Fire-rated glazing

Fire-rated glazing (požiarne odolné zasklenie) is glass that is built and tested as part of a complete fire-resisting assembly, so that it keeps a defined fire function when a fire burns on one side. Ordinary glass cracks and fails early in a fire, letting flames and heat through. Fire-rated glass is judged on what it still does during a standard fire test, and that result is what its class reports. In a family house it is a targeted product rather than a default, but where a glazed opening has to contain fire, ordinary glazing cannot be assumed to do the job.

What is fire-rated glazing and how is it classified?

Fire-rated glazing is a glazed element, usually a glass unit set in a frame with seals and fixings, tested as one system. The classification follows the European standard EN 13501-2, which sorts building elements by fire resistance. The class is a combination of letters and a number. The letters name the fire functions the glazing performs, and the number states how long, in minutes, the element keeps those functions under standard test conditions. Because the class belongs to the whole tested assembly, two panes that look identical can carry different classes.

What do the letters E, EW and EI mean?

The three letters used for glazing are defined by the criteria the element must meet during the test. The definitions below are textbook meanings, not product claims.

Class	Criterion	What it means
E	Integrity	The glazing stops flames and hot gases from passing through to the unexposed side, and does not develop cracks or gaps that let them through.
EW	Integrity and reduced radiation	The glazing meets the E criteria and also limits the heat radiated from its unexposed face, so people on the cool side are less exposed to radiant heat.
EI	Integrity and insulation	The glazing meets the E criteria and also limits how far the temperature on its unexposed face rises during the test.

EW and EI address different hazards. EW limits radiant heat, while EI limits the temperature rise on the cool face. Neither is a better general choice. The class a project needs is set by the fire safety design for the specific location, and the product must carry that class in its test documentation.

How does fire-rated glazing differ from laminated safety glass?

Laminated safety glass is made so that broken pieces stay bonded to an interlayer, which reduces injury from impact and keeps the pane in place after breakage. Its purpose is mechanical safety. Fire-rated glazing is judged on a fire test. Some fire-rated products do use laminated layers with special interlayers, but a laminated pane is not fire-rated simply because it is laminated. The same applies to tempered glass, which is strong in ordinary use yet does not carry a fire class by virtue of its toughening.

Property	Laminated safety glass	Fire-rated glazing
Main purpose	Safety on impact and after breakage	Containing fire and heat across a wall or opening
Basis of classification	Safety performance of the glass	Fire test of the complete assembly
Classes	Safety-related, not fire classes	E, EW or EI with a time figure
Typical position	Balustrades, skylights, low glazing	Walls, openings and boundaries that must resist fire spread

Where might a family house need fire-rated glazing?

A family house is not usually a high-hazard building, so fire-rated glazing is a targeted requirement, not a default. It appears where the fire safety design identifies a risk the glass has to contain. Two situations are common in family houses:

• A window close to the plot boundary or to a neighbouring building, where fire could pass from one building to the other through the opening.
• Glazing between an integrated garage and the living part of the house, where the wall or door separating the two forms part of the fire separation.

Glazed elements in staircase enclosures or party walls can raise the same question. Whether a given opening needs a class is a matter for the design, and the answer can differ from one window to the next on the same house.

Which Slovak documents set the fire requirements?

In Slovakia the fire safety requirements for buildings are set out in the STN 73 0802 and STN 73 0833 standards. For a specific building, the fire safety design (požiarnobezpečnostné riešenie) records how those requirements are met, including any glazing that must carry a fire class. Slovakia's building act, 25/2025 Z. z., in force since 1 April 2025, governs the permitting process in which the design is reviewed, and the fire authority's statement on it is part of that process, as described in Fire Authority Approval. The clauses that apply to a given opening are found in the standards and in the design itself, not in this summary.

How should fire-rated glazing be specified and installed?

The class attaches to the tested assembly, so a change to the frame, seals or fixings can invalidate it even when the glass itself is unchanged. These steps help keep the class intact:

• Request the classification report or certificate that names the exact product, frame and fixing system.
• Write the required class into the fire safety design and the tender documents, so the contractor cannot substitute a visually similar pane.
• Build the surrounding wall or opening to the tested detail, not to a generic one.
• File the documentation with the as-built records, because it is part of what is checked at occupancy.

What are the common misconceptions about fire-rated glazing?

Three ideas come up often in client conversations, and all three are wrong.

• Thick or toughened glass is fire-rated. Thickness and toughening do not create a fire class; only testing does.
• The glass alone carries the class. The class belongs to the complete assembly, so the frame and seals are part of the rating.
• Every window in a house needs it. Fire-rated glazing is used where a specific risk has been identified, not as a general standard.

Clearing up these points early avoids redesigns late in the permit or during construction.