When we consider the space in which we commonly conduct a service of tea, we become aware of the wide variety of layouts and sizes that these chambers or chashitsu come in. Each tea practitioner that lived and contributed to the development of the rite of tea throughout history, constructed and employed tea hermitages or tea chambers that suited his/her personal aesthetic and functional preferences. Although he was a very tall man for his time, Sen no Rikyū for example favoured very small, dark rooms; the tiniest of which ever built was his Tai-an [待庵], which is merely two full-tatami mats with a 120cm wide display-alcove in size.
Major styles of chashitsu
Hereunder I will discuss the three major styles of rooms. These have come to be know throughout the ages, and are contemporarily employed by practitioners in the rite of tea. Please bear in mind that for each layout of setting we observe the distinction between the following types. The summer service which employs the floor-brazier; the late summer use of the centrally-placed floor-brazier; the employment of the sunken heart in winter; and on certain occasions in mid-winter, the suspended cauldron above the sunken hearth. And for which the change of seasonal setting requires a different set of procedures and conduct in alignment with the very limitations or possibilities that the environment imposes on the practitioner.
The hiroma

The large reception room [広間; hiroma] is considered to be any room that is larger that 4.5 matting segments. Such a room is most often used for the service of tea because of its spacious and relaxed atmosphere. Such rooms were favoured by the military elite, who preferred comfort and spaciousness to crowded smaller spaces. A Grand Tea-chamber was usually equipped with a formal set of recessed and staggered-shelves; a display-alcove; and a built-in windowsill floor-desk. The variation of comportment in such a space is mostly prominent on the part of the guests. In a large reception room, a tea bowl, sweets or food plates are all handled outside of the matting border of the mat on which one is seated. This gives the guests a greater sense of area, resulting in a stronger feeling of relaxation.
Since such a large room is often much brighter than the Small Tea-chamber, the Host selects utensils suitable for use in such a room. A few examples. The implements shouldn’t be too small as they won’t be able to weigh up to the grandness of the room; Instead, it is favourable to use exquisitely detailed lacquer work. Because, in the brightness of the room the guests can better admire the beauty of the artwork.In this room it is also possible to employ the grand tea sideboard [台子; daisu] for the service of tea.
The koma chashitsu

In contrast to the Grand Tea-chamber stands the Small Tea-chamber [小間; koma]. A Small Tea-chamber is any chashitsu that is under 4.5 matting divisions in size, thus including Rikyū’s wabi-infused Tai-an tea hermitage. It is often in such chashitsu that – although it is common to have the sunken-hearth exterior of the utensil-segment matting – it could be positioned as an interior hearth in either the top left [隅炉; sumiro], or the top right [向炉; mukōro] corner of the utensil-segment. Each variation on the placement of the hearth requires the Host to adopt a different axis-of-seat. This alters the basic placement of the utensils. For the guests, as opposed to comportment for the Grand Tea-chamber, in this case, utensils have to be handled within the border of the matting on which they are seated. This expresses a much more intimate feeling within the narrow and compacted space, and with each other as well.
The daime-seki

The third variation is the room with a three-quarters-length utensil-segment [台目席; daime-seki]. This room usually consists of several (usually three) whole tatami mattings. The mat employed for the utensil-segment on which the Host sits to serve tea, is only three-quarters the size of a regular mat. This room, when first devised was intended to express the general air of simple but elegant rusticity.
The room uses naturally bent pillars with wall compartments that partially screen-off the service area to indicate a sense of humility. It is for the same reason that the utensil-segment has been reduced by one-quarter. The grandest – and oldest – service of tea, employing the grand tea sideboard requires a full mat for the sideboard to be placed on comfortably. The sideboard covers in itself a full quarter of a mat. By reducing the size of the utensil-segment by exactly that much space, the tea practicant expresses his humility. He indirectly indicates that he will never execute a service as grand as that employing the grand tea sideboard, for it won’t fit his tea-chamber.
About the daisu

The grand tea sideboard was, and still is the most formal service of tea. Some practitioners therefore wish to construct a tea-chamber that would simply not allow them to use the sideboard whatsoever. They thereby express their humility and recognition of their social standing in contrast to their much wealthier superiors.
The Host, when conducting a service of tea in a three-quarter room, bases his axis of seat on the bent pillar and arranges the implements necessary for the service of tea on the remaining quarter of the mat of what would be the further-half of a whole matting segment, thus limiting the space available to use in comparison to the Small or Grand Tea-chamber.
Thank you for this very informative article. I’m trying to create a tea space in my very small walled garden, and I’m inspired now to work with a three mat space. The two full mats and one 3/4 mat concept fits in with my practice of tea perfectly. I so appreciate you sharing this information, in english, as there is so little out there that I can draw from.