Upgrading Fire Behaviour of Wooden Doors in Historic Buildings

When it comes to fire safety in many buildings, including apartment buildings, old wooden doors often represent a weak point. Starting from this consideration, the Norwegian Foundation SINTEF (Stiftelsen forindustriall og teknisk forskning, “The Foundation for technical and industrial research”) in collaboration with RISE Fire Research Institutes and the the Norwegian Institute for Cultural Heritage Research NIKU (Norsk institutt for kulturminneforskning), published a guideline in 2022 that “presents possible solutions for the assembly of glazing, protective panels, sealing strips, door frames and door hardware when improving the fire resistance of old wooden doors with cultural heritage value.”

It is important to note that the document explicitly states that The document focuses on interventions on the door itself and is based on small-scale fire tests and previous knowledge and experience. The premises for using the guide are that:

• the doors used in the tests were 40 mm thick laminated wood, while real doors are often solid wood and can vary in thickness and type of wood;
• the improvement according to the guideline can increase the fire resistance of doors by up to approximately 30 minutes, but the actual fire resistance achieved may vary depending on the specific characteristics of each door;
• the doors tested were smaller than standard doors, so taller doors may experience greater deflection during exposure to heat;
• the doors tested were new, while real doors may be older and have different moisture content, which may affect their fire resistance.

On such basis, underlining the importance of considering the building as a whole and of evaluating compensatory solutions for the safety of escape routes, the Guideline (Fire Resistance Upgrade of Cultural Heritage Doors) deals with the intervention on the doors in cases where this is necessary. The approach is based on small-scale fire tests and knowledge from previous experience.

The strategy adopted by the document to improve the fire resistance of cultural heritage doors is defined by aiming to achieve a duration of approximately 30 minutes, similar to standard fire resistance tests. In general, this requirement is specifically aimed at situations where replacement of the door for historical or aesthetic reasons is not feasible or desirable.

The first result of the document, where older doors with a thickness of between 40 and 50 mm, consisting of a glass upper part and a thinner wooden door panel at the bottom, were considered, is that, to preserve its antiquarian nature, any changes should be minimally invasive and easily reversible. Additionally, four fire tests were conducted, each involving two models of small doors. Various methods for fitting fire glass, plasterboard and glazing strips were examined, leading to the following key findings:

1. Fire-resistant glass must have a minimum rating of 30 minutes (both integrity and insulation) and should be securely fastened using steel frames or angles.
2. Thinner components, such as fielded wooden panels, can be reinforced by incorporating stone wool and robust 12.5 mm gypsum boards.
3. To enhance fire resistance, both intumescent strips and silicone gaskets must be applied around the door leaf.
4. The gap between the door frame and the wall should be sealed using stone wool and fire sealant.

The guideline serves as a resource for ensuring the fire safety of older wooden doors in situations where maintaining historical integrity is a priority and replacement is not a viable option. The document is structured in three chapters:

• Background and premises
• Preservation of doors with cultural heritage value
• Guideline (3.1  Mounting of fire resistant glass;  Mounting of protective boards;  Mounting of sealing lists;  Door frame; Door hardware).

Finally, it is important to highlight that the document emphasizes that interventions on the door must be as minimally invasive as possible and reversible, to preserve the historical value of the door. It is also recommended to use products with a long life cycle and to plan fire maintenance of the building.

The document provides a reference bibliography to allow for a deeper understanding of the topics covered. Such bibliography also includes the citation of the IFE (Institution of Fire Engineers) document “Guide to the history of fire-resistant wooden panel doors“.