Technical Notes on Fire Safety in Engineered Joists
With the necessity for buildings to become more eco-friendly, those within the construction industry have begun to turn to engineered joists as an alternative to traditional timber. A well-insulated house offers a multitude of benefits, the most notable being reduced heat loss from the home which in turn lowers energy usage and costs, decreasing the impact on the environment. However, without ventilation a well-insulated home would become stuffy and uncomfortable. Ventilation installed alongside timber joists takes up a lot of room and reduces the amount of usable space within the home. Engineered joists, or I-Joists, however, have ventilation installed within them without taking up a huge amount of space.
Alongside the proven ventilation/space benefits, engineered joists offer further benefits. They can be made longer than traditional timber joists which helps reduce construction costs – ceilings and floors can be designed with fewer pieces. They are lightweight, yet extremely strong, offering easy installation and are generally longer lasting than timber joists, which can suffer weaknesses such as warping and bowing.
Of course, as with all timber structures (and construction in general!), fire safety must be priority number one. And building control have brought documentation to SOLID’s attention which helps streamline fire safety within timber buildings, including those which incorporate I-Joists and Metal Web Joists. Entitled ‘Structural Timber Buildings Fire Safety in Use Guidance’ the document by the Structural Timber Association is believed to be the first of its kind. It provides a comprehensive fire safety guidance for the design specifications and construction of timber buildings.
Originally published in 2020, the latest edition (Version 2.2 September 2022) now includes (within Part 4) the comprehensive breakdown of specifications and requirements for I-Joists and Metal Web Joists. Recommendations for the loading of floors in fire resistance testing are provided with an explanation about how the load influences the joist design. Structural requirements and specifications continue for ceiling lining, ceiling penetrations, insulation, and floor deck. The documentation also includes an approved list of downlighters that have been fire tested in conjunction with engineered timber joists, stating that downlighters not on the approved list should not be used. The requirements for positioning the down lighters are also included.
The full documentation can be found through the STA website. Working in partnership with CSIC (Construction Scotland innovation Centre), the University of Edinburgh and BRE Global and with funding from Swedish Wood and Scottish Forestry, The STA have tested multiple wall systems, intended to meet 30–60-minute minimum REI compliance requirements to EN1365-1 test standards. The STA also continues to collaborate with other test programmes to better understand the differing wall, floor and roof systems used in the marketplace.
This guide may not be commonly known about. We recommend you engage with the documentation and share with architects, M&E Consultants and others within the construction industry.