Fire Protection in the State Building Codes: Strategies for the Legally Compliant Design of Transparent Architecture

Large glass surfaces, open atriums and transparent escape routes shape contemporary design. But where the architect sees transparency, the building authority sees potential fire loads and hazard areas. In Germany, fire protection is not a mere recommendation but is strictly regulated by the state building codes (Landesbauordnungen, LBO) of the 16 federal states.

The complexity arises from German federalism: while the physical laws of fire are the same everywhere, the legal requirements for components such as fire-rated glazing often differ in detail between North Rhine-Westphalia, Bavaria or Berlin. For planners, architects and investors this means: anyone who does not know the subtleties of the LBO risks costly redesigns, delays in approval or, in the worst case, liability in the event of damage.

The Legal Basis: MBO vs. LBO

The Model Building Code (Musterbauordnung, MBO) serves as a framework for guidance, issued by the Conference of Building Ministers. It has no legal force of its own but is the template for the 16 state building codes.

Why the differentiation?

Each federal state has the right to adapt the MBO to regional needs. For example, the BauO NRW often contains stricter fire-protection requirements in densely populated urban areas, while the BayBO (Bavarian Building Code) has deviated from the MBO in recent years through simplifications in timber construction.

Important for planners: The decisive code is always the LBO of the federal state in which the building project is realised. In addition, the relevant special-building ordinances (e.g. for assembly venues, hospitals or retail premises) must be consulted, as they often tighten or specify the requirements of the LBO.

Building Classes (GK 1–5): The Backbone of Planning

• GK 1 & 2: Detached residential buildings or small units up to 7 m in height. Requirements for interior fire protection are moderate. Here, fire-rated glass is often relevant only for boundary developments or special boiler rooms.
• GK 3: Buildings up to 7 m in height but with more than two usage units. The LBO often requires „fire-retardant“ components (30 minutes). Transparent partitions in corridors must already meet fire-protection standards here – for example with ARDOREX® Arnold Fire in class EI 30, which as laminated glass achieves a light transmission of up to 86 % (Source: ARDOREX® data sheet, as of 11/2024).
• GK 4: Buildings up to 13 m in height and usage units up to 400 m². The requirement rises to „highly fire-retardant“ (60 minutes). This is a critical threshold, as the trade-off between E 60 (integrity) and EI 60 (insulation) often has to be made here. ARDOREX® Arnold Fire EI 60.18 offers a proven solution with a Ug value of 4.6 W/(m²K) in laminated glass.
• GK 5 & special buildings: Buildings over 13 m in height or buildings of special type and use. As a rule, „fire-resistant“ (90 minutes) applies here. In the stairwells of these classes, planning is barely possible without high-performance fire-rated glass (EI 90) if transparency is desired. ARDOREX® Arnold Fire EI 90.24 meets this requirement at a light transmission of up to 84 %.

Protection Objectives of the LBO: The Logic Behind the Regulations

1. Preventing the outbreak of fire: Glass plays a subordinate role here, as it is classified as a non-combustible building material (A1/A2 according to DIN 4102).
2. Limiting the spread of fire: This is where fire-rated glazing comes into its own. It must prevent a fire from jumping from one fire compartment to the next (fire walls, partition walls).
3. Rescuing people and animals: This is the most critical objective. Escape routes (necessary corridors and stairwells) must remain free of smoke and protected from radiant heat for a defined period. This is precisely where ARDOREX® shows its strength: the hydrogel layer keeps the temperature on the cold side, on average, below a 140 K increase over the initial temperature.

Technical Classification: E, EW and EI in Detail

Planners must master the European classification according to DIN EN 13501-2 in order to implement the requirements of the LBO correctly.

E (Integrity) – Room Closure

Formerly referred to as G-glass. These glazings only prevent the passage of flames and smoke. However, dangerous thermal radiation passes through the glass almost unhindered. Use according to the LBO: only where there are no combustible materials nearby and no persons are directly endangered (e.g. skylights, partitions without escape-route relevance).

EW (Radiation) – Radiation Limitation

An intermediate step that is rarely explicitly required in the German LBOs but is often used as compensation. EW glass limits radiant heat to a value below 15 kW/m² at a distance of one metre.

EI (Insulation) – Thermal Insulation

Referred to nationally as F-glass. This is the highest standard in terms of fire protection. EI glass provides full protection against flames, smoke and heat. On the side facing away from the fire, the pane may heat up by an average of no more than 140 K above the initial temperature. ARDOREX® Arnold Fire meets this requirement in classes EI 30 to EI 120 (Source: ARDOREX® data sheet, as of 11/2024). Use according to the LBO: mandatory for all glazing in necessary corridors and stairwells to ensure safe evacuation.

Specific Application Scenarios in Glass Architecture

Necessary Corridors and Stairwells

The LBO defines these as the building's life insurance. Walls of necessary corridors must generally be fire-retardant (GK 3) or highly fire-retardant (GK 4/5). If you want to open up these walls to bring light into the corridors, the glazing must have the same classification as the wall. ARDOREX® Arnold Fire in the advance variant offers a decisive advantage here: as double insulating glass it achieves a Ug value of 1.1 W/(m²K) and thus meets the requirements of the Building Energy Act (GEG) alongside fire protection (Source: ARDOREX® data sheet, as of 11/2024).

Practical tip: Use frameless fire-rated glazing (butt-joint systems) to visually widen the corridors without violating the EI requirements of the LBO.

Fire Protection at the Property Boundary (Fire Wall)

If a building is constructed directly on the property boundary, the LBO requires a fire wall. Openings are generally not permitted here. However, there are exceptions using fixed fire-rated glazing if it meets fire-resistance class EI 90 (fire-resistant) and cannot be opened. This is often the only way to bring daylight into rooms near the boundary in dense urban development. With ARDOREX® Arnold Fire EI 90.24 in a laminated-glass build-up, a solution is available with a thickness of just 50 mm and a weight from 54 kg/m².

Facade Fire Spread and Fire Barriers

With large-area glass facades there is a risk of fire spreading from one storey to the storey above it from the outside. Here the LBO often requires fire barriers of at least 1 metre in height made of non-combustible materials or corresponding fire-rated glazing in this area. ARDOREX® is CE-certified for use in exterior walls according to EN 16034 and EN 14351-1 (Source: ARDOREX® data sheet, as of 11/2024).

Planning, Approval and Implementation: The System Is Decisive

A serious mistake in practice is considering the glass pane in isolation. The LBO, however, requires the usability of the entire component.

The System Approach

Fire-rated glass only works in interaction with the tested frame profile (steel, aluminium, wood, plasterboard or lightweight partition), the correct glass holders and seals, and professional installation in the structure. ARDOREX® Arnold Fire is tested and approved in metal, wood and gypsum systems. The relevant general construction-type approvals include Z-19.14-1833, Z-19.14-2118, Z-19.14-1993 and Z-19.14-2652 (Source: ARDOREX® data sheet, as of 11/2024).

Verifications: abZ and aBG

Every fire-rated glazing must have a building-authority proof of usability. In Germany this is usually the general building-authority approval (abZ) or the general construction-type approval (aBG). If the execution deviates even slightly from the approval (e.g. larger pane dimensions), the approval lapses. In that case, for example, a project-specific construction-type approval (vBG) must be applied for at the highest building supervisory authority. ISOLAR supports planners with the necessary verifications and expert reports as early as service phase 2.

Costs, Cost-Effectiveness and Multiple Benefits

• Multifunctionality: ARDOREX® advance combines fire protection with thermal insulation (Ug down to 0.5 W/(m²K) in a triple insulating-glass build-up) and sound insulation (Rw up to 46 dB in laminated glass, F90). This can make an additional secondary shell unnecessary (Source: ARDOREX® data sheet, as of 11/2024).
• Insurance advantages: High-quality fire-protection concepts can have a positive effect on insurance terms for industrial and commercial construction.
• Durability: Thanks to a UV-resistant interlayer without additional UV protective film, the glazing retains its transparency throughout its entire life cycle (Source: ARDOREX® product brochure).
• Colour rendering: With an Ra value of up to 98 (laminated glass), ARDOREX® is almost colour-neutral – a quality feature for architecturally demanding projects (Source: ARDOREX® data sheet, as of 11/2024).

ARDOREX® advance: Fire Protection Meets the Building Energy Act

With the ARDOREX® advance range, ISOLAR provides an answer to the rising requirements for summer and winter thermal protection while maintaining fire protection at the same time. Whereas the classic laminated glasses (EI 30 to EI 120) are designed primarily for interior fit-out, the advance line is aimed specifically at facade and exterior-wall applications.

The key technical data at a glance (Source: ARDOREX® data sheet, as of 11/2024):

Note: In the double build-up, Ug values down to 1.0 W/(m²K) are possible, and in the triple build-up down to 0.5 W/(m²K).

The decisive advantage: with a low Ug value in the triple build-up, ARDOREX® advance meets the minimum energy requirements of the GEG without a separate thermal-insulation layer having to be planned. Sound-insulation values are tested and specified exclusively for the laminated (mono) build-up; the entire component must be measured individually on site.

The Path to a Safe Design

• Determine the building class according to the LBO.
• Identify the protection objectives of the affected walls (partition wall vs. fire wall).
• Ensure EI classification for escape routes.
• Check approval ranges (dimensions, frames) at an early stage.
• Involve ISOLAR consulting from service phase 2 – for verifications, vBG support and system advice.

These Topics Might Also Interest You

We explain exactly what lies behind the classes E, EW and EI in our basics article on fire-resistance classes.

For the building-law classification of fire-rated glass, read our foundation article on legal classification.

Our technical article on structure and layer systems shows how the hydrogel layer works in detail.