Loft Conversions
D.1 In the case of an existing single storey dwelling house to which a storey is to be added by converting the existing roof space into habitable accommodation, the converted dwelling house should comply with the provisions of 1.3.2.
In the case of an existing two storey dwelling house to which a storey is to be added by converting the existing roof space into habitable accommodation, the converted dwelling house should comply with the provisions of 1.3.3.
D.2 The following provisions D2.1 - D2.5 can only be applied as an alternative to those in 1.3.3 where the new second storey accommodation does not;
(a) exceed 50 m2 in area; or
(b) contain more than two habitable rooms.
Enclosure of existing stairway
D.2.1 The stairway in the ground and first storeys should be enclosed with walls and/or partitions which are fire-resisting,(see Appendix A) and the enclosure should either:
(a) extend to a final exit (Diagram 2(a)); or
(b) give access to at least two escape routes at ground level, each delivering to final exits and separated from each other by fire-resisting construction and self-closing fire doors (Diagram 2(b)).
New Stairway to additional storey
D.2.2 The new storey should be served by a Stairway meeting the provisions in Technical Guidance Document K - Stairways, Ladders, Ramps and Guards, 2014. The new stairway should be contained within an enclosure which is formed by extending the existing enclosure in fire resisting construction so that the new accommodation is separated from the existing stairway. Two alternative approaches are given in (a) and (b) below:
(a) The new stairway may rise over the existing stairway and within the same enclosure, in which case the stairway should be separated from the new room(s) by a self-closing fire door set in fire resisting construction;
(b) The new stairway may alternatively rise from the existing room, in which case the new stairway should be separated from the existing room and the rest of the dwelling house by fireresisting construction extending to the stairway enclosure with a self-closing fire door at the top or bottom of the new stairway.
Doorways
D.2.3 All doorways within the stairway enclosure to habitable rooms and cupboards should be fitted with a self-closing fire door where possible, or as a minimum with a self-closing fire door leaf or leaves in the existing frame. (See Appendix B)
Note: If the existing doors are considered to be of historical or architectural merit it may be possible to retain the doors or upgrade them to an acceptable standard.
Glazing
D 2.4 Any glazing in the enclosure to the existing stairway, including glazing in doors (whether or not they need to be fire doors), should be fire-resisting. There should be no openable glazed sections or other ventilation openings in the enclosure to the stairway.
This requirement does not apply to windows or external doors within the stairway enclosure.
Floors in Domestic Loft Conversions
D 2.5 The new storey should be separated from the rest of the dwelling house by fireresisting construction.
In altering an existing two storey dwelling house it would be reasonable to provide a modified 30 minute standard of fire resistance to the existing and new floors.
Note: “Modified 30 minute” standard satisfies the test criteria for the full 30 minutes in respect of loadbearing capacity, but allows reduced performances for integrity and insulation (see Table A1, item 3(a)).
Fire resistance of timber floors in existing dwelling houses
D3 In an existing dwelling house floors may be required to be 30 minute fire resistance (as per Table A1).
The techniques generally adopted to upgrade the fire resistance of timber floors are as follows:
(a) The addition of a fire-resisting layer, or layers, beneath the existing floor joists. There are many techniques and materials available for such purposes. In some cases it is also necessary to provide a protective layer on top of the existing floor-boards or between the floor joists.
(b) Filling the voids between the existing floor surface and ceiling below, or between the floor joists, with a suitable material. There are a number of proprietary systems available which are based on this method. These are often more appropriate than the method outlined at (a) above in buildings of historic or architectural interest, where existing plasterwork is to be retained.
Many of the techniques employed in upgrading timber floors involve the use of proprietary materials and systems. These must be capable of achieving the required performance in the situations for which they are adopted. Particular care and attention to detail in the execution of any such upgrading works is necessary to ensure the required performance.
Table 14 of Building Research Establishment Report "Guidelines for the construction of fire resisting structural elements (BR 128 1988)" provides guidance in relation to the construction of fire-resisting timber floors.
Guidance on fire-resisting timber floors is also available from the Timber Research and Development Association (TRADA) and in the trade literature produced by manufacturers of fire protection materials and products.
Guidance on upgrading the fire resistance of existing timber floors is provided in Building Research Digest number 208 "Increasing the fire resistance of existing timber floors (revised 1988)".
Escape windows
D.4 The room (or rooms) in the new storey should each have an openable window or roof-light for escape or rescue purposes which meets the relevant provisions in 1.3.7.
Fire detection and alarm systems
D.5 Automatic smoke detection and alarms should be provided throughout the dwelling house in accordance with the provisions contained in Section 1.3.6. The above requirements may be met by the provision of radio interconnected smoke and heat alarms, each incorporating a ten year battery.
External Fire Spread
D.6 Particular attention should be given to the provisions in Section 4: External Fire Spread, which provide for space separation to existing buildings, namely 4.5.9 Material alteration of existing building and 4.5.10 Material change of use of existing building.
