Select Committee on Environment, Transport and Regional Affairs First Report



The basic generic methods of cladding construction are set out in Figures 1 to 3. Whilst there are many variations in form and content these demonstrate in lay terms the basic concepts of external cladding.

External cladding serves a number of functions including;

  • providing weather protection;
  • insulation;
  • improving building appearance.

Cladding systems always include the outermost external envelope (the facade) of a building. In residential buildings cladding systems do not usually include the innermost surface of the building envelope. More often cladding systems (as the name suggests) are mounted on a supporting load-bearing structure. Hence, cladding systems are often called 'over-cladding' systems.

There are three main product types within the external cladding family:

    1)  External wall insulation (Render) systems, see Figure 1
    2)  Rainscreen (sheet boarding) systems, see Figure 2
    3)  Pre-formed in-fill systems, see Figure 3

1)  External wall insulation (Render) systems.

These systems consist of two components:

    i)  insulating material fixed to an external wall;
    ii)  external surface membrane (typically rendered) to provide weather protection.

The absence of a cavity within these systems means that thermoplastic insulants may be safely used if correctly designed. Building Research Establishment Report BR135 (1988) gives detailed guidance on appropriate combinations of insulant, fire barrier and fixing.

The fact that these systems may be applied quickly without need for a structural frame as well as their economic attractiveness explains why these systems make up in the region of 50-60% of all over-cladding installed in the UK.

2)  Rainscreen (sheet boarding) systems

These systems consist of three components:

    i)  structural frame affixed to external wall of building;
    ii)  insulating material fixed to external wall of building;
    iii)  external surface membrane board to provide weather protection.

There is a wide range of product types within the above generic descriptions, with the external sheeting being the most frequent variable.

The insulating material integral to such systems is open into a cavity alongside the external sheet. It is a well established practice but not mandatory (for tall buildings) that such insulation be of limited combustibility.

This precludes plastic products and hence evidence relating to the merits of polystyrene, polyurethane, polyisocyanurate insulants do not usually relate to this type of cladding product. It is also established following BRE Report BR135 (1988) that in tall buildings such systems should include cavity barriers at regular intervals.

The fire at Knowsley Heights, Liverpool, 1991 involved a rainscreen system. The fire tests commissioned by the Department of the Environment at the Building Research Establishment were predominantly undertaken on rainscreen systems.

Rainscreen systems constitute some 40% of the over-cladding market.

3)  Pre-formed in-fill systems

In-fill systems are typically pre-formed remote from the building and fixed in place on-site. They have a wide variety of configurations and differ from render/rainscreen systems in that they may be fitted to only limited areas of the building envelope, eg spandrel panels beneath windows.

In-fill systems are less often used for weather protection or building insulation and more often for improving appearance. Such systems do not cater to the same market as render/rainscreen systems and are considered by some to be outside the "over-cladding" family. However, such systems undoubtedly constitute external cladding and fall within the terms of the Committee's reference. The system at Irvine, Ayrshire is best described as a pre-formed in-fill system.

Figure 1

Figure 2

Figure 3

previous page contents next page

House of Commons home page Parliament home page House of Lords home page search page enquiries

© Parliamentary copyright 1999
Prepared 5 January 2000