Publication - Advice and guidance

Building standards technical handbook 2019: non-domestic

The building standards technical handbooks provide guidance on achieving the standards set in the Building (Scotland) Regulations 2004. This handbook applies to a building warrant submitted on or after 1 October 2019 and to building work which does not require a warrant commenced from that date.

Building standards technical handbook 2019: non-domestic
2. Fire

2.6 Spread to neighbouring buildings

Mandatory Standard

Standard 2.6

Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the spread of fire to neighbouring buildings is inhibited.

2.6.0 Introduction

In order to reduce the danger to the occupants of other buildings, one building should be isolated from another by either construction or distance. The distance between a building and its relevant boundary is dictated by the amount of heat that is likely to be generated in the event of fire. Generally, this will be influenced by how the building is used, compartmented (see guidance to Standard 2.1), separated (see guidance to Standard 2.2) and the extent of any openings or other unprotected areas in the external wall of the building.

The guidance for fire spread to neighbouring buildings should not be assessed in isolation and reference should be made to the guidance to Standard 2.4 for fire spread in cavities and the guidance to Standard 2.7 for fire spread on external walls.

Conversions - in the case of conversions, as specified in regulation 4, the building as converted shall meet the requirements of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion (regulation 12, schedule 6).

2.6.1 Fire resistance of external walls

External walls should have at least the fire resistance duration as shown in the table below, apart from the amount of unprotected area set out in clause 2.6.2. For guidance on automatic fire suppression systems, see clause 2.1.2.

The installation of an automatic fire suppression system greatly reduces the amount of radiant heat flux from a fire through an unprotected opening and this is recognised in the table to clause 2.6.1 and in the guidance to clause 2.6.2.

Table 2.6. Recommended fire resistance duration of external walls (see annex 2.D)

Use of building Not more than 1m from the boundary More than 1m from the boundary
No fire suppression system Fire suppression system No fire suppression system Fire suppression system
Assembly building Medium Medium [2c] Medium [1, 2c] None
Entertainment building Medium Medium [2b] Medium [2b] Medium [1]
Factory and Storage building Medium Medium Medium [3] Medium [1, 4]
Residential building (other than a residential care building or hospital) Medium Medium [2b] Medium [1, 2b] None
Residential care building and hospital Medium Medium Medium None
Shop Medium Medium [2a] Medium [2a] Medium [1]
Office Medium Medium [2d] Medium [1, 2d] None
Open sided car park Short Short None None


Additional information:

  1. Short fire resistance duration is sufficient where the building is single-storey.

  2. Short fire resistance duration is sufficient where the building is a multi-storey building and the area of any compartment does not exceed: (a) 500m2 (b) 1000m2 (c) 1500m2 (d) 2000m2 (e) 3000m2 and (f) 4000m2.

  3. Short fire resistance duration is sufficient where the building is a factory (Class 2), and is single-storey.

  4. No fire resistance duration is necessary where the building is a factory (Class 2).

2.6.2 Unprotected area

An unprotected area means any part of an external wall (including a door or window opening) which does not attain the appropriate fire resistance duration recommended in the table to clause 2.6.1.

An unprotected area does not include a fixed unopenable window where the frame and glazing has the appropriate fire resistance duration. Any wallhead fascia, soffit or barge board, or any cavity vents or solum vents may also be excluded from the unprotected area calculation.

Up to 500mm from boundary - where the external wall of a building is not more than 500mm from the boundary there should be no unprotected area, other than any wallhead fascia, soffit or barge board, or any cavity vents or solum vents.

500m to 1m from boundary - where the external wall of a building is more than 500mm but not more than 1m from the boundary, the level of unprotected area is limited to:

  1. the external wall of a protected zone

  2. an area of not more than 0.1m2, which is at least 1.5m from any other unprotected area in the same wall

  3. an area of not more than 1m2, which is at least 4m from any other unprotected area in the same wall (the 1m2 unprotected area may consist of two or more smaller areas which when combined do not exceed an aggregate area of 1m2).

More than 1m from boundary - where the external wall of a building is more than 1m from the boundary, the minimum distance to the boundary may vary with the amount of unprotected area. This is derived from the use of the building and can be calculated by:

  • the Enclosing Rectangle (Geometric) Method as set out in clause 2.6.3, or

  • the Building Research Establishment Report ‘External fire spread: building separation and boundary distances’ (1991, BR 187), or

  • The simple Geometry method - if the building is a factory (Class 2), a residential building, an assembly building or an office and is not more than 9m in height and the length of any side facing the boundary is not more than 24m, the unprotected area (in square metres) is six times the distance (in m) to the boundary. For example, if the unprotected area is 6m2, the distance to the boundary should be at least 1m and if the unprotected area is 12m2, the distance should be at least 2m and so on. If the distance to the boundary is 6m or more, the amount of unprotected area is unlimited.

2.6.3 The Enclosing Rectangle Method

The Enclosing Rectangle Method can be applied to a building or compartment more than 1m from the boundary using the Step by Step Guide below. The minimum distance from the boundary may be arrived at by interpolation between the percentages shown in the tables.

Table A should be used for storage buildings, factories (Class 1), shops, and entertainment buildings.

Table B should be used for residential buildings, offices, assembly buildings, and factories (Class 2). Table B should also be used for domestic buildings which exceed the limitations described in clause 2.6.3 of the Technical Handbook for domestic buildings.

Automatic Fire Suppression system - where the building or compartment is a shop, entertainment building, factory (Class 1) or a storage building, Table B may be used instead of Table A provided the building:

  • is located more than 1m from the relevant boundary, and

  • an automatic fire suppression system is installed (see clause 2.1.2) within the building.

Open sided car parks - there is no limitation on the amount of unprotected area for an open sided car park provided the external wall is more than 1m from the boundary.

Step by step guide to Enclosing Rectangle Method

Step 1 - establish a plane of reference which is the most favourable for the side of the building under consideration and which:

  1. touches all or part of the side

  2. however far extended, does not pass within the building, but may pass through projections such as a balcony or coping, and

  3. does not cross the relevant boundary.

Normally it will be best for the plane of reference to be roughly parallel to the relevant boundary. Where the boundary distance has not been set, an assumed relationship with the relevant boundary should be made.

Figure 2.3. Enclosing Rectangle Method

Enclosing Rectangle Method

Step 2 - on the plane of reference, and at right angles to it, project lines marking those proposed unprotected areas which are 80o or less to the plane of reference. Any external side of a building which makes an angle of more than 80° with the plane of reference can be ignored in the calculation of unprotected area.

Step 3 - construct a rectangle which encloses all the unprotected areas projected onto the plane of reference following the diagrams below. See also clause 2.6.3 for combustible cladding.

Figure 2.4. Diagram 2A - Setting Rectangle; Diagram 2B - 2D Determing size of rectangle

Diagram 2A - Setting Rectangle; Diagram 2B - 2D Determing size of rectangle

Step 4 - from the relevant table according to the use of the building or compartment, select an enclosing rectangle which is equal to, or next greater in both height and width to, the rectangle constructed under step 3. Compartmentation of the building can reduce the size of the enclosing rectangle in accordance with the diagrams below. The tables provide for enclosing rectangles of 3, 6, 9, 12, or 15m high, with widths in steps from 3m to no limit.

Figure 2.5. Diagram 3A Uncompartmented; Diagram 3B Compartmented; Diagram 3C Compartmented

Diagram 3A Uncompartmented; Diagram 3B Compartmented; Diagram 3C Compartmented

Step 5 - from the unprotected areas projected under step 2:

  1. calculate their total area, and

  2. express this total area as a percentage of the enclosing rectangle. This gives the unprotected percentage.

Step 6 - proceed to steps 7 to 9 where the boundary distance has been set, or steps 10 to 12 where it has not.

To find the maximum unprotected area for a given boundary position.

Step 7 - from the tables below find the unprotected percentage allowed for the distance from the relevant boundary. This distance relates to the plane of reference and not the side of the building, unless they coincide.

Step 8 - where the proposed total unprotected area relative to the size of the enclosing rectangle exceeds the allowable unprotected percentage for that distance, the design should be modified until an allowable unprotected percentage is established, and

Step 9 - repeat the process for all sides of the building situated more than 1m from any point on the relevant boundary.

To find the nearest position of the boundary for a given building:

Step 10 - from the tables below, find the minimum allowable distance for the unprotected percentage. This distance relates to the plane of reference and not the side of the building, unless they coincide.

Step 11 - repeat the process for all sides of the building, and

Step 12 - where these minimum distances are superimposed upon a plan of the building, a zone around the building is established upon which a boundary should not encroach.

Table 2.7. Table A: Storage buildings, factories (Class 1), shops and entertainment buildings

Height of enclosing rectangle (m) Width of enclosing rectangle (m) Minimum distance from relevant boundary (m) for unprotected percentage not more than:
20% 30% 40% 50% 60% 70% 80% 90% 100%
3 3 1.0 1.5 2.0 2.0 2.5 2.5 2.5 3.0 3.0
3 6 1.5 2.0 2.5 3.0 3.0 3.5 3.5 4.0 4.0
3 9 1.5 2.5 3.0 3.5 4.0 4.0 4.5 5.0 5.0
3 12 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 5.5
3 15 2.0 2.5 3.5 4.0 4.5 5.0 5.5 6.0 6.0
3 18 2.0 2.5 3.5 4.0 5.0 5.0 6.0 6.5 6.5
3 21 2.0 3.0 3.5 4.5 5.0 5.5 6.0 6.5 7.0
3 24 2.0 3.0 3.5 4.5 5.0 5.5 6.0 7.0 7.5
3 27 2.0 3.0 4.0 4.5 5.5 6.0 6.5 7.0 7.5
3 30 2.0 3.0 4.0 4.5 5.5 6.0 6.5 7.5 8.0
3 40 2.0 3.0 4.0 5.0 5.5 6.5 7.0 8.0 8.5
3 50 2.0 3.0 4.0 5.0 6.0 6.5 7.5 8.0 9.0
3 60 2.0 3.0 4.0 5.0 6.0 7.0 7.5 8.5 9.5
3 80 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 9.5
3 no limit 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0
 
6 3 1.5 2.0 2.5 3.0 3.0 3.5 3.5 4.0 4.0
6 6 2.0 3.0 3.5 4.0 4.5 5.0 5.5 5.5 6.0
6 9 2.5 3.5 4.5 5.0 5.5 6.0 6.0 7.0 7.0
6 12 3.0 4.0 5.0 5.5 6.5 7.0 7.5 8.0 8.5
6 15 3.0 4.5 5.5 6.0 7.0 7.5 8.0 9.0 9.0
6 18 3.5 4.5 5.5 6.5 7.5 8.0 9.0 9.5 10.0
6 21 3.5 5.0 6.0 7.0 8.0 9.0 9.5 10.0 10.5
6 24 3.5 5.0 6.0 7.0 8.5 9.5 10.0 10.5 11.0
6 27 3.5 5.0 6.5 7.5 8.5 9.5 10.5 11.0 12.0
6 30 3.5 5.0 6.5 8.0 9.0 10.0 11.0 12.0 12.5
6 40 3.5 5.5 7.0 8.5 10.0 11.0 12.0 13.0 14.0
6 50 3.5 5.5 7.5 9.0 10.5 11.5 13.0 14.0 15.0
6 60 3.5 5.5 7.5 9.5 11.0 12.0 13.5 15.0 16.0
6 80 3.5 6.0 7.5 9.5 11.5 13.0 14.5 16.0 17.5
6 100 3.5 6.0 8.0 10.0 12.0 13.5 15.0 16.5 18.0
6 120 3.5 6.0 8.0 10.0 12.0 14.0 15.5 17.0 19.0
6 no limit 3.5 6.0 8.0 10.0 12.0 14.0 16.0 18.0 19.0
 
9 3 1.5 2.5 3.0 3.5 4.0 4.0 4.5 5.0 5.0
9 6 2.5 3.5 4.5 5.0 5.5 6.0 6.5 7.0 7.0
9 9 3.5 4.5 5.5 6.0 6.5 7.5 8.0 8.5 9.0
9 12 3.5 5.0 6.0 7.0 7.5 8.5 9.0 9.5 10.5
9 15 4.0 5.5 6.5 7.5 8.5 9.5 10.0 11.0 11.5
9 18 4.5 6.0 7.0 8.5 9.5 10.0 11.0 12.0 12.5
9 21 4.5 6.5 7.5 9.0 10.0 11.0 12.0 13.0 13.5
9 24 5.0 6.5 8.0 9.5 11.0 12.0 13.0 13.5 14.5
9 27 5.0 7.0 8.5 10.0 11.5 12.5 13.5 14.5 15.0
9 30 5.0 7.0 9.0 10.5 12.0 13.0 14.0 15.0 16.0
9 40 5.5 7.5 9.5 11.5 13.0 14.5 15.5 17.0 17.5
9 50 5.5 8.0 10.0 12.5 14.0 15.5 17.0 18.5 19.5
9 60 5.5 8.0 11.0 13.0 15.0 16.5 18.0 19.5 21.0
9 80 5.5 8.5 11.5 13.5 16.0 17.5 19.5 21.5 23.0
9 100 5.5 8.5 11.5 14.5 16.5 18.5 21.0 22.5 24.5
9 120 5.5 8.5 11.5 14.5 17.0 19.5 21.5 23.5 26.0
9 no limit 5.5 8.5 11.5 15.0 17.5 20.0 22.5 24.5 27.0
 
12 3 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 5.5
12 6 3.0 4.0 5.0 5.5 6.5 7.0 7.5 8.0 8.5
12 9 3.5 5.0 6.0 7.0 7.5 8.5 9.0 9.5 10.5
12 12 4.5 6.0 7.0 8.0 9.0 9.5 11.0 11.5 12.0
12 15 5.0 6.5 8.0 9.0 10.0 11.0 12.0 13.0 13.5
12 18 5.0 7.0 8.5 10.0 11.0 12.0 13.0 14.0 14.5
12 21 5.5 7.5 9.0 10.5 12.0 13.0 14.0 15.0 16.0
12 24 6.0 8.0 9.5 11.5 12.5 14.0 15.0 16.0 16.5
12 27 6.0 8.0 10.5 12.0 13.5 14.5 16.0 17.0 17.5
12 30 6.5 8.5 10.5 12.5 14.0 15.0 16.5 17.5 18.5
12 40 6.5 9.5 12.0 14.0 15.5 17.5 18.5 20.0 21.0
12 50 7.0 10.0 13.0 15.0 17.0 19.0 20.5 23.0 23.0
12 60 7.0 10.5 13.5 16.0 18.0 20.0 21.5 23.5 25.0
12 80 7.0 11.0 14.5 17.0 19.5 21.5 23.5 26.0 27.5
12 100 7.5 11.5 15.0 18.0 21.0 23.0 25.5 28.0 30.0
12 120 7.5 11.5 15.0 18.5 22.0 24.0 27.0 29.5 31.5
12 no limit 7.5 12.0 15.5 19.0 22.5 25.0 28.0 30.5 34.0
 
15 3 2.0 2.5 3.5 4.0 4.5 5.0 5.5 6.0 6.0
15 6 3.0 4.5 5.5 6.0 7.0 7.5 8.0 9.0 9.0
15 9 4.0 5.5 6.5 7.5 8.5 9.5 10.0 11.0 11.5
15 12 5.0 6.5 8.0 9.0 10.0 11.0 12.0 13.0 13.5
15 15 5.5 7.0 9.0 10.0 11.5 12.5 13.5 14.5 15.0
15 18 6.0 8.0 9.5 11.0 12.5 13.5 14.5 15.5 16.5
15 21 6.5 8.5 10.5 12.0 13.5 14.5 16.0 16.5 17.5
15 24 6.5 9.0 11.0 13.0 14.5 15.5 17.0 18.0 19.0
15 27 7.0 9.5 11.5 13.5 15.0 16.5 18.0 19.0 20.0
15 30 7.5 10.0 12.0 14.0 16.0 17.0 18.5 20.0 21.0
15 40 8.0 11.0 13.5 16.0 18.0 19.5 21.0 22.5 23.5
15 50 8.5 12.0 15.0 17.5 19.5 21.5 23.0 25.0 26.0
15 60 8.5 12.5 15.5 18.0 21.0 23.5 25.0 27.0 28.0
15 80 9.0 13.5 17.0 20.0 23.0 25.5 28.0 30.0 31.5
15 100 9.0 14.0 18.0 21.5 24.5 27.5 30.0 32.5 34.5
15 120 9.0 14.0 18.5 22.5 25.5 28.5 31.5 34.5 37.0
15 no limit 9.0 14.5 19.0 23.0 27.0 30.0 34.0 36.0 39.0


Additional information:

  1. The minimum distance from the boundary may be arrived at by interpolation between the percentages shown.

Table 2.8. Table B: Residential buildings, offices, assembly buildings and factories (Class 2)

Height of enclosing rectangle (m) Width of enclosing rectangle (m) Minimum distance from relevant boundary (m) for unprotected percentage not more than:
20% 30% 40% 50% 60% 70% 80% 90% 100%
3 3 1.0 1.0 1.0 1.5 1.5 1.5 2.0 2.0 2.0
3 6 1.0 1.0 1.5 2.0 2.0 2.0 2.5 2.5 3.0
3 9 1.0 1.5 1.5 2.0 2.5 2.5 3.0 3.0 3.5
3 12 1.0 1.5 2.0 2.0 2.5 3.0 3.0 3.5 3.5
3 15 1.0 1.5 2.0 2.5 2.5 3.0 3.5 3.5 4.0
3 18 1.0 1.5 2.0 2.5 2.5 3.0 3.5 4.0 4.0
3 21 1.0 1.5 2.0 2.5 3.0 3.0 3.5 4.0 4.5
3 24 1.0 1.5 2.0 2.5 3.0 3.5 3.5 4.0 4.5
3 27 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.0 4.5
3 30 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.0 4.5
3 no limit 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.0 5.0
 
6 3 1.0 1.0 1.5 2.0 2.0 2.0 2.5 2.5 3.0
6 6 1.0 1.5 2.0 2.5 3.0 3.0 3.5 4.0 4.0
6 9 1.0 2.0 2.5 3.0 3.5 4.0 4.5 4.5 5.0
6 12 1.5 2.5 3.0 3.5 4.0 4.5 5.0 5.0 5.5
6 15 1.5 2.5 3.0 4.0 4.5 5.0 5.5 5.5 6.0
6 18 1.5 2.5 3.5 4.0 4.5 5.0 5.5 6.0 6.5
6 21 1.5 2.5 3.5 4.0 5.0 5.5 6.0 6.5 7.0
6 24 1.5 2.5 3.5 4.5 5.0 5.5 6.0 7.0 7.0
6 27 1.5 2.5 3.5 4.5 5.0 6.0 6.5 7.0 7.5
6 30 1.5 2.5 3.5 4.5 5.0 6.0 6.5 7.0 8.0
6 40 1.5 2.5 3.5 4.5 5.5 6.5 7.0 8.0 8.5
6 50 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.0 9.0
6 60 1.5 2.5 3.5 5.0 5.5 6.5 7.5 8.5 9.5
6 80 1.5 2.5 3.5 5.0 6.0 7.0 7.5 8.5 9.5
6 no limit 1.5 2.5 3.5 5.0 6.0 7.0 8.0 8.5 10.0
 
9 3 1.0 1.0 1.5 2.0 2.5 2.5 3.0 3.0 3.5
9 6 1.0 2.0 2.5 3.0 3.5 4.0 4.5 4.5 5.0
9 9 1.5 2.5 3.5 4.0 4.5 5.0 5.5 5.5 6.0
9 12 1.5 3.0 3.5 4.5 5.0 5.5 6.0 6.5 7.0
9 15 2.0 3.0 4.0 5.0 5.5 6.0 6.5 7.0 7.5
9 18 2.0 3.5 4.5 5.0 6.0 6.5 7.0 8.0 8.5
9 21 2.0 3.5 4.5 5.5 6.5 7.0 7.5 8.5 9.0
9 24 2.0 3.5 5.0 5.5 6.5 7.5 8.0 9.0 9.5
9 27 2.0 3.5 5.0 6.0 7.0 7.5 8.5 9.5 10.0
9 30 2.0 3.5 5.0 6.0 7.0 8.0 9.0 9.5 10.5
9 40 2.0 3.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5
9 50 2.0 4.0 5.5 6.5 8.0 9.0 10.0 11.5 12.5
9 60 2.0 4.0 5.5 7.0 8.0 9.5 11.0 11.5 13.0
9 80 2.0 4.0 5.5 7.0 8.5 10.0 11.5 12.5 13.5
9 100 2.0 4.0 5.5 7.0 8.5 10.0 11.5 12.5 14.5
9 120 2.0 4.0 5.5 7.0 8.5 10.0 11.5 12.5 14.5
9 no limit 2.0 4.0 5.5 7.0 8.5 10.5 12.0 12.5 15.0
 
12 3 1.0 1.5 2.0 2.0 2.5 3.0 3.0 3.5 3.5
12 6 1.5 2.5 3.0 3.5 4.0 4.5 5.0 5.0 5.5
12 9 1.5 3.0 3.5 4.5 5.0 5.5 6.0 6.5 7.0
12 12 1.5 3.5 4.5 5.0 6.0 6.5 7.0 7.5 8.0
12 15 2.0 3.5 5.0 5.5 6.5 7.0 8.0 8.5 9.0
12 18 2.5 4.0 5.0 6.0 7.0 7.5 8.5 9.0 10.0
12 21 2.5 4.0 5.5 6.5 7.5 8.5 9.0 10.0 10.5
12 24 2.5 4.5 6.0 7.0 8.0 8.5 9.5 10.5 11.5
12 27 2.5 4.5 6.0 7.0 8.0 9.0 10.5 11.0 12.0
12 30 2.5 4.5 6.5 7.5 8.5 9.5 10.5 11.5 12.5
12 40 2.5 5.0 6.5 8.0 9.5 10.5 12.0 13.0 14.0
12 50 2.5 5.0 7.0 8.5 10.0 11.0 13.0 14.0 15.0
12 60 2.5 5.0 7.0 9.0 10.5 12.0 13.5 14.5 16.0
12 80 2.5 5.0 7.0 9.0 11.0 13.0 14.5 16.0 17.0
12 100 2.5 5.0 7.5 9.5 11.5 13.5 15.0 16.5 18.0
12 120 2.5 5.0 7.5 9.5 11.5 13.5 15.0 17.0 18.5
12 no limit 2.5 5.0 7.5 9.5 12.0 14.0 15.5 17.0 19.0
 
15 3 1.0 1.5 2.0 2.5 2.5 3.0 3.5 3.5 4.0
15 6 1.5 2.5 3.0 4.0 4.5 5.0 5.5 5.5 6.0
15 9 2.0 3.0 4.0 5.0 5.5 6.0 6.5 7.0 7.5
15 12 2.0 3.5 5.0 5.5 6.5 7.0 8.0 8.5 9.0
15 15 2.0 4.0 5.5 6.5 7.0 8.0 9.0 9.5 10.0
15 18 2.5 4.5 6.0 7.0 8.0 8.5 9.5 10.5 11.0
15 21 2.5 5.0 6.5 7.5 8.5 9.5 10.5 11.0 12.0
15 24 3.0 5.0 6.5 8.0 9.0 10.0 11.0 12.0 13.0
15 27 3.0 5.5 7.0 8.5 9.5 10.5 11.5 12.5 13.5
15 30 3.0 5.5 7.5 8.5 10.0 11.0 12.0 13.5 14.0
15 40 3.0 6.0 8.0 9.5 11.0 12.5 13.5 15.0 16.0
15 50 3.5 6.0 8.5 10.0 12.0 13.5 15.0 16.5 17.5
15 60 3.5 6.5 8.5 10.5 12.5 14.0 15.5 17.0 18.0
15 80 3.5 6.5 9.0 11.0 13.5 15.0 17.0 18.5 20.0
15 100 3.5 6.5 9.0 11.5 14.0 16.0 18.0 19.5 21.5
15 120 3.5 6.5 9.0 11.5 14.0 16.5 18.5 20.5 22.5
15 no limit 3.5 6.5 9.0 12.0 14.5 17.0 19.0 21.0 23.0

Additional information:

  1. The minimum distance from the boundary may be arrived at by interpolation between the percentages shown.

2.6.4 External wall cladding

External wall cladding includes all non load-bearing external wall cladding systems attached to the structure, for example, composite panels, clay or concrete tiles, slates, pre-cast concrete panels, stone panels, masonry, profiled metal sheeting including sandwich panels, timber panels, weather boarding, thermally insulated external wall rendered systems, glazing systems and other ventilated cladding systems. For the purposes of compliance with Standard 2.6, external wall cladding includes spandrel panels and infill panels.

Not more than 1m from a boundary - External wall cladding not more than 1m from a boundary should have achieve a European Classification A1 or A2.

More than 1m from a boundary - Fire within the building may break-out through a window or door opening and as a consequence, the cladding, once ignited, would contribute to the heat generated from the fire. Therefore where the cladding is more than 1m from a boundary and is constructed from products more than 1mm thick with a European Classification B, C, D or E (as described in annex 2.E), the cladding should be included in the calculation of unprotected area.

See also guidance to Standards 2.4 and 2.7 for additional guidance on external wall cladding to buildings with a storey height more than 11m above ground and to entertainment and assembly buildings, residential care buildings and hospital buildings, regardless of storey height.

However combustible cladding need not be included in the calculation of unprotected area where:

  • the combustible cladding is attached to the structure of the building and the external wall contains no openings other than the small openings described in clause 2.6.2b, and

  • the wall behind the cladding (or the cladding itself) has the appropriate fire resistance duration from the inside.

In addition, a cavity formed by external wall cladding should be protected in accordance with the guidance to Standard 2.4 and fire spread on external walls in accordance with the guidance to Standard 2.7.

2.6.5 Detached buildings in the same occupation

Notional Boundary - there may be a risk of fire spread between buildings even when on land in the same occupation. A notional boundary therefore is used to determine the safe distance between buildings or compartments in this situation. In order to establish whether a notional boundary calculation is necessary, the size of the opposing buildings or compartments should be established first (see diagram below).

For example, in the diagram, where the combined area of building A plus building B exceeds the maximum allowable area of any compartment as set in the tables to clause 2.1.1, then a notional boundary calculation is necessary. The designer is free to set this notional boundary at any point between the 2 buildings under consideration and this distance will determine the amount of unprotected area. The buildings should be separated by a distance not less than the sum of the distances calculated in respect of each building relative to a notional boundary in accordance with clauses 2.6.1 and 2.6.2, as if the notional boundary were a boundary (see diagram below).

Opposing compartments - a notional boundary is also necessary in the case of a single building having opposing compartments externally.

The roofs of the buildings should be separated by a distance not less than the sum of the distances provided in relation to the notional boundary in accordance with the guidance to Standard 2.8 in respect of each roof.

New and existing buildings - where a notional boundary, described above, is to be established between 2 buildings, one of which is an existing building, for the purposes of this guidance, the existing building should be regarded as if it were a new building.

Figure 2.6. Notional Boundary

Notional Boundary

2.6.6 Combustibility

Every part of an external wall not more than 1m from a boundary should be constructed of products which achieve European Classification A1 or A2. This does not apply to insulation exposed in a cavity that is between 2 leaves of masonry or concrete at least 75mm thick, and which has a cavity barrier around all openings in the wall and at the top of the wall-head.

Also, in shared residential accommodation, a structural frame and any thermal insulation material in the frame not more than 1m from a boundary may be constructed from combustible products provided:

  • no storey height is more than 18m, and

  • the recommendations in clauses 2.6.1 to 2.6.3 have been followed, and

  • any external wall cladding (see clause 2.6.4) is constructed from products which achieve European Classification A1 or A2.

See the guidance to Standards 2.4 and 2.7 for additional guidance in relation to cavities and external wall cladding systems.

2.6.7 Supporting structure

Where an element of structure provides support to an external wall (including external wall cladding) which has a fire resistance duration (as recommended in the guidance to clauses 2.6.1 and 2.6.2) the supporting element of structure should also have at least the same fire resistance duration.