BUILDING PHYSICS 10 Flanking CLT BBS walls should be provided with a facing formwork that has decoupling effects (installation level on vibration mounts, shell spacing at least 5 mm or use stand-alone facing formwork – see Figure 6). Figure 6 – Facing formwork working with decoupling effect on one or both sides In the calculation of the sound transmission, the mass of the binderholz cross laminated timber CLT BBS wall and ceiling elements have a strong influence. The measurements show that directly applied plasterboard planking has a positive effect on the flank sound insulation. In detail, this effect is illustrated in the calculation example. Elastomers can be used for the sound decoupling in the case of vertical flank transmission, for example, on the supports of an apartment separating ceiling. The following table shows the improvement of the joint insulation values (input parameters for calculation of the sound insulation value incl. secondary paths R’w – see page 17). Only the upper elastomer has effects on the transmission path Fd and only the bottom elastomer affects the path Df. The paths Ff and DFf are influenced by both elastomers. Arrangement of the elastomers Position Data from the DAGA 2010 conference transcript New measured data top bottom top or bottom ∆Kij = 7 … 10 dB ∆Kij = 4 … 10 dB top and bottom ∆Kij = 8 … 19 dB ∆Kij = 13 … 15 dB Source: Vibro-acoustics research project NOTES The indicated values have a wide spread, as elastomers of different manufacturers have been used in combination with different wall and ceiling structures. The information applies only to decoupled mounting materials (angles with elastomer boards, bolts with lining and elastic insulating washers – see Figure 7). If conventional fasteners are used, the decoupled effect of the elastomer will reduce significantly. In that case, a ∆Kij of 2 to 3 dB can be assessed. Further planning bases for the influence of elastomer bearings with and without consideration of the installed fasteners can be found in the planning brochure of Holzforschung Austria entitled “Roof structures for multi-storey timber construction”. Source: Rothoblaas planning brochure Figure 7 – Decoupled fasteners with elastomer bearings of different manufacturers © Rothoblaas © Getzner Werkstoffe © Rothoblaas
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