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B1 – Fire safety


Part B1 of the Building Regulations covers fire safety. If your plans are being drawn up by an architectural technologist or an architect then they will ensure that this is taken care of.

Still, it helps to understand what the rules are about, especially in the context of eco building because in the UK the default wall construction method has usually been heavy masonry which generally performs well in fire (although of course floors and roofs are usually timber). All-timber construction can also meet the fire regulation standards but knowledge about how to do this is less available here, compared with most of northern Europe.

You can see the Approved Documents relating to the regulations, Part B volume 1 (Dwellinghouses)

The basic layout of the regulations follows the order:

  • Alarms  These need to be situated properly and have mains power supply with backup batteries etc. Wales may introduce sprinkler systems in 2013.
  • Means of escape This is about being able to get out of the house via a safe route
  • Internal fire spread (of lining materials). Different areas of walls and ceiling are allowed to spread fire at different rates
  • Internal fire spread (in the structure) Various parts of the structure have to resist fire for specific time periods
  • External fire spread  The possibility of fire spreading from one building to another has to be limited
  • Access and facilities for the fire service  Mainly about vehicular access around the building

The basis of the regulations

The following applies to England but Scotland, Northern Ireland and Wales use very similar principles.

The fire regulations are very sensible but they can have a massive effect on the design of a house in many ways. While alarms are a fairly easy issue to deal with, most of the other aspects can restrict design options quite seriously. The rules are very complex but rely on simple basic principles:

Fire detection and fire alarm systems

Section 1 is self explanatory

Means of escape

Section 2 mainly concerns being able to quickly get from a habitable room like a bedroom or living room, down the stairs and out without getting burnt or suffering from smoke on the way. Windows and doors used for escape have to be to certain sizes. So this entails that the escape route must be sufficiently fire proof and that smoke and fire should not enter this safe route from other rooms on the way.

For one and two storey houses the rules are fairly simple but above that the rules about protected areas and fire doors get quite involved. Gallery areas have special conditions and there are also conditions concerning the space you escape into (if it is an enclosed area). There are details on escape windows.

Internal fire spread (linings) 

Section 3 is about the speed at which fire can spread over surfaces such as walls and ceilings (but not floors). Wall and ceiling linings, such as plasterboard, timber boarding etc are classified for spread of flame and different classifications are allowed on different surfaces of rooms. There are special rules for thermoplastic roof lights and lighting diffusers.

Internal fire spread (structure)

Section 4  is about maintaining the stability of the structure of a house for a certain length of time during a fire.  It is very complicated indeed because it takes into account not only the height of the building but also the structural materials and how they are assembled. It can have a considerable influence on other factors such as thermal and acoustic insulation.


Section 5 concerns splitting buildings up in order to help prevent the spread of fire. With houses it mainly affects the party wall between houses (terrace houses or semis) and also the construction between a house and an integral or attached garage.

Concealed spaces (cavities)

Section 6. There is quite a big section on where cavity barriers need locating in order to prevent fire finding its way around a building. This also includes how to treat openings in cavity barriers. This is similar to but different from fire stopping (next section)

Fire stopping

This section is mainly about sealing holes and gaps where services such as pipes flues and electrics go through fire-separating elements.

External Walls

This section covers the fire resistance of the external walls including the external surfaces

Space separation

Section 9 . Fire can spread externally from building to building in two main ways. Radiant heat and flames from one wall can set fire to another wall if it is close enough or if the building materials allow it. It can also spread along adjacent roofs if the roofing materials allow. This section defines how close walls can be to site boundaries taking into consideration the building materials, and any unprotected areas such as windows.

Roof Coverings

Section 10. This is mainly about firebrands from a neighbouring fire landing on a roof. It includes how flammable the roof covering material is but not the supporting structure and also how far it is from the boundary. It also includes roof lights.

The Approved Documents

These are ‘standard’ ways of getting Building Regulations approval. There are other ways. see more

If you follow the principles and rules given in the documents you can be sure that they will be approved. Of course you don’t have to use the Approved Documents, as the Regulations make clear:

Approved Documents are intended to provide guidance for some of the more common building situations. However, there may well be alternative ways of achieving compliance with the requirements. Thus there is no obligation to adopt any particular solution contained in an Approved Document if you prefer to meet the relevant requirement in some other way.

In fact the Approved Documents are a bit of a mishmash of traditional ‘rules of thumb’ and technical standards and they have gaping holes in them. Whereas, for instance, there are many pages on how to construct traditional masonry walls, there is nothing about timber frame construction except the odd reference to British standards.

They are also struggling to keep up with the times. If the Passivhaus Standard or zero energy new house building is introduced at some point then whole swathes of the Approved Documents will need rewriting because many of the constructional principles are based on quite low levels of insulation.

There are other ways of satisfying the regulations. For instance they make copious references to BS, BS EN and BS EN ISO standards which may be another way of fulfilling the criteria. It is even possible in some very rare cases to prove that something works by building it first and then testing it afterwards (though this is not for the faint hearted).

Although a self builder cannot be expected to understand all the building regulations, it often pays to have a grasp of what is involved, especially if last minutes changes need to be made to construction details.

The full official set of Aproved Documents is available HERE.

See also: Chimneys, Fire Sprinkler Systems, Main Structure

Below is a direct link to the Gov.UK Approved Document, B1 – Fire safety (England).  (Document B2 concerns non-domestic buildings and is not covered here).

There is also the Building Regulations and Fire Safety Procedural Guidance.

Download (PDF, 2.88MB)

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