A couple of weeks back on LinkedIn & Twitter’s #TwoCentsTuesday, we asked our readers what makes a 4th surface LoE coating on a double glazed window better than a triple pane window. 20% said configuration options and cost, and the Window Geeks agree. Let’s take a closer look at why extra LoE coatings could be the right choice for your project.
U Values, Performance, and Environment
A 4th surface LoE coating may have a slightly lower U Value than a triple glazed window, but it can still achieve a similar rating. A 4th surface coat can have a U Value just above 1.20. A regular triple-glazed window, on the other hand, has a U Value just below 1.20. There’s certainly a time and a place for triple-glazed windows, but with BC’s moderate climate, the need for the additional U Value decimals is rarely there. The 4th surface LoE coating achieves close to the same performance, and it’s also better for the environment as less glass needs to be manufactured which means less greenhouse gas emissions are produced, and there's a reduction in embodied energy used throughout the process.
A third pane of glass will lead to the window being heavier, and their installation requires more labour. You’re also limited in sizes and configurations to help ensure the product can function and stand the test of time. Opting instead for a 4th surface coat of LoE saves on costs and labour, potentially improves design and configuration options, and makes it easier to meet your needs.
Are 4th surface LoE coatings less durable?
Some believe a 4th surface coating will make the glass less durable and prone to scratches, but this is a common misconception.
This report on scratch test results actually shows greater scratch resistance on glass with a 4th surface coat than regular glass. Most LoE coatings are on the inside of window panes and are silver. If silver coats were used on the outside they would oxidize and tarnish, which is why indium tin is used instead. Indium tin will not have these issues, which is why it is considered a hard coat that will last.
The main rule of thumb to remember if you do have a 4th surface LoE coating is to avoid acid-based cleaners. As long as you do, the coating will be fine and will remain durable. The coating itself is harder than the glass surface, so if you can scratch the coating, you would have scratched the glass anyway. This coating has a failure rate of just 0.2% over 20 years.
4th surface LoE & condensation
The NFRC uses condensation resistance factor values for rating and comparing window products and their potential for condensation. The term resistance is used because real-world environmental conditions vary from the standardized conditions used to determine these values. The standards aren’t meant to predict whether condensation will occur, as there are some circumstances where it is impossible to avoid.
Condensation is the result of a number of factors ranging from improper ventilation in a room to the airtightness of a home. There is no proven research available confirming that a 4th surface coat of LoE increases condensation potential. That being said, the relative humidity of a home and the climate zone will determine whether condensation forms and if you’re in a climate zone 7 or the relative humidity in your home is kept at above 40% then you may consider triple glazing instead of a 4th surface coat of LoE. That’s not the case in BC, where most people with good windows won’t experience condensation for the majority of the year due to the moderate climate. There may be a few cold snaps where it does occur, but that is to be expected.
So a triple-glazed window isn’t better?
Not really, if you take into account everything we’ve discussed. In BC’s climate it is unnecessary and a waste of material and labour, and will ultimately only serve to drive up your costs. The smarter choice here is the 4th surface LoE coating.
If you’re building to the Step Code and aren’t sure whether a 4th surface coating will be beneficial for your project, just reach out. Our experts are always willing to consult and help with your project. We’ll make sure you’re on the right track.
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