Historic timber buildings rely heavily on naturally aged wood. However, the influence of long-term environmental exposure on the thermal behavior and fire performance of such structural members remains insufficiently understood. This study evaluates the effect of natural aging on heat transfer, charring development, and the phase-change interval of free water in larch wood (Larix decidua). Medium-scale radiant panel tests were conducted on fresh and naturally aged timber beams. Internal temperatures were recorded at multiple depths and analyzed using derivative-based T-history methods. The temperature profiles of aged and fresh larch were highly comparable, exhibiting a strong correlation (R2 = 0.89). Aged wood, characterized by a slightly higher density, showed shallower thermal gradients and a marginally lower average charring rate (0.63 mm·min−1) compared with fresh wood (0.65 mm·min−1). In both materials, the charring rate decreased with depth. The phase-change interval of free water differed markedly: fresh wood showed water evaporation between 107.8–142.1 °C, whereas aged wood exhibited an earlier and narrower interval (93.6–116.3 °C), indicating facilitated dehydration due to microstructural degradation. Overall, natural aging did not significantly impair fire-relevant thermal properties, suggesting that aged larch retains charring resistance comparable to that of fresh wood and can reliably perform in passive fire protection applications for heritage structures.
Špilák et al. (Sun,) studied this question.