Effect of Natural Ageing on the Reaction-to-Fire Performance of Fire-Retardant-Treated Timber Façade Systems

Abstract

This study investigates the influence of natural ageing on the reaction-to-fire performance of fire-retardant-treated (FRT) timber façade systems. Timber samples were obtained from an existing building façade in İzmir, Türkiye, where they had been exposed to outdoor environmental conditions for approximately 14–18 months. Three sample categories were considered: unaged reference samples (UA), less severely exposed samples (A), and more severely exposed samples (B), including variations with and without surface coating.
The experimental program combined medium-scale corner tests based on the EN 13823 configuration and cone calorimeter tests according to ISO 5660-1. The medium-scale tests were used to evaluate fire growth behavior through parameters such as heat release rate (HRR), total heat release (THR), and Fire Growth Rate Index (FIGRA), which is the primary indicator for Euroclass classification. Cone calorimeter tests were conducted at multiple heat flux levels to assess ignition characteristics and heat release behavior, and to derive additional fire performance parameters, including the Thermal Response Parameter (TRP) and Fire Propagation Index (FPI).
The results indicate that natural ageing influences the fire behavior of FRT timber, although the effect depends on exposure conditions and surface characteristics. In general, aged samples exhibited changes in ignition behavior and heat release characteristics compared with unaged samples, consistent with previous findings on weathering-induced degradation of fire-retardant treatments. The analysis also shows that ageing is not the only governing factor; surface coating condition plays a significant role.
Furthermore, correlation analysis between cone calorimeter and medium-scale corner test results demonstrated that cone-derived parameters can provide useful indications of fire growth behavior at larger scales, although uncertainties remain due to differences in test configurations and scale effects.

Popular Abstract

Timber is becoming increasingly popular in modern buildings because it is renewable, sustainable, and stores carbon. Today, timber is used not only in structural systems but also in exterior façades. However, because timber is combustible, its long-term fire safety performance is an important concern.
To improve fire performance, timber can be treated with fire-retardant chemicals. These treatments reduce flame spread and heat release during a fire. Although fire-retardant-treated (FRT) timber performs well in laboratory tests, less is known about how weather conditions such as rain, sunlight, humidity, and temperature changes affect its fire performance over time.
This thesis investigates how natural outdoor ageing influences the reaction-to-fire performance of FRT timber façade systems. This research used timber samples taken from a real building façade in İzmir, Türkiye, after approximately 14–18 months of outdoor exposure. The samples were transported to Lund University and tested under laboratory fire conditions.
The study compared three groups of samples: new unaged reference samples, less weathered samples taken from a more protected façade area, and more heavily weathered samples exposed directly to environmental conditions. Some of the aged samples had also lost part of their surface coating over time. This made it possible to study not only the effect of ageing itself, but also the importance of protective coatings.
Both medium-scale façade fire tests and cone calorimeter experiments were carried out to study ignition behaviour, flame spread, and heat release characteristics. The results showed that natural ageing can influence the fire behaviour of FRT timber, although the effect depends strongly on environmental exposure and the condition of the surface coating. Samples with degraded or lost coatings often behaved differently from samples where the coating remained intact.
The findings contribute to a better understanding of the long-term fire safety of timber façades. As timber construction continues to grow worldwide, understanding how these materials perform after years of real environmental exposure is becoming increasingly important for safer and more sustainable buildings.

• author: Yarar, Coskun
• supervisor: Konrad Wilkens Flecknoe-Brown
• organization: Division of Fire Safety Engineering
• course: VBRM05 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Fire-retardant impregnated timber façade, natural weathering, field study, exterior timber applications, fire performance, Reaction to fire, Cone Calorimeter testing, time to ignition, heat release rate, flame spread, timber color indicator, fire-retardant durability, weather-exposure effects, long-term fire protection, TRP, FPI
• publication/series: LUTVDG/TVBB
• report number: 5765
• other publication id: LUTVDG/TVBB—5765--SE
• language: English
• id: 9229030
• date added to LUP: 2026-06-03 09:19:14
• date last changed: 2026-06-03 09:19:14