Preparing for ventilation first fix!
November 29, 2014
This week we had to do some preparation for the ventilation first fix, which is scheduled to start next week.
By having a lowered ceiling in the centre of the 'inner box' we have a zone for all of the ducting (and sprinklers, some of the plumbing, and whatever else we need to accommodate) which is totally below the intermediate floor construction. Whilst this has the advantage that we don't have to core any of the I-Joists that form the structure for this floor so we have no worries about compromising their structural integrity, it does mean we have to make sure some of the ceiling is in place first, as this is essential for both the acoustic and fire performance of the floor.
However, before the ceiling can be fitted there are several other layers that have to be fitted first.
On the upper floor we have had to fully insulate the perimeter of the roof construction to eliminate any thermal bridge here. The distance we have brought the insulation in towards the centre of the plan varies around the perimeter of the building depending on the particular build up of rim beam, joist direction, etc. - I have been calculating all of the PSI values of the junctions in THERM, which is pretty slow going, but which is verifying we really do have a thermal bridge free construction.
Then we fitted the Intello airtightness membrane, and followed this with localised areas (where the ducts are going to run) where we fitted the ceiling board.
For fire performance reasons we are using a denser 15mm gypsum 'wall board' on the ceiling of the upper floor. Although it is not ideal to have to cover areas of the Intello membrane before we do our airtightness test (as it will be much more disruptive if there is a leak up there!) it is necessary so that the ducting can be hung below this layer. We have been extra vigilant on the taping in these areas so fingers crossed!
On the lower level we have a slightly different circumstance. In order to meet the Gold level in Section 7: Sustainability of the Technical Standards we have to insulate our intermediate floor with which contributes to the floors acoustic performance of 45dB Rw. (This cannot be tested on site due to flanking transmission through doors and such like, so it has to be achieved with a system that has been certified as providing this rating in a laboratory situation.) This was by far the hardest aspect of this Standard to meet, however we feel it is really worth it - no one likes being able to hear a conversation in an adjacent room after all! We are using a Fermacell certified construction:
2 layers of 15mm Fermacell board
insulation equivalent to min. 100mm at 30kg/m3 density
22mm chipboard flooring
30mm thick Fermacell flooring system (10mm mineral wool bonded to 10mm board, with second 10mm board)
Finally comes the floor finish....
Again we are fully insulating a zone around the intermediate floor to eradicate any thermal bridging here. These photos show areas in the centre of the plan, below which the ducts will run.
We are supporting the insulation at intervals with small off-cut strips of the spano durelis boards (waste not want not!) and as you can see the joints in the 2 layers of Fermacell are staggered.
The resilient bars are fixed at 90 degrees to the joist direction, and screwed into one part of the shaped section directly to the joist. The ceiling board is then screwed into the other, lower, part of the bar and this means that this fixing is isolated from the joist itself. It is this isolation between ceiling board fixings and joists that creates a good acoustic performance as there is much less transfer of noise through the floor.
The plasterboard lifter has been amazing for this job - it means that essentially one person can work on their own getting these very heavy sheets of Fermacell (each 15mm thick board weighs 18kg/m2, which is about 51.8kg!) into place and screwed to the resilient bars whilst the other gets on with another job.