Interior Storm Windows, Commercial Product

Controlling the movement of air and heat through windows.
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Interior Storm Windows, Commercial Product

Postby BirminghamPoint » April 16th, 2012, 8:10 pm

There's currently no treatment for the correct installation and use of commercial grade interior storm windows, and I was wondering if there was any specific reason for this, or if the topic simply wasn't being considered by anyone. John Leeke's Interior Air Panel treatment is very closely related to this, but is focused on the construction of relatively simple, custom panels, rather than the correct handling of their commercial counterparts.

Advantages of interior storms are noise reduction, the fact that they don't disrupt the external appearance of historic wooden windows, prevention of condensation on the interior side of the primary sashes (e.g., during the fall and early winter, when adsorptive moisture captured by interior surfaces during the summer months starts to get released as the home is heated), relative ease of removal and installation by the home owner (mainly because they're on the interior, but also in the case of those held in place by spring tension only), and, of course, reduction of thermal transmission. Disadvantages include lack of protection of the primary sashes from weather on their exterior side, and durability issues if moisture gets trapped between the interior storm and the primary window.

However, some of the previous discussions here regarding weather stripping and the need not to seal things up too tightly, have me thinking about a possible protocol for handling interior storms. That protocol might, for example, consist of: (1) air sealing exterior and interior casings (as described by Bob Yapp), (2) applying weather stripping in such a manner so as to mostly exclude weather, yet still allow for some degree of air ventilation and drying (for example, by not weatherstripping some bottom-most portion of the lower stiles, to keep the sash and frame joints dry, as suggested by John Leeke in a previous reply to me), and (3) ensuring that the interior storm itself is indeed as air tight as possible, all along its perimeter.

This would ensure that any moisture infiltrating the space between the primary window and the interior storm could still get flushed out, exclude the flow of moist interior air into that space (especially during the early phases of the warming season), still maintain a layer of relatively warm air between storm and primary window, and admit no cold air drafts to the inside. The primary window would still have to be regularly monitored for moisture accumulation, of course.

I'd submit this as a proposed treatment, but can't do that legitimately, since I personally have no experience working with commercial interior storms. (All of what I've said above is based on observations by others, and inference on my own part). However, in my own forthcoming restoration and weatherization and energy testing efforts, I plan to include aluminum/plexiglass interior storms in some of my work. So I hope eventually to determine if this approach is valid or not, but probably won't be able to say until at least some time into next winter.

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Re: Interior Storm Windows, Commercial Product

Postby johnleeke » April 20th, 2012, 8:56 am

John, I agree with you that a standard is needed on commercial interior storms, and will add it to the Standards outline, so it is not forgotten. Here is the outline:

In the meantime we can continue the discussion here until someone with experience steps forward to write it up. It's OK if this takes time, because there will be a second edition of the Standards.
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