One of my ideas, on the non-operable (i.e. windows that don't open) windows was to have interior storm units. It struck me that I have plenty of space to put windows there, but he said that no, 2 inches is not enough. All of the dual pane units made in Canada, he said, are the same depth. I don't remember the exact figure he gave, but it was more than 3 inches. I have that much space on the sill, but only a touch more than 2 inches between the posts.
I'm wondering, is this provision of big frames from necessity (you don't want the units leaking air in, because then the argon leaves and you lose some of your insulation / noise reduction value, and risk condensation), or from habit? Yes, I can see that it could be tricky to devise a framing system which would keep the seal intact while the unit was being installed (torque applied to the unit) or if it suffered some trauma (like a ball hitting the glass, but with insufficient force to actually break the glass), against temperature gradients, or against differences in tension during installation.
He said there would be no problem fitting a *single pane* interior or exterior storm in the space available. If I want dual pane, low-e, argon filled, he says it's likely that I have to replace the wooden sash units with vinyl.
So my subsidiary question is: is there any sense in buying "naked" dual-pane units and making wood frames (similar to picture frames) for them myself? I repeat that I'm asking this only about non-operable windows. Brief idea: drill hole at bottom of existing sash (to allow air flow against condensation) affix good quality weatherstripping on existing windows, place new unit in frame against weatherstripping, fix in position (low compression), and seal any leaks.
What do you think? Likely to work, or likely to fail?