My main HT system is in a room addition that was built using SIPS construction for the ceiling and floor.... SIPS= closed cell foam sandwiched under very high pressure (usually) between steel and 1 1/2" outdoor grade chip board. It's not two feet thick, but the roof and floor are 14" of structural foam....You can literally sit a truck across one of the 4 x 12 sections. I think the thermal rating is 48 Its a very quiet room. ..... inspite of the 3 window walls. You hear very little sound outside when cranking the music.... lol which I never do lol nor from neighbors mowing lawns etc. The only issue we have is hail or very heavy rain on the metal roof we installed over that room.... that gets very loud, which is something I didn't expect.... The rest of the house is stand construction except 6" sidewalls and you can't hear the rain on the metal roof under the rest of the house.
I first ran into SIPS when we used it for floating docks in a marina project I worked on.... these were made using liquid closed cell foam, sandwiched in concrete, under very high pressure. The same type sections are also used as floating bridges and ocean break walls.
