I am building a house with low e argon gas filled high efficiency wood framed windows. The manufacturer's instructions say not to shim the top of the windows nor to nail the top flange to the frame. My builder says this is not important. I disagree, but I can't find any standard installation guides that speak to this issue. Can anyone help?

I have old wood frame storm windows that I put up each fall. They work fine. I just installed a second pane of glass to a single pane fixed picture window. I simply framed the second pane in wood like my other storm windows. However, I already have condensation between the two panes of glass. I don't imagine it is air tight, but none of the other storm windows are either. The only difference is the space between the glass in the old storm windows is about two inches and the space between the glass in the picture window is about 1/2 inch. I know that a broken seal in a dual pane newer window will cause the same problem, but these good old 30 year old detached storm windows have never had this problem. If I increase the space between the two panes of glass (like the detached storm windows), will that help this problem? Thanks for any suggestions!