In our house we have regular single-hung windows which are leaking cold air.

As usual, the double pane unit is encased in plastic trim. I can feel a draft coming out where the plastic has a seam with the glass. There is a bead of rubber going all along the seam, and it doesn't looked peeled off.

  1. Is this a common problem? Could I be imagining a leak in this spot?
  2. How do I fix it? Is applying a bead of silicone over the rubber seal a bad idea?

The arrows point to where the seam is:

enter image description here

  • 3
    For future reference, a "regular, double pane, slide up-down windows" is called a "double hung window". Some are single pane, most double pane and some are even triple pane. Now you can sound like a pro! Yes, pics are always good.
    – FreeMan
    Feb 11, 2021 at 20:12
  • 1
    Storm windows are an option
    – Kris
    Feb 11, 2021 at 21:48
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    Vertically sliding windows come in single hung and double hung. In single hung the lower section moves up and down but the upper section is fixed. In double hung the top section moves down and up. The hung part must come from the fact that heavy old wooden windows were held by cables or chains going up over pulleys and then down inside pockets on the sides to hanging weights, one on each side. Each weight would be half the total weight of that moveable section. Light modern windows are supported by friction, but they arecstill said to be "hung". Most modern windows are single hung. Feb 11, 2021 at 22:14
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    Double-paned windows are made as a single self-contained unit, factory sealed, which is then just clipped into the frame. The frame can be leaky without the sealed unit being damaged. If that's all it is, then yes, you can silicone round the edges, or see Ed's answer below for a more permanent fix - new seals.
    – Tetsujin
    Feb 14, 2021 at 12:31
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    @JimStewart very valid point about the single- vs double-hung distinction. However, I don't think "most modern windows are single hung". We just replaced ours 2 summers ago and none of the salesmen mentioned a single thing about a single hung (not even as an option). They all touted the tilt out feature on both sashes (slide the top one down to access it) for ease of cleaning. Of course, we're wandering off topic now...
    – FreeMan
    Feb 15, 2021 at 19:14

1 Answer 1


On the windows I have installed they have a clear plastic or white wiper that seals to the frame, when these windows get older that plastic seal fails then the outside air can make it through the gap. You may need to remove the slider and look on some windows I have seen several of these, wiper type weather seals. The seals pull out to a side if they don’t slide out with players look for a staple keeping them from moving.

You may be able to find a generic weather strip that will replace yours. It’s not horribly difficult pulling the window can be the hardest part.

The entire sliding part it probably will need to come out so you can remove and replace.

  • Often the plastic retainers just clip in/out - tougher to get out because there's no real way to get into them. A screwdriver blade will do it if you start at the corner with the most significant gap (they're almost never perfect on all 4 sides.) just lever directly towards you from one end, then you can pull the first one away. After that it's plain sailing. Ream out the old seals, replace with new & snap the retainers back in. I doubt it would be difficult to do in-situ, no matter whether it's a sash, or even tilt & turn. The retainers will be nowhere near any mechanism.
    – Tetsujin
    Feb 14, 2021 at 12:34

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