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ACD – Approved / Accredited Construction Details are a set of standardised construction details developed by regulators to deal with the issue of heat loss / gain and other issues.

ACM or ACP (Aluminium Composite Materials or Panels) with PE core – The ‘rainscreen’ façade used on Grenfell Tower was a PE cored Aluminium Composite Material (ACM), sometimes also referred to as an Aluminium Composite Panel (ACP). Polyethylene (PE) is included to provide strength and rigidity to the ACM and is not designed for, nor does it offer any, insulation properties.

The PE core of the ACM is the material being tested by the Building Research Establishment (BRE) during July and August’17 under the initial small-scale BS EN ISO 1716 test regime. PE is not insulation.

Acoustic Insulation – A product used to impede the transfer of sound, either via airborne or impact transfer. Typically internal constructions within buildings are required to utilise acoustic insulation products to aid in minimising the transfer of sound from one adjacent room into another. “Approved Document E” and “Part E – Robust Details” contain further information on common methods of controlling the transfer of sound in buildings.

Air Tightness – The uncontrolled leakage of air from a building through cracks, unsealed penetrations or interfaces between different building elements.

Aluminium – Naturally occurring metal, with a melting point of 660 Degrees C.

Ambient – When referring to heat, temperature, etc. ambient describes the surrounding conditions. i.e. the Ambient temperature is the average temperature surrounding a material.


Block / billet – (insulation) product generally of rectangular cross-section and with a thickness not significantly smaller than the width (EPFA EN 14314)

Blowing Agent – A substance used during the manufacture of cellular foam insulation products. These agents are typically used to enhance the thermal performance of the finished product by filling the cells within the insulation with a low thermal conductivity gas.

Board, slab – rigid or semi-rigid (thermal insulation) product of rectangular shape and cross section in which the thickness is uniform and substantially smaller than the other dimensions

Note 1 to entry: Boards are usually thinner than slabs. They may also be supplied in tapered form. (EN 13166 , EN 14314)

BRE BS 8414 large-scale testing – This is a large scale test, and is our recommended route to determine the compliance of a product/system for buildings with a storey above 18m. BS 8414-1 & BS 8414-2 exist. Extrapolation from an original base-BS 8414-1 or BS 8414-2 test must be allowed via desk-top studies (only performed by approved and competent personnel). This should only be allowed where the final product/system can be legitimately extrapolated from the original base test. In this regard, desk-top extrapolations must be permitted, as otherwise any variations (however small) from the original test product/system would have to be tested again. This is simply not feasible with the countless variations required and/or specified, coupled with the limited number of test-rigs available.

BRE tests based upon BS EN ISO 1716 – This is the ‘initial’ BRE test performed on numerous cladding systems. The test was, and still is being performed on the ‘PE element’ of ACM systems. The test is designed to determine the combustibility of the PE core. As part of this process, the core material is separated from the ACM and tested independently.PE cores will always be classified as ‘combustible’ under this test. Hence, in our opinion, the test is therefore not necessary. The tests undertaken do not relate to insulation (either PIR or MW). A reported ‘fail’ does not relate to the wider product/system in-place, only that the PE core is ‘combustible’. The complete product/system must be tested in accordance with BS 8414-1 or BS 8414-2 to determine its wider performance.

Breathability – A non–scientific term used when discussing moisture transport through a construction.

Building Control Bodies – Public and private organisations that assess and verify compliance with building regulations and standards. Building envelope separates the internal and external environments, such as a roof or walls. In order to provide the adequate protection against heat leakage, the building envelope should have as few thermal bridges and unintended gaps a possible.


Cavity Closers – Insulated extrusions for closing wall cavities at openings such as window reveals and door reveals. Cavity closers reduce heat transfer, avoiding thermal bridging, condensation and mould growth. They can even be used to pre–form openings when window and door frames are fitted later.  

CE Label – This shows compliance with EN and CEN standards.

Cellular Insulation – Insulation such as polyurethane, polyisocyanurate and phenolic insulation, which is made up of small individual cells.

Closed Cell Insulation – This has a more compact and denser structure than open cell insulation. As a result, it decreases the ingress of moisture and is more resistant to heat transmission. Insulation with a closed cell structure is also more resistant to flood damage. Because of its low water take–up, closed cell insulation panels recover from immersion in flood water more quickly than mineral fibre insulations for example.

Coating – functional or decorative surface layer, with a thickness less than 3 mm, usually applied by painting, spraying, pouring or trowelling, which is not considered as separate thermal insulation layer to be added to the thermal resistance of the product ( EN13166)

Cold Bridging – A type of thermal bridging that occurs when a structural element of a building lets heat flow through it because it has a lower thermal resistance than other components in the construction.

Combustibility – This terminology is used widely within AD-B. This should not be confused with ‘flammability’ and no reference to this should be made. In terms of AD-B, direct reference to ‘Limited Combustibility’ and ‘Non-Combustibility’ is made throughout. However, ‘Combustible’ materials are also permitted. Numerous test routes exist within AD-B to determine the combustibility classification of a product/system/material. For ease of use and to avoid confusion, rather than specify ‘low, none, limited etc.’, it would be our recommendation to simply specific the use of BS 8414-1 or BS 8414-2 products/systems/materials for buildings with a storey above 18m (see further explanation within BRE tests based upon BS EN ISO 1716 and BRE BS 8414 large scale testing).

Composite thermal insulation product – product which can be faced or coated made from two or more layers bonded together by chemical or physical adhesion consisting of at least one factory made thermal insulation material layer (, EN 13166)

Compressive Creep – The measure of how much a material changes under long–term load. Heavy duty insulation materials ideally have a low compressive creep so they have a suitable durability in heavy duty applications.

Condensation – The conversion of a substance (typically water when referenced in the construction industry) from the vapour state to a liquid due to a change in temperature or pressure, e.g. such as warm moist air hitting a cold surface causing: a reduction in temperature of the air; and moisture vapour to condense out of the air. The two main occurrences of condensation are:

  • Surface Condensation which can lead to mould and staining through its formation on the visible surface of a material.
  • Interstitial Condensation occurs between the layers of a construction. This type of condensation can both reduce the effectiveness of insulation components and reduce their lifespan.

CRA – Condensation Risk Analysis is performed on the construction elements of a building, taking into account the order in which they appear, and the building’s geographical location.


DPM – A Damp Proof Membrane is used with some insulation to prevent moisture building up on the insulation layer.


Emissivity – The ‘shininess’ of a material. A high emissivity will increase the amount of heat transfer through radiation. It is measured in watts per square metre (W/m2) in relation to an ideal black surface as a ratio from 0 to 1. The closer to 0 the emissivity ratio, the lower the emission of heat as radiation. A foil facing on an insulation board allows a low emissivity to be taken when calculating the thermal resistance of an unventilated airspace eg. in a cavity wall construction.

End-use application – real application of a product in relation to all aspects that influence the behaviour of that product under different fire situations.

End-use application parameter – aspect of the mounting and fixing arrangement of a product reflecting/simulating its end use application (for example: type of substrate, lining, fixing method, position and type of joints) which may or may not affect the fire performance

EPC – An Energy Performance Certificate is required upon completion of a dwelling in accordance with the English, Scottish and Welsh building standards. This necessitates energy calculations e.g. SAP or SBEM. They measure on a scale of A–G, the green to red scale covers the energy efficiency rating, while the blue to grey scale measures the environmental impact rating of the construction.

EPS – Expanded Polystyrene is a light rigid foam insulation that has low thermal conductivity and high impact resistance.

EWI – External Wall Insulation – insulation installed on the outside or cold side of a wall.


Facings – functional or decorative surface layer, with a thickness less than 3 mm, e. g. paper, plastic film, fabric or metal foil, which is not considered as separate thermal insulation layer to be added to the thermal resistance of the product (EPFA, 13166) 

Fibrous Insulation – An insulation material made up of fibres rather than cells.

Fully Bonded – Typically used in reference to flat roofing, and refers to where a bond between two materials is considered to cover the whole surface. As a full bond covers a greater proportion of the roof area, these systems can generally provide greater restraint against wind uplift than partially bonded systems.


Geotextile Membrane – A non–woven geo–synthetic membrane used in a variety of applications within the construction industry to act as separation and filtration membranes.


ISO – International Standardisation Organisation is a certification body that provides assessments such as 9001- quality management, 14001- environmental management, 18001- Occupational Health and Safety (OHSAS), and 50001- energy management.

IWI – Internal Wall Insulation, insulation on the inside or warm side of a wall.


Kappa Value – This relates to the thermal mass of a construction. It is the measure of how much heat will be stored per metre squared of a building and represents ‘k’ in the unit of measure kJ/m2K. ‘k’, or the heat capacity of a building, can be calculated using the following equation:

k = 10 – 6 x Ʃ (dj rj cj)

dj = thickness of layer (mm)

rj = density of layer (kg/m3)

cj = specific heat capacity of layer (J/kg·K)

The calculation is over all layers in the element, starting at the inside surface and stopping at whichever of the following conditions is encountered first (which may mean part way through a layer):

The total thickness of the layers exceeds 100mm

The midpoint of the construction is reached

An insulation layer is reached (defined as thermal conductivity ≤ 0.08 W/m.K)


Lambda Value – Sometimes called the ‘k–value’ or ‘ʎ–value’, this measures the thermal conductivity of a material. k–value is shown in units of W/m.K where ‘m’ represents the thickness of the material in metres. Insulants have a low thermal conductivity meaning heat cannot pass through them easily. The k–value shows the general performance of a material with regards to thermal conductivity and does not relate to the material’s thickness.

LCA – Life Cycle Assessment is how the environmental impact of a building is assessed from raw materials to disposal or recycling.

Loose Fill Insulation – For example, cellulose or mineral insulations that are typically installed in the air cavities of buildings through a gap or drilled hole in the building element.

Loss Prevention Standard LPS 1181 / Factory Mutual FM 4880 / 4881 / 4471 – Insurance industry fire performance standards. The Loss Prevention Certification Board (LPCB) that controls the Loss Prevention Standards (LPS) is the leading international Certification Body in the fields of security and fire protection. LPCB approval is recognised by governments and regulatory authorities across the world.


Metal faced insulated panels (PIR & MW core) – These are not to be confused with ACMs or ACPs (described previously) and are a completely different product/system. Unlike the built-up construction of a rainscreen façade cladding system, insulated panels are factory-made, solid single units that are fixed directly to the structural frame. They typically comprise of an insulation layer held within metal facings to provide a strong, durable unit. There is no cavity within this single unit design. These products/systems offer the same weather protection as rainscreens, with equally appealing aesthetics. BS 8414-1 & BS 8414-2 certified insulated panels for use on buildings with a storey above 18m are available using PIR or MW, and are recognised as an approved solution for high-rise buildings by the Department for Communities and Local Government (DCLG),

Metal faced PIR core insulated panels – These are not to be confused with ACMs or ACPs and are a completely different product/system. Insulated panels manufactured are single, factory-engineered components that are typically fixed directly to the structural frame to provide insulation and weather protection. These products/systems offer the same weather protection as rainscreens, with equally appealing aesthetics. The thermosetting PIR core is auto-adhesively bonded to metal facings to provide a strong, durable unit with proven fire safety performance, and satisfy the requirements of the European standard for sandwich panel systems: BS EN 14509:2013 “Self-supporting double skin metal faced insulating panels. Factory made products”.BS 8414-1 & BS 8414-2 certified insulated panels for use on buildings with a storey above 18m are available using PIR.

Moisture Ingress – The act of water entering something. In construction terminology the term is typically used in reference to external moisture (i.e. ground moisture or precipitation) entering a construction.

Multi-layered thermal insulation product – product which can be faced or coated made from two or more layers of a thermal insulation material from the same European Standard, which are bonded together by chemical or physical adhesion either horizontally and/or vertically.


Non-ventilated applied finishes – These systems require a continuous background structure, such as an external wall, to give the necessary support and fixing for the materials forming the external face of the building. The system is typically composed of two elements:

  • The insulating material, which is fixed to the background structure, typically an external wall, to provide the necessary level of thermal performance, and;
  • the external surface membrane that provides the weather protection to the insulating layer.


Open Cell Insulation – This insulation has a structure that allows moisture and vapour to permeate through it.


PE (Polyethylene) – PE is included to provide strength and rigidity to ACMs and is not designed for, nor does it offer any, insulation properties. This should not be referred to as insulation.

Phenolic Foam – Rigid cellular foam, the polymer structure of which is made primarily from the polycondensation of phenol, its homologues and/or derivatives, with or without aldehydes or ketones. (, EN 13166, EN 14314) This is insulation, and has proven fire performance.

Pipe section / section – (insulation) product in the shape of a cylindrical annulus which may be split to facilitate application.

Plenum – In ductwork, a plenum is a space above a ceiling that allows the collection of air in order to let it move between different spaces in the building.

PIR – rigid cellular thermoset polymeric insulation product with a substantially closed cell structure based on polymers mainly of polyisocyanurate groups. For the purposes of the European Standard EN 13165, regarding the properties described in that standard, PIR and PUR types are not distinguished separately This is insulation, and has proven fire performance.

Prefabricated ware – pieces cut, abraded or otherwise formed from a board or block of product, e.g. elbows, T-pieces, etc.

PU (Rigid polyurethane foam) – family of rigid cellular thermoset polymeric insulation products with a substantially closed cell structure including both polymer types based on PIR and PUR

PUR – rigid cellular thermoset polymeric insulation product with a substantially closed cell structure based on polymers mainly of polyurethane groups. For the purposes of the European Standard EN 13165, regarding the properties described in that standard, PIR and PUR types are not distinguished separately This was replaced by PIR in the UK in 2004 and has not been used by UK manufacturers of metal faced insulated panels since that time.


Rainscreen – A rainscreen is the aesthetic cladding that is attached to a weather-resistant and insulating layer of a building. Irrespective of the chosen assembly or materials used, BS8414-1 and BS 8414-2 approved/certified systems/products are available. Rainscreens comprise 3 distinct elements:

Rainscreen Façade: a non-structural, aesthetic layer or thin panel on the outer of the building that protects everything inside it from the weather elements. Material: Rainscreen façade panels can be made of a wide range of materials, including steel, aluminium, zinc, glass, ceramic, timber, laminates and Aluminium Composite Materials (commonly known as ACMs). Critically, the purpose of this layer is to form the external aesthetic of the building and to keep out the weather elements NOT to provide insulation properties.

  • A supporting frame: on which the rainscreen façade is structurally fixed;
  • An internal layer comprising insulation and a vapour barrier: This sits next to the structure, insulating the building and acting as the final protection against moisture ingress.
Example of rainscreen system construction:



Site assembled layer comprising cementitious board, insulation and a vapour barrier, insulation can be PIR/Phenolic or mineral fibre (see image)


Insulated panel backup wall systems can be used to  replace

the site assembled components

Site assembled rainscreen systems require a cavity between the rainscreen façade and the internal layers to prevent moisture from entering the main building structure, by ventilating the cavity.   ‘Insulated panels backup wall systems’ may not require a vented cavity.

Rainscreen Cladding System – The term ‘cladding’ refers to components that are attached to the primary structure of a building to form a non-structural, external surface. This differs from traditional buildings where the external surfaces are formed by structural elements, such as masonry walls, or applied surfaces such as render.  A rainscreen (sometimes referred to as a ‘drained and ventilated’ or ‘pressure-equalised’ façade) is part of a double-wall construction that can be used to form the exterior walls of buildings.

Retrofit – The installation of insulation over pre–existing building elements or insulation.

R–Value – This demonstrates thermal resistance of a material in relation to its thickness. It is measured in units of m2K/W where ‘m’ represents the thickness of the material in metres which is divided by its value.


SIPs – Structurally Insulated Panels are a combination of insulation and structural elements such as timber facings in one board.

Soffit – The underside of an architectural component, for example an arch, beam, staircase or underneath car park decks


Thermal Conductivity – The measure of thermal conductivity used on materials in which heat transfer occurs through conduction, convection and radiation.

Thermal Mass – This is how well an element absorbs, stores and releases heat per metre squared

Thermal Resistivity – As with thermal conductivity, this measures a material’s ability to resist heat transfer through conduction, convection and radiation in relation to the material’s thickness or surface emittance

Thermoplastic – Expanded polystyrene (EPS) is the most widely used product in this group, which also includes extruded polystyrene (XPS). It can be supplied in both a fire-retarded and non-fire-retarded form. Again the material is generally supplied as 600 mm ´ 1200 mm batts at various thicknesses to meet thermal performance requirements.

Thermoset – Products such as polyurethane foam (PUR), polyisocyanurate foam (PIR) and phenolic foam are used to provide insulation for external cladding systems and are typically provided as 600 mm ´ 1200 mm sheet product of varying thicknesses to meet thermal performance requirements. These products are often faced with materials such as glass fibre or aluminium foil

Thermoset materials will not run, melt or drip when exposed to fire.


U–Value – The sum of the thermal resistances of the layers that make up a building element (i.e. walls, floors, roofs etc.). It includes adjustments for any fixings, air gaps etc. This value shows in units of W/m2K the ability of an element to transmit heat from a warm space to a cold space in a building and vice versa. The lower the U–value, the better insulated the building element is.


Ventilation – The process of “changing” or replacing air in any space to remove excess moisture or other pollutants, such as carbon dioxide or ground gases such as radon and replaced with external air (see MVHR).

Ventilated cavities – These systems typically consist of an external wall with an inner structural leaf, insulated on its outer face. There are a number of different types of product represented within this description. They include rainscreen cladding systems and drained and/or ventilated cavity systems. The principle behind this type of system relies upon an airspace that can be drained, back ventilated and, if required, pressure-equalised. The systems have an external surface membrane or cladding assembly, and an insulation layer fixed to either the external wall or the cladding panel, together with an appropriate breather membrane. In practice, the insulation layer may not always be present.


Wind Uplift / Wind Load Calculations – Wind can apply a positive or negative force onto objects depending on the construction detail, its orientation to the direction of wind, and the difference between internal and external air pressures. Wind load calculations are particularly important for systems restrained to the outside of a building, such as warm or inverted flat roofs and external wall insulation systems such as EWI render and rainscreen systems. A wind load calculation considers a number of factors, such as the location and altitude of the building plot, local topography (i.e. geographical features, valleys, hillside etc.), adjacent structures which may shelter or funnel wind towards the building, also the construction type, its height from ground, and position on the construction in relation to the prevailing wind direction.


XPS – Extruded Polystyrene has high resistance to condensation damage and has a high thermal resistance.


Y–Value – An approximation of a specific building’s heat loss via its junctions. It is calculated by dividing the HTB (overall thermal bridging coefficient) by the building’s total exposed area (see HTB).