B8 (1) A dwelling house shall be so designed and constructed that, in the event of fire, its stability will be maintained for a reasonable period.

(2) (a) A wall common to a dwelling house and to one or more adjoining buildings shall be so designed and constructed that it offers adequate resistance to the spread of fire between those buildings.

(2) (b) A dwelling house shall be sub-divided with fire resisting construction where this is necessary to inhibit the spread of fire within the dwelling house.

(3) A dwelling house shall be so designed and constructed that the unseen spread of fire and smoke within concealed spaces in its structure or fabric is inhibited where necessary.

(4) For the purposes of sub-paragraph 2(a), a dwelling house in a terrace and a semi-detached dwelling house are each to be treated as being a separate building.

3.1 Internal Fire Spread (structure)

3.1.1 General The purpose of the requirement of Regulation B8 is to ensure the stability of buildings in the event of fire, that there is a sufficient degree of fire separation within dwelling houses and between adjoining buildings, and to inhibit the unseen spread of fire and smoke in concealed spaces in buildings.

3.2 Performance

The requirements of B8 may be met:

(a) if the structural elements of the building are capable of withstanding the effects of fire for an appropriate period without loss of stability,

(b) if the building is sub-divided by elements of fire-resisting construction into compartments,

(c) if any openings in fire separating elements are suitably protected in order to maintain the fire integrity of the element, and

(d) if any hidden voids in the construction are sealed and subdivided to inhibit the unseen spread of fire and products of combustion, in order to reduce the risk of structural failure and the spread of fire, in so far as they pose a threat to the safety of people in and around the building.

The extent to which any of these measures are necessary is dependent on the use of the building and, in some cases its size, and on the location of the element of construction.

3.3 Introduction to Provisions

3.3.1 Provisions for loadbearing elements of structure are given in sub-section 3.4. Subsection 3.5 is concerned with the subdivision of a building into compartments, and subsection 3.6 makes provisions about concealed spaces (or cavities).

Sub-section 3.7 gives information on the protection of openings and on fire-stopping which relates to compartmentation and to fire spread in concealed spaces. Common to all these sub-sections and to other provisions of this Document is the property of fire resistance.

3.3.2 Fire Resistance

The fire resistance of an element of construction is a measure of its ability to withstand the effects of fire in one or more ways:

(a) resistance to collapse, i.e. the ability to maintain loadbearing capacity (which applies to loadbearing members only);(R in European Classification)

(b) resistance to fire penetration, i.e. an ability to maintain the integrity of the element (which applies to fire separating elements);(E in European Classification)

(c) resistance to the transfer of excessive heat, i.e. an ability to provide insulation from high temperatures (which applies to fire-separating elements);(I in European Classification)

3.3.3 Provisions Elsewhere in Technical Guidance Document B concerning Fire Resistance

There are provisions in Section 1 concerning the use of fire-resisting construction to protect means of escape.

There are provisions in Section 4 for fire resistance of external walls to restrict the spread of fire between buildings. Appendix A gives information on methods of test and performance for elements of construction.

Appendix B gives information on fire-resisting doors.

3.4 Loadbearing Elements of Structure

3.4.1 Introduction

Premature failure of the structure can be prevented by provision for loadbearing elements of structure to have a minimum standard of fire resistance, in terms of resistance to collapse or failure of loadbearing capacity.

The purpose in providing the structure with fire resistance is threefold:

(a) to protect the occupants;

(b) to protect fire fighters who may be engaged in search or rescue operations (though this is limited and is not intended to cover fire-fighting operations generally);

(c) to reduce the danger to people in the vicinity of the building who might be hurt by falling debris or by the impact of the collapsing structure on other buildings.

3.4.2 Fire Resistance Standard

Structural frames, beams, columns, loadbearing walls (internal and external), floor structures, should have at least the fire resistance given in Appendix A, Table A1.

3.4.3 Application of the Fire Resistance Standards for Loadbearing Elements (see Appendix A, Tables A1 )

The measures set out in Appendix A include provisions to ensure that where one element of structure supports or gives stability to another element of structure, the supporting element has no less fire resistance than that required for the other element.

The measures also provide for elements of structure that are common to more than one building or compartment, to be constructed to the standard of the greater of the relevant provisions.

Special provisions about fire resistance of elements of structure in single storey buildings are also given, and there are concessions in respect of fire resistance of elements of structure in basements where at least one side of the basement is open at ground level. See "Application of the fire resistance standard in Table A1" in Appendix A.

3.4.4 Exclusions from the Provisions for Elements of Structure

The following are excluded from the definition of elements of structure for the purposes of these provisions:

(a) a structure that only supports a roof, unless the roof performs the function of a floor, or as a means of escape (see S1) or is essential for the stability of an external wall which is required to have fire resistance (see S4);

(b) the lowest floor of the building.

3.4.5 Additional Provisions

Additional provisions are required if a loadbearing wall is also:

(a) a separating wall (this includes a wall common to two buildings) (see 3.5);

(b) a wall between a dwelling house and a domestic garage (par. 3.5.2);

(c) protecting a means of escape (see Appendix A : Table A1)

(d) an external wall (see S4, sub-section 4.4 and 4.5);

3.5 Compartmentation

3.5.1 Introduction

The spread of fire within a building can be restricted by sub-dividing it into compartments separated from one another by walls and/or floors of fire-resisting construction. The object is twofold:

(a) to prevent rapid fire spread which could trap occupants of the building; and

(b) to reduce the chance of fires becoming large, on the basis that large fires are more dangerous, not only to occupants but to people in the vicinity of the building.

Compartmentation may be complementary to provisions made under Section 1 for the protection of escape routes, and to provisions made under Section 4 against the spread of fire between buildings.

3.5.2 Forms of Compartmentation

Compartment walls should be provided in dwelling houses in the circumstances described below,

Special forms of compartmentation to which particular construction provisions apply, are:

(a) walls common to two or more buildings (separating wall),

(b) Any wall between semi-detached dwelling houses, or houses in a terrace, should be constructed as a separating wall and the dwelling houses should be considered as separate buildings.

(c) If a domestic garage is attached to (or forms part of) a dwelling house, the walls, floors and ceilings should provide the fire separation from the rest of the dwelling house as indicated in Diagram 9.

Diagram HB9 - Separation between garage and dwelling house - Extract from TGD B Vol. 2

(d) Where a door is provided between a dwelling house and the garage, the door opening should be positioned at least 100 mm above garage floor level (see Diagram 9) and should be fitted to open into the garage. Alternatively the floor of the garage should be laid to fall not less than 1:100 to allow fuel spills to flow away from the door.

(e) In the case of a single storey house in order to maintain a 30 minute fire separation between the house and the garage either:

the wall between the house and the garage should be taken up to the underside of the roof; or
the ceiling of the garage should have a minimum period of fire resistance of 30 minute.

3.5.3 Limits to Compartment sizes

There is no limit on the floor area or cubic capacity of a compartment in a Residential Dwelling of Purpose Groups 1(a),1(b) or 1(d).

3.5.4 Construction of Compartment Walls

Every compartment wall/separating wall should:

(a) form a complete barrier to fire between the buildings they separate;

(b) have the appropriate fire resistance as indicated in Appendix A, Table A1;

The performance requirements for fire resisting elements of construction are indicated in Appendix A, paragraph A5.

3.5.4.1 Openings in fire resisting construction

Any door provided between a dwelling house and a garage should be protected by means a fire door, in accordance with the provisions outlined in Appendix B and Table B1.

Openings between compartments for the passage of pipes, ducts and other services should be protected in accordance with the provisions outlined in sub-section 3.5.4 for framed compartment walls see 3.5.4.3.

Note: No openings are allowed in separating walls (see 3.5.4.4)

3.5.4.2 Separating walls

Separating walls should run the full height of the building in a continuous vertical plane and should be constructed of non-combustible (see Appendix A, Table A7) materials. Adjoining buildings should only be separated by walls, not floors.

3.5.4.3 Separating walls in timber framed construction

An exception to the requirement for separating walls to be constructed of noncombustible materials may be permitted in the case of separating walls in timber frame dwelling houses built in accordance with I.S.440: Timber Frame Construction, Dwellings and Other Buildings; between buildings of up to three storeys, (four storeys where the provisions of section 1.3.4 (g) are complied with) where the design, materials and workmanship used in the manufacture and construction of the wall are in accordance with the provisions of Technical Guidance Document D (Materials and Workmanship).

3.5.4.4 Services in separating walls

No services should pass through or breach separating walls.

In timber framed construction, where necessary, a service cavity external to the un-breached linings of the fire resistant separating wall should be provided to accommodate services as outlined in I.S. 440.

3.5.4.5 Junction of separating wall with other walls

Where a separating wall meets an external wall, the junction should be fitted with a cavity barrier in accordance with Diagram 12 or where no cavity exists, maintain the fire resistance of the separating wall, or in the case of external insulation systems a fire stop within the insulation in the plane of the separating wall.

3.5.4.6 Junction of separating wall and roof

The junction between a separating wall and the roof of a building should be capable of restricting fire spread between the buildings.

A separating wall should be taken up to meet the underside of the roof covering or deck and fire stopped where necessary at the wall/roof junction.

The construction of the wall, particularly between any ceiling and the roof, should not contain imperfections that would provide a route for fire penetration or premature failure of the fire resistance performance of the wall.

The gap between the wall and the underside of the roof should be as small as practicable (generally not greater than 50 mm) and be filled with suitable fire stopping material over the full width of the wall.

Where structural roof members such as beams, purlins and rafters are built into a separating wall, any openings for them should be as small as practicable and any gaps should be effectively fire stopped with non-combustible fire stopping material over the full width of the wall.

No structural roof member should be carried across a separating wall (except where specified at (a) below).

The design and detailing of the junction between a separating wall and any roof valley, gutter, or other roof configuration, should be carefully considered so as to ensure that a means is not provided at the junction for premature fire spread between compartments or buildings.

If a fire penetrates a roof near a separating wall there is a risk that it will spread over the roof to the adjoining building. To reduce that risk, the junction between a separating wall and a roof should be constructed in accordance with the following:

(a) In dwelling houses not more than 15 m high a zone of the roof at least 1.5 m wide (see Table 4.3) on both sides of the wall should have a covering of class BRoof(t4) (European class) or AA, AB, or AC (National class) (see table A4 to Appendix A). Where timber tiling battens or combustible boarding used as a substrate to the roof covering, are to be carried over the separating wall, they should be fully bedded in mortar or other suitable non-combustible fire stopping material for the full width of the wall. Boarding should not exceed 25 mm in thickness, and any cavities within the thickness of the roof, above and below the sarking felt or similar membrane along the line of the wall and at the eaves should be adequately fire stopped (see Diagram 10(a)).

(b) As an alternative to (a) above the separating wall may be extended above the line of the external roof surface by a height of not less than 375 mm to form a parapet wall (see Diagram 10(b)).

(c) As an alternative to (a) or (b) above, any other system which has been shown by test to be equally effective in restricting the spread of fire at a separating wall / compartment wall/roof junction may be used.

Diagram HB10 - Junction of separating wall with roof for dwelling houses not more than 15 m high - Extract from TGD B Vol. 2

3.6 Concealed Spaces (Cavities)

3.6.1 Introduction

Hidden voids in the construction of a building provide a ready route for smoke and flame spread. This is particularly so in the case of voids above other spaces in a building, e.g. above a suspended ceiling or in a roof space. As the spread is concealed, it presents a greater danger than would a more obvious weakness in the fabric of the building. Provisions are made to restrict this by interrupting cavities which could form a pathway around a barrier to fire, and subdividing extensive cavities.

It should be noted that cavity barriers should not be provided above separating walls as these walls are required to be carried up full storey height to the roof. The fire resistance standards for cavity barriers are lower than for a separating wall and it is important to use a separating wall in this situation to maintain the standard of fire resistance.

3.6.2 Provision of Cavity Barriers

Cavity barriers should be provided in accordance with the following:

(a) At the top of an external cavity wall (masonry or framed construction) including any gable wall.

(b) Vertically at the junction of separating wall and any such wall with an external cavity wall (see Diagram 12).

(c) Above the enclosures to a protected stairway (see Diagram 11).

(d) Around all openings (windows, doors, vents, service boxes etc.) in framed construction

Diagram HB11 - Roofspaces over protected stairway in dwelling houses (alternative arrangements) - Extract from TGD B Vol. 2

Diagram HB12 - Vertical cavity barrier at junction of separating wall - Extract from TGD B Vol. 2

3.6.3 Construction and Fixings for Cavity Barriers

Every cavity barrier should be constructed to provide at least 30 minutes fire resistance (see Appendix A, Table A1, item 10).

Notes: Any cavity barrier required in framed construction may however be formed of:

(i) steel at least 0.5 mm thick, or

(ii) timber at least 38 mm thick, or

(iii) polythene sleeved mineral wool, or mineral wool slab, in either case under compression when installed in the cavity.

A cavity barrier may be formed by any construction provided for another purpose if it meets the provisions for cavity barriers.

Cavity barriers should be tightly fitted to rigid construction and mechanically fixed in position wherever possible. Where this is not possible (for example, in the case of a junction with slates, tiles, corrugated sheeting or similar materials) the junction should be fire-stopped.

Where cavity barriers are fitted in roof spaces the roof members to which they are fixed do not have to be fire resisting.

Cavity barriers should also be fixed so that their performance is unlikely to be made ineffective by:

(a) movement of the building due to subsidence, shrinkage or thermal change and movement of the external envelope due to wind;

(b) collapse in a fire of any services penetrating them;

(c) failure in a fire of their fixings; or failure in a fire of any material or construction which they abut.

3.6.4 Openings in Cavity Barriers

Any openings in a cavity barrier should be limited to those for:

(a) the passage of pipes which meet the provisions in sub-section 3.7;

(b) the passage of cables or conduits containing one or more cables;

(c) ducts which are fire resisting.

3.7 Protection of Openings and Fire-Stopping

3.7.1 Introduction

Earlier sections of this Document describe the provision of barriers to fire, and the circumstances in which there may be openings in them. This Section deals with the protection of openings in such barriers. If an element that is intended to provide fire separation (i.e. it has requirements for fire resistance in terms of integrity and insulation) is to be effective, then every joint, or imperfection of fit, or opening to allow services to pass through the element, should be adequately protected by sealing or fire stopping so that the fire resistance of the element is not impaired. Building service installations should be designed in accordance with BS 8313:1997 (Section 13).

Provisions for door openings and fire doors are given in Appendix B.

Note: The measures are intended to delay the passage of fire. They generally have the additional benefit of retarding smoke spread but the test specified in Appendix A for integrity does not stipulate criteria for the passage of smoke as such.

3.7.2 Openings for Pipes

Pipes which pass through a wall or floors which are required to be fire resisting , or cavity barrier, should meet the appropriate provisions in alternatives A, B or C below.

Note: No pipework should pass through any separating wall (see 3.5.4.4)

Alternative A: Proprietary Seals (any pipe diameter)

Provide a proprietary sealing system which has been shown by test to maintain the fire resistance of the wall, floor or cavity barrier.

Alternative B: Pipes with a restricted diameter

Where a proprietary sealing system is not used, fire-stopping may be used around the pipe, keeping the opening as small as possible. The nominal internal diameter of the pipe should not be more than the relevant dimension given in Table 3.4.

Alternative C: Sleeving

A pipe of lead, aluminium, aluminium alloy, asbestos-cement or uPVC, with a maximum nominal internal diameter of 160 mm, may be used with a sleeving of non-combustible pipe extending not less than 1m from the fire resistant element. The specification for noncombustible and uPVC pipes is given in the notes to Table 3.4.

Table HB3 - Maximum nominal internal diameter of pipes - Extract from TGD B Vol. 2

3.7.3 Ventilating Ducts

Where ventilation and air conditioning ducts pass between fire resisting elements (floors, protected stairwells etc.), they should be protected in accordance with the recommendations contained in paragraph 1.3.9.3.

3.7.4 Flues

If a flue, or duct containing flues or appliance ventilation duct(s), passes through a fire resisting wall or fire resisting floor, or is built into a separating wall, the walls of the flue or duct should have a fire resistance of at least half that of the wall or floor in order to prevent the by-passing of the compartmentation (see Diagram 13). The walls enclosing the flue or duct should be of solid non-combustible construction.

Diagram HB13 - Flues in separating walls - Extract from TGD B Vol. 2

3.7.5 Fire-Stopping

In addition to any other provisions in this document for fire-stopping:

(a) joints between elements which serve as a barrier to the passage of fire should be fire-stopped; allowing for movement where appropriate.

(b) all openings for pipes, ducts, conduits or cables to pass through any part of an element which serves as a barrier to the passage of fire should be:

kept as few in number as possible, and
kept as small as practicable, and
fire-stopped (which in the case of a pipe or ducts, should allow thermal movement).(see also Section 1, 1.3.9.3

Notes

1. A non-combustible material (such as cast iron or steel) which, if exposed to a temperature of 800°C will neither soften nor fracture to the extent that flame or hot gases will pass through the wall of the pipe.

2. PVCu pipes complying with I.S. EN 13291:2014, BS 4514: 2001 and BS 5255: 1989

3. no pipes, wires or other services are allowed to pass through or breach separating walls.(See 3.5.4.4)

3.7.6 Displacement

To prevent displacement, materials used for fire-stopping should be reinforced with (or supported by) materials of limited combustibility in the following circumstances:

(a) in all cases where the unsupported span is greater than 100 mm, and

(b) in any other case where non-rigid materials are used (unless they have been shown to be satisfactory by test)

3.7.7 Proprietary Seals

Proprietary sealing systems (including those designed for service penetrations) which have been shown by test to maintain the fire resistance of the wall or other element are available.

Other suitable fire-stopping materials are:

cement or lime mortar,
gypsum based plaster,
cement or gypsum based vermiculite/perlite mixes,
glass fibre, mineral wool, crushed rock, blast furnace slag or ceramic based products (with or without resin binders)
intumescent mastics.

These may be used only in situations which are suitable for the particular fire-stopping materials.

3.7.8 Further Guidance

Further information on the generic types of systems available, their suitability for different applications and guidance on test method is given in the Association for Specialist Fire Protection, (Red Book): “Fire Stopping and Penetration Seals for the Construction Industry”

Guidance on the process of design, installation and maintenance of passive fire protection is available in “Ensuring best practice for passive fire protection in buildings” produced by the Association for Specialist Fire Protection (ASFP).

B8 Internal Fire Spread (Structure)