A reading room hangs from the roof of a former prison watchtower in Hefei

The upper reading room projects beyond the tower shaft beside a pedestrian crossing

The patrol platform of a former prison watchtower in Hefei is now a place to sit with a book. At the northwest gate of Hechai 1972, SZ-Architects has extended the upper floor beyond the tower’s seven-square-metre footprint, hanging the new structure from the roof. A Very Small 24-hour Bookstore has 70 square metres of floor space in all, with reading desks set along the windows where guards once looked out across the grounds.

Aerial view of the former prison grounds and the surrounding neighbourhood in Hefei — SZ-Architects

The tower glimpsed between trees beyond a car park — Mata Okawa

View across the road towards the park entrance and the guard tower — Mata Okawa

Wide view across the junction towards the former guard tower — Mata Okawa

A pedestrian passing beneath the projecting balcony on the east side — Mata Okawa

View from the east towards the bookstore and parked bicycles — Mata Okawa

The tower dates to 1997, when the site was part of Anhui Provincial Hefei Prison. It stood unused as the grounds around it became a creative park. Zhikun Zhang and Yue Liu’s practice came across the building while visiting the site for a restaurant project and proposed a bookstore that neighbourhood residents could enter at any hour.

The former watchtower and perimeter wall before conversion — SZ-Architects

The disused guard tower seen from the street before the renovation — SZ-Architects

Original patrol platform above the narrow tower shaft — SZ-Architects

The former guard tower on the far side of the junction — SZ-Architects

Former gun opening in the tower wall — SZ-Architects

Original gun mount at a barred opening overlooking the grounds — SZ-Architects

The client, A Very Small Bookstore, began on the Qinhuai River in Nanjing, where readers contributed books from their own collections and left handwritten postcards on the walls. In Hefei, a wall around the stair was set aside for messages. Outside, platforms on the north and south sides provide space for coffee and for events organised by the bookstore and the park.

The projecting reading floor seen above a low wall at the south-west corner — Mata Okawa

Street trees and a paved forecourt at the foot of the tower — Mata Okawa

The bookstore rising above a row of stalls on the south-west approach — Mata Okawa

A street vendor beside the approach to the tower — Mata Okawa

Outdoor canopy beside the base of the bookstore — Mata Okawa

Ground-level entrance beneath the overhanging reading floor — Mata Okawa

Pale green entrance door beside a tiled wall — Mata Okawa

As the tower’s original drawings had been lost, the team commissioned new ground and structural surveys. The four concrete corner columns were wrapped with steel angles, the upper slab was strengthened and the existing concrete roof beams were enlarged. The work retained traces of the tower’s former use, including barred openings in the walls of the old observation post.

Scaffolding around the tower during wall removal — SZ-Architects

Steel reinforcement inside the stripped tower during construction — SZ-Architects

Perspective section through the stair and upper reading room

Eight steel channels laid across the reinforced roof beams carry the extended reading floor below. The channels are paired back to back and grip vertical steel hanger rods. A second set of channels beneath the original patrol platform connects to the same rods and supports the new deck. Wood-plastic composite boards keep the extension relatively light. The extra width leaves room for two people to pass alongside a seated reader.

Animation showing how the roof beams and hangers support the new reading floor

Exploded isometric drawing of the suspended steel structure

Connection between a steel hanger and the overhead beams — Mata Okawa

Detail of a reading desk with a vertical rod and diagonal support — Mata Okawa

Steel connections beneath the projecting balcony — Mata Okawa

The shape of the roof owes as much to the street as to the floor below. Two high-voltage lines pass close to the west side of the tower. To clear them, the architects rotated the roof in plan and clipped its corners, producing a four-lobed outline. The study models show the relationship between the broad roof, the projecting balcony and the narrow shaft that meets the ground.

Sequence of study models exploring different roof and floor forms — Mata Okawa

Aerial view of the handmade model of the tower and grounds — Mata Okawa

Model of the bookstore seen from the south-east — Mata Okawa

South elevation of the handmade model — Mata Okawa

Model detail showing the projected floor and roof — Mata Okawa

Corrugated roof and open corner on the handmade model — Mata Okawa

The bookstore above the perimeter wall on the north-west side — Mata Okawa

Scooters and pedestrians on the street below the reading room — Mata Okawa

The tower and street stalls at the north-west corner of the park — Mata Okawa

The angled roof and upper reading room seen from the south-east — Mata Okawa

South side of the tower beside the old wall and trees — Mata Okawa

Readers reach the upper floor by the reinforced stair. Its plasterboard enclosure forms a service shaft, with shelves around the core at the entrance to the reading room. Removing the low walls beneath the old window sills made room for shelving on all four sides. A combination of diagonal props and slender hangers supports the desks at the perimeter.

Stair flight beside the enclosed core — Mata Okawa

A stool on a landing beside the stair window — Mata Okawa

Doorway into the reading room beside shelves in the central core — Mata Okawa

Bookshelves lining the core beneath exposed roof beams — Mata Okawa

Reading stools and a continuous desk beside the windows — Mata Okawa

Hanger rods beside a reading desk under the green roof — Mata Okawa

Sliding windows open at the four corners, leaving the desks beside them open to views of the park. After dark, the lit room is visible from the junction above the old perimeter wall.

A single stool at the open corner of the reading room — Mata Okawa

Traffic passing the tower on the north-east side — Mata Okawa

The projecting floor seen across a busy junction at dusk — Mata Okawa

Street stalls and the lit upper room at the north-east corner — Mata Okawa

The bookstore above the perimeter wall at night — Mata Okawa

Light from the upper windows seen through trees at dusk — Mata Okawa

The lit upper floor of the bookstore above trees in Hechai 1972 — Mata Okawa

Drawings

Map locating the bookstore at Hechai 1972 in Hefei

First-floor plan showing the tower and surrounding platforms

Plan through the tower at a height of 5 metres

Plan through the tower at a height of 6.6 metres

North elevation of the converted guard tower

Section through the original shaft and extended upper floor

Second section through the reading room and stair

Project Credits

Project A Very Small 24-hour Bookstore
Location Northwest Gate, Hechai 1972, Hefei, Anhui Province, China
Gross built area 70 m²
Design period June 2024 to April 2025
Completion December 2025
Client A Very Small Bookstore

Architecture SZ-Architects / @sz_architecture
Lead architects Zhikun Zhang, Yue Liu
Design team Yaning Shen, Deyong Kong
Structural design iStructure Design & Consulting Co., Ltd. (Xiaotian Yang, Kunying Wu, Zhe Wang)
Landscape Nanjing Jianzhi Horticulture Co., Ltd.
Contractor Hefei Guyu Construction Decoration Engineering Co., Ltd.
Structural reinforcement Zhongbai Engineering Design Group Co., Ltd.
Property management Hefei Bintou Cultural and Creative Development Co., Ltd.

Materials Wood-plastic composite flooring, green strip tiles, silver corrugated colour-coated steel sheets and white latex paint
Photography Mata Okawa / @mata_okawa and SZ-Architects / @sz_architecture
Cover photograph Mata Okawa
Project film SZ-Architects
Film music A-muzik studio