Maeda Family Residence Outdoor Toilet

A Stone Privy on a Volcanic Island

The Outdoor Privy of the Maeda Family Residence (前田家住宅外便所, Maeda-ke Jutaku Sotobenjo) stands in the village of Honson on Niijima, an island belonging to Tokyo Metropolis roughly 150 kilometres south of the city, was built in the mid-Taisho period, and became a Registered Tangible Cultural Property in 2004. It is a single-storey stone building of 8.8 square metres, and it was the first structure on Niijima to enter the national register.

A toilet as a national cultural property invites a double take. The reason is the material and the craft. The plan is a rectangle 3.6 metres by 2.4 metres. Over it runs a barrel vault, and walls and vault alike are built entirely of coursed stone, no timber frame beneath. The stone is koga-ishi (コーガ石, also written 抗火石 and read kogaseki), a biotite rhyolite produced by the Mukaiyama volcano at the southern end of Niijima. It is glassy, full of small bubbles, light enough that good pieces float on water, soft enough to cut with a saw, and resistant to fire.

Niijima burned repeatedly. A fire in 1870 destroyed a reported 105 houses, and the westerly winds of winter carried flames through thatched roofs faster than anyone could stop them. Building in stone was the islanders' answer, and by the Taisho period the local masons had turned necessity into a craft, imitating timber details in stone and borrowing Western mouldings where they liked them.

How It Was Built

The construction is documented in unusual detail by the Niijima Kokaseki Structures Research Association, a group of architects from outside the island who have surveyed these buildings for more than two decades.

Wall thickness steps as it rises. From ground level up to 0.9 metres, the equivalent of three shaku in traditional measure, the stones are 0.18 metres thick and 0.3 metres long. Above that line the thickness drops to 0.15 metres, the length staying the same. A heavier base, a lighter top, worked out by eye and hand.

Where the vault meets the wall runs a cornice, and the surveyors identify its profile as a variant of the cyma reversa, the wave moulding with a convex upper curve and a concave lower one. A ventilation turret sits at the centre of the vault with a cornice of its own, and the hood over the south window repeats the semicircular curve of the roof with the same moulding again. The mason was working a single idea through three different scales.

The building occupies the western edge of its plot. Together with the stone wall continuing north, it forms a firebreak protecting the main house behind. The ground inside the plot sits lower than the village road to the west, a deliberate move to duck below the winter wind. Nothing here is decorative only.

Local tradition credits the work to Uematsu Genshichi, an island mason, and holds that the building stood through the earthquake of 27 December 1936, which killed three people and destroyed or damaged most of the housing stock on Niijima. Because Uematsu's active years ran from the Taisho period into the early postwar decades, the surveyors place construction in the mid-Taisho period, matching the Agency for Cultural Affairs entry of 1912 to 1925. Registration followed on 17 February 2004, notified on 4 March, under registration number 13-0171 in the fortieth round, on the criterion that the building serves as a model of design.

Visiting Niijima and Seeing the Building

Before anything else: this is a private house. The privy stands within a residential plot where people live, and there is no visitor entrance, no ticket desk and no interior access. What you can do is look at it from the village road on the west side, which is how the surveyors themselves photograph it. Keep to the road, do not enter the plot, and be considerate about photographing over a household wall.

Occasional exceptions arise. During Tokyo Cultural Properties Week, usually in late October and early November, some of Niijima's koga-ishi buildings open to the public, with explanatory cards distributed and events held at particular sites. Dates vary year to year and are announced by the village.

Getting to the island takes either forty minutes or most of a day. Shin Chuo Airlines flies nineteen-seat Dornier aircraft from Chofu Airfield in western Tokyo to Niijima Airport in about thirty-five to forty minutes. Tokai Kisen runs a high-speed jetfoil from Takeshiba Pier in central Tokyo in roughly two and a half hours, and a large overnight ferry that leaves late and arrives the following morning. Shinshin Kisen sails from Shimoda on the Izu Peninsula. Honson village lies on the west coast and is walkable end to end; the village runs a free circulating bus.

Once there, the privy is worth seeing in company. Five more koga-ishi buildings joined the register in 2023, among them the stone warehouse and privy of the Umeda family, the main house and hearth shed of the Kino family, the main house of the Kokubo family, and the hearth shed of the former Maeda residence known locally as Kinde, which faces the village office. That last one shares a surname with the subject of this article but is a separate property at a separate address. The village museum sets out the quarrying history, and around seventy per cent of buildings on Niijima still use koga-ishi somewhere, so the walk between them is itself the exhibit.