Re: Electrical box depth and codes
The "spirit" of the code is that no flammable surfaces would be "visible" to the interior of the box. This is to protect from fire should there be arcing inside the electrical box. Gypsum is considered non-flammable; not sure how the paper facing is treated by the code.
I believe the code does allow for some variation in the box not being flush with the surface, but I don't remember how much it is. I would think the extensions should be fine, since the nail-on boxes tend to be larger than old-work boxes. It seems like I've seen plastic extensions sized for nail-on boxes in the local Home Despot, but I haven't really paid attention since I haven't ever needed one.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.