Application of the Wood Degradation Model to an Actual Roof Assembly subjected to Rain Penetration

Abstract

Rain penetration through building materials is frequently observed in actual damaged buildings with wooden frames in regions with coastal climate. The penetrated water finally causes decay of wooden materials and reduces their strength against natural disasters such as typhoon and earthquake. To assess the impact of hygrothermal behavior on structural performances, we developed a model integrating hygrothermal analysis with wood degradation process. This model can simulate wood decay extension and moisture production by the chemical reactions of wood-decay fungi.This study focuses on the application of the integrated model to the damaged roof assembly of a house. A disassembly investigation of the damaged roof assembly was implemented to quantify the decay rate of plywood used as the sheathing board and to clarify the water flow path through the roof finishing and the underlayment. In addition, wood decay predictions were made using the model to estimate the initiation of wood decay and rain penetration into the plywood. The calculation and measurement results indicated that rain penetration started at least a few years after completion of the construction.