I put my fingers toward the window jamb and feel a slight draft of cold air coming from the silver-colored metal rail that the lower sash slides on (See picture).

By holding a piece of cardstock at the corner between the upper sash and that rail and putting my hand on either side of it, I've determined the cold air is coming from the silver rail area, as opposed to from between the upper sash and the jamb. The window sashes have some fuzzy weatherstripping between the sash and jamb.

So it feels like air is infiltrating through the side of the window. Why would this happen, and is there anything that could be done? I have several windows, and they are all similar.

Note, in learning about window anatomy, I've observed that "rail" refers to the top of a window sash. But here, by rail, I mean the silver metal pictured upon which the window sash slides. I don't know what it's called. Maybe channel is the correct term?


  • Hello, and welcome to Home Improvement. It's hard for us to help without more info (e.g. is this worse on windy days? is this an apartment building). And, you should probably take our tour so you'll know how best to participate here. Dec 7, 2019 at 17:30
  • It's an apartment building. It's not windy today, and I can feel a slight draft. It feels worse on cold days, probably because the incoming air is colder. The draft is very slight, as if the air there is colder. But I think it lowers heating efficiency, and makes areas by the windows feel cold.
    – bernie
    Dec 7, 2019 at 17:49

3 Answers 3


Apartment buildings are notorious for poor weatherproofing - especially around windows. If there is a gap that cold air is passing through you can seal it with a can of spray insulating foam. Better yet have the apartment super do it for you. But the heat loss is probably the result of poor weatherizing. Those metal windows are heat bridges conducting heat out of your apartment. In an apartment you have no option to upgrade windows so the best answer is warm window covers (blinds or curtains) that can seal around the window and reduce your heat loss. They can be costly but at least you'll be comfy and reduce your energy costs. However, if this is just a short term rental, anything that has reasonable insulating properties that you can hang or tape over the window should help. Otherwise, wear a heavy sweater.

  • Re. weatherization. My suspicion is that on the exterior, there are some gaps that let air come in from around the window. Hence, I feel cold air from the silver area I've pictured. I've put up packing tape on the window channel, and I'll see how it feels.
    – bernie
    Dec 9, 2019 at 2:15

They have string-type weatherstripping putty that would be ideal for your situation. You can push the string putty into the gap and/or cover the gap for the winter, then remove it by peeling it off when the weather warms up and you want to open the window.

The long-term solution is for the sash to be removed and the integral weatherstrip (that fuzzy stuff you saw) to be repaired/replaced. Even then, old windows were not made for optimum heat conservation...

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  • I'd like to add that I've been told the windows are <10 years old. The cold air is coming from the silver metal area, as opposed to from between the sash and jamb, so I think the fuzzy weatherstripping on the window sash is doing its job. Taking inspiration from your suggestion, I've taken some packing tape, and I've taped over the window channel (over the silver part of the window) for a few of my windows. I'll see how it feels.
    – bernie
    Dec 9, 2019 at 2:04

The best solution I've found is to put plastic window insulation up. The thin sheet of plastic completely seals the window, preventing exchange of air from the outside to the inside. This creates a large barrier of still air that is far thicker than the gap inside a double-pane window.

That bead caulk might plug some gaps, but the full measure solution is the plastic window insulation.

  • Not a bad idea at all, but it is ugly and some folks may not like that. Also, the tape can damage paint when removing it, and renters may not be willing to fix the damage/pay the damage deposit. Just a couple of considerations...
    – FreeMan
    Jan 26, 2021 at 14:32

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