Run a palm along a guest-room wall in Hotel Leo, St. Gallen, and you touch ground that sat somewhere else not long ago. Each wall is built from unfired earth blocks, 80 x 20 x 15 cm and about 50 kg each, pressed from nearby excavation spoil. On 4 September 2026 the Erich Mendelsohn Award gave the building Gold in Office and Commercial Buildings. The hotel opened in July 2023. The prize is the news. The building is the story.

Two jobs, two materials

Boltshauser Architekten split the building’s body cleanly. As Baunetz Wissen describes it, prefabricated concrete supports carry the load and the stair cores take the horizontal forces. Every non-load-bearing partition is earth. In DETAIL, Barbara Zettel needed one line for it: unfired clay blocks between columns of red-pigmented concrete form the interior walls. The architects call it a hybrid construction. Nobody asks the earth to hold the tower up. It adds mass, buffers humidity and gives the room a surface you want to touch.

The chain behind the block

The blocks come from Terrabloc, a Geneva company founded in 2011: Terrapad M at 80 cm in the rooms and Terrabloc S at 25 cm in the entrance hall. As Sabine von Fischer reported for espazium, co-founder Laurent de Wurstemberger stresses that each batch uses the nearest available excavation, so transport stays short. The mix is local spoil with 4 % cement as a stabiliser. Von Fischer cites studies from the Technical University of Denmark (2005) and the University of Bath (2014), which found that 3–5 % cement barely changes the blocks’ permeability, so the walls still take up and release moisture. The trade-off is plain: the cement makes the blocks tougher, but a stabilised block cannot simply be wetted and returned to the field the way raw clay can.

The supplier sits in a longer line. Roger Boltshauser has worked with rammed earth for years, much of it with Martin Rauch in Vorarlberg, and his research teams at ETH Zürich and EPFL traced how the technique reached Switzerland from France along 18th-century textile-trade routes, the same trade that made St. Gallen. The material has come home.

Star Wars fans have stood in a building like this without knowing it. The interior of the Lars homestead on Tatooine was filmed in Hotel Sidi Driss in Matmata, Tunisia, a troglodyte hotel dug into the ground because earth holds back desert heat and cold. Luke’s moisture farm and a Swiss business hotel share one thermostat, older than either of them: mass.

Good manners on a tight plot

The slab rises eight storeys, stepping down to seven in part, and holds about a hundred rooms, a restaurant, co-working space and a spa under the roof in about 3,500 m² of usable area. The client was the Pensionskasse Stadt St. Gallen, the budget CHF 19 million (BKP 1–9), the project 2018 to 2023. It is tall and thin so that the 1878 Villa Wiesenthal, recently renovated by Pfister Schiess Tropeano, could stay on the site. Greenish and white-grey clinker wraps it, with terracotta perforated-brick strips in front of the window ventilation flaps. The Mendelsohn jury wrote that the hotel “fulfils all the principles of good manners in architecture”, after Trystan Edwards’ 1924 book, and that its placement “creates a small public square”.

Building-sense: A building with this body would feel the afternoon arrive late. Every partition is a slow lung that takes in humidity when the room fills and gives it back when the room empties. My sensors would see a smoother curve, and my controllers would have less to do.

←TODAY: In 2026, a Swiss pension fund’s hotel with unfired earth from nearby excavation in about a hundred rooms won Gold for it.
→3012: Zurich-3012 reads every excavation pit as a quarry for the walls of the next building.
Fulcrum: Because the decision sits in the partition schedule, not the structural concept, any concrete frame can adopt it.

Atelier: For a 12-person Zürich studio, Hotel Leo makes earth a line item rather than a manifesto: frame and engineering stay the same, only the infill changes. The Monday move is to tag every non-load-bearing wall in the current project as a separate partition class, so the earth option can be priced instead of just admired.

Hack: Count how many 50 kg blocks your partitions would absorb, straight from the Rhino model. Put the non-load-bearing wall centrelines on their own layer, then run this in a GhPython component, with H as your clear height in metres and the blocks laid 80 cm long and 20 cm high:

import rhinoscriptsyntax as rs, math
crvs = rs.ObjectsByLayer("PARTITION_EARTH")
L = sum(rs.CurveLength(c) for c in crvs)
n = math.ceil(L / 0.80) * math.ceil(H / 0.20)
print(n, "blocks,", n * 0.05, "t of earth")

It is plain arithmetic with no openings deducted, but the tonnage is a number a contractor and an excavation firm can discuss. The PAZ Grasshopper↔Archicad Library carries that partition class into the BIM model, the handover drilled in the BSS course.

Open your current model, isolate the walls that carry nothing, and find out how much ground they could hold.