resilient bars
The acoustic ceiling system.
This week we began the installation of the acoustic ceiling system. This is coupled with insulation laid between the joists and an acoustic flooring product above, all of which together forms a complete system which has been laboratory tested to achieve the demanding 45dB Rw rating which is a requirement of the house achieving Gold in Section 7: Sustainability of the Technical Standards. More on this build-up later,
The first step for the ceiling was to install the resilient bars: these are fixed perpendicular to the joists at 400mm centres with min. 30mm screws.
The first board of the two-layer ceiling is then fixed to the resilient bars, taking care not to coincide the fixings with the joists above. As we are using 15mm thick Fermacell boards, which weigh 18kg/m2 (which is 51.84kg per board!) we decided to invest in a plasterboard lifter, which has turned out to be the best £109.99 spent on tools so far!
The second layer of sheeting is ideally placed perpendicular to the first (although this isn’t always possible in narrow spaces), or with staggered joints, and at the very least with min. 200mm between sheet edges.
This separation of ceiling board from joists helps to reduce the amount of airborne noise that passes through the intermediate floor. As we are achieving the Gold Level in Section 7: Sustainability of the Technical Standards we have to install a lab tested system that meets an airborne noise level of min. 45dB Rw. This has been the single hardest, and most expensive, aspect of the Gold Level to achieve, and for a JJI joist such as we have here, Fermacell were the only manufacturer we could find who could provide this.
The whole build up from bottom to top is therefore: 2 layers 15mm Fermacell board; min. 13mm resilient bars (we are using 16mm) at 400mm centres perpendicular to the joists; min. 100mm insulation of min. density 30Kg/m3; 22mm flooring chipboard; 30mm thick Fermacell acoustic flooring system which consists of 10mm mineral wool bonded to 2 layers of 10mm thick Fermacell boards (more on this later); and the final floor finish, which in our case will either be 20mm thick oak parquet or linoleum, depending on the location. Phew. I am sure it will be worth it!
Interestingly in October this year the Technical Standards are due to change again, and the Noise section will see a decrease in the standard required for acoustic airborne separation provided via internal partitions from the current standard of 43dB to 40dB, which will bring this aspect of our regulations in line with the rest of the UK. The standard for intermediate floors will be remaining at 43dB.