A recent meta-analysis of dampness in homes has shown that dampness and mold in indoor environments are factors in approximately 30-50% of all respiratory and asthma-related health ailments. Although the specific indoor dampness factors related to such issues have yet to be fully explored, there are clear and urgent needs for improved architectural techniques and optimized occupant behavior patterns that can prevent or eliminate excessive dampness inside buildings. Furthermore, if the underlying structures linking dampness to adverse health effects could be more closely estimated through epidemiological surveys, prevention methodologies for serious problems related to indoor dampness might be discovered. With these points in mind, we previously proposed a home dampness estimation method based on occupants’ self-reported answers to questions regarding indoor dampness during winter. This resulted in an indoor dampness index covering a range from 0 to 24 that classifies houses into four ranks, with those in Rank 4 presenting the most serious dampness-related problems.

 To clarify the relationship between home dampness levels and indoor environmental quality, another questionnaire survey was conducted and several physical environmental items such as indoor temperature, humidity, and microbial flora from floor dust were measured in 119 detached East Japan houses during the winter season. Herein, we describe the surveyed results and the distribution of the dampness index. The questionnaire also included child health-related symptoms that show onsets within 3 months, and the prevalence of each symptom is presented in relation to each dampness index rank. The characteristics of indoor temperature and humidity resulting from home dampness levels were also clarified by comparing the dampness index and measured results of these physical items.

 Analyzing the survey results, we found that the prevalence of nasal- and eye-related symptoms increased approximately in tandem with the dampness index ranking. In particular, more than 50% of the children residing in Rank 4 homes reported nasal problems, and there was a high prevalence of throat and skin symptoms in Rank 3 homes. However, despite these values, there are still no clear links between the dampness index and the reported health-related symptoms.

 Next, the statistical values of temperature, relative humidity, and the humidity ratio during evening time in living rooms and bedrooms were analyzed for each dampness index rank. To test the significance of these associations, Kruskal-Wallis testing was performed to determine whether the samples in each dampness index rank originate from the same distribution. Moreover, the significant differences among each rank’s samples were tested in multiple comparisons. As for temperature results, no significant association was found among the dampness index ranks. This presumes that living room temperatures are affected by heating behaviors at the time of occupancy.

 On the other hand, both the relative humidity level and the humidity ratio were found to be strongly associated with the dampness index rankings; with higher humidity levels in the living room and bedroom presaging higher dampness index ranks. In addition, the relative humidity and humidity ratios in Rank 2, 3, and 4 living rooms were significantly higher in comparison with Rank 1 living rooms, while the median relative humidity values in Rank 4 living rooms and bedrooms were around 50% and 70%, respectively. Significantly, the humidity ratios in Rank 4 homes were found to be the highest among the surveyed houses and it was expected that these houses had severe environmental problems related to indoor dampness.