window glazing systems - condensation, prevention strategies,

Window Glazing Systems: Are You Making the Right Choice for Your Building Project?

Foreword by Ian Thompson, Editor

What window glazing systems are you specifying? Should you specify single glazed, double glazed, or triple glazed windows? Thermally broken or not? Why does condensation form on double glazed window units? How can we prevent it, and why is it important? If you plan to design and build a genuinely healthy home, understand that windows are often the least thermally efficient parts of our wall assemblies. Even triple-glazed units fall into this category. Therefore, it’s crucial to specify the correct window joinery in combination with good HVAC control units to effectively manage this.

In today’s video, Matt Risinger from The Build Show demystifies the frustration caused by condensation forming on your window glazing with proven prevention strategies. Matt explains why moisture collects on glass surfaces and how to prevent it from doing so.

We unveil why non-thermally broken aluminum and even up-to-code vinyl windows are prone to excessive condensation, especially in cold climates. Through real-world examples, you’ll understand how factors like window construction, indoor humidity, and exterior temperatures interact to cause puddling and frost.

Gain valuable tips on selecting optimal window materials and triple glazing to minimize window condensation risks. Learn straightforward DIY adjustments like humidity control to create drier indoor conditions.

Achieve the clear view you deserve while avoiding potential water damage and mold. Matt’s guide provides you with the knowledge to combat window condensation through proper window selection, installation, and maintenance.

Over to you, Matt!

Mastering Window Condensation: Expert Prevention Strategies and Insights

Video Transcript

window condensation, prevention strategies, window construction, humidity control

On the build show today, we’re going to answer an age-old question: Why is there condensation forming on my window glazing at certain times of the year? I’m going to get into some nerdy science. I’m going to use my house as an example and we’re going to talk about lots of different window styles.

Today’s build show: window condensation. Let’s get going.

Okay y’all, let’s talk window condensation. This photo is a non-thermally broken aluminum window. This is like a 1990s built house in Texas. A friend sent this to me and said “Hey, why is this happening on my windows in the winter time?”

And you know, years ago when I first encountered this as a builder, I think that my, uh, production builder I was with kind of trained me to say “Oh, you need to use the bath fans. The humidity is too high in the house in the winter time.” All these kind of standard answers.

But condensation sometimes even happens so much that it puddles underneath the windows. And this is that same house that my friend sent me the photos and they said “Look, it’s actually puddling at the base of the windows.”

Uh, now again, this was an aluminum window, non-thermally broken, meaning the aluminum from the inside is transferring to the outside and this is a winter day. So you can probably guess what’s happening here: The windows were cold and any moisture that was in the air was finding a dew point on the window.

So would this happen in a more modern window now? This window on the other hand, uh, is from a house in a Northern climate and this is a vinyl window. And vinyl windows typically have a pretty good U-factor. A lot of times you’ll see a vinyl window that has a U-factor of 0.32-0.30.

Uh, maybe slightly lower than that, which means it meets code to put that in in a, a good amount of places. But this window having so much condensation that it’s actually causing a puddle at the base of the window…if you fast forward to a really cold day, that puddle, that condensation could actually turn to frost on the inside.

And maybe that’s how you found this video: “Why are my windows frosting in the winter time?” That’s really just condensation that’s gotten cold enough to actually freeze.

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Let’s fast forward to a real life example at my personal house. You know I built a house for my family. I’m doing a whole re-look series on that, go check it out called the Real Rebuild. But this window here is a composite window. Uh, it is a double glazed window.

Uh, it meets all the codes, uh, for my state and would meet code if you were building this in a Northern house. But last winter I got some condensation on several windows and it got me thinking: “What’s, what’s happening here that even a window that meets code on a newly built house would have condensation?”

So here’s the condensation on those windows. I just kind of took a pan shot so you can see it’s happening, uh, all across the kind of base of the window. And it was happening so much it was actually pooling a little bit in the corner of my window. So I could actually get moisture on my finger as I did that.

Now in another part of my house, same manufacturer but a different window, this is a wood window with triple glazing, meaning three panes of glass. So this is more than code, this is a really nice, uh, window with really good U-factors. The U-factor on these is probably something like, uh, 0.17, uh 0.18 something like that.

Now this window, uh, same time I made the other video, not a drop of condensation anywhere on this video. I’m just kind of zooming in here to show you that same window, uh, you know, just a separate room, slightly different room, zero going on.

Let’s look at the conditions as I took this video. You can see from my iPhone here it was 1:00 in the afternoon. Outdoor temperature was 28°F. So a little chilly for Austin but certainly not cold for many of you in the north. Uh, overnight lows were 13° so it got pretty cold, maybe the night before. But let’s look at the indoor conditions: 72°.

My wife likes a little bit warmer inside the house. But 37% relative humidity—that’s a pretty low humidity setting. In fact, most dehumidifiers, if you have them set, won’t actually dehumidify below or get you below 40% or sometimes 35%.

So in other words, there’s not a high humidity event going on here. This isn’t someone took a 2-hour shower in my house, uh, or even “Hey, you forgot to turn your dehumidifier, your bath fans on.” This is pretty low, uh, humidity percentage.

So what we need to figure out is what’s the dew point in the house at those conditions to figure out if condensation is going to form. Uh, Santa Fe makes a, uh, free psychometric chart which is basically a way to figure out what the dew point is under certain conditions.

You can download it on the App Store. I did that on my phone and I saw that 72°F at 37% relative humidity means the dew point, the place where dew will form, is anything that’s 44°F or lower.

You know, if I had a glass of cold water here we’ve all seen that: Iced tea on a summer day that sweated on the outside. That’s exactly what’s happening there is that dew is forming on the outside.

So let’s look at the conditions of my house now that we know those conditions. Here’s that same window that had condensation. Through my FLIR gun that I took a photo of, you can see the corner of that glass is 42.2°F.

And remember from that slide previously, that’s the dew point under these conditions, which means even a good window that meets code, that’s, uh, you know, thermally broken, this happens to be a composite window, is having condensation issues. It’s simply a matter of what’s the, uh, temperature of the window and what are the interior conditions that dew might form.

Now let’s go back and look at that triple glazed, uh, window. You can see the wall temperature around that is pretty high. I have a well-built house. I have a very airtight house and I have 2 inches of exterior insulation on my house. So my house would perform really well even if I’d built it in Minnesota, let’s say, even though I’m in Austin, Texas.

The wall temperature here in this really cold day, 68°. Although you with that FLIR gun, you can actually see my individual studs and look above that where it says 68°F, you can tell that it’s a little colder, uh, in that corner from that FLIR gun ’cause cold, uh, is a dark color and warm is a yellow color on this.

So now let’s, let’s turn it onto video mode and let’s take a look at that glass. Remember this is that same triple glaze glass that we saw earlier and there’s really no surfaces that are much colder than 50 some degrees. Let’s say it looks like is about the coldest I’m seeing on there. I really like that thermal imaging camera. This happens to be the one that I plug into my iPhone.

Okay, now I’ve got one other window that I haven’t mentioned on my house and that’s this one. Uh, this happens to be a triple glazed window, or actually it’s beyond triple glazed.

This is a passive house certified window. I installed a couple windows from a company called Fener, which is a Canadian company that makes these really ultra-bomber windows and this happens to have light zone glass in it which is a really bomber glass.

And this one’s even warmer. Check this out: The window frame, uh, coming onto the glass, there’s really nothing that’s below 60°, you know, two degrees maybe. And remember the dew point’s 42°F. So there’s really nothing that’s going to cause any condensation whatsoever in that area with that glass being that warm.

There’s my Labrador coming into the scene. That’s Benny.

So what’s the takeaway here and what can we learn from this from a building science perspective for my builder audience? Really the takeaway is that many windows, or really any window, can have condensation issues. Certainly you’re going to see that more in a non-thermally broken window, a steel window, an aluminum window, something that doesn’t have a thermal break in there. But I think another big takeaway for me as a builder and for you is humidity control does not equal condensation control.

Remember that young Matt Risinger, superintendent, who was telling customers “Oh you gotta turn on the bath fan” or maybe “You got to use your dehumidifier.” That’s not really true. That’s not necessarily going to control that humidity really well. And we also need to set correct expectations with our clients on all these same issues, that “Hey look, you might have some condensation.”

I think the other takeaway that you want to think about is if you have a window that may be a code-approved window but not a triple glaze, not a passive house certified window, you’re going to make sure you’re not using moisture sensitive materials around that window. You saw my window early on where it was pooling water. I have real wood painted trim in there. So about the worst that would happen is if we got some condensation, puddling is maybe I’d have some paint that would bubble in that area. But I don’t have, for instance, MDF trim which would blow up and have a problem.

So be cautious about sensitive materials like drywall, let’s say, or MDF, or maybe hardwood floors touching those windows and doors if there’s some risk of condensation. And be sure to alert your clients whenever they choose a window, even if it’s a code-approved window, that condensation can occur even with a code-approved window under the right indoor and outdoor conditions.

Hopefully you guys learned a little bit about condensation and windows from this video. And I think the last takeaway is, uh, if you really want to reduce that risk of condensation, uh, you want to go to a window that has a higher, uh, condensation resistance number, and you can see that on the NFRC charts. And of course when you go to a triple glaze window, when you go to a more insulative window with a lower U-factor, you’re going to reduce that chance of condensation.

Guys, always love talking nerdy building science. If you’re not a subscriber, hit that subscribe button below. And by the way, if you haven’t seen our Build 101 series, we’ve got a 10-part series that my buddy Steve Baczek and I filmed right here in this studio giving you all the basics of building science. This is just a little bit of a taste of that, but it’s a several hour program that’s all free and we’ll give you a certificate to show you that you passed.

I’m hearing lots of builders like Stephanie Daly are incentivizing their crew with a crisp $100 bill to go watch that. You really need to have a good building science education, guys. Follow us on TikTok or Instagram, otherwise we’ll see you next time on The Build Show.

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