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Glossary of terms - Terrace doors and windows

What are the individual elements of the windows called? What is hidden in the description of their parameters?

We explain the most common terms used in the context of terrace windows and doors.


Window frame (also known as the casing) - A structural element of the window embedded in the wall, which permanently connects it to the window opening. One or more sashes are attached to the frame via hinges.



Window sash - The openable part of the window. It is equipped with a handle that enables operation and control of the sash. The sash, depending on the fittings used, can be tilted, turned or tilted and turned.



Window seals - Elements that ensure the tightness of windows. As standard, there are two types of gaskets installed in the windows: glazing and retaining gaskets (known as bumpers or notches). Both prevent the water from getting inside the window profile and prevent the fittings from rusting. The thrust seals also act as a barrier against wind, dust and noise. There are always two glazing gaskets, one on the outside and the other on the inside of the window. Their flexibility and resistance to changing weather conditions are ensured by the material they are made of, i.e. EPDM or TPS.



Heat transfer coefficient - A value that tells you how much heat is lost per square metre of surface (windows and doors) in one hour, if the outside air temperature is one degree lower than in the room. We denote the heat transfer coefficient by the symbol U [W/m2K]. The lower its value, the better. Low heat transfer coefficient means that the windows and doors have good thermal insulation properties and guarantee the reduction of heat loss.



Acoustic insulation - The degree of attenuation of noise coming from outside the building, which is determined by the Rw (dB) coefficient. The higher the coefficient value, the better protection the window provides against noise. The value is influenced by several elements: window tightness, their dimensions, acoustic insulation of glass inserts and the profile structure.



RC (resistance classes) - A six-level scale that defines the class level of burglar-proof protection for windows and doors. In a detached home, the most commonly used products are in classes RC2\RC3. The PN-EN 1627 standard provides six classes of burglar-proof protection for building openings, like windows and doors. Certificates confirming increased resistance to burglars are issued by certification bodies operating in the field of conformity assessment, which have active accreditation for this scope of tests.



PVC window profile class and the number of chambers - Classes of profiles differ in terms of thickness of the profile walls and are determined in accordance with applicable standards. The class of window profiles mainly affects the window profile’s stiffness and the load-bearing capacity of the welded corners of the profiles. The window profile itself consists of chambers, the task of which is to improve the thermal properties of windows. Nowadays, five chambers seem to be standard, and this number should not be smaller in order to keep the window thermal insulation at a satisfactory level.



Class A profiles - The minimum thickness of the visible wall is greater than or equal to 2.8 mm, while the minimum thickness of the invisible wall is greater than or equal to 2.5 mm. This solution provides greater stability of the window, better thermal insulation properties and, with the use of appropriate glazing, effective protection against external noise.



Class B profiles - The minimum thickness of the visible wall is greater than 2.5 mm, while the minimum thickness of the invisible wall is 2 mm (Class C includes profiles, for which the minimum thickness of the visible and invisible wall has not been defined). A window with a profile classified as class A will, therefore, be more rigid and stable than class B and C windows.



Fittings - Window elements that maintain tightness and open, close and tilt window or door sashes. Fittings are also responsible for security and protection against burglars. One of their key components is the handle, as it is used to change the position of the sash. Today, the most common window fittings are perimeter fittings and they are located around the perimeter of the sash. When closed, they press the sash evenly against the frame, which ensures tightness and prevents profile deformation. What kind of perimeter fittings we choose depends on how our windows will open. We can choose from hinged windows, which allow you to open the window, and tilt windows, which allow only to tilt the sash. The most convenient solution is fittings that combine both functions.



Micro-ventilation - A function provided by appropriate fittings, which give the possibility of incomplete closing of the window sash. When using this opening variant, the sash does not come into close contact with the frame and a gap of several millimetres is created between them. This allows air to circulate while, at the same time, protecting the sash against an opening in the event of a strong gust of wind.



Fixed post / Movable post - The post is an element of the window structure that separates its sections. Depending on the window's structural capabilities or investors' preferences, it can be in a fixed version or the so-called movable version. The fixed post is an element permanently connected to the window frame and makes the structure more resistant to strong wind or burglar attempts. In such a solution, each sash works independently, which allows the use of a tilt and turn mechanism in both sashes (with double sash windows).



In the case of the movable post version, elements of the window structure are not permanently connected to the frame of the sash and the post is created by overlapping the rebate parts of the sashes. With this option, only one handle is used, and opening the second sash requires (after opening the first one) unlocking the catches inside the sash frame. An advantage of the movable post is that the opening clearance is not limited by the vertical post. It is almost always used for balcony doors.



Glazing package - A standard solution in the field of glazing windows and doors. Currently, the standard is the use of a double or triple glazing, separated by a spacer and filled with noble gases. The space between two panes separated by a spacer is called a chamber. One-, two- or three-chamber glazing units are available on the market.



Spacer frame (inter-pane) - An element of the glazing unit sealing the edges of the glazing units and separating the panes from each other. Frames are most often made of aluminium, as the high thermal conductivity allows heat to escape through the window. The frames are available in various colours and have different parameters, including a warm frame.



Safety glass - Glass that does not pose a risk of injury in the event of damage, but it is not burglar-proof. After breaking the safety glass, it will shatter into non-sharp pieces or will hold its whole shape after being damaged.



Muntin bars - Decorative, thin slats that divide the panes into fields. The most commonly used solutions are Viennese muntins, which are glued to the glass from the outside, and the internal muntins, which are placed inside the insulating glass units.