Sukashi blocks: the patterned walls nobody photographs

Walk any residential street in Japan built before about 1980 and you will pass dozens of them: grey concrete blocks set into garden walls, each one pierced with a pattern — overlapping waves, a split diamond, a fan of rays like a rising sun. They are 透かしブロック (sukashi burokku), "openwork blocks," and they are so ordinary that almost nobody in Japan looks at them either, until somebody points out that the patterns have names and that no two streets have quite the same mix. There is no official catalogue, no copyright on the designs, and no reliable count of how many exist. There is, however, a deadline: since a schoolgirl was killed by a collapsing block wall in 2018, Japan has been steadily taking them down.

What they are, and why holes

A sukashi block is a concrete masonry unit with the middle cut away into a pattern. They are also called 穴あきブロック (ana-aki burokku), "holed blocks." In a Japanese garden wall they are usually not the whole wall: a run of solid blocks forms the base, and one or two courses of patterned blocks go on top, as a decorative band at eye level.

The holes are doing several jobs at once, which is why the type persisted for decades.

• Privacy without a barricade. A solid wall at head height turns a small Japanese frontage into a box; a perforated course screens the view while keeping the street visible.
• Air and light. Japanese summers are humid, and houses sit close together. A wall that lets a breeze through matters.
• Wind. A perforated wall gives typhoon wind somewhere to go instead of taking the full load.
• Cost. Decoration that comes as part of a standard-sized mass-produced unit costs almost nothing extra.

The patterns, and their names

Japanese enthusiasts sort them into broad families — wave types, diamond types, round types — and individual designs carry names, several of which are traditional Japanese textile and crest motifs pressed into concrete. Recorded names include seigaiha (the overlapping-wave motif), hishi (diamond), warihishi (split diamond), sorihishi (warped diamond), hinode (rising sun), hanabira (flower petal), miyama (deep mountains) and kirakira (twinkle).

The schematics below show the underlying geometry of five of the commonest families. They are diagrams, not photographs of specific products — real blocks vary in proportion, rib thickness and finish from maker to maker.

Once you have these five in your head the street changes, which is the entire appeal. The wave motif in particular is worth recognising: seigaiha is an ancient design found on textiles, ceramics and formal kimono, and somebody in the 1960s decided it should also be available as a hollow concrete unit for a suburban garden wall.

Where they came from

Concrete block walls spread through Japan during the post-war high-growth decades, roughly the 1950s and 1960s, replacing the wooden board fences, earthen walls and clipped hedges that had enclosed Japanese houses before. Reinforced concrete block construction had arrived, the material was cheap, and a block wall could be built quickly by a small crew.

Sukashi blocks are a product of that same moment: mass-produced units, standard dimensions, made by a large number of regional block manufacturers, each offering its own catalogue of decorative designs. A wall built in 1968 in one prefecture therefore does not carry the same patterns as one built the same year three prefectures away — the mix reflects whichever local maker supplied the builder.

Nobody owns these designs

This is the detail that explains everything about how the patterns behave. Japanese enthusiasts note that these decorative designs carry no copyright, and the consequence is visible in the walls: any maker could copy a rival's popular pattern, adjust it slightly, and sell it. So the record is not a set of discrete named products but a continuum — countless small variations on the wave, on the diamond, on the circle, drifting away from each other across decades and regions.

Which is why nobody can tell you how many exist. There is no registry, no standards body cataloguing decorative patterns, and no single manufacturer whose catalogue would cover even a fraction of them. The documentation that exists has been done by amateurs, photographing and classifying blocks street by street.

The morning that started the demolition

Japan's building code sets out the limits plainly: a block wall may not exceed 2.2 m from ground level, buttresses are required once a wall passes 1.2 m, and those buttresses must appear at intervals of no more than 3.4 m and project at least one-fifth of the wall's height.

The response was a nationwide inspection of school walls, and the numbers show its scale. By 1 September 2020, of 51,082 schools, 38,477 (75.3%) had no block wall or had removed theirs, and a further 8,320 (16.3%) had been confirmed safe or repaired — 91.6% with measures completed. Municipal subsidy schemes for removing private block walls followed, and are still running in many places.

This is entirely the right outcome; a wall that can kill a child should come down. But it does mean the specific thing described in this article is being removed from Japanese streets on a schedule, and mostly without anyone recording what the patterns were. The blocks that survive longest will be the low ones — the single decorative course on a wall under 1.2 m, which was never the dangerous configuration.

Okinawa is a different story

If you go to Okinawa you will see far more of these, used far more ambitiously — whole facades and balcony screens rather than a band on a garden wall. In Okinawa they are called 花ブロック (hana burokku), "flower blocks," and they are treated as a regional architectural signature rather than as generic hardware. The reasons are climatic and historical: intense sun, heavy rain, typhoons and a concrete-dominated post-war building stock make a ventilating, shading, wind-permeable screen genuinely useful rather than merely decorative.

English readers who have encountered "breeze blocks" will most likely know them from mid-century Palm Springs, where they are a well-documented feature of American modernist architecture with an active restoration market. That tradition is real, and separate. The Japanese one runs in parallel — same basic idea, different motifs, different reasons, and almost no English documentation.

How to look at them

You need no plan and no ticket. Head into an older low-rise residential district — the streets behind a suburban station, not a new development — and look at garden walls at eye level. Some things to notice:

• Whether the patterns match. Repairs and later extensions often use whatever was available, so a wall can carry two or three different designs.
• Orientation. Many patterns are directional, and a block set upside down relative to its neighbours is a common and quietly satisfying find.
• Where the course sits. Usually the top one or two courses; occasionally a single block set into an otherwise solid wall like a window.
• Buttresses. Once you know the 1.2 m rule you will start noticing which walls have the projecting piers and which do not.

The Japanese you'll actually use

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