Memorandum by the Department of the Environment,
Transport and the Regions (ROF 31)
The following memorandum is intended to address
the issues that the Committee wish to examine.
1. WHETHER A
The following points under this section are
intended to set out the risks associated with external cladding.
Some background information is also provided which it is hoped
will help explain the philosophy behind the Building Regulations
(section 3) that were developed to minimise the risk.
Schedule 1 of the Regulations contain functional
requirements which, where relevant, must be complied with. Part
B of schedule 1 deals with fire safety and Requirement B4 (1),
which has particular relevance to cladding systems, states:
"The external walls of the building
shall resist the spread of fire over the walls and from one building
to another, having regard to the height, use and position of the
1.1 External fire spread
External walls or the cladding attached to external
walls can contribute to the fire spread both internally and externally
if adequate precautions are not taken. The main function of an
external wall in the context of external fire spread, is for it
to be able to confine the fire to the building. This is intended
to restrict the fire from hazarding a nearby building and can
also aid fire-fighting. The origins of this requirement lie in
the great fire of London. However the extent to which external
fire spread needs to be considered is largely dependent on the
amount of space that there is around the building. An external
wall is considered to be an element of structure if it has a loadbearing
function and it should then not collapse prematurely in fire.
To achieve this and to help prevent external fire spread it may
need to have fire resistance. In tall blocks of flats the loadbearing
element is usually the structural frame of the building and the
infill walls will only need to have fire resistance if they are
located sufficiently close to a boundary. The standard of fire
resistance needed depends on the use and height of the building.
If the side of a building is sufficiently removed from the boundary
then it need not have any fire resistance. Conversely, where the
wall is on or very close to the boundary, then most or all of
the wall will need to be fire-resisting.
1.2 Flammability at external wall surfaces
In addition to fire resistance, it is necessary
to consider the outside face of the wall in terms of its susceptibility
to ignition and subsequent flame spread over its surface. Typically,
sources of ignition could be flames issuing out of windows or
other openings caused by a fire within the building or alternatively
from an external fire source. External fire spread to the cladding
can be caused by fire radiation from another building or from
a source immediately adjacent to the cladding such as the ignition
of refuse caused by arson. The standard of fire precautions that
are necessary is affected by:
(a) the distance to the boundary;
(b) the height of the building; and
(c) the use of the building.
Where external fire fighting might be difficult,
high standards of performance against fire propagation and spread
of flame are needed. Therefore where the external wall of a building
is on or very close to a boundary these standards apply. Because
of this difficulty in fighting external fire spread in the upper
parts of high buildings it is necessary to apply higher standards
of fire performance to the upper parts of such buildings regardless
of the distance to the boundary. Where a low building is not close
to a boundary, there is no restriction on the flammability of
external wall claddings. Also a lesser standard of performance
is acceptable for the lower parts of a high building unless it
is on or close to the boundary.
1.3 Materials of limited combustibility.
In high buildings the risk from fire spread
is such that the combustibility of materials used in the construction
of external walls, including thermal insulation materials, needs
to be limited. The exception to this is where both leaves of the
cladding are of masonry construction, such as brick or block,
in which case the insulating material need not be of limited combustibility.
A material of limited combustibility is a material with a performance
specification: this includes non-combustible materials or materials
that are defined by reference to a method of test. Typically,
plasterboard would be considered as a material of limited combustibility.
Hidden voids in construction can provide a route
for fire spread throughout or around the building and this can
be particularly relevant in the context of external cladding systems.
Any void between the new cladding and the existing building should
be closed at regular intervals or at the line of compartmentation.
Typically the floor of each flat will form the line of compartmentation,
an issue covered in paragraph 3.1.
1.5 Surface Flame Spread
Construction materials and their behaviour in
relation to fire are classified using a number of standard tests
such that the performance of particular elements of buildings
can be specified without reference to specific materials.
The provisions necessary to reduce the spread
of flame over the surface of a material are based on the comparison
of the results of small scale fire tests with larger scale fire
research and experience of real fires. Any guidance that is given
must be sufficient to provide a satisfactory level of safety whilst
being practical in its application.
The surfaces of materials (including cladding
systems) are classified by reference to two British Standard test
methods. These are the spread of flame test which measures the
distance a flame will spread across the surface of a sample and
the fire propagation test which assesses the contribution that
the sample makes to fire development. The spread of flame test
has four classes. These are class one to class four, with one
being the highest performance rating. Class "O" is a
further class, defined for the purposes of the Building Regulations,
that is used for critical situations where a higher standard of
performance than that of Class one is appropriate. The Building
Regulation issues relating to flame spread are covered in paragraph
Whilst non-combustible materials are inherently
of the Class "O" referred to above, many materials that
are by definition combustible will also achieve this classification.
The intent of this methodology is to identify materials that will
have a low risk of fire spread.
2. THE EXTENT
2.1 The Department does not collect statistics
on the use of cladding systems but it is believed that external
cladding systems are widely used.
2.2 The Department has a call-off contract
with the Fire Research Station to investigate real fires and this
highlights any areas of concern that affect Building Regulations.
The following are fires notified to the Department that involved
external fire spread but were not necessarily attributed to the
Knowsley Heights, Liverpool, 1991. Deliberate
fire spread up and behind rainscreen cladding, extended over 11
floors. Building Regulations were changed as a result of this.
Mercantile credit building, Basingstoke, 1991.
Fire on 8th floor spread up the building behind glass curtain
Three storey block in Milton Keynes, 1995. Roof
Alpha House Coventry, 1997. Flames travelled
up the outside of the block from 13th to 17th floor. No fire penetration
of the flats.
Butler House, Grays, Essex, 1997. Fire in top
flat of 14 storey block caused uPVC window frames to melt and
drip, which in turn caused some damage to cladding.
3. THE ADEQUACY
3.1 In England and Wales (Scotland has a
different set of Building Regulations) where new buildings are
erected, or existing buildings materially altered, or in certain
cases where there is a material change of use, then the work is
required to comply with the Building Regulations 1991. As far
as fire is concerned, the purpose of the Regulations is to secure
reasonable standards of health and safety for persons in or about
buildings (and any others who may be affected by buildings, or
matters connected with buildings). Schedule 1 of the Regulations
contains the functional requirements and Requirement B4(1), which
has particular relevance to cladding systems, is given in paragraph
Guidance on how to comply with the functional
Requirements of Part B is given in Approved Document B (fire safety).
Approved Document B includes several provisions to restrict the
materials used in external walls and cladding by reference to
the surface spread of flame rating. These provisions are as follows:
The external surfaces of walls of any building
closer than one metre to its boundary (and therefore closer to
other buildings) should be class "O" in order to reduce
the risk of external fire spread from one building to another.
Where a building is 20 metres or more in height,
the external surfaces of walls more than 20 metres from ground
level should achieve a class "O" surface spread of flame
rating. Below this height timber cladding at least 9mm thick,
or some other materials that are less restrictive than class "O"
materials, could be used. This is to reduce the risk of fire spread
over the walls of tall buildings whilst allowing certain commonly
used materials to be retained in positions where fire fighting
operations from the ground could be effective.
In the case of the outer cladding of a wall
of "rainscreen construction", which has a drained and
ventilated cavity, the surface of the outer cladding which faces
the cavity should also satisfy the provisions detailed above.
This is to take account of the specific problems associated with
this type of construction.
Approved Document B states that the external
envelope of the building should not provide a medium for fire
spread if it is likely to be a risk to health or safety. The Document
also points out that the use of combustible materials for a cladding
framework, or of combustible thermal insulation, may present a
risk in tall buildings. Therefore in a building with a storey
at more than 20 metre above ground level any insulation material
used in the external wall construction should be a material of
With regard to fire stopping Approved Document
B suggests that a cavity barrier should be provided at the junctions
between an external cavity wall that is not of masonry construction
and every compartment floor. The BRE guidance on avoiding risks
with thermal insulation, which is referenced in the Approved Document
that deals with energy efficiency, recommends that to prevent
fire spread, cavity barriers should be provided at every floor
level. We have asked the Fire Research Station to review and update
their report on the fire performance of external thermal insulation
for walls of multi-storey buildings, referred to in Approved Document
The current Approved Document B is being reviewed
but there are no changes proposed that will affect cladding systems
other than the 20 metre height mentioned above is being reduced
to 18 metre to fall in line with other height dimensions relating
to fire fighting. In general it is considered that the risk of
serioius fire spread via external cladding will be minimal if
the guidance given in Approved Document B is followed.
The Fire Precautions (Places of Work) Regulations
may have a bearing on cladding issues but these Regulations are
the responsibility of the Home Office.
4. WHAT ACTION
4.1 The Building Regulations in England
and Wales only apply to new building work, and thus cannot be
used to require any alterations to existing buildings although
the Department is reviewing this in respect of the conservation
of energy. The provisions of the Building Regulations as set out
in the preceding section do, however, apply when new buildings
are erected and thus such work is covered.
The Building Regulations also apply to building
work that is classified as a material alteration. An alteration
is material if, at any stage of the work, it would result in the
building not complying with certain requirements of the Regulations
where it previously did. The most pertinent requirement with regard
to cladding is external fire spread, but structural requirements
could also be an issue.
Thus with regard to the alteration (or replacement)
of cladding, if this was the only work being carried out, and
if it at no time made the external fire spread or structure any
worse that it was already, the work would not be controlled by
the Building Regulations. There is therefore the possibility that
external cladding installed some time ago, and thus not complying
with the current Building Regulations, could be replaced without
being controlled by the Regulations as long as the building was
not made any worse with regard to these particular requirements
in the process. This is a possible problem area and one that the
Department may need to review.
The Building Regulations would need amendment
to ensure that all such work was covered. It is possible that
the Building Act might also need to be extended to support this.
Any such amendment would need careful drafting to ensure that
an undue burden was not inadvertently imposed on replacement and
repair work. However a balance needs to be struck between construction
costs and safety.
5. OTHER MATTERS
5.1 The Department has funded the Fire Research
Station (BRE) to produce a method of test for "Assessing
the fire performance of external cladding systems". This
report will be referenced in the revised Approved Document B and
it is proposed that it will become a British Standard.
5.2 Review of Building Research Establishment
Report 1351998 "Fire performance of external thermal
insulation for walls of multi-storey buildings". This review
is required to give better design guidance for cladding systems,
particularly with regard to cavity barriers.