It still appears we have confusion across the construction industry with selecting the right soffit solution.
In simple terms we need to ask, “what is the performance required from the soffit solution?”
- Thermal performance only
- Thermal performance and also non-combustible?
- Thermal performance with a proven fire rating to protect structural concrete soffits?
Soffit linings are mostly used to provide thermal insulation to concrete structures but the fire performance is often a last-minute consideration.
When selecting a lining’s fire performance, the categories are usually described as Class ‘0’, non-combustible or Fire rated. To offer a little clarity, we have the summarised the performance of each:
Class ‘0’ is purely a reaction to fire classification under BS476 parts 6 & 7, but such a classification does not mean the material has a proven fire resistance to protect the structure. These soffit linings can often be combustible insulation materials that add to the buildings fire load.
Class ‘0’ can be wrongly interpreted as being the highest fire performance but in reality, such a classification is only middle of roads as the illustration (Fig 1) shows
Common products we often see are materials such as PIR or Phenolic and, whilst they are employed for thermal insulation for soffits, they would need interrogating for suitability if fire is a concern.
Non-Combustible linings are those that are made from materials that are specifically and have a proven classification in combination of Non-Combustible to BS476-4 and/or A1 Non-Combustible to EN13501-1. Such materials do not add to the fire load of the building and subject to thickness employed, can offer the required Thermal Performance for the structure. These products however, do not provide a proven fire rating or resistance to fire for the construction element protection unless it carries the appropriate test evidence or assessment report such as EN1363-1.
For this category, materials such as Knauf Soffit Liner Board Standard or Knauf Soffit Liner Board Extra are ideal solutions.
Fire Rated soffit linings are products that have test evidence, such in accordance with EN13501-1 proving non-combustibility but with the extra performance tests/assessments of providing specific fire ratings for the structure it is attached to, under tests such as EN1363-1. Fire ratings up to 4 hours can be achieved with some soffit linings thus providing complete protection to the structural concrete soffit for a tested period of time.
Recognised soffit solutions that offer fire ratings include Rockwool Soffit Slab, Rockwool High Impact Soffit Slab and Promat TLFR.