Thanks JoseD3,
Does the PVB have any soundproofing ability or it is just for strength?
The aluminum rails allow for an insertion of a panel 7mm thick. If I were to make another layer, I would need to make another rail, which would double the cost. If I make 2 glass panels 3mm thick, and somehow create a 1mm space between them for a total of 7mm wall, you think that would work?