What does "by half an inch" mean when talking about rest channel?

Question

This video shows how to install the resilient channel to the ceiling.

It sound like the tutorial is saying (a video link with a time stamp)

because we're installing the rest channel by half an inch, so you want to make sure that you lower all your device boxes about half an inch

Does "by half an inch" mean the height between the bottom of the resilient channel and the ceiling joist is equal to half an inch?

The distance between the top plane and bottom plane of a resilient channel should be determined by the manufaturer, rather than the builder, right?

The cited talking gives me a feeling that the distance is determined by the builder, which confuses me.

Any ideas?

Answer 1

The video narrator misused the term, it has no proper english meaning the way he used it.

You are correct in that the depth of the channel itself is only determined by the choice of channel, but an installer could shim a channel to make it drop lower than the manufactured dimension (depth).

It would have been more appropriate had the narrator said something like "we are installing our channel directly to the ceiling joists with no shims or furring strips, and this channel is 1/2", so the electrical boxes should be mounted to accomodate the lower ceiling..."

Answer 2

"Because we are installing the res' channel" is parenthetical, "by half an inch" is talking about the ceiling, not the channel.

"We are going to be lowering the ceiling (because we are installing the res' channel) by half an inch"

"We are going to be lowering the ceiling by half an inch"