Building regulations require 30 minutes fire resistance for the structure, increasing to 60 minutes where the number of storeys is four or more. Concrete and masonry do not burn and are the most common basement construction solution. In addition to fire resistance, means of escape is also a key design consideration for basements.
Fire resistance and separation
The basement is not counted when assessing the numbers of storeys for fire resistance and means of escape. Typically, for a two-storey house over a basement, 30 minutes fire resistance is required for the structure, increasing to 60 minutes where the number of storeys is four or more. Both requirements are easily exceeded using concrete.
Fire separation between the basement and upper storeys is required if the height of the top floor is more than 4.5 metres above the lowest external ground level. This situation is only likely to occur in two-storey dwellings if the basement floor level is less than 1.2m below the external ground level, or located on a very sloping site. The 30-minute separation required can be simply and cost effectively achieved using concrete.
The walls and floor between garage and house requires 30 minutes fire separation which also applies if located in a basement.
Ground floor flats or maisonettes with a basement level and direct main entrances require no fire separation over and above typical fire separation between apartments. Since concrete floor construction can easily provide the fire and acoustic separation needed for a separating floor, it can be possible to convert basements into separate dwellings, provided all the necessary fire escapes and ventilation etc. are provided, where such floors are utilised.
Please refer to Part B (Fire Safety) of our building regulations guide for further information. All information correct as of 2013 amendments.
Means of escape
Habitable rooms in basements require a safe means of leaving thevbuilding. This could be provided by the main stair of the house, provided it is protected and is connected to a final exit. Alternatively, escape can be provided by an additional stair, leading to an alternative final exit. The stair can be internal, but more commonly external. Escape through windows is also permissible if designed to permit escape as defined by the building regulations. The last two options offer cost effective solutions, particularly in terms of optimising usable space, provided the external stair is positioned away from other windows.
It is worth noting that non-habitable rooms, such as kitchens, utility rooms and bathrooms can be classed as inner-rooms and, depending upon the layout, may not require separate means of escape.
It is permissible to exit into gardens or courtyards, provided they have an exit to a place of safety or are at least as long as the height of the house.