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Think your windows are energy-efficient? Check this

11. 08. 2026

A child plays with a dog in a warm home while it is snowy outside

When discussing a building's energy efficiency, attention most often turns to the thickness of thermal insulation, facade quality or the heating system. Windows are often viewed as just one of the building's elements. However, modern windows and doors play a much more complex role.

A window today is more than a frame with glass separating the interior from the outdoors. It is part of the building's energy envelope and must work with the facade, glazing, installation method, building orientation and architectural design.

Choosing a quality window should therefore not be considered in isolation. Even a very high-quality window system will not achieve its full potential unless it is properly designed, selected and installed in relation to the rest of the building.

1. The window system, glazing and facade must function as a whole

Heat loss through windows depends on several factors. It is not enough to ask whether a window is made of PVC, aluminium or wood. The more important question is the overall performance of the complete window unit.

With modern windows, important roles are played by the profile, thermal insulation properties, glazing, spacer, hardware, sealing and installation method. Together, they determine how much heat will pass through the window and how well the interior will be protected from outside temperatures.

One important indicator is the Uw value, the heat transfer coefficient for the entire window. The lower the Uw value, the more energy-efficient the window. However, the window's value should not be considered separately from the properties of its glass and profile.

This brings us to another common misconception: quality glass alone does not mean the entire window is energy-efficient.

Overall performance is also affected by the profile and the way the glass and frame are connected. Modern insulating glazing uses different configurations and coatings that can improve thermal properties, control the passage of solar energy and increase indoor comfort.

Equally important is the facade. If a building has quality thermal insulation but its windows are a weak point in its energy envelope, some of the insulation's potential remains unused.

Windows, the facade and other parts of the building envelope should therefore be considered as a single system.

This is especially important for modern buildings with large glass surfaces. Large glazed walls can bring abundant natural light into a space and provide a good visual connection with the surroundings, but they also require careful selection of glazing, profiles and solar shading.

In other words, energy efficiency does not simply mean having as few windows as possible. The aim is to design appropriate window areas and choose a system that provides a good balance between natural light, thermal protection, solar gain and comfort.

2. A good window is only as good as its design and installation

Even when a quality window system and appropriate glazing have been chosen, the work is not finished. One often overlooked aspect of energy efficiency is window installation.

The window must be correctly positioned in relation to the wall and facade layers, and the joint between the window unit and the building must be constructed to reduce the possibility of air infiltration and thermal bridges.

Modern construction therefore pays increasing attention to installation details. Producing a quality window is not enough: its designed characteristics must also be realised after installation.

This is especially important in energy-efficient and low-energy buildings, where every element of the envelope is designed to reduce unnecessary energy losses.

How to choose the right windows and doors?

There is no single window system that is universally best for every building.

The criteria important for a family house may differ from those for an office building, hotel or contemporary architectural project with large glass surfaces.

PVC windows and doors can be a sensible choice for various types of buildings, particularly when thermal insulation, functionality and economy are priorities.

Aluminium systems allow slim profiles, large dimensions and high architectural flexibility, making them particularly appealing for modern buildings and large glass surfaces.

Wooden windows and doors provides a natural material, a distinctive aesthetic and good thermal insulation properties, while wood-ALU systems combine the natural appearance of wood with the additional protection of aluminium cladding.

This is precisely why the choice of windows and doors should not be reduced to “PVC or ALU?”. The real question is:

Which window system best suits the specific building, its location, architecture and energy requirements?

When designing a building, it is also necessary to consider window orientation, the size of glass surfaces, climatic conditions, thermal and sound insulation requirements, the amount of natural light and how the space will be used.

When all these elements are properly coordinated, the window ceases to be merely a building component that closes an opening in a wall. It becomes an important part of the building's overall concept.

The energy efficiency of a modern building does not depend on a single product. It results from a properly designed whole in which the facade, thermal insulation, window systems, glazing and installation method work together.

When choosing windows and doors, the focus should therefore extend beyond profile material or window appearance. It is important to consider the overall performance of the system and its compatibility with the building.

A well-designed and properly installed window can simultaneously help reduce heat loss, improve comfort, make better use of natural light and enhance the building's long-term value.

In contemporary architecture, it is therefore no longer enough to ask: “Which windows and doors should I choose?”

The real question is: “How will my window system work with the entire building?”

Long-term value with the SAPLAST standard

At SAPLAST, we deliver solutions meeting high technical, functional and aesthetic demands. Our expertise, modern technology and individual approach are recognised throughout Bosnia and Herzegovina and the European Union.

For Building trust for 29 years through quality workmanship, reliable installation and long-term aftercare, because our goal extends beyond filling openings to opening long-term partnerships.