Please help with this single pane sliding door
October 19, 2021 6:49 PM   Subscribe

The room-width (144") sliding door to the balcony is delightful in summer, a nightmare in winter. Details below the fold.

The balcony door in my living room is single pane and faces north and west. In the winter, the cold radiates about 6' into the room ... which is where I sit and where the furniture fits. When it's really cold, the condensation on the inside of the glass freezes solid. As far as I can tell, there aren't drafts per se ... just cold coming in through a thin piece of glass.

I can run a space heater next to the sofa all winter, but would rather not. There are currently vinyl vertical blinds, which I usually leave mostly open for light. Since the landlord isn't going to replace this, what are my options? That old fashioned plastic shrink wrap would mean I can't use the balcony when winter weather is nice. (And it often is.) I can ceiling mount a curtain rod like this and then ... will curtains help? I hate losing the daylight (have a great view), but don't want to spend another winter freezing. Any other suggestions welcome. Thanks!
posted by cyndigo to Home & Garden (21 answers total) 2 users marked this as a favorite
Is there no way to shrink wrap the panes and still have the door slide, even partway? That'll be a much better solution if you can make it work so I would really try and do that.

Curtains will definitely help stop air movement, especially if they brush against the floor and overlap each other and the walls on either side.
posted by goingonit at 7:10 PM on October 19, 2021

You could have some custom window inserts made (I've never used that company; this is not an endorsement).
posted by mezzanayne at 7:27 PM on October 19, 2021 [1 favorite]

Since you can't upgrade to double pane, I do think that perhaps a double curtain rod - sheers and a heavier blackout style curtain. -- might help. I'm not sure if there are ceiling mounts for that but for us, leaving a middle section of the heavy curtains open allows the sheers to let in some light while still blocking some cold air.
posted by sm1tten at 7:46 PM on October 19, 2021 [1 favorite]

Ypou could try to coat it with bubble wrap.
posted by FungusCassetteBicker at 7:59 PM on October 19, 2021 [3 favorites]

In some states/localities the landlord is legally required to maintain an apartment in a 'healthy' state. Having freezing condensation on the inside does not see 'healthy' to me. Contact whatever agency oversees landlord/tenant law in your location and see whether this is an issue that they would or could take an interest in. If you feel this is too adversarial and fear losing what seems to be an apartment you like, then don't take any action; but if you are within your rights to ask for this health risk to be abated, go for it.
posted by TimHare at 8:23 PM on October 19, 2021

Response by poster: Thanks for the answers so far! It's otherwise a gorgeous apartment, so I don't want to antagonize my landlord or put up something unsightly. Unfortunately there's no way to half shrink wrap the sliding part of the door. I've sent for information about those panels, to see if they'd work for sliders.
posted by cyndigo at 8:43 PM on October 19, 2021

There are plastic films designed to increase the insulation value of glass.

Here is one example. The size on that page won't fit your twelve-foot-wide door, but you may be able to find a larger sheet.

As I was poking around, I saw that there are some that are static-cling and thus easier to add and remove for seasonal or moving-out-and-want-the-security-deposit-back reasons.

I've installed the privacy versions of these materials before - it's a bit tricky to avoid air bubbles, so you might want to plan on throwing at least one sheet away.
posted by Hatashran at 9:36 PM on October 19, 2021

A single pane of glass is going to offer totally shitty insulation regardless of what you do with films. Glass, especially in typical window or door thicknesses, is just too good at conducting heat.

What you need to engineer is a small pocket of dead air between you and the cold outside, and if what you currently have is effectively a wall made of single-thickness glass, your best option would be a heavy curtain with a tightly woven lining on the window side, that covers the entire glass area when closed, has folds that touch the wall all the way up on both sides, and sits nicely on the floor so that cold air doesn't flow out underneath it.

The idea is to make the closed curtain and the glass form a bucket that retains a body of cold air. The bucket will be open at the top where the curtain rod is, but as long the curtain is a tight weave and mostly not leaky at the sides or along the bottom, the cold air won't move into the room.

Air is a lousy heat conductor compared to glass, so it's the air trapped between the curtain and the glass that will insulate your room. As long as it doesn't mix with the room air, the fact that it is itself freezing cold won't affect its ability to do that. And if there's a sheer inside the cold-air bucket as well, so much the better - this will impede interior convection currents and make it an even better insulator, in much the same way (if somewhat less effectively) as the filling in a puffer jacket.

Best of all would be to replace all the single-layer glass with multiple layers that have their own trapped dead air zone between them and anti-radiative coating treatments, but that costs more than you're likely to see in a rental.
posted by flabdablet at 10:17 PM on October 19, 2021 [7 favorites]

Could you elaborate on why film on the glass will not work?
Could you put the film on the outside of one side of the door and on the inside of the other?
So that there is no film where the doors ‘slide’ by each other.
posted by calgirl at 10:19 PM on October 19, 2021

Could you elaborate on why film on the glass will not work?

Films on glass are designed to cut the amount of electromagnetic radiation that passes through it, specifically radiation in the infra-red (IR) region of the electromagnetic radiation spectrum.

About half of the heat transferred to the Earth by radiation from the Sun arrives via that IR part of the spectrum; most of the rest is via visible light. IR treatment films are mostly transparent to visible light, which is why you can still see through windows that have them applied. If your eyes were sensitive to IR rather than visible light, an IR treatment film applied to glass would make it look more like a mirror.

So IR films can be somewhat effective at reducing radiative heat gain into a space when the issue is that too much unshaded glazing has been designed in on the sun-facing side. And since the electromagnetic radiation emitted by items at typical home-interior temperatures is all infrared, films can make some contribution to reducing night-time heat loss as well. But the way single glazing removes heat from an interior space on a freezing cold night is overwhelmingly not by radiation, but by conduction and convection.

The outside surface of the glass is exposed to freezing cold night air. The glass is thin and has relatively good thermal conductivity whether a film has been applied or not, so it conducts away whatever heat exists inside itself and dissipates that on the outside, which makes the inside surface of the glass end up very nearly as cold as the outside air.

Interior air that touches the inside surface of the glass is therefore rapidly cooled by conduction. Cool air is denser than warm air, so you end up with a convective current of cold air flowing down the inside of the glass and across the floor into the room, mixing with the room air and cooling the room. The cold interior surface of the glass also encourages any water vapour in room air that touches it to condense on the surface, and the cold glass conducts away the latent heat of condensation (and, later, the latent heat of freezing) to the exterior. Both these processes remove even more heat from the circulating room air.

By arranging for the air nearest the glass to be trapped there in a space small enough to discourage convective air currents, the only way for heat to move outward through the glass is by radiation (which a heavy curtain will also block), or by conduction through the trapped air pocket (which is minimal because air is such a poor thermal conductor). You also stop heat being lost by condensation and freezing, because most of the water vapour in the room air just never gets a chance to touch the glass.

This is also how double-glazing works. The air gap between panes in a double-glazed window or door is very small (only a millimetre or two) but because of that very narrowness it's basically impossible for a circulating convective current to start up inside that gap, which means that the only ways to transfer heat through the window is via conduction through the air gap (minimal, because even thin layers of air are much worse thermal conductors than glass) or radiation. Triple glazing works twice as well because it has two air gaps, and superwindows have more air layers and inbuilt IR-selective surface treatments and work better still.

But plain old heavy curtains, especially with a sheer between the heavy curtain and the window, work too - and in fact this use case is pretty much exactly what they were invented for.
posted by flabdablet at 11:24 PM on October 19, 2021 [12 favorites]

Yes, curtains will help a lot. Fairly heavy and/or lined would be best, although you might need to be careful about the weight that the curtain rod will hold. You should close the curtains as soon as it gets dark and don't open them until it is properly light. We often leave ours closed when it is very overcast, but you can choose how you use them.
posted by plonkee at 3:35 AM on October 20, 2021 [1 favorite]

I wonder if clear vinyl curtains would help? Either shower curtains or hardware stores sell it by the yard at varying thicknesses, some very thick. Sew or glue a gusset at the top or punch holes through for curtain rings.
posted by TWinbrook8 at 4:41 AM on October 20, 2021

You have raised a "window" problem and have received very good window advice - curtains.

Another thing to know, more for owners/buyers/DIYers --
Excessive condensation such as you describe at this door frame is likely to lead to sill damage [accelerated weathering; rot; insect damage] and hidden structural damage under that sill, so it is not just a comfort issue!
posted by Glomar response at 6:10 AM on October 20, 2021 [2 favorites]

If you are willing to forgo being able to access the balcony say December - February, then a patio door shrink film kit will work really well. Make sure to wipe down and let drive the molding or wall section the tale will adhere to, for best results.
posted by walkinginsunshine at 7:21 AM on October 20, 2021

If you really like the apartment then offer to split the cost for a new door. It'd be like $1000 each. Do you pay for electricity? Then this might eventually save you money.
posted by The_Vegetables at 8:24 AM on October 20, 2021 [1 favorite]

There is polythene film meant for isolating single pane windows, that you cut one inch larger each side than the pane is, then stick it on the frame using thin double-sided tape. Don't know if it's available in large enough sizes to cover that door in one go, but as a fix you could (again using double-sided tape) stick wooden or pvc slats on to the glass to create surfaces that the film can be stuck to. They should be about an inch wide and as thick as the inside thickness of the frame or slightly thinner, and spaced to fit the width of the film.

As there's barely any thickness added to the frame it should not foul the fixed part of the frame when you want to open the door.
posted by Stoneshop at 8:26 AM on October 20, 2021 [1 favorite]

thermal curtains or blinds will be your friend; curtains are probably easier and cheaper. see: and

good luck!
posted by mollymillions at 8:52 PM on October 20, 2021 [1 favorite]

There is polythene film meant for isolating single pane windows, that you cut one inch larger each side than the pane is, then stick it on the frame using thin double-sided tape.

Unlike the IR-blocking films designed to be applied to the glass surface, what you'll end up with this kind is going to be roughly equivalent to double glazing: an outer glass membrane, then an air gap, then an inner plastic membrane. The thickness of the air gap will be set by the extent to which the glass is set back from the framing surface that the plastic is attached to.

A trapped air sandwich even only a few mm thick will get you a marked reduction in conductive heat loss through the glass, but a very thin sandwich might cause issues due to thermal expansion and contraction of the trapped air. If the air is perfectly sealed inside the gap, and the glass gets much much colder than it was when the plastic inner layer was first applied, then the trapped air will contract - and if the gap was narrow to begin with, you might find that it contracts so much as to suck a fair bit of the plastic layer into contact with the glass and put you back in ineffective surface-film land.

So if you're going to try out that kind of film treatment, use the heat-shrink kind to get the plastic layer taut and flat so that it doesn't snuggle up to the glass by pure flop action, and don't be too conscientious with the tape; be sure to leave at least a pinhole-sized leak to let the air pressure inside the sandwich equalize with the room air. A tiny leak won't cost you enough thermal performance to be noticeable, but should be enough to keep the plastic layer from being sucked onto the glass.

That said, I still think that heavy curtains drawn at night would probably be both more effective (they also address conductive losses through the framing materials, which can be substantial especially if that's aluminium) and more landlord-acceptable.
posted by flabdablet at 8:32 AM on October 21, 2021

Response by poster: Thanks I've emailed maintenance asking them if they can install shrink film on each individual panel. I work on one side of the freezing glass wall in the daytime (so love and need the light) and enjoy the skyline view at night on the other side (so hate to block it). Hopefully they can figure something out and if not, I'll ask about splitting the cost of a double-pane replacement.
posted by cyndigo at 5:46 PM on October 21, 2021

Just make perfectly sure they understand that what you're asking for is the kind of film treatment that leaves an air gap sandwiched between the film and the glass, or you'll end up with IR film bonded to the glass itself and stay cold.

If you want to go the whole hog with films, you could bond an IR film to the glass and install air-gapped shrink film on both the inside and outside of the doors, to make a double-cavity almost-superwindow on the cheap. But make sure the glass is super clean and streak-free before you start, because noticing a smudge on it that you've sealed in beyond removal would be really annoying.
posted by flabdablet at 5:47 AM on October 22, 2021

That air gapped shrink film really does do a good job, and if its installed correctly you can barely tell it there looking through the window.

I'd still recommend a good insulative curtain. And in the meantime, can you buy a dehumidifier to at least cut down on the condensation? Maybe from Walmart so you can return it later.
posted by ananci at 10:39 AM on October 22, 2021

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