Plastic Sheeting Over Windows: Right against window or leave an air pocket?

My landlord’s going to replace my crappy 50+ year old windows when spring rolls around. Problem is, of course, we’ve just hit our first cold snap (32 is our daily high).

So I’m putting up plastic over the inside of our windows. Would it be better to put the plastic right against the window, or leave a 2-3 inch gap between the window and plastic?

I’m guessing that leaving a little space would be best, since it would provide a small barrier made up 50’ish degree air (cold outside air + heated inside air). Of course, I could totally be overlooking something as well. We have blinds on all the windows, so the plastic doesn’t really present an eye-sore problem in either position.

You need a gap. The trapped air is the insulation. If the plastic’s right against the glass, you only get the insulation value of maybe 2 mils of plastic, which is pretty much, but not exactly, zero.

The plastic is usually applied to the inside of the window trim, which leaves 3-4 inches of trapped air.

In a prior home I used the 3M kits that had plastic strips adhered to the surface of the window casing. Plastic sheeting was snapped on, then shrunk tight with a hair dryer. Worked pretty well.

As I recall from one of my solar heating books, the optimum spacing is something like 1/4" - 3/8"
Anything smaller sacrifices insulation, anything bigger leads to convection losses. Bit, if you can’t get it that close, it’s still better than nothing.

Its best if you can manage a 1/4 inch space between the glass and the
plastic, what you are trying to do is create a still layer of trapped air between the two surfaces, if the gap is much larger the air will circulate inside the
gap, and if the gap is smaller than that, you lose some of the insulation.:eek:

Very cool, 2 independent confirmations of not only leaving space, but leaving 1/4" inch of space specifically. Thanks a bunch guys. If it’s only 1/4" for optimum insulation, I might throw on a second layer if that’s only gonna bring it in to a total of 1/2" inch. Since I know the windows are getting replaced in 4-6 months, I’m just going all staple-gun on the stuff anyways, way less work.

We might be able to get away w/ wearing T-shirts indoors this winter for once. :slight_smile:

Not staple gun. Use two-sided tape, go all the way around the front surface of the frame, and leave no gaps in the tape. Then get the heat-shrink kind of plastic, kinda roll it onto the tape on the frame from one side, take it all the way across, and then use a heat gun or hair dryer set on ‘hot’ to shrink the plastic until it is taut and tight as a drum. You want NO circulation into or out of the air pocket.

They sell kits of the tape and plastic, usually near the weatherstripping.

Good call. That would be one of those things from the OP when I mentioned there might be something that I didn’t even consider. Thanks

Another vote for the 3-M kits - they work like a charm down to some extreme temperatures. I’ve used them more than once in the past, and have a couple of windows to do in our newest house, too.

All good stuff. By the way, even if the plastic is right against the glass, it still may do some good, if it also goes beyond the glass. Some windows leak air, and the plastic can block that. The effect could be substantial, and might not be noticeable at the window (an upstairs window will leak warm air outward and make the downstairs colder but not feel cold right there).

I lived one cold winter in a house so drafty that the inside curtains would wave when a big truck passed on the street outside, even with the windows closed.

However, certainly, the plastic does more good with air gaps as discussed. Just pointing out that there are at least two ways the plastic can help.

I plastic over the whole thing, windowsill/molding and all. 110-year old, poorly insulated house with crappy windows. It helps a good bit. Granted it doesn’t get THAT cold in North Carolina, but it’s nice not feeling a cold draft on me when I’m within a few feet of a window.

I have bought 4mil plastic sheeting it says create energy saving storm windows and door of any size, use for painting, storage, and protection indoors and out. can i use a heat gun to shrink the plastic sheeting or not?

Regardless what we say or the instructions say, your best bet, here is to get a small piece of the plastic, stretch it out, and hit it with the heat to see whether you have the right technique. (Are you using a ConAir blow dryer or a paint stripper? I would think the latter would be difficult to avoid melting the sheet.)

4mil plastic is thick. you can make a frame with wood and make storm windows and doors with it.

the plastic window kits has a plastic that heat shrinks. the 4mil plastic for protection and drop cloths is not made to heat shrink, though you can stretch it tight manually by cutting the plastic large; wrap one edge around screen door trim a few times and staple to frame, wrap opposite side similar a few times and stretch even and staple to frame (this may take a few trials as to length and number of times to wrap. you can make translucent storm windows and doors this way, plastic usually will last one season before becoming more opaque and brittle where thy are exposed to sun.