Tear the sheet across the width instead of tearing it lengthwise.
Running wires in insulated ceiling no attic.
In addition your light fixture may require mounting to a ceiling joist or to two short blocks nailed.
Running electrical wire through the channel between ceiling joists is generally easiest.
Locate the wall studs with a stud finder in the area where you re snaking your wires.
New lighting cable computer networking and sound systems can all require wiring that may need to come through the ceiling.
If the wire is too tight to the wall to make that easy you have a second option.
First you can tear or cut the insulation sheets in half and lay half behind the wire and half in front.
There are two ways to insulate around wires.
Worst can you open the ceiling 5 inches from the wall and work from there.
A 3 inch strip of drywall is enough to run receptacles around a room.
On a single story home or the the upper floor of a multiple story home this means accessing your attic to run wire.
For vertical work you can cut about 6 inches below the wall ceiling joint drill through the top plat and then fish from the opening ion the ceiling.
Cold cobweb filled crawl spaces damp basements and tight attics are all just a part of the job.