Expert Garage Door Repair,
Service, & Installation in
Chula Vista, CA

Most of an opener really is overhead: the head unit, the rail, the trolley, the arm running down to the top section, and the framing all of it is fastened to. The part that does the protecting is not up there. The federal standard takes any of four devices as satisfying it, and on a residential opener it is almost always the pair of photoelectric eyes bracketed either side of the opening, low down — and the height those eyes are allowed to sit at is published before anybody arrives. DASMA, whose members are the companies that build these operators, puts it in a single line: "These sensors must not be installed higher than six inches above the garage floor."

It is worth reading what shape that figure is, because it is a maximum and not a target. It bounds the height in one direction only. There is no such thing as a sensor mounted slightly too low, and every way one ends up outside the rule is upward. Two ways it happens are familiar enough to name: a sensor knocked out of line, and a sensor mounted high on purpose, to keep a door from stopping when nothing is in its way.

The one-way bound is what settles the second of those. Up is the single direction the rule takes away, whatever raising them might do for the symptom — so a door that reverses with nothing under it has to be found rather than designed around. That means the two eyes sighted against each other and against the floor immediately below each of them, the brackets they are clamped to, the lens faces, and the wire run back up to the head unit. Whatever comes out of that, the eyes finish the visit at the height DASMA gives them.

None of it is anything the census could have told us, and the census has plenty to say about Chula Vista otherwise. There are 90,535 housing units on the record here, and the biggest block of them by a distance is the 20,480 finished between 2000 and 2009 — clear of every other ten-year period on the table by more than the sampling error on that difference, in each case. Three of the earlier decades sit inside each other's error instead — 11,922 units are recorded for 1990 to 1999, 12,315 for 1960 to 1969 and 12,720 for 1970 to 1979, and the widest gap among those three is 798 units against a root-sum-square margin of 1,241 on that difference. Three separate decades, and no way to rank them. Around them, 39,445 units were already standing before 1980 and 29,218 have gone up since 2000, 43.6% and 32.3% of the stock, either side of a median build year of 1986 — which puts the middle of the record about forty years back.

So the profile is detailed, and all of it is about buildings: when they were finished, how many there are, which ten years put up the largest share. The six inches is not about a building. It is a height picked for somebody lying on a garage floor rather than standing in the doorway, which is why a pair of eyes that has crept up the jamb still looks like it is working. It stops a car, and it stops a person on their feet, exactly as it did before. What it has stopped doing is watching the floor.