Fire Regulations
In England and Wales, Scotland and Northern Ireland there are
separate documents for domestic and non-domestic buildings.
There is much detail in the Fire safety documents that has
little relevance to insulation materials. This section, therefore,
concentrates on the requirements for:
- Cavity barriers
- Structural fire protection
Cavity barriers
Relevant sections:
- Approved Document B (Domestic) B3 – Section 6:
Concealed spaces (Cavities)
- Approved Document B (Non-domestic) B3 –
Section 9: Concealed spaces (Cavities)
- Scottish Technical Handbook 2 – Fire Section
2.4: Cavities
- NI Technical Booklet E – Section 3: Provision
of cavity barriers
Fire and smoke spread in concealed spaces is particularly
hazardous because fire can spread quickly whilst remaining
undetected. The regulations give guidance on two types of cavity
barrier:
- Small cavity barriers that form a potential pathway around a
fire-resisting wall or floor.
- Extensive cavities, such as pitched roof spaces or suspended
ceilings above offices.
Small cavity barriers
Cavity barriers should be provided to seal the edges of
cavities, including around openings. In addition, where a
compartment wall, floor or other part of a building abuts a
structure containing a cavity, a cavity barrier should be installed
so as to extend the line of the structure. There are a number of
exceptions to this rule, the main one being a masonry cavity wall,
which does not need cavity barriers at junctions with other
fire-resisting constructions.
The Summary (Table 27) lists where cavity barriers are required
by the Regulations. The table is taken from the Northern Ireland
Technical Booklet E.
Small cavity barriers should provide at least 30 minutes fire
resistance. Acceptable materials are:
- steel at least 0.5mm thick
- timber at least 38mm thick
- polythene sleeved mineral wool, or mineral wool slab under
compression
- calcium silicate, cement or gypsum based boards at least 12mm
thick
Table 27: Summary of small cavity
barrier provision
|
Item
|
Cavity barriers to be
provided
|
Purpose group to which the
provision applies*
|
| |
|
1a |
1b,1c |
2 |
3,4,5,6,7 |
| 1 |
At the top of an external cavity wall
and at the junction between anexternal cavity wall and a
compartment wall that separates buildings,except for masonry
external cavity walls
|
Y |
Y |
Y |
Y |
| 2 |
Above the enclosures to a protected
stairway in a dwellinghouse of three or more storeys
|
n/a |
Y |
n/a |
n/a |
| 3 |
At the junction between an external
cavity wall and every compartment floor and compartment wall,
except for masonry external cavity walls
|
Y |
n/a |
Y |
Y |
| 4 |
At the junction between a cavity wall
and every compartment floor, compartment wall, or other wall or
door assembly which forms a fire-resisting barrier, except for
masonry external cavity walls
|
Y |
n/a |
Y |
Y |
| 10 |
At the edges of cavities (including
around openings)
|
Y |
Y |
Y |
Y |
|
* Key to purpose groups in
tables
|
|
1a
|
Flat |
3 |
Offices
|
|
1b
|
Houses with three storeys |
4 |
Retail and commercial
|
|
1c
|
Houses up to two storeys |
5 |
Assembly and recreation
|
|
2
|
Residential (institutional), eg hotel,
hospital wards, halls of residence
|
6 |
Industrial
|
| |
|
7 |
Storage
|
Large cavities
Cavity barriers should also be used to sub-divide larger
cavities. The requirements for England and Wales, Northern Ireland
and Scotland are shown in the tables below.
Table 28: Summary of large cavity
barrier provision
|
Item
|
Cavity barriers to be
provided
|
Purpose group to which the
provision applies*
|
| |
|
1a |
1b,1c |
2 |
3,4,5,6,7 |
| 1 |
In a protected escape route, above and
below any fire-resisting construction which is not carried full
storey height or (in the case of a top storey) to the underside of
the roof covering except for masonry external cavity walls
|
Y |
n/a |
Y |
Y |
| 2 |
Above any bedroom partitions which are
not carried full storey height, or (in the case of a top storey) to
the underside of the roof covering
|
n/a |
n/a |
n/a |
n/a |
| 3 |
Above any corridor enclosures which
are not carried full storey height, or (in the case of a top
storey) to the underside of the roof covering, where the corridor
(which is not a protected corridor) is subdivided to prevent fire
or smoke affecting two alternative escape routes simultaneously
|
n/a |
n/a |
Y |
Y |
| 4 |
To subdivide any cavity (including any
roof space) so that the distance between cavity barriers does not
exceed the set dimensions (see tables below)
|
n/a |
n/a |
Y |
Y |
| 5 |
Within the void behind the external
face of rainscreen cladding at every floor level, and on the line
of compartment walls abutting the external wall, of buildings which
have a floor more than 18 m above ground level
|
Y |
n/a |
Y |
n/a |
| 6 |
At the edges of cavities (including
around openings)
|
Y |
Y |
Y |
Y
|
Table 29: Maximum dimensions of cavities in
non-domestic buildings (England, Wales and N.I.)†
| Location of cavity |
Class of
product/surface exposed in cavity |
Maximum dimension in
any direction |
| |
National
class |
European
class |
(m) |
| Between roof and a ceiling |
Any |
Any |
20 |
| Any other cavity |
Class 0 or Class 1 |
Class A1, or Class A2-s3, d2, or
Class B-s3, d2, or Class 3-s3, d2 |
20 |
| |
Not Class 0 or Class 1 |
Not any of the above |
10 |
Notes:
The National and European classes do not correspond
exactly
† Purpose Groups 2-7
Table 30: Recommended distance
between cavity barriers in roof spaces above undivided spaces
(Scotland)
|
|
Where surfaces are
non-combustible or low risk materials (m)
|
Where surfaces are medium,
high or very high risk (m)
|
|
Intended for sleeping
|
20 |
15 |
|
Not intended for sleeping
|
No limit ‡
|
20 |
‡ Limit of 20 m should be applied
in residential care buildings and hospitals.
Structural fire protection
Relevant sections:
- Approved Document B (Domestic) B3 – Section 4:
Loadbearing elements of structure
- Approved Document B (Non-domestic) B3 –
Section 7: Loadbearing elements of structure
- Scottish Technical Handbook 2 – Fire Section
2.3: Structural protection
- NI Technical Booklet E – Section 3: Fire
resistance of elements of structure
Every building must be designed and constructed in such a way
that in the event of an outbreak of fire, the load-bearing capacity
of the building will be maintained to:
- enable all occupants to escape
- reduce the risk to firefighters
- reduce the danger of collapse to people in the vicinity
The level of fire resistance required is between 15 and 120
minutes and depends on:
- the use of the building
- the height of the building both above and below ground
- whether a sprinkler system is installed, or not
The important point to consider is the ability of the element of
structure to maintain its load-bearing capacity in a fire for the
period set out in the relevant table. The following tables list the
level of fire resistance required for specific applications:
- Approved Document B (Domestic) – Appendix A,
Table A1
- Approved Document B (Non-domestic) – Appendix
A, Table A1
- Scottish Technical Handbook 2 – Fire – Tables
to clause 2.1.1 and Appendix 2D
- NI Technical Booklet E – Table 3.2 Minimum
periods of fire resistance
