The society lays stress on today's buildings, particularly in terms of energy-efficient buildings and ecology of buildings. Accordingly, not only from a technical technical point of view, it is important to give sufficient attention to the foundations of building. The popular way of foundation of lightweight buildings is due to the growing interest in timber houses the foundation above a ventilated air gap so called Crawl Space. The article deals with the temperature and humidity field which is located in the air gap under the construction of wooden building in the climatic conditions of the Czech Republic.