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Installing pocket windows: Proper way to insulate old window cavity

2 months ago
last modified: 2 months ago

I plan to install 15 Marvin Elevate pocket windows to replace old weight-and-pulley 80-year-old windows. I prefer not to disturb the trim. I understand that, during the installation of the pocket windows, I will have an opportunity to insulate the old weight cavity. I see four options, and would appreciate your views about the best option to pursue.

1. Remove the casing trim to expose the weight cavity. Remove the weights. Use rigid insulation. (like Tom Silva is doing in this video However, I do not want to mess with the trim, so I would prefer not to pursue this method.

2. If there is access to the cavity via an access panel, remove the panel, remove the weights, and slip fiberglass insulation (like Tom Silva, contradicting himself from option #1, is doing at minute 0:40 in this video:; he criticizes this method in the video in #1 ). A Marvin dealer told me this is the method they use. The potential minuses are that the insulation could be compressed and lose its R value, and that it might not have much impact in terms of air insulation.

3. If there is no access to the weights, then leave the weights at the bottom of the cavity and then make a few small holes every foot or so on the side jambs and use minimally expanding spray foam (like this guy is doing here this guy is doing here at minute 1:40 The potential minuses are that the weight will remain inside smothered in spray, that funky things might happen with the foam inside the cavity, and, perhaps most importantly, that the foam cures with air and there is no air inside the cavity.

4. Do nothing, and not insulate the cavities. Just install the pocket windows. The insulation loss of having the cavity is not different from what I current have,

I am inclined to do #3, unless there are compelling reasons to do something else. I’d appreciate your expert views. Thanks.

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