What it means
A block wall is the gray concrete fence that runs around the back and sides of nearly every house in Scottsdale, and the first thing Midwestern visitors ask about from the airplane window: a grid of tan roofs, each in its own small concrete box. The term is literal. The wall is built of concrete masonry units, CMU to the trade, stacked and mortared to roughly six feet, sometimes capped, sometimes painted the color of the house, often left the color of the block.
Locals use the phrase constantly and never explain it. “Over the block wall” is where the neighbor’s dog went. “Along the block wall” is where you find the scorpions with a blacklight, as the first-year note recommends. “The block wall” is what separates your pool from the alley, your patio from the street noise and your evening from the people next door. The moving guide calls the result a city of private backyards, and that is the whole point: the wall trades a view for a room you can sit in at night in July.
Where you’ll meet it
Everywhere south of the Preserve. The purest examples are the 1950s and 60s ranch-house blocks of South Scottsdale, where walls, citrus and carports make the pattern. In the north the wall is still there, just stuccoed, colored and specified down to the cap by the HOA.
Where the word came from
The material came first, then the habit. In 1944 three Phoenix men, Coach Thomas, Bill Thomas and Gilbert Olson, put up $3,500 to start Builders Supply Corporation and make a lightweight concrete block from volcanic scoria mined at Winona, near Flagstaff. The block was lighter than a standard unit, strong, fire-resistant, a reasonable insulator and, at 8 by 4 by 16 inches, far faster to lay than brick. It was also made here, which in a postwar boomtown short of lumber mattered more than anything. By 1955 the company’s block was in about three-quarters of new Valley construction; in 1960 it renamed itself Superlite; by 1965 it claimed around 80 percent of all wall construction in the metro, with John F. Long specifying six million units for Maryvale alone.
Phoenix’s historic preservation officer, Michelle Dodds, told KJZZ in 2021 that the 1950s were the creative decade for block: houses, screens, planters and fences all in the same material, built by a local labor force that knew how to lay it. The reasons it stuck are plain. Concrete does not rot in flood irrigation, termites do not eat it, the sun does not chalk it, and it needs no paint. A wood fence here is a ten-year project; a 1958 block wall is still standing, probably with a lean.
The word itself is just description. Nobody coined “block wall”; the Valley simply built so many of them that the phrase became a fixture of the local vocabulary, the way “the Greenbelt” or “the 101” did.
What it is not
A block wall is not adobe, though slump block was designed to look like it, and not a retaining wall, which is engineered to hold back earth. It is also not a wildlife fence. The desert wildlife field guide is blunt: to a coyote a six-foot wall is a step, and bees like the hollow cores.
The fine print
Three sets of rules shape the wall. The first is the state’s pool law, ARS 36-1681, which requires a barrier at least five feet tall, with no opening a four-inch sphere can pass through, set at least twenty inches from the water, with a self-closing, self-latching gate, wherever a child under six lives in the house. In practice the perimeter block wall does most of that work, and the yard gate is where inspections fail; see pool season for the rest. The second is the city’s zoning code, which caps wall heights by zone and setback; a taller wall at the street needs a permit and often a variance. The third is the HOA. In the master-planned north the CC&Rs usually fix the wall’s height, finish and color, require owners to maintain their side and the shared cap, and treat a cracked or leaning wall as a violation that arrives in the mail.
The physics are worth knowing. Block is thermal mass: it soaks up afternoon heat and gives it back after dark, which is pleasant in January and the reason a west-facing block patio is still warm at ten on a July night. The hollow cores conduct sound less than you would expect and harbor more life than you would like; pest companies treat the wall line for exactly that reason. And block is heavy. A wall built on unbroken caliche stands forever; one built on fill or beside an irrigated lawn settles, and the horizontal crack along a mortar joint is the tell.
Walls are generally shared on the property line, and Arizona law leaves repair to the neighbors or the association. Ask who owns the wall before you buy. Someone does, and it is usually both of you.