Anyone who sits next to the window on a cold winter’s day will probably notice it immediately: windows let in quite a bit of cold. Investing in glass insulation can therefore be a smart way to reduce energy costs. Which considerations are important?
Since gas prices have gone through the roof, Milieu Centraal has seen a sharp increase in interest in energy saving. “And insulating windows is certainly in the top ten topics that people want to know more about,” says Puk van Meegeren, energy expert at the information organization.
Five forms of glass insulation
There are currently five types of glass that homeowners may have to deal with: single glass, double glass, HR++ glass, triple glass (also known as HR+++ glass) and vacuum glass. The name already reveals what single and double glazing is.
But what exactly is HR++ glass? “That is also double glazing, but with two important differences,” says van Meegeren. “It has an insulating coating and between the glass plates is the noble gas argon, which also has an insulating effect.” Triple glazing has the same characteristics as HR++ glass, but it consists of three panes of glass, making it even better insulated.
Just think: which insulates better? A cavity wall filled with twenty centimeters of insulation material or a pane of glass three centimeters thick?
Vacuum glass is a relatively new form of glass insulation. It is double glazing with a very small amount of space in between. It insulates just as well as triple glazing, but is only 8 millimeters thick and therefore a lot lighter. As a result, it can also be suitable for old homes and monumental buildings, where the window frames are sometimes not strong enough to bear heavier panes. Major drawback: it is about three times more expensive than other forms of glass insulation.
What is the U-value of glazing?
The insulation value of glass is expressed in U-value. The following applies: the lower it is, the better. Eddy Hagedoorn, sustainable living advisor at De Energiesavers, explains: “The heat in your house ‘leaks’ to the outside, as it were. The more resistance the heat experiences when leaking through windows, the lower the U-value.” Single glass insulates very poorly and has a U-value of 5.8. Triple glazing (in a new frame) insulates very well and has a U-value of between 0.9 and 0.4.
But… no matter how well insulated a window pane is, it is and remains the weak point of your house, emphasizes Hagedoorn: “Just think: what insulates better? A cavity wall filled with twenty centimeters of insulation material or a three centimeter thick window pane?”
Price tag and payback period
In addition, glass insulation has a hefty price tag. Van Meegeren: “Let’s assume a corner house – in terms of energy loss, that is between a terraced house and a detached house. With 22 square meters of window area. Then the total costs for HR ++ glass are around 3,700 euros.”
Good news: you can get back up to 30 percent of the investment through the Investment subsidy for sustainable energy and energy saving (ISDE). But then you are still on a price tag of about 2,500 euros. By way of comparison: cavity wall insulation (minus subsidies) costs an average of around 1,500 euros.
If you have single glass, I would call the glazier today.
Of savings that you realize with cavity wall insulation, is significantly higher than that of glass insulation. Hagedoorn: “Most homes in the Netherlands have at least double glazing. This already has a U-value of 2.8. The savings you realize with a switch to HR++ glass (U-value: between 1 and 1, 2) is then limited. Cavity wall insulation usually pays for itself within one to three years. With glass insulation, you often talk about a payback period of ten years.”
When is it smart to invest anyway?
When is it smart to invest in glass insulation? “If you have single glass, I would call the glazier today,” says Van Meegeren. “That is such a big energy leak, it pays very much to switch to, at least, HR ++ glass as soon as possible.”
In addition, double glazing can be leaky, adds Hagedoorn: “Then there is moisture between the two glass plates, it no longer has an insulating effect and it must be replaced anyway. Then you might as well go for HR++ or triple glazing.”
Do you already have scaffolding next to your house because painting is being done? Ideal time to also invest in glass insulation.
But there are more reasons to consider glass insulation. It also provides comfort gains. “There is often a couch or chair in front of the window. The better you insulate, the more comfortable you sit there,” says Van Meegeren. “And another advantage: it dampens outside noise better.” Hagedoorn agrees that glass insulation leads to more living comfort: “But hanging thick curtains in front of the windows can also work wonders.”
Combine chores
Nevertheless, investing in glass insulation can also be interesting for people who already have double glazing, concludes Van Meegeren. “What we sometimes advise is to combine jobs. Suppose your window frames need to be painted soon, then there will be scaffolding next to your house anyway. That is an ideal time to also invest in glass insulation. If you provides good gap sealing and new draft strips, you will save a lot less money down the line.”
Hagedoorn adds another important piece of advice: “Also pay attention to the ventilation. The moisture in your house must be properly drained and that is more difficult in a well-insulated house. Insulation is good, ventilation is better, I always say.”
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