Facades & Fire Safety: Under 18? It’s all about classes and cavities
When deciding which route to take for fire safety compliance, one of the first things to check is how tall the building actually is, or more specifically, how far above ground level the top ‘habitable storey’ is. This is measured from the ground level on the lowest side of the building, to the floor surface on the tallest habitable storey (this term excludes roof-top or top storey plant areas).
If the highest habitable storey is lower than 18 metres from ground level then achieving compliance can actually be relatively straightforward. To ensure separation, a boundary is created using the building’s plot. If more than one building is located within a single plot then a notional boundary is created between the buildings using the spacing factors for the existing building. Similarly if the plot adjoins an area which is unlikely to be built on, such as a road, then the notional barrier can be expanded to the centre of this area.
Performance of External Surfaces or Walls
Once the boundary is drawn up, specifiers can select the façade and the insulation material that is to go within the cavity based on the following criteria:
- Where the distance to one or more boundary is less than 1 metre – The products must be rated Class 0, or Euroclass B-s3-d2 or better when installed on buildings in England or Wales. In Scotland, the façade material must be non-combustible.
- Assembly or recreation buildings where the distance to all boundaries is greater than 1 metre – In England and Wales, the products installed on assembly or recreation buildings above 1 storey must be rated Euroclass C-s3, d2, or, when tested to BS 476-6, have an index no greater than 20.
- In Scotland, the façade material of assembly or recreation buildings no more than 10 metres above the ground must be rated “low risk” (at least B-s3, d2 or Class 0). There is no specific requirement for buildings between 10 and 18 metres.
- All other buildings under 18 metres where the distance to all boundaries is greater than 1 metre – There is no specific boundary provision but the wall constructions must meet the minimum period of fire resistance.
- The maximum dimension of cavity spaces between barriers should be no greater than 20 metres. This distance is reduced to 10 metres if the fire rating of the material facing into the cavity is lower than Low Risk in Scotland, or lower than Class 1 in England and Wales.
Over the course of the next three blogs we’ll look in detail at the different routes to achieving fire safety compliance on buildings with habitable stories above 18 metres. This will begin with an examination of the potential benefits, and significant limitations of the linear route on 1st December.
If you’d prefer to get into the detail of the full technical bulletin right away simply click here.
See other posts in the Facades & Fire Safety Series:
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