, naturally occurring, radioactive noble gas that is formed from the decay of radium. High levels of radon can build up when houses and other buildings are constructed in areas where the underlying geology contains Uranium 238 (typically, but not exclusively granite and limestone areas).

Rainwater harvesting - Rainwater harvesting The gathering, or accumulating and storing, of rainwater.

Rammed earth - A construction technique where earth is compacted between formwork to make a homogeneous mass wall.(see also: Rammed earth )

Reclaimed material - A material that is recovered from a building as part of the deconstruction process.

Recycling - The processing of used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution (from incineration) and water pollution (from landfilling) by reducing the need for "conventional" waste disposal, and lower greenhouse gas emissions as compared to virgin production.

Reflective insulation (radiant barrier) - A material typically composed of a core material such as fibreglass or polyethylene foam sandwiched between sheets of aluminium foil. Manufacturers claim that the material can stop up to 97% of radiant transfer. However, much debate continues around both the efficacy of the claims and testing methodology.


Solar shading - Devices that control heat gain as well as controlling light level, particularly in summer.

Source control - An approach to urban drainage which deals with water at the place where it falls as rain, and collects, cleans and releases surface runoff slowly to streams, rivers and groundwater.

Stack effect - The flow of air that results from warm air rising, creating a positive pressure area at the top of a building and a negative pressure area at the bottom of a building.

Standard Building Energy Method (SBEM) - A software package developed by the BRE for calculating the carbon emissions of building other than dwellings. The user inputs data relating to the building design and the software compares the actual design with a notional building of the same design built to 2002 standards.

Standard Method of Measurement (Seventh Edition), SMM7 - A methodology used by Quantity Surveyors for preparing Bills of Quantities (aka ‘shopping lists’).

Strawbale construction - A building method that uses straw bales as structural elements, insulation, or both. It is commonly used in natural building. It has advantages over some conventional building systems because of its cost, easy availability, and its high insulation value

Sulfur dioxide (SO2) - A gas formed when fuel containing sulfur, such as coal or oil, is burned. S02 dissolves in water vapour to form acid, and interacts with other gases and particles in the air to form sulfates and other products that can be harmful to people and their environment.

Sun pipes - Used to direct sunlight into deep plan spaces with no access to natural light. Sunpipes normally consist of an aluminium tube with a silver-coated mirror finish. Light enters the upper end and is internally reflected downwards through a ceiling-mounted prismatic diffuser.

Surface water attenuation - The controlled release of surface water into the ground. Surface water is collected and stored in a number of ways including attenuation cells (aka ‘storm cells’). The water is then released into the ground at a rate that can be absorbed.

Sustainable - The state of having met the needs of the present without endangering the ability of future generations to be able to meet their own needs.

Sustainable drainage systems (SUDS) - An approach to drainage which seeks to decrease the amount of surface runoff, decrease the velocity of surface runoff, or divert it for other useful purposes, thereby reducing the contribution it makes to sewer discharge and flooding.

Sustainable Energy - The provision of energy such that it meets the needs of the present without compromising the ability of future generations to meet their needs. Sources include biofuels, solar power, wind power, wave power, geothermal power and tidal power. (see also: Low-carbon energy technologies )

SAP rating - The SAP rating is the 'Standard Assessment Procedure' which provides an indication of the overall energy efficiency of a dwelling. It is measured on a scale of 1-100 where the higher the number, the better the performance.

Scottish Ecological Design Association (SEDA) - Founded in 1991, SEDA promotes ‘…the design of communities, environments, projects, systems, services, materials and products which enhance the quality of life of, and are not harmful to, living species and planetary ecology'. SEDA’s design guides are particularly highly-regarded. (

Sequestration (Carbon) - The removal or storage of carbon in a place (a sink) where it will remain. Types of sequestration include 'geological' where CO2 is captured and buried underground and 'biological' where CO2 is absorbed during the growth of plants and trees.

SIPs - A composit consisting of a sandwich of two layers of structural board with an insulating layer of foam in between. The board can be sheet metal or oriented strand board (OSB) and the foam either expanded polystyrene foam (EPS), extruded polystyrene foam (XPS) or polyurethane foam. SIPs share the same structural properties as an I-beam or I-column. The rigid insulation core of the SIP performs as a web, while the OSB sheathing exhibits the same properties as the flanges. SIPs replace several components of conventional building such as studs and joists, insulation, vapour barrier and air barrier. As such they can be used for many different applications such as exterior wall, roof, floor and foundation systems.

Site Waste Management Plan (SWMP) - Required for all projects valued over £300,000. SWMPs record the amount and type of waste produced and how it will be reused, recycled or disposed of. (see also: Site Waste Management )

Smoke test - Where used in buildings, smoke testing is a convenient method of detecting air leakage. The building is pressurised whereupon smoke is introduced and is forced through gaps in the building envelope.

Soakaway - A subsurface structure into which surface water is conveyed to allow Infiltration into the ground.

Soft strip - A term referring to the first stage of demolition, includes removal of internal finishes, M&E services and non-load bearing elements of the structure.

Solar gain - Heat absorbed through direct transmission through glazing (primary transmittance). Energy is also absorbed by the glazing and subsequently transferred inwards by convection and radiation (secondary transmittance).

Solar Heat Gain Coefficient (SHGC) - Is the US equivalent of G-value. The only difference between the numbers is that SHGC uses an air mass of 1.5 and the g value uses an air mass of 1.0

Solar panel/collector - A device for extracting the energy of the sun directly into a more usable or storable form. (see also: Solar hot water collectors )

Solar PV - Solar Photovoltaic (Solar PV) panels allow you to generate your own electricity using energy from the sun. When light hits the silicon cells in the solar panels, electrical energy is created. This electricity then flows through a cable and is collected at a central point. The electricity is then converted from DC to AC current and is carried on into the household electricity system or back to the grid.


Thermal resistance (R-value) - Thermal resistance is the measure of a component’s ability to restrict the passage of heat across its thickness. The R-value is calculated by combining the lamda value (thermal conductivity, or 'k-value') and the thickness of the material. Hence R=t/λ, where 't' is the thickness. Units are measured in m2W/K. Used in connection with insulation, the higher the R-value, the more effective the insulation. The R-value is also used to calculate the U-value (see below)

Thermal store (heat bank) - A way of ‘saving’ heat for future use as space or water heating. Heat is added to water contained in a cylinder (resembling a regular hot water cylinder) from sources such as a solar hot water collector or boiler and then withdrawn for space or domestic hot water heating at a later time. Another form of thermal store is the ‘rock store’. Containers containing rock or gravel are located beneath the ground floor. Air warmed in an adjoining sun space is directed into the store where it heats up the rock for later release as warm air or underfloor heating. (see also: Thermal storage )

Thermal transmittance (U-value) - Thermal transmittance is a measure of the overall rate of heat transfer, by all mechanisms under standard conditions, through a particular section of construction. This measure takes into account the thickness of each material involved and is calculated from R-values of each material as well as constants accounting for surface transmittance (Rsi and Rso, inner and outer surfaces respectively) and also for a small standard air gap (Rso). Thermal transmittance is measured in W/m2K

Timber certification - A process which results in a written statement (a certificate) attesting to the origin of wood raw material and its status and/or qualifications, often following validation by an independent third party eg FSC. (see also: The Forest Stewardship Council (FSC)

TRADA - The Timber Research and Development Association (TRADA) is a source of information on the use and specification of timber and wood products in construction. (

Target emission rate (TER) - The calculated target CO2 emission rate for new buildings other than dwellings, expressed in kgCO2/m2/year. The predicted emissions from the actual building design are known as the building emission rate (BER) and may not exceed the TER.

Thermal (heat) emitter - A material or device that emits heat. The term is commonly used with reference to space heating where for example a radiator is a thermal emitter as is a concrete floor used as thermal mass. Another example of a (unwanted) thermal emitter is where a balcony acts as a thermal bridge between an internal floor slab and the exterior; The large surface area of the balcony renders it as an efficient emitter.

Thermal (storage) capacity - The ability of the constituent materials in a building to store heat, for a given rise in temperature, measured in units of kWh/K for a whole building or in Wh/K.m2 to indicate the building's thermal capacity per unit floor area.

Thermal break - An element of low thermal conductivity placed in an assembly to reduce or prevent the flow of thermal energy between conductive materials. A typical example would be that found in a metal window frame to reduce the conduction of heat from the outside to the inside.

Thermal bridge - A thermally conductive material which penetrates or bypasses an insulation system; such as a wall tie, metal fastener, concrete beam, slab or column. Thermal bridging lowers the overall thermal insulation of the structure by creating areas where heat loss is greater in one area than it is for another. The effect is to reduce the overall u-value of the construction element. The heat loss per unit length of thermal bridge is known as the Ψ-(psi) value and is measure in W/mK.

Thermal bypass - Heat transfer enabled by the uncontrolled air movement within and through walls. A recently identified example of thermal bypass occurs within cavity walls acting as separating walls (party walls) between adjoining houses or flats. Cavities in these instances are not normally insulated thus allowing warm air to enter the cavity and by means of convection to rise through the space and escape into an attic or through the roof covering.

Thermal conductivity (K-value) - A measure of the rate at which heat is conducted through a particular material under specified conditions.

Thermal envelope - The insulated external fabric of the building.

Thermal flanking - Heat loss by means of thermal bridging around areas of insulated construction.

Thermal mass - The ability of construction materials to absorb, store and release heat. Thermal mass can be used effectively to absorb daytime heat gains (reducing cooling load) and release the heat during the night (reducing heat load), thereby maintaining a constant level of comfort through stable temperature. Materials of high thermal mass include water, stone, earth, brick and concrete. More recent innovations include ‘phase change’ materials that store energy whilst maintaining constant temperatures. The quality of thermal mass is usually described in terms of ‘admittance’. Admittance is the ability of a material or construction such as a wall to exchange heat with the environment when subjected to a simple cyclic variation in temperature. For buildings, this is 24 hours. Admittance is measured in W/m2K, where temperature (K) is the difference between the mean daily value and actual value within the space at a specific point in time. Key variables that determine admittance are thermal capacity, conductivity, density and surface resistance. (note that 'K' is used in a slightly different way from that involved in the calculation of u-value)


Useful space heating energy - The amount of heat actually put into the heated space.

U-value (thermal transmittance) - Thermal transmittance is a measure of the overall rate of heat transfer, by all mechanisms under standard conditions, through a particular section of construction. This measure takes into account the thickness of each material involved and is calculated from R-values (where U=1/R) of each material as well as constants accounting for surface transmittance (Rsi and Rso, inner and outer surfaces respectively) and also for a small standard air gap (Rso). Thermal transmittance is measured in W/m2K


y-value - A notional additional U-value, spread uniformly over the whole thermal envelope. THIS GLOSSARY AND THE INFORMATION CONTAINED IN IT WAS SUPPLIED BY GREENSPEC