I have noticed recently that a lot of builders and project homes promote Hebel / CSR panels (which I assume are steel) as party / separating wall for attached occupancies vs double brick wall. They argue that these panels are cheaper and are built faster and also achieve the same sound proofing and fire rating and overall strength as brick. I know that if a double brick separation wall doesn't have a cavity in between it is no good but other than that is there any merit to using these panels instead of Brick? Also I have noticed that if you have a double story attached duplex / occupancy, a lot of builders recommend using 75mm hebel panel slab instead of full brick construction for the first (ground) floor and for the second floor they usually promote timber as opposed to concrete. Is there a huge cost difference between the two (lets say over a 80 SQM floor)? I know timber will be very noisy which makes concrete ideal but will concrete break the bank?