Where do you live? It makes a difference on where your vapor barrier goes.
If you are someplace where you run the heat more than the A/C you want the
barrier on the house side. That is where the warm moist air comes from, the
attic is cold.
If you are in Florida you reverse that. The warm moist air is in the attic most
of the time and the house is cold. Water forms in the insulation if you don't
have the barrier on the top. It will turn your cellulose into grey mud that
eventually just rots to clumps of dust.
Want some, I have an attic full. I will mail you some.