Building Safety Terminology

The language of building safety is technical, and often tricky to navigate for residents. Below, you will find an explanation of some of the names and acronyms that are often used in our communications to you.

If we've used a term in our building safety communication to you, and you don't understand what it means, then you won't be the only person who feels like this. Please email us, and we'll update this glossary with all the technical terms that our residents find confusing.

What is "ACM"? 

Aluminium Composite Material, or ACM for short is a type of MCM cladding material often found on residential buildings. It consists of a thin, three-layer sandwich panel made up of two precoated aluminium sheets bonded to a structural core that is often made out of a plastic material called polyethylene (PE).  
Although ACM has been reported as being highly combustible, a limited amount of this type of cladding will not significantly increase the spread of flame across the external walls and the level of risk as fire assessor sees will depend on other features of the building, such as the quantity and quality of cavity barriers. 

What is a "cavity barrier"? 

Cavity barriers are non-combustible or limited combustibility materials, which means they have a low-risk of catching fire, or spreading an existing fire. They are fitted along the wall lines between flats to prevent fire spread from one home to another.  
Cavity barriers should run along the horizontal and vertical separation between flats i.e. along the wall separating your home from the home next door and along the ceiling/floor line separating the flats above/below, as well as from the common areas. They should be present within the cavity of the external wall itself and the cavity found between the cladding and the external wall.  
In some buildings, these barriers have been poorly installed, meaning that they cannot do the job they are meant to do. There is also some evidence that the barriers are not in place in some areas, which adds to the perceived risk.  
What is a "cavity closer"? 
Cavity closers are required for a number of reasons within a building to protect it from various factors, including water, damp, heat loss and condensation. They also help to prevent the spread of smoke in the event of a fire. 
The cavity closer acts as a seal, preventing external water vapour and damp from entering the cavity wall and the building, whilst also preventing heat from being lost through the gap. Cavity closers can be used in a range of different constructions, including masonry, timber frame and steel frame systems. 
What is a “compartment”? 

Each home within a building is a separate “compartment” designed to be isolated both from other flats, and the communal areas. This is a technical term, and residents may prefer to think of a “compartment” as every resident’s separate home or flat. 

What is “compartmentation”? 

Fire compartmentation is an element of passive fire protection to inhibit fire spread within the building.  
When we talk about “compartmentation”, we are talking about the methods required to keep a flat completely isolated in the event of a fire. This is achieved by dividing the premises into 'fire compartments' using fire doors, floors and walls of fire-resisting construction, cavity barriers within roof voids and fire stopping to services which penetrate through these elements, such as wastewater pipes and electrical cabling. 

What does an “External Wall System” consist of? 

The External Wall System, or EWS, refers to all the materials within external walls, and includes insulation, various coverings and related fixtures and fittings with the purpose of providing protection to the building structure and the occupants from the elements while providing a visually attractive finish to the building. 

What does "fire stopping" mean? 

Fire stopping is a form of passive fire protection that is used to seal around openings and between joints in a wall or floor assembly. Fire stops are designed to maintain the fire resistance of a wall or floor assembly to slow the spread of fire and smoke. Fire barriers are typically recommended to have a fire resistance rating of more than 60 minutes of integrity and insulation. 
What is "HPL"? 

High-Pressure Laminate, or HPL, is a type of cladding material made from resin- impregnated paper, which is then manufactured under high pressure into laminate sheets. 
Residents will no doubt find the prospect of their walls sounding like they are covered in paper alarming, but like ACM, a limited amount of this type of cladding will not significantly increase the spread of flame across the external walls. The appointed fire engineer will make a qualified assessment of the risk and advise us whether the material should be removed, or whether it can be treated, or even safely left in place in some circumstances. 

What is "MCM"? 

Metal Composite Material, or MCM, is a thin, typically 3-5mm, three-layer panel consisting of two precoated metal sheets. fixed to a structural core that is usually plastic or mineral in nature. The metal is often made of a metal such as copper or zinc. 
One of the better-known types of cladding, ACM, is a form of MCM. 
What is "sealant"? 

Sealant is a pliable substance used to fill the gap and block the passage of fluids and/or air through the joints or openings in materials. In the construction of residential property, you will often find a type of sealant known as “mastic”, which is designed to create a seal around pipes, conduits, busways, cable trays and ducts which penetrate walls, floors and ceilings.  

Some sealants do have a risk of being flammable, and fire engineers often recommended that it is removed and replaced. 

What is "trunking"? 

Cable trunking is installed as a protective routing and covering system for electrical cables and wires which prevents accidental damage. In your home, you might have used a similar product to hide loose telephone or television cables and keep them fixed to a wall or skirting board. In construction, trunking serves a similar purpose, in running cabling through communal areas of a building. 

Most construction trunking is historically made from plastic, but it is now thought of as a potential fire risk. The preferred material is metal-based, and so we are often asked to replace the plastic with metal to lower the risk of fire.