Unlike many other building materials that typically require treatment with chemical preservatives, earth is non-toxic. This cannot be said for commercially sold timber and brick products.
this cannot be said for... = this is not the case for/ it is not true about...

acoustic - relating to sound. They mean they have good natural sound-proofing.
Another one:
Houses entirely made of earth have acoustic properties = ?
 nona the brit's reply was promoted to an answer.