The quality of thermal comfort in a house depends on how the openings received daylight. Low-cost apartment in Jakarta was built using various types of openings to receive maximum daylight. However, nowadays, daylight is no longer the most important element for the dwellers. Because of the lack of space and also the habit of Jakartans, the openings are covered with their own daily objects, causing darkness, even in the middle of the day. This causes the daylight to be no longer required, when in fact, visual comfort is a very important basic aspect of a good dwelling. The calculation of average daylight factor is needed to be studied to provide the better options for natural daylight. Using simulation-based analysis in Autodesk Ecotect, this paper will discuss the result of simulation in a preoccupied and post-occupied building, to find out the how the thermal comfort affects the dwellers' life in low-cost apartments in Jakarta.