[quesera]

Extensions springs are the old way. Common for a few decades at least. Torsion springs are the new way. They're safer, and smaller, and require less maintenance.

Unfortunately, they're also a bit more fragile. Speculation (mine) is that the metallurgy required to make a big torsion spring makes the material more brittle than standard spring steel. Or maybe they're just thinner and cheaper.

They sure are loud when they snap though.

[fubarred]

Loud, yes. Extension springs are still found on single-piece doors.

[quesera]

Single piece doors aren't legal in many states, but interestingly it's not because of the safety issues (which are much greater than tracked folding doors with extension springs, due to the angle of extension).

I've never even seen them outside of California.

[jahmed]

I was interested by this but couldn't find anything about single piece doors being illegal. Being from California I've lived in a few places where these types of doors are common.

[quesera]

> Single piece doors aren't legal in many states, ...

Sorry, I phrased that poorly.

There are many states where the typical California tilt-up single-piece door with levered extension springs does not meet code.

Apparently they are not secure in very high winds, so they're especially dangerous in hurricane/tornado country.

[jahmed]

Ahhh that makes perfect sense. Thanks for the explanation.