Glossary of external wall insulation and rendering terms and abbreviations

If you’re researching the various options for render and external wall insulation, getting to grips with the terminology can sometimes be a bit of a challenge.  We’re often asked what different acronyms and abbreviations mean. 

We’ve compiled a handy list of the most common terms and abbreviations you’re likely to encounter to help you navigate your way through the terminology. If we’ve missed any off, please let us know! 


The undercoat used to create a smooth surface and aid thermal performance before the top render is applied. 


The British Board of Agrement (BBA) are UKAS approved to independently test and certify external wall insulation systems. This ensures they meet the strict building regulations. It is worth mentioning that the UK's Health and Safety regulations are among the strictest in the world. 


Beading is used in rendering, plastering and external wall insulation systems and is a thin piece of metal that has a straight edge running along its length, giving the applicator a precise corner for plastering.

Beading is used for when you are applying render or plaster to a wall around corners allowing for neat, sharp corners and to reinforce weaker areas of the substrate that might be prone to cracking. 


The ability of a material to allow water to pass through its structure and evaporate. 

Cold Bridging

(also referred to as thermal bridge/heat bridge) 

This is where cold is transferred through the solid walls of your home from the outside to the inside. Masonry is a good conductor of temperature so the cold passes through the wall quickly. This is why single skin buildings feel colder inside. 


Damp Proof Course/Damp Proof Membrane – situated at the base of the wall, the DPC acts as a barrier to prevent moisture rising through the structure from the ground. 

ECO Funding  

Energy Company Obligation funding is money provided to installers by energy companies to help reduce the cost of energy efficiency measures to customers that meet the funding criteria. The scheme is regulated by Ofgem. More information can be found here.

EPS Insulation 

Extruded Polystyrene Foam is a lightweight, rigid and tough, close-cell foam. It is made using solid beads of polystyrene which are then expanded during production to form perfectly closed cells. It is highly resistant to corrosion and minimizes the effects of moisture and vapour. It forms a key part of many wall insulation systems. 

external wall insulation

EPC Rating 

An ‘Energy Performance Certificate’ provides an overview of the energy efficiency of different parts of a building and will give an indication how much a building costs to heat and light. Insulation can make a huge difference to the EPC rating. 

EPC Rating


External Wall Insulation – where insulation is applied to the outer surface of the main exterior walls before being covered over with a protective render coating. As 30%- 40% of a home’s heat can escape through the walls this is an effective insulation system for many properties.  


Anchors that are used at a length to suit the substrate and insulation thickness being installed allowing the insulation boarding to attach properly and safely.

First Pass/Second Pass 

‘Passes’ refer to applying separate layers of a material, e.g. first pass/layer of the basecoat. 

Grain Size 

Grains run through certain types thin coat renders. These are available in different sizes, enabling you to choose the level of texture that you prefer, whether it’s only very slightly textured (1mm) or extra rough (3mm). 

Go Off 

Leave to dry. E.g. ‘leave the basecoat to go off’ – means leave the basecoat to dry/set. 


Insulated Concrete Formstype of modern building material consisting of polystyrene insulation filled with concrete and steel. 


Internal Wall Insulation - where insulation is applied to the inside surface of the main exterior walls before being plastered and repainted.


Monocouche renders are a more modern render with the addition of colour pigment to achieve a customizable, through-colour render finish. 


When two render layers are applied, with a fibreglass mesh inserted between to provide strength to the coating. 

Mineral Wool  

Mineral Wool is popular product for thermal insulation. Typically, rock, silica or ceramic is heated until molten then spun into very fine threads. These threads are treated with resin to bind them, and a mineral oil to make them water-repellent. The individual threads are woven to create insulation boards, thereby trapping air which provides very good insulation properties. 

PAS 2030  

Publicly Available Specification’ is a form of standard published by the British Standards InstitutePAS 2030 is entitled “Improving the energy efficiency of existing buildings” and outlines the quality management, implementation and service requirements for any such works as undertaken by installers or tradespeople. 

Installers working under these schemes must adhere to this standard for all works carried out including where existing domestic buildings are being upgraded from an energy efficiency perspective. 

Pebbledash / Dry Dash / Roughcast 

A traditional decorative finish. It is created by applying a layer of mortar to the external surface, before throwing pebbles/gravel/shells at the mortar to create a rough finish. 

Polymer Modified 

Polymer modified renders are renders that contain silicone or acrylic additives. 


A type of plaster applied to the external walls of a property to protect against the weather. 


An underlying substance or layer – i.e. the existing wall to be rendered/insulated. Substrate primers are applied directly to the substrate before any other materials are applied. 

Scratch coat 

A rough coat, scratched before it is completely dry to provide a key and ensure that the next coat bonds completely. Professional plasterers use an over-sized comb-type tool for this.

Thin coat render 

A specific type of render (usually silicone or acrylic) that is applied in a very thin layer. 


Sand/cement/lime based render that has added pigment to produce a coloured effect throughout the body of the material. The pigment is mixed into the render product as part of the manufacturing process. 


This is a measurement for how quickly heat transfers through a building element such as a wall or window. The lower the number the better that particular element is at retaining heat. U-values are measured in W/mk². 

Have you come across any terminology you don't understand? Contact us to let us know and we'll add it to this glossary of EWI terms.



Luke Ball

Written by Luke Ball

An Experienced Energy Industry professional, with a passion for process improvement, customer service, and quality. Highly skilled in business/product development and strategic thinker. A proven track record for delivering results, developing & implementing strategies.