Heat stress is a common issue for roofers and road construction workers, specially in warm seasons and hot areas. This project assesses construction workers' heat stress by using wearable biosensors. The project assesses heat stress by analyzing biological signals such as Electrodermal Activity (EDA) and Blood Volume Pressure (BVP). The biological signals are collected from 18 subjects performing roofing tasks in a chamber room in different temperatures and humidities. Then, the machine learning model is trained and an automated health monitoring system for the construction sites is developed.