BUILDING CONTROL - THE THIRD ELEMENT
Steve Evans - Building Control Manager
We are all familiar with protecting elements of structure so that they have the required fire resistance.
This could include boarding out a ceiling to give the floor half hour fire resistance or encasing a beam over an opening. Likewise, we are familiar with enabling the means of escape by providing escape windows on the first floor or protecting the staircase to provide an escape route.
There is a third element to protecting the structure and providing means of escape which is taken for granted and almost included by default but nonetheless, just as important and critical if it is not right, and that is the ability of wall and ceiling linings to spread fire or “surface spread of flame” as it is more commonly known.
REQUIREMENT B2 OF THE BUILDING REGULATIONS
The choice of materials for ceilings and walls can significantly affect the spread of a fire even though it is not likely that they are the first to be ignited. This is particularly important in circulation spaces where if the linings allow the fire to spread rapidly the ability of the building occupants to escape could be seriously affected.
Requirement B2 of the Building Regulations asks that to inhibit the spread of fire all internal linings should therefore adequately resist the spread of flame over their surface and have, if ignited, a rate of fire growth or heat release which would be reasonable in the circumstances where they are being used.
Floors and stairs are excluded from the provisions contained in the Approved Document because it is felt that they are not significantly involved in a fire until it’s well developed and therefore do not play an important role in allowing the fire to spread in the early stages which is the critical time in allowing means of escape. Likewise, furniture and fittings are excluded because it would not be possible to control these through the building regulations.
The Approved Documents recommends that walls and ceilings should meet the classifications set out in the table above.
The National class relates to our own British Standard whilst the European Class relates to exactly what it says the European test. It is important to remember that if a material has been tested to a National Standard Class 1 it would not be able to be specified as a European Class C-s3, d2. In order to achieve a European Class it is tested under the European Standard as the two standards are not transferable.
For the purposes of the regulations a wall includes the surface of glazing (except in doors), parts of a ceiling that slope more than 70 degrees to the horizontal or any permanent cladding placed over the surface such as timber linings etc. A wall would not include:
- Doors, door frames, architraves, moulds, surrounds or skirtings
- Fireplace surrounds or mantle surrounds
- Wallpaper, paint or any other temporary covering.
A ceiling would include the surface of any glazing, any part of the wall which slopes at less than 70 degrees to the horizontal, the underside of a gallery or the underside of a roof exposed to the room below. Similar to a wall, a ceiling would not include:
- Trapdoors and frames
- Frames of windows or roof lights
- Architraves, mouldings, exposed beams or other similar narrow members.
The good news is, for most common linings or materials that are used in the industry there isn’t a problem. Exposed brickwork, block work, concrete, ceramic tiles and plasterboard all achieve a National Standard Class O and therefore meet the regulations easily for any location.
Timber, plywood, hardboard and wood particle board will all normally achieve a National Class 3. Therefore if it was proposed to use these in a room over 4m2 or in a circulation space to a dwelling it would be necessary to treat them with a suitable product to bring them up to the required National Class 1.
- All materials used to line walls and ceilings are required to limit the spread of fire to allow occupants time to escape the building
- Materials can be tested to National class or European Class and materials need to be tested to one or the other, there is no equivalence between classifications
- Brickwork, blockwork and plasterboard normally comply
- Timber cladding may need treating to allow its use in certain circumstance.