The most clients with two storey houses do select concrete slabs (like Ducon) instead of timber joists nowadays, to achieve a better performance for sound proofing and load bearing. A common slab is still the hollow core version, which requires some attention regarding air tightness.
Because of its access to the cavity, there is a risk of air infiltration into the building through the hollow cores, through the joints in between the slabs, at the junction where the ducon slab sits on the external wall and at the junction, where the slab lays alongside in front of the external wall.
The most builders and self-builders do wrap the hollow core slab with an air tightness membrane during the installation. Please select a heavy duty membrane for this purpose, because standard membranes could get torn during the installation of the floor slabs.
On the following photos I´d like to show some steps, to create a good air tightness strategy for the building envelope area between the suspended ceiling and the underside of the hollow core slab.
I´m pretty convinced that there are different strategies available and would appreciate any thoughts and comments, to develop an even better (easier) technique for the future.