This study determines influence of thermal insulation on conductive heat transfer through roof-ceiling construction when thermal insulation material was integrated to roofing system. Among two pairs of two identical rooms, respective roofs were equipped with insulation to be tested as follows: i) polystyrene and its identical pair with no insulation; and ii) fiberglass, and its pair with no insulation material. Roof with no insulation was considered as reference. Roof with polystyrene performed better than fibreglass.