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Anatomy of a High-Performance Window

What are “high-performance windows”? There are several characteristics to consider when purchasing windows. Considerations span across design (frame material, aesthetic, sizes) code-requirements (landmark/historical), geography, performance criteria (u-value, SHGC, acoustic), and more. In this article, we’ll explore Ikon Windows’ custom engineering capabilities and key considerations for your next window purchase.

One of the most important but often overlooked criteria to consider is the U-value and SHGC (Solar Heat Gain Coefficient) factors.

U-value – Determines how much heat energy is lost or gained. The lower the U-value (closer to 0), the better insulation and the more energy you will save. For example a U-value of 0.20 performs better than 0.40.

SHGC – Determines how much sun’s energy (solar radiation) is admitted through the windows, SHGC values range between 0 and 1. The lower and window’s solar heat gain coefficient, the less solar heat transmits. The closer to 1 the more solar heat is transmitted through the window. In an environment where it is hot year-round, we recommend lower SHGC values (this will keep cooling costs down).

The table below references the U value and the SHGC values recommended for Passive homes depending on where you live in America. Since Passive homes are ultra-high energy-efficient homes, these numbers will differ from Energy Star. Whether you are building a Passive home or not, we recommend getting as close to those numbers as possible as it impacts tenant comfort and utility bills.

ASHRAE/IECC/DOE North American Climate ZoneOverall installed window U value Btu/h.ft2.fCenter of glass u-value Btu/h.ft2.FSHGC- SouthSHGC- North, east, west
8≤ 0.11≤ 0.10≥ 0.50Any
7≤ 0.12≤ 0.11≥0.50Any
6≤ 0.13≤ 0.12≥ 0.50Any
5≤ 0.14≤ 0.13≥ 0.50Any
4≤ 0.15≤ 0.14≥ 0.50≤ 0.40
Marine North≤ 0.16≤ 0.15≥ 0.50≤ 0.40
Marine South≤ 0.22≤ 0.20≤ 0.50≤ 0.30
3≤ 0.18≤ 0.16≤ 0.50≤ 0.30
2 West≤ 0.18≤ 0.16≤ 0.30≤ 0.30
2 East≤ 0.20≤ 0.18≤ 0.30≤ 0.30


Ikon windows is located in Brooklyn, New York and we experience colder climates during the winter. For this reason, we recommend (as budget allow), optimizing the U value to be as low as possible. In states like Florida, where winter climates are more mild, we can get away with high U-values as the chart shows. Finding the optimal balance based on geography is critical to avoid overpaying for windows.

Frame Materials

At Ikon Windows, we have a variety of frame materials to choose from such as uPVC, wood, wood with aluminum cladding, aluminum and steel. Depending on what you choose, there are trade-offs to consider as it relate to thermal performance, cost, design, durability, and longevity. For example, wood is naturally better as a thermal insulator compared to aluminum.

Wood windows or wood-clad windows are already naturally great insulators. One way to increase the insulation is by increasing the depth of the frame. Our standard entry-level frame is 68mm (2.67″) with a uf of 0.25 while our 92mm (3.66″) has a uf of 0.19.

At Ikon windows, we have two wooden window lines: a Classic (100% wood) and Alu Clad (wood interior, aluminum exterior). The Classic line is the standard full wood tilt and turn windows and doors. They are made entirely of wood with different species of wood to choose from. In the Alu Clad line, we add aluminum cladding to the exterior of the window. The benefits of aluminum as an exterior cladding option greatly improves the longevity of the product because it can better withstand outside elements. For our Passive House Windows, we may add additional foams or materials between the aluminum and the wood to achieve even greater performing uf values.

Alu Clad wood window

Thermal Breaks

For our aluminum and steel series windows we have to add an additional thermal break between the inside and the outside of the window. If you take a look at the picture below you can see the exterior aluminum and interior aluminum has a different material in the middle. That material is a plyamide thermal break which improves the thermal performance of this frame. Similar to our wood windows we can increase the uf of the aluminum or steel window by increasing the depth of the thermal break and adding chambers into the polymide strip which will further increase thermal performance. Our entry level frame has a uf value of 0.26. Ikon’s Passive house aluminum window which also utilizes aerogel achieves a remarkable uf of 0.125. You can find more of our aluminum window profiles by clicking on the picture.

Passive house aluminum window

uPVC windows are similar: the deeper the window, the lower the uf, in addition, the number of chambers within the frame will also impact the overall performance. By adding an additional chamber, we are increasing its thermal performance. The added chambers trap air, aiding insulation by preventing mini convection current moving the air around inside the frame. As an added benefit foam or other materials can be used to fill this frame and increase the uf even further.

uPVC window


High-performance windows also have lower air infiltration. Have you ever experienced a draft coming from a window that is closed? An older window may have issues with how tightly the window close which can result in air going in and out between the sash and the frame. To eliminate this problem, Ikon Windows incorporates multiple gasketing systems and multi-locking point systems on all our windows.

Let’s start with gaskets. To ensure we are getting a tight seal, we recommend at least two gaskets: interior and exterior. In higher performing windows you will see an additional gasket typically in the middle. Depending on how deep the frame is there may be room for additional gaskets. At Ikon Windows we specialize in European window system such as tilt and turn windows. The tilt and turn window has another advantage with the longevity of its gaskets compared to a double hung for instance. A hung window will need to utilize a sliding seal between the sash and frame. After years of use the friction on the seal begins to degrade the gasket resulting in failures in thermal efficiency as well as air and water leakage. On tilt and turn windows there is zero friction due to the seals being compressed by the multi-point locking system.

To ensure the proper seal around the perimeter of the window, multiple locking points are installed around the window. When the window is in a closed position, the locking point will compress the sash into the frame, compressing the seals completely around the entire window system. This complete seal will result in an air and water tight window.

Next up: Glass! It takes up the most surface area of your opening and plays a pivotal role in thermal performance. The first section I would like to cover is often overlooked because you do not really think it is an important part of the insulated glass unit (IGU) and that is the spacer. A spacer is the metal bar that goes around the perimeter of the glass that separates the panes and bonds to the glass to create an airtight seal so that fas can be filled between the panes. In traditionally-made windows, the spacer is made from a hollow piece of aluminum or steel which by now we should know that these by themselves are very conductive. Traditional spacers will create a thermal bridge between the outside and inside. This can cause condensation to build up around the window and allows heat to be transferred with ease. In high-performance windows what you should be looking for are Warm edge spacers. These spacers are typically filled in a high insulating material that will increase thermal performance and stop gas and moisture and vapor transmission. At Ikon Windows, we use the Swisspacer Ultimate on all of our products – as it is widely recognized as the leader in spacer technology.

Next in the IGU, of course, is the glass composition: applied films and glass fills. By increasing the number of panes in the IGU, for example using three panes of glass, we are then able to have gas-filled chambers. Taking a look at Ikons’ IGU, our standard double-pane IGU will have a u-value of 0.17, a triple pane will have a u-value of 0.088 and a quad pane IGU can achieve u-values as low as 0.05. The gas is also important to see what type of insulation will be achieved with the IGU. Argon gas is primarily used in high-performance windows. This gas is six times denser than regular air providing a better insulation factor. We can also use Krypton gas that is twelve times as dense as air. At Ikon we recommend going with Argon gas in a triple pane IGU as it demonstrates great thermal values and is less expensive then Krypton. While gas increases thermal performance, Solar heat entering the home can be a huge factor, especially in hot climates. As mentioned prior, when we discussed SHGC, this is typically where the films come in. Depending on your location, we want to choose appropriate parameters that will reflect the sun heat according to the graph provided earlier or similar.

Call us or email us at info@ikonwindows.com to find out how Ikons high-performance windows can take your home or upcoming project to the next level in comfort and thermal performance.

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