Fredxxx wrote:

Andy Burns wrote:

My semi-detached is built with upside down bricks, the result is a
lighter wall due to all the empty frogs that is more transparent to
sound from the neighbours than you'd expect.

This suggest mass is good and voids bad news for sound travel:
http://www.ibstock.com/pdfs/technica...ged-bricks.pdf

Yes, I wasn't suggesting it was a good thing!