junction-boxscrews
A plastic box junction box shall be mounted to a drywall industrial ceiling with two screws. The box will be filled with many low voltage wires before it is brought to the worksite (making it very difficult, if not impossible, to screw down from the inside).
Is there a clever method to first screw-in the screws to the ceiling, then mount the box to screws, which are protruding from the ceiling?
That is called fan-fold insulation. Typical for under vinyl siding in older homes.
Very surprising that there is no sheathing, but not unheard of. What I would do is get a round cut-in style fixture box and mount it directly to the vinyl block. This seems like your only option, apart from removing some siding and replacing the vinyl block with a fixture box style piece from Arlington Industries.
or
http://www.aifittings.com/catalog/siding-mounting-blocks/siding-mounting-block/
Buy a ceiling hugger style fan (the ones without a stem or with the option to mount without the stem).
Mount the fan's bracket directly to the ceiling with toggle bolts or other such fastener. This way the fan is not support by the box at all.
Good luck with your project!
Best Answer
You pull the wiring out of the box enough to allow you to attach the screws safely without nicking a wire. It really helps to hand-drive the screw with care, not just smash it in with a power-driver.
If you don't like all that care, then you use a type of junction box that has ears on the outside, like this.
Or a metal box which, while you do not see any ears, they come in the accessory kit and you can attach them one of several ways.