ANNEX 2
MAIN TYPES OF EXTERNAL CLADDING SYSTEM
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
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