The direct answer: BS 476 Class 0 is legacy terminology. It is no longer the current reaction-to-fire classification route in Approved Document B for new building work in England, subject to the published transitional arrangements.
Current specifications should use the appropriate European classification under BS EN 13501-1. An old Class 0 result cannot simply be renamed or converted into Class B.
Current England position: UK Government — removal of National Classes.
01 · The legacy classification
What did Class 0 actually mean?
Class 0 was the highest National product-performance designation used by Approved Document B for wall and ceiling linings. It was not a classification awarded by one individual British Standard test.
A material could achieve Class 0 if it was composed throughout of materials of limited combustibility, or if it met the following requirements:
A surface-spread-of-flame test. The product first needed the required Class 1 result under the test conditions.
A fire-propagation test. Class 0 used limits for the overall index I and the initial sub-index i1.
The historic criteria required a Class 1 surface-spread result, an overall fire-propagation index I not exceeding 12 and a sub-index i1 not exceeding 6.
Class 0 described how a surface contributed to fire growth and flame spread. It did not mean that timber would maintain loadbearing capacity, integrity or insulation for 30 or 60 minutes. Those are fire-resistance properties of a tested construction or building element.
02 · The current classification route
Did Class B replace Class 0?
Not directly. Approved Document B in England now uses the European reaction-to-fire classification system under BS EN 13501-1.
There is no automatic one-line conversion
Older guidance often displayed Class 0 alongside a Euroclass such as B-s3,d2, but the national and European systems use different test methods and classification rules. A Class 0 result should not simply be renamed as a Euroclass. Evidence must come from the appropriate test and classification route for the product and end-use.
View BSI’s BS EN 13501-1 overview →A1, A2, B, C, D, E or F, determined through the applicable European test and classification framework.
s1, s2 or s3 where included, describing smoke-production performance within the classification.
d0, d1 or d2 where included, addressing flaming droplets or particles within the classification.
Further information: Approved Document B and BSI — the changing status of BS 476.
03 · Current internal-lining requirements
Which European classification does wood need?
The required classification depends mainly on where the timber is used. For internal wall and ceiling linings in buildings other than dwellings, Approved Document B generally identifies:
For small rooms with an internal floor area no greater than 30m².
For other rooms, including garages.
For circulation spaces, including corridors and escape routes.
These are minimum classifications within the guidance. A project specification, fire strategy, insurer or approving authority may require a higher classification.
Requirements for external walls, structural fire resistance and other specialist uses are separate and should not be confused with these internal-lining classifications.
04 · Timber classification evidence
Can treated timber automatically be described as Class B?
No. A fire-retardant treatment can improve the reaction-to-fire performance of timber, but the classification must be supported by evidence covering the relevant timber-and-treatment system.
The evidence may need to cover
- Timber species and density
- Thickness and profile
- Surface finish
- Treatment product and application rate
- Substrate or backing
- Air gaps and fixing method
- Internal or external use
- The permitted field of application
A classification achieved by one tested timber-and-treatment combination should not automatically be applied to every type of wood or installation.
05 · Older specifications and reports
What should you do if a specification asks for Class 0?
Do not automatically replace the words “Class 0” with “Class B.” Ask the person responsible for the specification to confirm the current performance requirement and the evidence expected.
A useful question to send
“Please confirm the required BS EN 13501-1 reaction-to-fire classification and whether the requirement applies to the timber product, its surface treatment or the complete installed construction.”
An old Class 0 report cannot simply be rewritten as a Class B classification. It may remain useful as a historical record, but whether it is acceptable for an existing building or transitional project must be determined for that particular situation.
This guide describes Approved Document B guidance for England. Scotland, Wales and Northern Ireland have their own building standards or guidance.
06 · Common questions
Class 0 questions
Is Class 0 still a current fire classification for wood?+
Class 0 is legacy National terminology. It is no longer the current reaction-to-fire specification route in Approved Document B for new building work in England, subject to transitional arrangements.
Is Class 0 the same as B-s3,d2?+
No. Older guidance sometimes listed them as alternative National and European specification routes, but also stated that the classifications did not automatically equate.
What replaced Class 0?+
Current Approved Document B guidance uses European reaction-to-fire classifications under BS EN 13501-1. The required class depends on the location and application.
Does all internal timber need Class B?+
No. Approved Document B generally identifies C-s3,d2 for wall and ceiling linings in ordinary rooms and B-s3,d2 for circulation spaces. Certain small non-residential rooms may use D-s3,d2.
Is Class B the same as 30- or 60-minute fire protection?+
No. Class B is a reaction-to-fire classification. Thirty- and sixty-minute ratings relate to fire resistance and use different standards and construction details.
Can treated timber automatically be described as Class B?+
No. The classification must be supported by appropriate evidence covering the timber, treatment and intended application.
What should I do with an old specification asking for Class 0?+
Ask the person responsible for the specification to confirm the required BS EN 13501-1 classification and the evidence expected for the project.