Fire-safe trusses are used in sites where the roof structures are categorized in fire safety grade P1 or P2. Depending on the fire safety grade, the loadbearing section of the structure has been determined a time which it needs to resist fire without collapsing.
In fire safety grade P1, the fire-resistance requirement R of the loadbearing structure is 60 minutes. For such a site to be able to withstand fire, we recommend a truss with a loadbearing bottom chord in a fire situation where the chord is fire-engineered to resist a fire for 60 minutes. In fire safety grade P2, the fire resistance R of the loadbearing structure is 30 minutes. A fire-safety grade P2 can be reached by using one of two options. The first option is a truss with a loadbearing bottom chord in a fire situation, where the chord is fire-engineered to resist a fire for 30 minutes, and the second option is a SEPA R30 truss (= a bundle of fire-safe trusses).
A truss with a loadbearing bottom chord in a fire situation (R30 or R60)
The product’s bottom chord, which is primarily made from solid wood, is fire-engineered to endure the determined fire-resistance period. The product’s bottom chord must be protected*. Depending on the protection method, the remaining cross section of the bottom chord is determined and taken into consideration in the calculations, together with the length, potential intermediate struts and applied loads. Based on the engineering, the bottom chord’s buckling support span and potential additional beams are determined, if the structure has long spans. The buckling supports are installed either between or on top of the bottom chords.
* Protection options include:
1) Protection with sheets of rock wool (as strips or as a carpet over the entire roof)
2) Protection with sawn timber
3) Protection with gypsum board
4) Combinations of the above
Note: The cross sections of the buckling supports must take a potential fire into consideration or they must be protected so that they endure the stress caused to them during a fire, regardless of potential charring. Other bracing components are NOT required to have fire-resistance characteristics.
Potential intermediate struts for a fire situation facilitate the calculation of a product’s endurance in a fire, and significantly decrease the need for additional beams demanded by fire engineering
SEPA R30 truss (= a bundle of fire-safe trusses)
The product is a nail-plate truss structure which, unprotected, complies with the fire-resistance requirement of 30 minutes (Fire-safety grade P2 – Fire-resistance requirement R30) – Eurofins Expert Services Oy, Statement No. EUFI29-19003939-T1.
Note: The battens, buckling supports and other bracing components must endure fire, which means that there are minimum cross sections specified for the sawn timber used for these components and the protection boards to be installed on top of them.
The sawn timber must be softwood, the battens must have a minimum strength grade of C24 and a cross section of 63 x 100 mm². The sawn timber used for the buckling supports and bracing must have a minimum strength grade of C24 and a cross section of 50 x 100 mm². The minimum cross section for the protection boards must be 36 x 125 mm².
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