Controlling indoor dampness can be challenging for schools, especially in the warm and humid southeastern United States. Failure to control indoor humidity directly impacts air quality, and indirectly may lead to problems with mold and dust mites and infestations by roaches and rodents. These potential allergens can trigger adverse health effects in school building occupants, especially in teachers who may work in one building for many years. Our first aim was to describe the problem of relative humidity (RH) control in schools and to examine associations between building-related factors and RH control. Our second aim was to estimate the risk of asthma and cold/allergy symptoms among teachers exposed to high (>50%) and low (<30%) compared to recommended (30-50%) humidity levels in their classrooms. We measured daily symptoms from a cohort of 122 teachers from 10 schools in two NC school districts. We logged RH every 15 minutes in 134 classrooms (n= 852,519 observations) and recorded information on building-related factors. Polytomous logistic regression was used to quantify associations between these structural factors and average daily RH below, within, or above the recommended level of 30-50%. Symptom data were analyzed using modified Poisson regression models for correlated binary outcomes, clustered by classroom. The odds of high RH (>50%) were 6.64 (3.96, 11.12) times higher for classrooms with annual vs. quarterly heating, ventilating, and air conditioning (HVAC) system maintenance. The odds of high RH were also 3.07(2.04, 4.63) times higher for classrooms in buildings with an economizer vs. none. During occupied time periods, the odds of high RH in classrooms with programmed thermostat setbacks were 3.48 (1.89, 6.38) times the odds of those with no setbacks. Among those present in the school building, the risks of asthma symptoms were slightly elevated for participants in classrooms with low vs. recommended RH [risk ratio (RR)=1.09 (0.84, 1.35)] or high vs. recommended RH [RR=1.09 (0.84, 1.35)]. Atopy at baseline and presence in the school building were independently associated with asthma and cold/allergy symptoms. These findings suggest practical remedies for poor air quality in schools and highlight the effects of indoor air quality on teachers' health.