27/8/2026·AI
The Nakagin Capsule Tower Was Designed to Change. So I Built One That Does.
Kurokawa's Nakagin Capsule Tower, Tokyo 1972: 140 prefabricated capsules bolted onto 2 concrete cores, every one of them designed to be unbolted and swapped out on a 25 year cycle. None ever were, and the building was demolished in 2022 having never once done the thing it was designed to do, which means the idea was built exactly once, at one height, in one packing arrangement, and then stood for 50 years as a single frozen sample of a system that was supposed to have variants. This is the tool that generates the variants, and the starting point was a file nothing on the machine could open. Nakagin+Capsule+Tower.skp is SketchUp's closed binary format with no converter available, no assimp, no Blender, no licence, so every normal route to a mesh was shut. What is true of a .skp and not widely known is that SketchUp writes PNGs into the file, the saved model view plus a thumbnail for every component, so scanning the bytes for the PNG magic number and cutting to the end marker recovers images out of a file you cannot otherwise read. That returned the saved model view and 3 capsule thumbnails, blank end, mirrored, and the one with the round window, which is all that was needed: the raked oxblood blade over each lift overrun, the white 2 storey podium with its recessed shopfront band, and the square-edged capsule. A static mesh could not have driven a parametric tool anyway, so what was wanted from that file was never geometry, it was intent, and everything else came from the published dimensions. The seed of the whole thing is 5 numbers: a capsule 2.3 by 3.8 by 2.1 m at about 8.7 m2, a round window 1.3 m across on the outboard end, 2 cores at 11 and 13 storeys, 140 capsules, 52.5 m. 8.7 m2 is the number worth sitting with, because that is the entire dwelling, sold to Tokyo salarymen as a second home for the working week. The part that separates a parametric model from a pattern of boxes is that capsules seat rather than float: each one bolts to whichever core face it lands on, so the distance out is solved by a ray from the core centre hitting the box that is the core rather than set as a fixed offset, which is what lets the whole ring twist 7 degrees a floor with every capsule staying seated instead of drifting into space or driving into the concrete. Then every candidate is tested by separating-axis against every other core and against every capsule already standing on that floor, and anything that would drive through a neighbour is dropped rather than drawn interpenetrating, which is why placement has to run floor by floor: a slot can only be tested against what is already standing at the same level. That produces the 2 readouts that are the actual point of the tool, slots filled and clashes dropped, against the usual capsules, cores, storeys, height and GFA. The original tower opens at 140 capsules, 73% filled, 44 dropped, and those 44 are not a bug, they are the staggered pair of cores getting in each other's way exactly as they do in the real building. It matters because raising the core count does not simply multiply the capsule count and pushing the cantilever out can send it down, so the counter tells you the moment a move has stopped adding accommodation and started making a shape. Any tool that only counts what it drew will tell you every scheme is a success; this one counts what it refused to draw. 4 presets ship, and they are 1 solver at 4 parameter sets rather than 4 models. Three towers puts the same capsule across a row of 3 cores at 5 m centres, staggered in height and tied at every 4th floor by a bridge, and returns 256 capsules at 78% filled on a footprint 3 slots wide. Taller version pushes the concept to 36 storeys and 118.8 m with banded packing putting a service floor every 4th level, 2 clear storeys at the base and cores widened to 6 m, and the answer it gives back is the interesting one: double the height of the original and you get 280 capsules rather than 140, at 56% filled with 88 dropped, so it scales and it scales badly, the service band eating a quarter of the floors while the fatter cores throw more capsules into each other. Spiral stack is 1 core, 3 faces, capsules rotating 7 degrees a floor with a 0.4 m slide and a varying cantilever, and comes back 100% filled with 0 dropped because a single core has nothing to clash with, which makes it the cleanest scheme by the numbers and the least buildable in every other respect, a useful reminder of what those counters are not measuring. The modulation group is where the modular idea gets stretched: packing rule as full, scatter with density and seed, checker, banded, stepped or spiral; how many faces of the core are used and how many capsules sit side by side on each; twist per floor; a triangle-wave slide with a period of 4 floors; cantilever and its variation up the tower; and the 2 joints, stacked and side by side, controlled separately. Scatter runs off a deterministic generator so seed 7 always rebuilds the same tower, because a random arrangement you cannot get back to is not a design option, it is an accident. The solver is 1 file of about 300 lines with no React in it, returning core positions, capsule transforms, link bridges and metrics, and the drawing is a separate problem, which is why capsules go into 4 instanced meshes, shell, glass, frame and bolted bracket, and a thousand-capsule scheme still turns at full speed in a browser tab. Save PNG takes the current view; Export GLB writes the building and only the building, with the ground grid and shadow catcher deliberately outside the exported group because their textures are generated in code and cannot be serialised into glTF. Limits are named plainly. It is a massing and quantity study, not a building: no structure, no capsule fixing, no lift calculation, no fire escape, no smoke shaft, no services, so it will report GFA and packing efficiency and will confidently draw a 36 storey version that does not have enough lifts. The capsule is an envelope rather than the real monocoque with its fitted interior. The clash test is in plan only, and nothing tests a capsule against the bridge running past it. And it is not the Nakagin: it opens on the Nakagin's numbers because that is an honest place to start, but the real building has an irregular arrangement no rule reproduces exactly, so 140 capsules at 73% filled is a faithful reading of the logic rather than a survey of the building. The close is about the input rather than the tower. The input was a file that could not be opened, in a format there is no software for, of a building that no longer exists, and the usual response to that is to give up or to spend a day modelling it by hand from photographs. Instead: read what the file would give up, take the published dimensions, write down the rules the building was built on, and generate every version the architect never got to test. Modelling gives you 1 building; writing the rules down gives you the whole family, and it takes about the same evening. Kurokawa's argument was that a building should be able to change. The building never did. The rules still can.
