What determines the quality of windows?

Sep 2019

Windows are an extremely significant part of a home, affecting its many aspects – appearance, functionality, security, energy efficiency. They are often the first thing that catch the eye and determine your overall impression of the building. Here we explore what makes quality windows.

  • Material

There are several perceptions on the quality of the different materials used for windows. But it’s more about how the material is used that determines the quality of the final product.

For PVC, high-grade profiles from top manufacturers like Veka or Aluplast should be considered. Interestingly, PVC is fully recyclable at end of life, so it can be considered the most eco-friendly. Steel reinforcements in all PVC windows & doors is absolutely necessary to ensure strength and stability. This creates extraordinary possibilities, like the Oknoplast PVC sliding doors reaching up to 6.5m in width.

Timber is generally not very suitable for the Irish climate, where moisture is ever-present. While exposure can be reduced through Alu-clad externally, the timber may still be affected by water vapour in the air. It’s imperative for the timber to be well treated/protected in production, and maintained regularly throughout its lifetime.

Aluminium offers the highest level of durability and structural ability. However, thermal brakes are extremely important to ensure acceptable insulation parameters.

  • Technical parameters

The numbers that determine the performance of windows are very important indeed, but need to be seen in the right perspective – only when we put them together, we see the whole picture.

U-value tells us how much heat escapes through the window. It’s therefore crucial to know the calculated U-value of the entire window, not just the centre pane. Triple-glazing is the current standard for energy efficient buildings across Europe. With a second chamber of the insulating Argon gas, it’s roughly twice as efficient as double-glazing.

Air-tightness determines how well-sealed the window is and affects its energy efficiency. Class 4 is the benchmark for Passive windows, but can be achieved by some high quality near-passive windows too.

The water-tightness rating of a window tells us how well it prevents water ingress under pressure – an important factor to consider.

Sound insulation is another property worth considering. We all appreciate a quiet house when we need one. Good windows can reduce noise by around 35dB, e.g. bringing down the noise level of a driving truck to that of a quiet conversation.

Solar Factor – too much emphasis is sometimes put on this parameter. While solar gain may be significant during a cold but sunny winter in south Germany, it will rarely have the same effect in the Irish climate.



  • Design

Good windows don’t have to be beautiful, but great ones do. After all, windows are installed for a lifetime so it’s very important to love the way they look. Their style should follow latest architectural trends, while colour choices should be abundant and exciting – ultimately, colour is a way of expressing the owner’s style. Thoughtful design makes a difference, such as that in the Oknoplast Pixel window system – maximising the amount of light entering the room but maintaining great U-values.

  • Security

This point is simple but very important. No window is impossible to break in through, but the resistance it gives can often make the difference between a successful and unsuccessful break-in. The number and positions of the locking points are worth looking at. Windows absolutely must be internally glazed – an externally glazed window is as secure as an open window, as unglazing is a very simple procedure.

  • Functionality

A window should do more than just fill the hole in the wall, open and close. While only gaining popularity in Ireland at the moment, Tilt & Turn windows are the standard across Europe. This is largely due to their superior technology and improved functionality. Tilt & Turn windows can also achieve significantly greater sizes due to the more advanced hinges. Tilt and micro-ventilation functions are also useful for additional airflow.

  • Installation

Installation is arguably the most important part of the window sourcing process. Proper procedures should be in place, starting with a thorough site survey. Solid fixing of the window is essential – a minimum of 8 brackets per window is a reasonable requirement. Air-tight sealing of all openings with low-expansion foam is a European industry standard which should not cost extra. Taping around the windows further improves the air-tightness of the building, and should be available from the window supplier.


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