Due to the high number of variations in the construction of engineered timber joists, where each manufacturer offers a different profile, it is not possible to provide a generic solution. We recommend that you contact the manufacturer of the engineered joists who should have relevant test reports and assessments.  

These solutions will often include plasterboard as part of the build-up. If the system is being used in an unheated environment such as an undercroft or carport it may be possible to under draw the plasterboard ceiling with 9mm thick Promat MASTERBOARD®. 

Promat MASTERBOARD® is a calcium silicate board suitable for a semi- exposed environment where plasterboard would not be suitable as the final finish. 9mm MASTERBOARD® weighs approximately 9.3kg/m², we would therefore recommend that the engineered joist manufacturer is consulted to ensure that this additional load is acceptable.

If no fire test data is available, an alternative approach would be to fit solid timber joist either instead, or alongside the engineered joists and use a Promat SUPALUX® solution, please refer to Chapter 4- Promat Fire Protection Handbook.