WBDBO is perhaps the most important abbreviation in passive fire safety. It stands for resistance to fire penetration and fire spread: the time, in minutes, that it takes for a fire to spread from one space to another. In this article you will learn what the requirement involves, which values apply, how the WBDBO is determined and what you need to do to demonstrably comply with it.
Fire penetration and fire spread: the difference
Fire penetration is the spread of fire through through a separating structure: via a wall, floor, door, or penetration. Fire spread is the spread of fire via the outside air: from one window to the window above it, or to a neighbouring building. The WBDBO takes both routes into account.
Which requirements apply?
The requirement depends on the situation. The Bbl (Dutch Buildings Decree) distinguishes between new construction, existing buildings and renovation, and within new construction between uses. So a new-build table does not simply apply to every building.
| Situation | Starting point |
|---|---|
| New construction: between fire compartments | At least 60 minutes (Article 4.53(1) Bbl). This also applies towards, among other things, a safety escape route. |
| New construction: residential function towards an enclosed space with an extra-protected escape route | At least 30 minutes (Article 4.53(2)). |
| New construction: reduction for a residential function | 30 minutes if the permanent fire load of the fire compartment does not exceed 500 MJ/m² and no floor of an occupied area in the building is higher than 7 metres (Article 4.53(3)). |
| New construction: reduction for other functions | 30 minutes between spaces on the same building plot if no floor of a usage area is higher than 5 metres, for the uses for which Table 4.49 indicates this (Article 4.53(4)). Not for a fire compartment larger than 1,000 m² (Article 4.53(5)). |
| Existing building | At least 20 minutes as a rule. |
| Renovation | The lawfully obtained level applies to the altered part, with the existing-building level as the lower limit and new construction as the upper limit. If a renovated separation has less than 30 minutes, it must then achieve at least 30 minutes. A higher existing level remains decisive. |
| Towards another plot | Assessed using an imaginary mirrored building on the other side of the plot boundary, taking account of the distance and the façade. There is no fixed allocation per building. |
So an existing building does not automatically have to be upgraded to 30 or 60 minutes. The exact requirement follows from the Bbl, the approved drawings and the building's fire safety concept. Your fire safety adviser can establish this per separation. The Informatiepunt Leefomgeving explains the rules for new construction and for renovation.
How is the WBDBO determined?
The determination method is set out in NEN 6068. The standard looks at all routes by which a fire can get from one space to another: through the wall or floor, through a door or window, through a penetration, and via the façade. The route with the lowest resistance is decisive. The amendment NEN 6068 + A1:2024 also states this explicitly. The WBDBO is therefore not an average by area: a 60-minute wall with one unsealed cable penetration does not achieve 60 minutes.
The standard is accompanied by NPR 6668, with guidance on using NEN 6068 and a simplified calculation method.
Smoke resistance is a separate requirement
Fire resistance and smoke resistance are different performances. An EI classification does not automatically demonstrate that the smoke resistance requirement is met. NEN 6075 describes how the resistance to smoke passage between spaces is determined. The requirements use Ra and R200; Sa and S200 are classifications of the smoke leakage of components, such as doors.
The current smoke resistance requirements using Ra and R200 were added to the Bouwbesluit 2012 on 1 July 2021, for new construction and in some cases for renovation. They apply, among other places, around protected sub-compartments and escape routes. The Bbl, in force since 1 January 2024, continues this approach.
Where things go wrong in practice
- Penetrations. Unsealed or incorrectly sealed cable and pipe penetrations are one of the most common causes of an inadequate WBDBO.
- Connection details. The joint between a fire-resistant wall and the floor above, or around a frame, is often forgotten.
- Later modifications. A new cable through an existing seal can fall outside the system's substantiated field of application. After the change, check whether the seal still falls within the conditions of application, and repair where necessary.
- Doors. A fire door that does not latch because of an incorrectly adjusted closer does not deliver the required performance.
How do you demonstrably comply with it?
- Map out the compartment boundaries. Which walls and floors are fire separations, and what WBDBO requirement applies to them?
- Inventory every penetration. Every door, every window, every penetration on that boundary.
- Repair with substantiated systems. The installation must fall within the system's substantiated field of application.
- Record it. For each component: location, type, installation date, the system applied with its documentation, and photos. A logbook makes this easy to present during an inspection.
This article is informational and does not replace advice for your specific building. Want to know whether your compartmentalization meets the required WBDBO? Request an inventory or first take the free quickscan.
Frequently asked questions
That, as determined under NEN 6068, a fire takes at least 60 minutes to get from one space to another along every relevant route: through the construction (fire penetration) and via the outside air (fire spread).
No. The fire resistance of the wall is one building block. The WBDBO looks at all routes between two spaces, including doors, glass, penetrations and the façade. The route with the lowest resistance is decisive.
Not automatically. For existing buildings, at least 20 minutes generally applies. For renovations, the lawfully obtained level applies, and a renovated separation of less than 30 minutes must then achieve at least 30 minutes. The 60 minutes is the starting point for new construction.
Where a requirement for resistance to smoke passage applies, yes. That is a separate performance, determined in accordance with NEN 6075. The current requirements using Ra and R200 have applied since 1 July 2021 to new construction and in some cases to renovation, including around protected sub-compartments and escape routes.
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