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 28) 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 28: 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 29: 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 30: 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 31: 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
Residential refurbishment
Fire precautions mainly come into play when a
property is being converted into flats, or a dwelling is being
extended by means of a loft conversion. The main consideration with
conversion to flats is ensuring a safe means of escape.
Loft conversions are a very popular way of
extending houses and bungalows. However, the implications for
complying with the Fire requirements of the Building Regulations
are complex. We set out the main considerations in this section.
This guidance offers advice on loft conversions to existing
bungalows and two storey dwellings – if you already have a three
storey house and wish to convert the loft, you are advised to speak
to your local Building Control department.
From 6th April 2007, the revised Approved
Document B came into force, introducing significant changes to the
fire requirements for loft conversions. Most of the previous
concessions relating to loft conversions have now been removed.
Existing two storey houses with a new loft conversion are to be
treated as new three storey houses.
Loft conversions
Form a protected escape route.
The revised Regulations require a fire
resistant protected escape route from the loft to the dwelling’s
final exit. This is to enable the occupants to make a safe escape.
The protected escape route should either:
- discharge into a hall served by an external
door, or
- there must be at least two separate escape
routes available to an external door – separated by fire resistant
construction and fire doors.
The protected escape route should be enclosed
by construction (doors and walls or partitions) capable of
resisting fire for at least 30 minutes. Existing walls should be
assessed for their fire resistance and upgraded as necessary.
Penetrations of the fire resisting
construction should be suitably fire stopped or fire protected eg
tops of walls / around services / drainage pipes /air vents etc
If fire doors are not to be fitted to the
bathroom (due to low fire risk – unless boilers are fitted) - then
the fire protection needs to be checked around the perimeter of the
bathroom walls as an extension of the escape route
fire-protection.
The condition of existing doors and frames
opening onto the protected stair must be assessed. If they do not
provide at least 20 minutes fire resistance, they must be replaced
with doors capable of achieving at least 20 minutes fire
resistance.
Any glazing openings facing the protected
escape route, other than those serving toilets or bathrooms, should
be at least 1.1m above the floor level or stair pitch line and
changed to achieve 30 minutes fire-resistance.
If escape windows are to be provided, they
must have a clear opening of sufficient size to escape through and
be located in a position amenable to rescue by ladder. For most
properties, the escape windows must be provided on the front
elevation.
Staircases
If the dwelling has an open plan staircase, it
will need to be enclosed. The new loft access stair must be an
extension of the existing stair enclosure to avoid the creation of
inner rooms. Alternatively if there is only one room in the loft
space, the loft stair can be contained within the room itself and a
fire door provided at the base of stair landing position, where it
exits onto the existing first floor landing. This guidance assumes
the existing dwelling has at least two stories. The means of escape
and fire protection required where a bungalow is to have a loft
conversion are less onerous.
Fire resistant floors
For loft conversions to existing two storey
dwellings, the new floor must have 30-minute fire-resistance ie 30
minutes load bearing capacity, 30 minutes integrity and 30 minutes
insulation (30/30/30). If the existing ceilings are retained, they
may need to be upgraded to achieve this rating. This can be done
from above – see page 108.
If the building has a basement its ceiling
should achieve at least 30 minutes fire resistance and the basement
is to be separated from the ground floor by fire resisting
construction.
Smoke detectors
Mains powered and battery backed up smoke
detectors must be installed on each storey in accordance with BS
5839-6: 2004 – Grade D – category LD3 standard. All detectors must
be interlinked so that they all sound even if only one is
triggered. They must be placed in the circulation spaces or
protected stairway. If the new loft has no circulation space, a
smoke detector should be fitted in the loft room itself.
Position detectors so that they can be reached
easily for maintenance and testing ie not over stairs.
Dormer windows
If the conversion involves forming a dormer,
dormer cheeks within 1 metre of a boundary should achieve at least
30 minutes fire resistance in both directions. The dormer roof
should also be capable of resisting external fire spread for at
least 30 minutes.
Conversion to flats
Where an existing house or other building is
converted into flats, this counts as a material change of use under
the Building Regulations and Approved Document B should be
followed.
Approved Document B, Volume 2 – Buildings
other than dwellings sets out comprehensive requirements for
providing adequate means of escape for flats.
For buildings up to three storeys high where
the means of escape is in accordance with Approved Document B, a 30
minute standard of fire resistance could be accepted for the
elements of structure, including any timber separating floors.
Where it is desirable to retain an existing ceiling, it is possible
to upgrade a timber floor by inserting insulation from above. Doors
to individual flats must have a 30 minute fire resistance. It is
usual to design a protected entrance hall to each flat. The diagram
shows a typical arrangement for a flat conversion.
For buildings with four or more storeys, at
least 60 minutes fire resistance is required. Floors above
basements also require at least 60 minutes fire resistance. This
may be difficult to achieve with existing timber floors.