This study investigated energy-efficient renovation strategies for traditional Thai wooden houses through constructing a demo building and computational assessments. The study addresses the challenges posed by climate change and increasing comfort demands, which have led to increasing use of air conditioning in these historically significant structures. A demo building, designed to replicate a traditional Thai house, was constructed, featuring two rooms: one insulated with magnesium-bonded Typha boards and the other uninsulated. The effectiveness of the insulation was evaluated through hygrothermal simulations and real-time temperature and humidity measurements. The frequently occurring problem of missing measurement data was solved by approximately determining unknown variables through iterative adjustment and comparison of simulation results with measured data. The results indicate that the Typha-insulated room maintained a stable indoor climate, with significantly lower energy consumption from air conditioning than the uninsulated room. Since the air conditioning system was insufficiently powerful in the uninsulated room, it is not possible to quantify the energy savings precisely using measurement technology. However, subsequent hygrothermal simulations enabled a comparative assessment of the energy-saving potential of various measures. Depending on insulation measures and manner of room use, savings of 75–80% could be achieved. Such computational and practical studies can contribute to the preservation of historic buildings.