Reprinted from the Omotesenke Fushin'an website

In the tea ceremony, a room with four and a half tatami mats or more is called a hiroma, and a room with four and a half tatami mats or less is called a koma. A four and a half tatami mat room is large enough to be either a hiroma or a koma. A koma is a tea room that does not use any shelves, including daisu, and is used for carrying the tea ceremony. In a hiroma, tea ceremony can be performed with various shelves, including daisu, decorated. In other words, a koma is the world of wabi-cha, and a hiroma is the world of shoin. In a koma, the only place for decoration is the floor, but in a hiroma, shelves and shoin can be installed in addition to the floor. A koma has a low ceiling and a small, low entrance, while a hiroma is no different from an ordinary tatami room, and may have an entrance or veranda. For example, a four and a half tatami mat room is larger than a four and a half tatami mat room, but since the daime arrangement is in accordance with the tea ceremony method for a koma, it cannot be called a hiroma. The term "chashitsu" became widespread in modern times. In the past, rooms were simply called zashiki or kozashiki, or four-and-a-half tatami mats or three tatami mats, depending on the size. Furuta Oribe and Kobori Enshu came to call them sukiya. Today, it seems that rooms used exclusively for tea ceremonies are called tea rooms, and buildings that look like tea rooms with a slightly more casual style are called sukiya. Tea rooms and roji When tea rooms became hermitage tea rooms, the connection was lost. Instead, a space with a doma eaves was created. Did the tea room cut off its connection with the outdoors (nature) by surrounding it with walls? Guests walk up the stepping stones to the stepping stones, open the nijiriguchi door, and proceed onto the tatami mats. Here, the stepping stones and tatami mats in the garden are directly connected. And the space for the tea ceremony is designed to be integrated not only with the tea room, but also with the garden outside, called the roji. The roji is not a garden to be viewed from inside the tea room, but a path to the tea room. The tea ceremony begins when you enter the rojiguchi. It is also important for guests to sit on a bench while waiting for the host to greet them and to rinse their hands in the water basin. The roji is, after all, a garden used for the tea ceremony; it is a teahouse that opens up to the open sky, except that it does not have a roof. The tradition of "the garden and the house being one" lives on here as well. Rikyu called the roji "the outer path of the floating world." It was a path that separated the space of the tea ceremony from the secular world and sanctified it. There is something in common with the structure of a sacred forest, with a shrine at the very end of a long approach to a shrine.

Tea room

[The role of the tea room]　　　　　

　
　A tea room is a room set up for holding tea ceremonies in the tea ceremony, where guests are invited and tea is served.
The typical size is four and a half tatami mats, with a tokonoma alcove,
a hearth, a nijiriguchi (a gate for guests) and a chadoguchi
(a tea ceremony entrance for the host).
A room size of four and a half tatami mats or less is called a koma(small room), and a room size of four and a half tatami mats or more is called a hiroma (large room).

[The origin of the tea room]　　　　　　　　　　　　　　　　　　　　
It originated from the "chaya" during the "Higashiyama culture" in the mid-Muromachi period (1444 to 1491), and it is thought that the space divided by folding screens and other items was the beginning of the tea room (shoin-style tea room). After the power of the samurai class declined due to the Onin War, it was merchants of Sakai such as Sen no Rikyu who actively practiced the tea ceremony. The tea room they favored was the Mountain villa in the city. Even in the midst of busy city life, people sought a quiet and calm environment for socializing in the tea room. Tea rooms became smaller, natural materials were used, and rooms with a rustic, rustic atmosphere like thatched huts became popular. Rikyu further aimed to establish his own unique world by making the tea room as small as possible. Contemporary tea masters also preferred small tea rooms smaller than four and a half tatami mats, and began to use various ingenuity in the limited space. The Warring States period in which Sen no Rikyu (1522-1591) lived was a time when lord-vassal relationships were strong, but the entrance (nijiriguchi) was made low to show that everyone was equal in the tea room. Samurai and merchants alike had to bow their heads to enter the nijiriguchi, regardless of their status, and samurai could not pass through it unless they took their precious swords, and above the nijiriguchi there was a hanging device called a katana-gake for storing swords.