Like ordinary Japanese houses, tea rooms are made of wood and clay and paper. But for soan (thatched cottage style) tea rooms, even more natural materials are used. For the pillars and many other parts, the wood is not shaped so that is has corners, but left in its natural round shape as a log. Compared to square timber, logs give a feeling of gentleness. Logs of sugi (Japan cedar) were especially popular. Also, logs retain the shape they had when still standing, so that they are not of a uniform thickness, but have curves and indentations. They are used because they remain so natural.
When building soan tea rooms, the architectural skills necessary for making use of such logs were required. These call for a slightly different kind of inventiveness than those involved in a structure that is made entirely of squarely cut timber. Buildings are constructed from horizontal and vertical beams, so irregularly shaped logs must be used in a way that does not look unnatural. Each log has a different character. Being able to bring out this character created by nature depends on the sensitivity and skill of the craftsman. The frame of the toko at Tai-an is one example of a masterpiece. Logs are sometimes used with the bark still on and it is not unusual for different kinds of wood to be used together. In the soan tea room we can enjoy unlimited contact with natural materials.