Exterior windows and the dreaded triple-leaf

[mbene085]

Hi all,

I've hit the end of the road in terms of how much I can figure out myself from reading Rod's book, this forum, etc, so I was hoping I could get a quick "reality check" from someone here.

I'm in the process of moving, and my future studio space has two 54" square, double-pane windows at opposite ends of a ~500 square foot/4000 cubic foot room. I'm in a relatively quiet, low density area and am not currently planning a full reno for optimum isolation - I mostly plan to just treat the interior of the room as effectively as I can, and only worry about a full reno for isolation and improved acoustics if I discover there is more bothersome sound leakage than anticipated, and/or that the room modes are completely unmanageable.

Having said that, the windows are large and are the obvious weak link in isolation between interior and exterior, and I was hoping to bring them closer in line to the standard (for Canada) 2x6-framed exterior walls around them without just building overtop of them and losing the natural light.

I've encountered many storm window type products that claim significant improvements in isolation by adding an airspace behind a pane of thick laminated glass in an airtight frame, but the thing I'm not clear about is whether the double glazing of the original window (with a gap of roughly 1cm between panes) represents a triple-leaf in this scenario.

As far as I can tell, the new system would go "laminated pane-> 10-15cm air gap->single pane->1cm air gap->single pane."

There are companies posting graphs showing big improvements in STC rating over a double-pane window alone, but it looks to me like a triple-leaf system.

Are these products a reasonable approach to decreasing transmission of sound through the window? Or should I be budgeting to pull out the existing windows and build a two-leaf window with thick laminated panes and a generous air gap? Or does the 10:1 mismatch in air space between the two sides of the middle leaf diminish the harmful impact of the triple-leaf system to a degree where it would still improve isolation significantly compared to the original window?

I don't want to go overkill on the windows right now because, like I said, I'm not renovating the walls or ceiling at the moment, and if I choose to do so at a later date, I imagine it will have been better to design a window with dimensions and performance suited to the plan and construction methods chosen for the reno. There's no point in chasing a level of performance from the window that exceeds the surrounding walls.

Any insight or advice is appreciated.

[gullfo]

if you go with a quality brand, the exterior storm windows are generally pretty good and i think you'll find it will do a good job with isolation. the existing windows due to their lower mass is not likely to create a strong 3 leaf effect. brands like Pella, Andersen, Marvin, etc are pretty commonly available and should do the job.

[mbene085]

Thank you kindly for the quick reply! I knew there had to be an element I was missing - that makes sense. The middle leaf is a thin pane of glass, low mass, so not as much of an effect.