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The window panes in my West Seattle home are cracked. Can I just replace the pane, and not the whole glass unit?

The window panes in my West Seattle home are cracked. Can I just replace the pane, and not the whole glass unit?
The window panes in my West Seattle home are cracked. Can I just replace the pane, and not the whole glass unit?
By BettyLoucal Sep 05, 2017


This is a tricky question. Most windows today – at least in homes where people live, but less so in places like warehouses – windows are more often than not double or even triple-glazed. That means there is more than one pane of glass in a single frame. So what, for example, can be done if just one of the panes is cracked or broken, and not the other one or two within the same frame unit?

It’s usually best to replace the whole, sealed window unit

In some cases, it’s actually possible to replace a single pane, while ignoring the others, or at least, working around them carefully while you only replace the one pane. In most cases, however, the best solution is to replace the whole unit of glass with the one frame. Why? Because most multi-glazed windows contain inert, insulating gas between the panes, and are thus designed to be replaced as a single unit. It is probably going to be cheaper and easier to simply replace the whole unit, and not just a single pane.

When double glazing and triple glazing first emerged on the market, the space between the panes was simply air. The gap itself, if sealed, works well as an additional barrier to stop expensive warmth from leaving you home, or to stop high summer heat from entering. At least, it can slow it down considerably, and significantly more than having, for example, double the thickness of a single pane. That extra ‘layer’ of air works like the capillaries in a the down covering most of a duck’s body. (That’s why down comforters are so effective and so popular). Light can pass freely through several panes of glass, but heat insulation is vastly improved by that gap (or gaps) of air between the panes. Furthermore, rather than just having plain old dry air in those gaps, one of a number of inert gases can be used; ones that reduce the amount of heat transfer – at the same air pressure – as ordinary air. In a world where energy costs money, any help is appreciated, and a major factor in opting for multi-glazed windows is the enormous potential to reduce the transfer of heat through a window.

Even if a pane is in perfect shape, the window seals may have failed

Nothing lasts forever, but you can still expect most glass units within each of your window frames to last decades. That is, the seal that keeps the gas inside the gaps airtight and effective. Even a tiny hole or a minute crack in the glass will cause several problems. The first is, the conduction reducing gas will escape. As air pressure increases and drops again, the once-was sealed glass unit will eventually “breathe” out all the gas it was given during manufacturing, and will replace it with regular atmospheric air, whatever it is around your house. That means moisture will also collect inside the glass frame unit, and fog up the inside. That’s something that you cannot ‘wipe off’ the window, obviously, because it is inside the once-was sealed unit. Over time, even a tiny leak in such a window unit can ruin the transparency of a window or door. When that happens, it might be time to replace your whole window unit, actually, because they often reach the end of their lifetime around about the same time. In other words, there is no point in spending lots of money to replace the inserted glass pane units, only to have to replace the whole window a couple of years later.

Double or triple glazed windows? It’s worth it!

So what else can double or triple glazing do for a home owner? Top of my list – perhaps because I live in a city – is sound insulation. I remember the first time I came home to my house the evening of a complete window replacement project on the street-facing side. I walked into one of the bedrooms of the house, and the first thing I noticed was, silence! I opted for triple glazing because of its extra privacy, but the drop in ambient street level sound was remarkable. We get used to ambient noise. If you’ve ever gone to live in an isolated place out in the hinterland, you might notice the quiet when you sleep. For some of us, it’s too quiet, but I have definitely gotten to like my quiet!

Protection from ultraviolet light

This doesn’t necessarily come standard with a multi-glazed window, but more and more often these days, it does. Windows are not just there to “let in light and keep cold out”, but are a multi-functional product you add to your home for many reasons.

Have you ever looked at a building and thought, that glass looks green? No glass is perfectly transparent. In regular, home-use industrial glass, there is always some tint to it. In fact, it can vary slightly on a batch to batch production run, but most people would not notice that without test equipment. The variance is so slight, you’d need a light meter to measure it. Green is the natural tint an ordinary sheet of glass will have, but manufacturers know that glass can really be tinted with almost any color a market tasks them to produce. Today, though, glass is often delivered with a 5% UV let-through. That is, for every 100 units of ultraviolet light meeting the outside of the window pane head-on, only 5% makes it through. And that’s at a perpendicular angle to the glass. Usually when it’s at that angle, it’s either early or late in the day, and there is little or no UV light in it. At the hottest time of the day, when the sun is high in the sky, the light hits the glass at an angle. The sharper the angle, there is going to be more UV light, but as that angle increases, so too does the thickness of glass it must penetrate increase. There is also more reflection, which reduces further the amount of UV light that can enter your home. Furniture, drapes, carpets and other property is all protected.

Come back next week, when we dig deeper into the differences between double- and triple-glazed windows.

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