If I want to insulate my attic, what is the best way, and do I need a vapour barrier?
For older homes (and especially cottage retrofits), insulating your attic is one of the best home upgrades for seeing a return on investment. You can easily be losing hundreds of dollars worth of heat into a poorly insulated attic every heating season, so payback can be pretty quick.
One of the most effective and affordable ways to insulate an attic is with blown-in cellulose. It creates a seamless blanket over the entire surface, so heat won't be creeping up between cracks like it can with batt insulation. Cellulose insulation is made almost entirely from recycled newsprint, so it's quite affordable, and one of the more ecologically responsible building products you will come across.
If you already have pink batt insulation up there, you can blow cellulose right over top with no problem. Keep in mind that you need to ensure proper venting and airflow through your attic. If any of this makes you scratch your head, it may be best to get a pro to look at it. This is not something you want to do wrong, poorly installed insulation can cause serious moisture damage.
And a fluffy pile of cellulose will limit your future access, so make sure everything is in order first, namely ensure kitchen and bathroom fans are vented outside instead of right into the attic.
As for vapour barriers, yes, you should have one if there isn't one already. What you might want to look into are vapour retarder primers [paint]. While they are seriously under-utilized in the construction industry, they do the job and even exceed the requirements of building codes. In some cases painting on a vapour barrier can be easier than crawling around in your attic with a sheet of polyethylene.